2-way lighting, switch
Switch 3-way lighting, switch
Distribution panel, breaker panel
Residual current device (RCD)
Ground fault circuit interrupter (GFCI)
In general, the word energy refers to a concept that can be paraphrased as "the potential for causing changes", and therefore one can say that energy is the cause of any change. The most common definition of energy is the work that a certain force (gravitational, electromagnetic) can do.
The aim of this is guide is to provide an idea about how to transform and use the electric energy in to electric power where electric current is used to energise the equipment and devices needed in the humanitarian interventions. Understanding the basic electric concepts, knowing how to properly size the installation, how to efficiently manage it with all the safety and precautions measures in place.
Electricity is the movement of electrons. Electrons create charge, which are harnessed to produce power. Any electrical appliance - a light-bulb, a phone, a refrigerator - are all harnessing the movement of the electrons to work. The three basic principles for this guide can be explained using electrons, or more specifically, the charge they create:
- Voltage is the Voltage - The difference in charge between two points.
- Current (Ampere) is the - The rate at which any given charge is flowing.
- Resistance is a Resistance - A material’s tendency to resist the flow of charge (current).
- Power represents the - The energy consumed by the load.
- Energythe - The amount of electricity consumed or produced during a given period of time.
Electric Potential Difference (Voltage)
Voltage (U) can be is defined as the amount of potential energy between two points on a circuit. This difference in charge between the + and – poles in a generator is measured in volts and is represented with the letter “V” in equations and schematics“V". Sometimes voltage can be called “electric pressure,” an appropriate analogy because the force provided by electric potential difference to electrons passing through a conductive material can be compared to water pressure as water moves through a pipe; the higher the volts, the greater the “water pressure”.
The available energy of the free electrons in motion is what constitutes electrical energy. Electricity production consists of forcing the electrons to move together through a conducting material by creating an electron deficit on one side of the conductor, and a surplus on the other. The terminal on the surplus side is marked (+), that on the deficit side (–).
THE VOLTAGE IS DETERMINED BY THE DISTRIBUTION NETWORK:Voltage is determined by the distribution network. For example, 220 V between the terminals of most electrical outlets, or 1.5V between the terminals of a battery.
An Electrical Current (I) is the flow of a free electrons between two points in a conductor. As electrons move, an amount of charge moves with them; this is called current. The number of electrons that are able to move through a given substance is governed by the physical properties of the substance itself conducting the electricity - some materials allow current to move better than others. Electrical current (I) is expressed and measured in Amperes (A) as a base unit of electrical current. Typically, when working with electrical equipment or installations, current is usually referred to in amperes. If volts (V) can be compared to the water pressure of water passing through a pipe, amperes (A) can be compared to the overall volume of water capable of flowing through the pipe at any given moment.
When a light bulb is connected to a generator, a certain quantity of electrons passes through the wires (filament) of the bulb. This electron flow corresponds to the current (I), and measured in amperes (A).
CURRENT IS A FUNCTION OF: THE POWER Current is a function of: The power (P), THE VOLTAGE The voltage (V), AND THE RESISTANCE and the resistance (R).
|I = U / R|
Sometimes electrons are held within their respective molecular structures while other times they are able to move around relatively freely. The resistance of an object is the tendency of this object to oppose to the flow of electric current. In terms of electricity, the resistance of a conductive material is a measure how the device or material reduces the electric current flow flowing through it. Every material has some degree of resistance; however it can be very low – such as copper (1Ohm 1-2 ohm per 1 meter) – or very high – such as wood (10000000 ohm per 1 meter) –. As an analogy to water flowing through a pipe, resistance is bigger when the pipe is narrower, decreasing the flow of water.
The Resistance (R) is expressed in ohms. Ohm defines the unit of resistance of “1 Ohm” ohm” as the resistance between two points in a conductor where the application of 1 volt will push 1 ampere. This value is usually represented in schematics with the reek Greek letter “Ω”, which is called omega, and pronounced “ohm”.
Resistance determined by load. For example: , wire conductors with a larger cross section offer less resistance to current flow and results , resulting in a smaller voltage loss. Inversely, resistance is directly proportional to the length of the wire. To minimise voltage loss, a current needs the shortest possible wire with a large cross-section. (see cabling section) Note also that the kind of wire (copper, iron, etc.) also affects a cable’s resistance.
When the resistance in an electrical circuit is near zero, the current may become extremely large, sometimes resulting in what is called a “short-circuit.” A short-circuit will cause an overcurrent within the electrical circuit, and can cause damage to the circuit or device.
Electric power (P) is the amount of work done by an electric current in a unit of time. It represents the amount of energy consumed by a device connected to the circuit. It is calculated by multiplying the voltage by the current, and is expressed in Watts (W).
Electric energy is often confused with electric power, but they are two different things;:
- Power measures capacity to deliver electricity
- Energy measures total electricity delivered
Electric energy is measured in Watt-hours (Wh), but most people are more familiar with the measurement on their electric bills, kilowatt-hours (1 kWh = 1,000-watt-hours). Electric utilities work at a larger scale and will commonly use megawatt-hours (1 MWh = 1,000 kWh).
There are devices that can convert current from one format to another, or from a higher voltage current to a lower voltage current and vice versa are universally referred to as “transformers.” Any time voltage or current type is transformed, there will always be some sort of energy loss, even if very small.
- A transformer that converts a higher voltage current to a lower voltage current is called a “step down” transformer, and can work works by either converting high voltage low current loads to low voltage high current loads, or by adding resistance between two circuits to limit the voltage output, resulting in lower power being received on the output side.
- A transformer that converts to a higher voltage is called a “step up” transformer, and works by converting low voltage but high currents into high voltage but low currents. A step up transformer does not add additional electrical power to the circuit, it only increases overall voltage.
- A transformer that converts a current from DC to AC is called an inverter, and physically induces an alternating current on the output side. Inverters typically consume electrical power for the conversion process, and thus are less energy efficient than other forms of transformers.
- A transformer that converts a current from an AC to DC can be called a "battery charger" (for charging batteries) or a "power supply" (for direct powering of a radio, etc.), depending on how the conversion process works.
Direct Current (DC)
The main characteristics characteristic of a Direct Current – or DC – is that the electrons within the current always flow in the same direction, from the side with a deficit to the side with a surplus. This is the kind of current supplied via the chemical effect by batteries, or via the photovoltaic effect by solar panels. The terminals are marked + and – to show the polarity of the circuit or generator. The voltage and current are constant in time.
- Advantages: batteries Batteries can supply DC directly and it is possible to add the sources in parallel or series.
- Disadvantages: In reality, the use of the batteries limits the voltage to a few volts (up to 24 volts in some vehicles). Those low voltages prevent the transportation of this type of current.
The frequency is defined as the number of sinusoidal oscillations per second:
- 50 oscillations per second in Europe (50Hz).
- 60 oscillations per second in the US (60Hz).
AC is the type of current supplied by electric utility companies because AC voltage can be increased and decreased with a transformer. This allows the power to be transported through power lines efficiently at high voltage and transformed to a lower, safer, voltage for use into in businesses and residences. Therefore, it is the form of electrical energy that consumers typically use when they plug an appliance into a wall socket.
- Advantages: Can be transported over long distances without too much loss using high tension lines. It is easy to produce.
- Disadvantages: AC current cannot be stored; it must be created. AC current can also pose a greater health hazard for living organisms that come into contact with it.
A single-phase current is the most common type of current, and thus is usually the configuration delivered by public networks, but also by a single-phase generator. A single-phase AC current is supplied via two lines (phase and neutral), usually with a 220 V voltage difference between them. Plugs can be inserted in both ways.
Because the voltage of a single-phase system reaches a peak value twice in each cycle, the instantaneous power is not constant and is mainly use for lighting and heating but cannot work with industrial motors.
A single-phase load may be powered from a three-phase distribution transformer allowing stand-along single-phase lighting circuit to be connected phase-to-neutral and a three-phase motor, an allowing a three-phase motors motor to be connected to all three phases. This eliminates the need of a separate single-phase transformer.
Once Power needs are increased, in the use of large electrical motor for example, constancy and If there is an increased need for power, thin consistency and balance pay a key role. Three-phase is circuit is the common current configuration for electricity companies, and can also be produced with a three-phase generator. A three-phase current is the combination of three single phase currents.
To carry a given power with 3 separate single-phase cables, 9 wires are needed. To carry the same power in a three-phase cable, only 5 wires are required (3 phase, 1 neutral, 1 ground), which it is why there can be significant savings when properly planning a three-phase current: . Cost savings include saving on wires, cables, and also in apparatus using or producing electricity: three phase motor or alternator will . Three-phase motors or alternators will also be smaller than the single phase equivalents of the same power produced by three single phase equivalent unitsproduction.
Grouping Circuit Components
In every circuit there will be resistor(s) and generator(s), their number the numbers of which will the depend of the power requisites. Both components can be grouped depending on the what is required to keep constant, the current or the voltage. There are two basic ways to groups components in series or in parallel. (additional information in connecting batteries section)
The basic idea of a “series” connection is that components are connected end-to-end in a line to form a single path through which current can flow:
The basic idea of a “parallel” connection , on the other hand, is that all components are connected across each other’s leads. In a purely parallel circuit, there are never more than two sets of electrically common points, no matter how many components are connected. There are many paths for current flow, but only one voltage across all components:
What ties all the components together in an electrical system are the cables. Cables supply the power to run appliances, and from the power sources for distribution to appliances, lights and equipment. Unfortunately, the most common installation error is to under-size cables relative to the load/s or from the recharge sources.
Proper installation is primarily a matter of sizing a cable to match its task, using the correct tools to attach terminals, and providing adequate over-current protection with fuses and circuit breakers. Cable sizing is fairly simple enough. It ; it is a function of the length of a cable ( measuring from the power source to the appliance and back), and the current (amperage) that will flow through it.
The longer the cable, or the higher the amperage, the bigger the cable must be to avoid unacceptable voltage losses. And there There should always be plenty of extra margin for safety because an appliance may actually use more current than what it is rated for because of heat, low voltage, extra load, or other factors. There’s never a performance penalty if a cable is marginally oversized; there is always a performance penalty (- and possibly a safety hazard ) - if it’s undersized.
The ground (negative) cable is as much a part of a circuit as the positive cable; it must be sized the same. In general, each appliance should be supplied from the distribution panel with its own positive and negative cables, although lighting circuits sometimes use common supply and ground cables to feed a number of lights (in which case the supply cables must be sized for the total load of all the lights). For 24v systems, the cables size is half that of a 12v setup. Always read product recommendations, or check with the supplier to know and understand exactly what size cable is required for the products.
Cable Length in Meters
10% Voltage Drop (Non-Critical)
3% Voltage Drop (Critical)
The above cable sizing table is used by running across the top row until the column with the relevant amperage is found, and then moving down the left-hand column until the row with the relevant distance is reached. The colour coding in the body of the table at the intersection of this row and column is the wire size. Compare this with the Cable Conversion Table to see what size cable to use.Wire sizes are denoted by colour coding.
A common way for referencing a cable size is its “gauge.” The AWG ( American Wire Gauge (AWG) is used as a standard method of denoting wire diameter, measuring the diameter of the conductor (- measured as only the bare wire ) with the insulation removed. AWG is sometimes also known as Brown and Sharpe (B&S) Wire Gauge.
Also listed Below is a conversion chart from AWG/B&S to mm². This table gives the closest equivalent size cross references between metric and American wire sizes. In Europe and Australia, wire sizes are expressed in cross sectional area in mm².
Cross Section (mm2mm2)
While is possible to use the same cables , (as far the diameter will be the appropriate one) for AC and DC circuits, it is advisable to use different coloured cables between the two types of currents, both to increase handling safety but also to make installation and repair work much faster. In If existing appliances or installations have colours, logistics managers may consider replacing or standardising them by re-colour coding the wires with an external paint or marking in a method that makes sense.
A general colour cod for AC looks like:
- Neutral: blue Blue.
- Phase: brown Brown or black.
- Ground: green Green/yellow.
The neutral and the phase are the two connections for the electricity, the ground is for safety.
+ = red or blue
- = black or brown
However, many Many differing international standards apply however. Please reference the below table for colour coding of different countries and regions around the world
Standard Wire Colours for Flexible Cable
(e.g. Extension Cords, power cords and lamp cords)
Region or Country
European Union (EU), Argentina, Australia, South Africa
Australia, New Zealand
United States, Canada
Standard Wire Colours for Fixed Cables
(e.g. In/On/Behind the wall wiring cables)
Region or Country
European Union and UK
UK Prior to March 2004
Australia, New Zealand
Any colours other than:
, , , ,
Recommended for single-phase:
Recommended for multi-phase:
bare conductor, sleeved at terminations (formerly)
, , ,
bare conductor, sleeved at terminations
(120/208/240V) (brass), ,
(ground or isolated ground)
(single-phase isolated systems)
(three phase isolated systems)
Important points to bear in mind note when wiring. :
- All circuits should be removed from the floor and be as be high as possible with no connections in or near water or damp areas.
- All cable lug connections should be securely crimped to the wire termination with a band, and not soldered in place.
- Tinned cable – copper wire that has been coated with a thin layer of tin to prevent corrosion - It is preferable to use where possible in a marine environment or near salt water.
- Never tap into or splice existing circuits when installing new equipment; run a properly sized new duplex cable (positive and negative cable in a common sheath) from the distribution panel (or a source of power) to the appliance.
- It is recommended to label all cables at both ends, and to an updated wiring plan to aid in future troubleshooting. Copies of the wiring plans can be even be stored in locations such as the fuse box or distribution box so that future users can reference them.
- Each circuit should have an independent ground cable, and all the ground cables should eventually be tied back to a common ground point/bus bar which is grounded to the battery negative; if devastating stray current is to be avoided, this is the only point at which the grounds should be interconnectedbusbar.
- Unless in a conduit, cables should be physically supported at least every 450mm.
- Although black is often used for DC negative, it is also used for the live wire in AC circuits in the USA. That means there is potential for dangerous confusion. DC and AC wiring should be kept separate; if they have to be run in the same bundle, one or the other should be in a sheath to maintain separation and ensure safety.
Protective devices for electrical circuits ensure that under fault conditions a high current cannot flow under faulty conditions, protecting the installation and equipment , and preventing injury and harm to persons nearby handling or handling the circuit or in the near vicinity of equipment. Protection Overcurrent protection is assured through physically detaching the power supply in a circuit through overcurrent protection, which removes fire hazards and risk of electrocution.
Protective devices might include:
- Miniature Circuit Breakers (MCBs).
- Residual Current Devices (RCDs).
- Residual Current Breakers with Overcurrent (RCBOs).
All of the aforementioned devices protect users and equipment from fault faulty conditions in an electrical circuit by isolating the electrical supply. Fuses and MCBs only isolate the live feed; with while RCDs and RCBOs isolate both the live and neutral feeds. It is essential that the appropriate circuit protection is installed to ensure an electrical installation is safe.
A fuse is a very basic protection device used to protect the circuit from overcurrent. It consists of a metal strip that liquefies when the flow of current through it surpasses a pre-defined limit. Fuses are essential electrical devices, and there are different types of fuses available in the market today based on specific voltage and current ratings, application, response time, and breaking capacity.
The characteristics of fuses like time and current are selected to give sufficient protection without unnecessary disruption.
Miniature Circuit Breaker (MCB)
An MCB is a modern alternative to fuses, and are maybe usually centrally located in buildings – usually called a “fuse box” or “breaker box”, or attached to specific equipment. They are just like switches, turning off when an overload is detected in the circuit. The basic function of a circuit breaker is to stop the flow of current once a fault has occurred. The advantage of MCBs over fuses is that if they trip, they can be reset without having to replace the whole MCB. MCBs can also be calibrated more precisely than fuses, tripping at exact loads. Circuit breakers are available in different sizes from small devices to large switch gears which are used to protect low current circuits as well as high voltage circuits.
Residual Current Device (RCD)
Residual Current Devices (or RCDs) are designed to detect and disconnect supply in the event of a small current imbalance between the Live live and Neutral neutral wires at a pre-defined value - typically 30mA. RCDs can detect when a live conductor touches an earthed equipment case, or when a live conductor is cut through; this type of fault is potentially dangerous and can result in electric shocks and fires.
An RCD does not give safety against a short circuit or overload in the circuit. It cannot detect – for example - a human being accidentally touching both conductors at the same time. An RCD cannot replace a fuse in function.
RCDs can be wired to protect a single or a number of multiple circuits - the advantage of protecting individual circuits is that if one circuit trips, it will not shut down the whole building or distribution system, just the protected circuit.
Residual Current Breaker with Overcurrent (RCBO)
An RCBO combines the functions of a MCB and an RCD in one unit. CRBOs are a safety device which detects a problem in the power supply and is capable of shutting off in 10-15 milliseconds.
They are used to protect a particular circuit, instead of having a single RCD for the whole building.
These devices are testable as well as resettable apparatusare able to be reset. A test button securely forms a tiny leakage condition; along with a reset button again connects the conductors after an error state has been cleared.
Uncontrolled electricity can injure or even kill humans or animals. One A common and effective way to control electricity is through grounding. Grounding is a physical connection to the earth that draws electric charge safely to the ground allowing a large space for electrons to dissipate away from humans or equipment. A grounding system is gives excess positive charge in electrical lines an attractive place to go – the access to a negatively charged ground wire – wires, eliminating the dangers of fire and electrocution.
The term "ground" refers to a conductive body, usually the earth. "Grounding" a tool or electrical system means intentionally creating a low-resistance path to the earth’s surface. When properly done, current from a circuit follows this path , thus preventing the buildup build-up of voltages voltage that would otherwise result in electrical shock, injury and even death. Grounding is used to dissipate the damaging effects of an electrical short, but also used to prevent damage from lightening as well.
- System or Service Ground: In this type of ground, a wire called "the neutral conductor" is grounded at the transformer, and again at the service entrance to the building. This is primarily designed to protect machines, tools, and insulation against damage.
- Equipment Ground: This is intended to offer enhanced protection to the people themselves. If a malfunction causes the metal frame of a tool to become energised, the equipment ground provides another path for the current to flow through the tool to the ground.
A major precaution aspect to grounding to be aware of: a break in the grounding system may occur without the user's knowledge. Using a ground-fault circuit interrupter (GFCI) is one way of overcoming grounding deficiencies.
The lower the resistance, the better it a grounding system will work.
Grounding System Components
The connection between metal parts and grounding is made using a third wire in the electrical circuit. Ground wires usually have a green-yellow colour and must have the same gauge as the biggest wire used on the installation to protect.
- Plugs and sockets have a grounding pin.
- Plugs with grounding pin are actually connected to a 3-wire network.
- Ground wires are well connected to each other on the distribution board, normally through a grounding pad or a connecting strip in metal.
- The grounding pad or the connecting strip is connected to the ground and this link must be done with a high-thickness wire (for example, 16mm²).
- This wire is connected to the ground.
|Ground Connecting Cables in Use|
A grounding system typically consists of a grounding conductor, a bonding connector, its grounding electrode (typically a rod or grid system), and the soil in contact with the electrode. An electrode can be thought of as being surrounded by concentric rings of of earth or soil, all the same thickness - each successive ring having a larger cross-sectional value and offers less and less resistance until a point is reach that it adds negligible resistance.
Electricity is potentially dangerous and has inherent risks, especially from ; a circuit failure, misuse, inexperienced handling, or negligence. The effects on the humans. , appliances, and other objects can be very devastating. When installing an electrical circuit - the whole system or just an extension - , extending an existing circuit, or looking for a new office or guest house , it is recommended perform a full assessment to on the facility. Full assessments should ensure that the circuit can safely handle the current flow needed, proper protections devices exist, the circuit is grounded, and there are no potential hazards.
For equipment, the dangers of an improperly installed or secure circuit are short circuits and overloads. For people, the dangers are come from insulation faults that lead to direct or indirect contact with electrical currents.
A short circuit is a strong overcurrent of short duration. In single-phase systems, a short circuit occurs whenever the phase and neutral wires accidentally come into contact; in three-phase systems, this can occur when there is contact between two of the phases. For DC, a short circuit can occur when the two polarities come into contact.
Physical damage can expose cables inside of insulation, while a sudden temperature increase of the conductors can cause the insulation and copper cores to melt.
An overload is caused from by a weak overcurrent occurring over a long duration. Overloads can be caused by a current that is too high with respect to be conducted through the relative diameter of the conductorsconducting cable.
There are two kinds of overload:
- Normal overloads, which can occur when a motor starts up. Normal overloads are short-lived and pose no danger.
- Abnormal overloads occur when too many appliances are connected to the same circuit or the same outlet at the same time, or when a connection terminal isn’t properly tightened. These problems are common in old buildings with too few outlets, but can occur on any installation as the number of electric devices increase. The current is lower in an abnormal overload than that of a short circuit, but the results are identical: overheated wires, damaged insulation, high risk of fire.
Insulation faults are caused by damage to the insulation of one or more phase conductors. These faults problem problems can lead to electrical shocks from current-carrying lines, and if the damaged conductor touches a metal surface or casing, can cause appliance and equipment to be electrified to the touch as well.
These faults can be very dangerous, especially when a person comes into direct contact with the conductor (directly), a metal casing, or a defective electrical appliance (indirectly). In all cases the human body become becomes part of the electrical circuit causing an electric shock.
This image depicts an electrical current as it flows through the human body.
The arrows demonstrate indicates the flow of electricity from the point it enters the body to the nearest exit point. The blue arrow demonstrates the flow of current through the head to the heart then to ground, which is the most lethal scenario.
|Level of Exposure||Reaction|
More than 3 mA
Painful shock- cause indirect accident
More than 10 mA
Muscle contraction – “No “Cannot Let Go” danger
More than 30 mA
Lung paralysis, usually temporary
More than 50 mA
Ventricular fibrillation, usually fatal
100 mA to 4 A
Certain ventricular fibrillation, fatal
Over 4 A
Heart paralysis, severe burns
To avoid or reduce the damaging effects current can have in a human body, is highly recommended to use protection protective equipment and take precautions when handling electrified circuits and equipment.
- Rubber Gloves – to To prevent touching hands from directly making contact with the current. They must be close fitting and have an excellent grip.
- Tight Sleeves and trouser Trouser Legs – To prevent unintentional contact or being pulled into dangerous equipment.
- Remove rings from fingers.
- Rubber Boots – To prevent the body from forming a complete conducting electrical circuit.
Electric shock occurs when the human body becomes part of the path through which current flows.
The direct result is electrocution. The indirect result can is injury resulting from a fall or uncontrolled movement into machinery because of a shock.
Burns can result when a person touches electrical wiring or equipment that is energised.
Arc-blasts occur from high-amperage currents arcing through the air. This can be caused by accidental contact with energised components or equipment failure.
The three primary hazards associated with an arc-blast are:
Explosions occur when electricity provides a source of ignition for an explosive mixture in the atmosphere.
Electricity is one of the most common causes of fires both in the home and in the workplace. Defective or misused electrical equipment is a major cause of electrical fires.
Safety signs keep persons aware of hazards. It is important to located them accordingly so persons working around the hazard can take proper precaution. They should be in visible places and include the maximum possible information about the source of danger and properties of itthe danger. In case of an incident, this information can be a valuable information.
Example of these sings can besigns include:
|Voltage Warning Labels||Electrical Voltage Symbol||Danger of Death from Electricity Warning||Switch Off when not in Use|
|Electric Shock Warning||High Voltage Warning||Overhead Cables Warning||Live Wires Warning|
|Buried Cables Warning||Mains Voltage Warning||Danger - Do not Enter Sign||Warning - Isolate Before Removing Cover|
Electricity is one of the most common causes of fire. Electrical current and the chemical reaction of fire are both methods of transferring energy; while electricity involves the movement of negatively charged electrons, a flame consists of the dispersal of both positive and negative ions. Therefore, faulty wiring for example can cause arcing and sparking that can easily become a flame if the conditions to produce a fire are present (, such as oxygen, heat and or any kind of fuel).
Power sources that are directly related to electrical fires can be any of the following:
Electrical fires need to be put out by a substance that is non-conductive substance, unlike the water or foam found in class A fire extinguishers. If someone attempts to put out an electrical fire with something like water, there is a high risk of electrocution since water is conductive. This is why class Class C fire extinguishers exist; the substances that can be found in these types of extinguishers are use monoammonium phosphate, potassium chloride, or potassium bicarbonate, which do not conduct electricity. Another option would be is a class C extinguisher that contains carbon dioxide (CO2). CO2 is great for suppressing fires because it takes the fire’s oxygen source away as well as diminishes the fire’s heat since the CO2 is cold when expelled from the extinguisher.
Prevention is the most effective measure to mitigate risk. Some of these preventive measures /actions planners can take when working around electricity include:
- Never plug appliances rated at 230 V into an 115V electrical socket.
- Place all lamps on level surfaces and away from things that can burn.
- Use bulbs that match a lamps’ rated wattage.
- Do not overload an electrical outlet by connecting several devices into a single receptacle using any device.
- Do not tug or pull any electrical cords.
- If an outlet or switch is feeling warm, shut off the circuit and call an electrician to check the system.
- Follow manufacturer’s instructions for plugging a device into an electrical outlet.
- Avoid running extension cords under carpets or across doorways.
- Do not connect the cord of an old electrical device to a newer cord.
- Replace and repair frayed or loose cords on all electrical devices.
- Keep all electrical appliances away from water.
- Contact electricity authority if any damage done to overhead cables, outdoor panel boxes, or trees touching high voltage lines is seen.
- Review architectural drawings and/or contact electrical authorities before doing any work involving digging.
- Take heed to all warning signs indicating electrical hazards.
- Ensure a fire extinguisher is placed where the likelihood of a hazard occurring is great.
- Always wear safety equipment when around electrical equipment.
Most humanitarian interventions - and especially the ones performed during emergencies - take place in remote or jeopardised communities with a poor availability and/or limited reliability of the electrical public grid. To operate, humanitarian organisations premises are frequently equipped with at least one independent power supply (batteries, generator or solar equipment), either as back up in case of grid failure or as the primary method of producing electricity. Independent power supplies include batteries, generators and solar-electric equipment.
Purchasing, installing and running such equipment requires important investments that can be reduced with a proper sizing and energy demand management. Electricity is not cheap, and running a generator can become quite expensive. Energy production also has an environmental impact and has the potential to damage the perception that the community could have about the organisationof organisations.
It is often possible to reduce electricity consumption without degrading the quality of service by improving the energy management, focusing on reducing the demand, and choosing the correct supply.
- Energy demand managementDemand Management: minimise Minimise energy consumption without reducing the quality of service and avoid unnecessary energy consumption.
- Energy supply managementSupply Management: selecting Select the best main and back-up power supplies in accordance to with the particular situation, properly sized to optimise investment and running costs.
To manage both demand and supply management, a proper diagnostic to understand the installation power and energy needs is required. Continued diagnostics it will be necessary at each step of the energy management process, mainly:
- To calculate the total energy and power needs of a planned operating environment and help sizing size the power supplies (generator, solar, or other).
- To identify the appliances and services that account for a significant part of the total energy and power needs.
- To understand the variation of the power and energy needs within a day and identify the peak periods.
It is normal to take electricity for granted, however it always will come with some costsenergy always comes at a cost. To improve the way the energy is used, avoid unnecessary consumption and minimise the inevitable without degrading the quality of the service. It is important to think in terms of service instead of devices, and try to find the most effective solutions to accomplish the required service.
- Identify high-impact services to understand what services have significant impact on power and energy consumption and when the peak periods occur.
- Examine potential alternatives – working tools, refrigerators, and lighting are obvious consumers of electricity and hard to avoid. Other consumers of energy offer other possibilities, such as water heaters and stoves. Consider possible solutions according to feasibility and initial cost, energy consumption and running cost and service quality.
- Reduce losses, increase efficiency by choosing efficient and well-sized appliances according to the purpose and number of users, and by using them in a way that maximises their efficiency, such as cleaning and maintaining equipment and appliances to increase their efficiency.
- Reduce unnecessary use by switching off and unplugging appliances when not in use. It may be required to display posters or leaflets to reminder users.
- Optimise consumption over time, identifying peak periods and if possible, avoid or postpone the use of the most powerful appliances during peaks or when running on battery/solar back-up systems. Mark powerful appliances for which who's use can be postponed, such as ones those for comfort or non-urgent tasks with red stickers and with one label the unpostponable ones used for , and differentiate those used or work, security, communications with another so users can tell one from the other.
Energy Supply Management
Properly choice Proper selection of main and back-up power supply will have a large impact not only in on cost savings, but in the way the energy consumption is optimised. The chosen combination must be able to:
The decision on the type of main power supply will depend mainly if the building is connected to the public electricity grid or not, which by default grid. Connection to a public grid is considered optimal where available and should be the first option if available. Only if If there is no grid, or the grid is not reliable at all should , then a generator be considered.
A back-up or generator can and will be required if a grid runs the risk of power outages, or when a redundant electrical system is required as a an essential safety measure.
The There are multiple options for a back-up system the options are wide - , including batteries, solar or smaller generators - and there . There are other considerations things to take in to account when selecting among thema back-up system, including what and how reliable the main source is.
Total Cost After 1 Year
Total Cost After 2 Years
Solar (covering 30% of energy needs)
Simulation of the global cost during 24 months (fuel price = 1€/L)
The The below decision tree will help guide the choice of the back-up power supply can follow this decision tree.
Main, Back-up and Possible Combinations
In many contexts, the main power supply is the electricity provided by the local power company. The A back-up is a generator that should be able to cover all electricity needs of the installation excluding appliance marked as non essential. (see See energy demand management).
Generator + Generator
In a generator only configuration, electricity is provided by a two or more generators. For using two generators:
- Both generators can either be identical or capable of producing the same amount of power, and can be used interchangeably and following a detailed use plan.
- One generator can be smaller than the other, and be used as a back-up only. In the case of two differently powered generators, the smaller unit it will not need to or be able to cover the entire electricity needs of the operating context, and may need to be wired specifically to power essential items only (see energy demand management).
Permanent noise and maintenance hassle
Grid + Batteries
In this configuration, the main power supply is the electricity provided by a local power company, while the back-up is a battery system that provides a limited autonomy to the installation in case of outage.
Generator + Batteries
In this configuration the main power supply is a generator that provides electricity during peak hours. The back-up is a battery system that accumulates electricity when the generator is running and supply supplies the installation during low consumption hours.
Public Grid OR Generator + Solar
In this configuration, electricity is provided by the main source - grid or generator - during peak hours and by solar system during the day. A battery system accumulates electricity from both all sources and supply supplies the installation when they are off.
A generator is a combination of an engine (prime mover) that produces mechanical energy from fuel and an electrical generator (alternator) that converts mechanical energy into electricity. These two parts are mounted together to form a single piece of equipment.
Mechanical generators as a source of power is the most are common one in the humanitarian sector apart from the public grid, mainly because it is they are usually available and can be acquired and installed relatively quick quickly almost everywhere. Generators are built on a well-known technology and it may not be hard to find a good technician to install one in many contexts. However, operating a generator is expensive, requires frequent and complex maintenance as well as a constant fuel supply and . Generators can also cause many problems, such as noise, vibration, pollution, and more.
The following are the main characteristics that have to take in consideration consider when selecting the appropriate equipment to cover the installation needs.
The first thing to evaluate when looking for a generator is its size - how much power can it generate?
Power rating is standardised as ISO-8528-1, the . The most common standards are:
Most of the time, only PRP is relevant when purchasing a generator. When acquiring a generator, check if the power of the generator is indicated without reference to a standardised rating method. If no rating model is indicated, either consult it with the manufacturer or obtain documentation from the seller.
A rating in watts indicates a real power (P); a rating in volt-amperes indicates an apparent power (S). Only the real power has to be considered when planning consumption. Real power is the power actually consumed or utilised in an AC Circuit, and therefore it is the way power needs and energy consumption is calculated in a diagnostic exercise.
If only the apparent power (in kVA) is indicated, you can evaluate the real power with the following general formula:
|P(W) = S(VA) × 0.8|
Here, 0.8 of apparent power is the assumed real power factor. This may vary from one machine to another, but 0.8 is a reliable average value.
Take lower operating rates (derates) into account: the The power a generator can provide decreases with increases in altitude and temperature. The following chart indicates correlations in environmental factors to derates:
(Note that temperature inside the generator room can be far higher than ambient temperature).
Example: A generator has an apparent power of 10kVA, and will operate at 1,000m elevation, and in a generator room with an average temperature of 45°C. What will the anticipated power output be:
Elevation adjustment: 10kVa x (1 - 0.099) = 9.01kVA
Average temperature of 45°C: 9.01kVa x (1 – 0,054) = 8.52 kVA
The “actual” apparent power is 8.52 kVa.
- 1,500 RPM: intended for intensive usage (running more than 6 hours) capable to reach high power.
- 3,000 RPM: intended for short term usage, with better power/volume and power/weight ratios but higher hourly consumption of fuel.
1500 rpm RPM generators should be preferred by most humanitarian actors.
An engine running is very noisy while running. The noise Noise level of a generator is an important consideration while looking for a generator, as it is usually running during working or resting hours. A continuous noise even at very low level can become exhausting over long period of time.
Noise levels are indicated in dB(A) LWA. For comparison purpose here are some common soundsounds .
Refrigerator at 1 m distance
Vacuum Cleaner at 5 m distance
Main road at 5 m distance
High traffic on an expressway at 25 m distance
Jackhammer at 10 m distance
Threshold of pain
- dB(A) @ 4 meters ≈ dB(A) LWA – 20.
- Then noise Noise level decreases by 6dB each time the distance doublefrom the source doubles.
Example: There is a 97 dB(A) LWA generator in a generator room located at 15 meters from a building. What volume will be heard in the building?
97dB(A) LWA is equivalent to 77dB(A) @ 4 meters
77dB @ 4m = 71dB @ 8m
71dB @ 8m = 65dB @ 16m
The noise level in the building will be approximately 65 dB(A), maybe lower depending on the acoustic isolation of the generator room and the office. This is an acceptable level for an office but not for a guest-house at night.
A generator cannot be refuelled while it is running, thus the tank capacity is one of the main factors determining autonomy. A conservative estimation of a 1500 RPM generator hourly consumption is 0.15 L x rated power. Fuel A fuel tank must be chosen accordingly.
Example: An 8kVA PRP generator powers an office without refueling refuelling it during working day (10 hours). Knowing these numbers, what is the suggested tank size?
The hourly fuel consumption of that generator is: 0.15 x 8 = 1.2L/hr
The calculation for the fuel tank is: 1.2 x 10 = 12L
Then the fuel tank capacity must be at least 12L
The choice of fuel must be determined according to the local price and availability of both type of fuel. One point to consider is what type of fuel the vehicles in the organisations use, using the same fuel for both generators and vehicles can reduce complexities of keeping multiple types of fuel in stock. Safety may also be a concern for very large stock quantities of fuel - diesel fuel also has a significantly higher flash point than gasoline, meaning it will ignite in the open air only above 52°C while gasoline can ignite in below freezing temperatures.
Generators must be equipped with a residual current circuit breaker, so that power surges and short circuits can trip the breaker locally, making it easier to reset and preventing damage from occurring further down the circuit. Additionally, generators usually have a manual breaker/transfer switch to control the connection of electricity to the installed circuit of the office or compound.
Generators generally require a specific place to be domiciled. Unless a generator is specifically designed for mobile applications, generally they do not usually move. A generator’s location has an impact in on its functioning and lifespan, thus and needs to be well planned.
It is good practice to install some kind of shock absorber to reduce generator vibrations, such as timber or rubber pieces. These help This helps reduce vibration by slightly raising the equipment, and also help control heat while making the unit easier to inspect and identify leaks.
Depending on the layout of the required operating space, generators may be installed in stand-alone rooms, be housed in some sort of open-sided generator shed, or may be exposed to air. Ideally, generators will have at least a roof or other form of covering above them to protect from rain, snow or excessive direct sunlight, all of which can impact the operation of a generator. Due the size and weight of generators, the shed or room may have to be built after the generator has been delivered, offloaded, and installed.
Passive Air Vent
Alternate Air Intake
Hot Air Output
Fresh Air Intake
The room or storage area must cover several purposes; isolate the generator to decrease the noise and environmental impact on its surroundings, and preventing non-authorised access from staff, visitors, animalanimals, or others. Even if a generator is relatively exposed, such as a covered awning with no walls, it is still advisable to have some sort of access control to the physical generator. Generator’s The generator’s storage areas may require additional physical built up walls on one or more side of the generator to block noise and prevailing winds.
Although construction materials can vary, the orientation must be planned carefully, taking advantage of the wind currents and minimising the noise and heat disturbances. A generator space should always be well ventilated, including the use of soffit vents or entirely exposed walls. If a generator is in a tightly enclosed space, a specially made air outlet ducts is are required. Ensure all outlets don’t discharge into areas where humans and animals work or access frequently. If no other option is available than to ventilate into areas where humans and animals access, then all discharge points should be at least two meters from said spaces and be well marked.
Wherever possible, position fuel or other DG set dangerous goods so that the prevailing wind do not enter into the radiator/exhaust outlet. If this is not possible, install a wind barrier.
In general, proper management of a generator starts by having an accurate and up to date monitoring system. Monitoring is crucial to be able to perform for performing analysis, identify potential failures and misuses, and inform informing future repairs and decision making. It is important to maintain records at least on:
Even though PRP generator types are rated for “unlimited” usage, this does not mean generators can run for an unlimited continuous time. Generators are still machines, which suffer from degradation and can overheat or break down. The continuous operation of generators may vary from machine to machine, but generally speaking the generators that humanitarian agencies obtain in field contexts are not designed to operate for more than 8 to 12 hours of continuous use at one single time. Running a generator for longer than an 8 to 12 hour period can dramatically shorten the life of a generator as well as and lead to a higher frequency of break downs.
Generators usually must be switched off for a cool down period, which is why many agencies will install two primary generators in a compound or office. The two generators are generally installed near each other if not in the same storage room, and are both connected to the main electrical circuit of the facility. If two generators are installed in tandem, there should be a large external transfer switch to route power coming from either one or the other generator at one time. A no point should both generators be able to supply an electrical current to the same closed circuit at the same time – this could cause catastrophic damage to facilities and equipment.
Use The use of two generators can be planned according to needs – either both generators should have identical power supplying capability, or the secondary generator is used for hours when load requirements are less. Solar power and other backup power supplies can also be connected to the external transfer switch. Usually, the act of switching between generators includes starting the incoming generator while the outgoing is still running. This will allow the incoming generator to warm up. It will also allow the main transfer switch to move between generators while power is being supplied, to minimise disruption to offices or living quarters.
Starting and Stopping a Generator
Generators above a certain size , and made for medium to long term usage generally have an internal switch used to connect or disconnect the unit from the main installed circuit of the office or compound. If the generator switch is set so that the generator is not disconnectedconnected, the motor will still run and the alternator will still produce electricity, however the main circuit will not be able to receive an electrical current.
Generators must never be started or stopped while connected to the installation, also called “loaded”. When
When a generator turns on, there may be spikes or stalls to the power produced, due to air in the fuel lines, debris or a other normal part parts of the startup start-up process. These surges in power can exceed the load rating of any given installation and can damage equipment if not properly protected. It is a good practice to have a poster or leaflet in the language of the persons operating the generator in all explaining the process to start and stop the equipment that includes photos of the main parts to touch and the actions to be taken.
- Warn users that the power will be cut.
- Open the generator circuit breaker (if the generator does not have a circuit breaker: open the installation main breaker).
- Wait 2 minutes and.
- Stop the generator.
- Record time of stoppage on the associated log book.
- Refuel if necessary.
Care & Maintenance
A generator must be regularly maintained to ensure it provides quality power throughout its life. Routine maintenance is relatively straight forward - there are general guidelines on what and when services are needed to prevent failures or enhance the equipment functioning.
While best generator maintenance best practice is following the manufacturer's maintenance and schedule provided by the manufacturer, the following controls and operations can be applied as a close approximation, especially if the manufacturer guidelines are unknown.
Daily or every 8 hrs
Every 150 hrs
Every 250 hrs
Every 500 hrs
Check Engine Oil & Fuel Level
Clean and Check Battery
Check Grounding connection
Clean Spark Arrester
Clean Fuel Filters
Drain fuel Tank
Change Engine Oil
Replace Air & Fuel Filter Element
Clean Engine Cooling Fins
Replace Spark Plug(s)
Check fuel injection nozzle
Replace Fuel Filter
Adjust Valve Lash
The service Service hours are tracked in “running hours,” meaning only the hours while the generator is actually on and supplying power. Note that even if running a generator for an average of 12 hours, reaching 250 or 500 hours of total running time can occur extremely quickly, meaning the service intervals for generators can be quite frequent. Small investments made in replacing components and maintaining generators on a regular basis can save expensive and unnecessary upgrades or even replacement of the entire unit in the future.
When performing routine maintenance, each action taken should be logged, as well as the readings and parameters recorded along with the date of inspection and the hour meter reading. These sets of readings are compared with the next set of data collected. Any considerable variation of reading may indicate faulty performance of the unit.
Load testing of automatic transfer switches in regular intervals keeps track of the electrical components and mechanical integrity in the actual mechanical transfer operation. Other factors to be checked periodically include starting and timing relays, start signal continuity, and utility phase sensing.
Preventative maintenance thus ensures that the organisation get has an uninterrupted power supply for all the their needs.If If a generator is rarely used, it is essential to start it at least once a week to keep it in good condition.
As often as required
At least once a week
150 hours maintenance
Every 4 months
250 hours maintenance
Every 3 month
|500 hours maintenance||Every 6 months||Every 2 years|
In some programs or sites of operation, it makes sense to have a trained repair technician permanently as part of the team. In most of the cases, is recommended to identify and establish a long-term agreement or other form of service contract with a trusted provider, . Service providers should be in charge of the main maintenance and be ready in case of breakdowns. Important criteria when selecting a third-party provider is their ability to supply spare parts for the required equipment. If a third-party provider cannot supply spare parts, then organisations will need to maintain a stock of their own spare parts.
A generator set is the combination of an engine and an alternator plus wiring, controls, protections and connections. Therefore, that is what needs These are the components that need to be checked when looking for a failure.
- The engine does not start.
- The engine starts, but it stalls or misses.
- The engines works all right but starts overheating after a while.
- The engine runs smoothly, but the electricity is not properly generated.
It is recommended to refer to the user manual for specific fault-finding instructions as designs vary between manufacturers. Faults liable to occur in these devices will depend upon the design of the control scheme supplied. Unless a problem is immediately identifiable, a professional generator technician or a qualified electrician may be required.
- A generator must never be operated in an occupied a room continually occupied by persons or animals.
- Generator A generator room must be correctly ventilated.
- Fuel and oil must not be stored in the generator room.
- A fire extinguisher rated for electric and fuel fires (preferably a CO2 fire extinguisher) must be available outside the generator room. Fire sand bucket can be an option when extinguishers are not available or as a complementbackup.
- All generator must be properly grounded/earthed. Usually, the generators came with a grounding bolt in the frame market marked with the ground symbol where connect the ground line, to which ground cables should be attached. If there is notno evident bolt, the ground line can directly be connected to the metallic frame of the generator.
A battery system leverages chemical reactions to store electricity for later use, be it electricity from a generator or public. In technical terms the electricity itself cannot actually be stored, but the relative energy equivalent is stored as potential energy through chemical reaction, and can be transformed into electricity later. Chemical batteries work by charging a solution that retains the charge long enough to be discharged again and distributed later.
As each battery has a limited capacity, battery power supplies require special equipment to monitor and control the flow of electricity entering a battery, called a charge controller. A charge controller will continuously monitor the charge state of a battery – recognising how “full” it is – and should automatically terminate charging once a battery is full. Batteries are highly energetic and can be extremely dangerous of if over charged! An overcharged battery can spark, start fires, and even explode, possibly throwing hazardous chemicals while it does. No battery power backup should be attempted without a proper charge controller in place.
A battery is a storage device capable of storing chemical energy and converting it into electrical energy though through electrochemical reaction. There are many different types of chemistry that are used, such as nickel-cadmium batteries used to power small portable devices or Lithium-ion (Li-on) batteries used for larger portable devices. The most proven type of chemistry and the longest used however is the lead acid battery.
Batteries are made with several materials and shapes suitable for different purposes. This guide will focus on the most common batteries used as a back-up of a for power generation sources. The two main types can be summarised as:
These batteries contain a combination of a liquid electrolyte that is free to move in the cell compartment. The user has Users have access to the individual cells and can add distilled water (or acid) as the battery dries out. The main characteristic for of this kind of batteries battery is their low cost, which makes them available almost everywhere in the world and widely used in low income or developing economies. Handling flooded batteries are quite easy, and they can be charged with a simple unregulated charger. However, these batteries require periodic inspection and maintenance, and extreme climates can have a greater effect on battery lives due to the electrolyte solution inside the battery having the ability to evaporate or freeze.
These batteries are commonly made with two terminals and 6 caps allowing access to each 2V compartment or cell, giving 12V in total. For this type of battery, the typical absorption voltage range is 14.4 to 14.9 volts ; and a typical float voltage range 13.1 to 13.4 volts.
Car or truck batteries are not suitable to be the permanent system for storage. There Vehicle batteries are designed to provide high current during short periods, specifically to start a combustion engine. There are lead-acid batteries that are specifically designed recently for storage applications.
Valve Regulated Lead Acid (VRLA) battery is a term that can refer to a number of different makes and designs, but all share the same property - they are sealed. VRLA batteries are sometimes referred to as sealed or onnon-spillable lead acid batteries. The sealed nature of the batteries make transport easier and less dangerous, and may even be transported via aircraft under certain circumstances. Being sealed however reduces their lifespan as they cannot be refilled – on average their life span is 5-year years at 20°C - as they cannot be refilled.
VRLA batteries are usually more expensive and require a fully regulated charger, which makes them less common throughout the world. These batteries may still use lead acid as a chemical solution, but the they used may use threaded pins instead of chambers and terminals.
The namesake of the battery comes from a valve regulating mechanism that allows a safe escape of hydrogen and oxygen gasses during charging. There are also more advanced designs, including:
AGM (Absorbed Glass Mat (AGM) Batteries
The AGM construction allows the electrolyte to be suspended in close proximity with the plate’s active material. This enhances both the discharge and recharge efficiency.
Since there are is no liquid inside, these batteries scan perform better than flooded batteries in applications where maintenance is difficult to perform, however they are sensitive to over or under charging affecting their life and performance. AGM batteries perform most reliably when their use is limited to the discharge of no more than 50% of battery capacity.
AGM batteries are usually the type of batteries selected in off-grid power systems.
Gel Cell Batteries
Gel cell batteries have a water-acid in gel form. The electrolyte in a gel cell battery has a silica additive that causes it to set up or stiffen. The recharge voltages on this type of cell are lower than the other styles of lead acid battery batteries, and gel cells are probably the most sensitive cell in terms of adverse reactions to over-voltage charging.
Gel batteries are best used in very-deep cycle applications and may last a bit longer in hot weather. Unfortunately a total deep discharge will irreversibly destroy the battery. If the incorrect battery charger is used on a gel cell battery, poor performance and premature failure is certain.
Note: It is very common for individuals to use the term gel cell when referring to sealed, maintenance-free batteries, much like one would use Kleenex a brand name when referring to facial tissuean entire product category. Be very careful when specifying a charger . More - more often than not, what when someone is referring to a gel cell they really mean sealed, maintenance-free VRLA or AGM-style battery. Gel cell batteries are not as common as AGM batteries, and would be hard to source in humanitarian contexts.
A battery capacity depends on:
- Discharge duration: Duration: Usually manufacturer indicated capacity at 20hrs, noted as C20. For a C20 batter, the same battery will be able to deliver more energy in 20 hours than in 10. Usually manufacturer indicated capacity @ 20hrs, noted as C20.
- Temperature: capacity Capacity can increase or decrease with external temperature. Rating is benchmarked at 20°C.
Also keep in mind that cycling a battery through its full capacity will likely damage it if done repeatedly. To increase battery lifespan, there should always be some energy left in it before recharging; for . For this reason, usually only 50% of the capacity is used. As a result, the energy a battery can actually deliver is better measured by looking at half its full capacity.
As a rule of thumb, the larger the battery and the higher the capacity, the more efficiency increases and while the price per watt-hour decreases. It is recommended to use the battery type with the highest capacity available, and then work off multiples of that battery type to reach the overall energy storage needs. Continually adding smaller, lower capacity batteries will lead to higher costs and more problems later on.
Float life is the expected service life of a battery if undergoes continuous charge, and is never discharged. When a battery is installed in an electrical system that constantly receive a charge and can be switched to in case of a power cut, it is called “float charging.” Float life "float charging." If power is cut and float charged batteries are switched to, the "float life" indicates how long these batteries can last. Float life decreases with temperature and manufacturer float life is usually rated at 20°C. As a general rule, float life will reduce by approximately half for every average temperature increase of 10°C.
Example: A battery with a rated float life of 10 years at 20°C. How long will it last if the average temperature is 30°C?
10 / 2 = 5 Years
It will last 5 years if the average temperature of the battery room is 30°C and only 2.5 years if the average temperature of the battery room reaches 40°C.
In addition to Float float life, Cycle "cycle life" is the number of cycles that the battery can withstand during its service life. A battery cycle is defined as a battery being fully charged and then fully discharge, making one full “cycle.” Is It is common to have this information in the technical specifications, always and it is recommended to buy batteries with a Cycle cycle life number bigger of more than 400 cycles.
Cycle life depends on the depth of discharge. A 50% depth of discharge is a good compromise between over-investment and quicker degradation.
The other characteristics of a battery are:
- Its selfSelf-Discharge Rate: Self-discharge rate : useful is defined as how quickly a battery will dissipate electricity if stored full but unused. Useful only if the batteries are intended to be stored for long duration. A lead-acid battery self-discharge rate is generally below 5% a month.
- Its freezing point: a Freezing Point: A battery will be destroyed if its electrolyte solution freezes. The freezing temperature depends on its construction, composition, and rate of charge - , and a discharged battery freezes more easily. A battery freezing point is almost always below that of water, however.
Number of Batteries Needed
Which The type of battery should be used in required for an installation will depend on the power needs, the budget, in the country of operations, and the conditions under which they system has to perform.
Once the battery model has been identified, the number of batteries required must be calculated. This can be done with the following formula, always rounding the number up.
|Number of battery = (Energy consumption)/ (max cycle depth × Battery voltage × Battery capacity)|
Note that all the batteries used in a battery system must be exactly the same:
- Same capacityCapacity: if 500Ah are needed it is not possible to use 2 x 200Ah + 1 x 100Ah. The system would require 5 x 100Ah or (preferably) 3 x 200Ah.
- Brand and Model: As much as possible, batteries should the same brand and model.
- Age: As far as possible, all batteries should have the same “history”: . It is strongly recommended to not mix old and new batteries, even if it is they are the same model.
While is important to select batteries that have the correct storage capacity and design, inverter-charger devices have the ability to can increase the efficiency of the system. Equally, an inverter-charger can damage a system if it is installed incorrectly, or of it is malfunctioning or poorly designed. The purpose of an inverter-charger is to transform current from AC to DC to charge batteries, and from DC to AC to discharge batteries. Inverter-chargers can do much more however – they can function as the “brain” of the electrical installation, coordinating the energy flows between the main source (generator or grid), batteries, and the end user. A proper inverter-charger can provide a far better quality of service than any other back-up systems, including:
- Increased power: power Power available from the inverter can be as high as 4 times the maximum power of the main power supply.
- Increased generator lifespan.
- Regulated voltage and frequency.
- Uninterrupted power supply.
Battery Cable Connections
The cables that join the batteries together play an important part in the performance of the battery system. Choosing the correct size (diameter) and length of cable is important for overall system efficiency. Cables that are too small or unnecessarily long will result in power loss and increased resistance. When connecting batteries, the cables between each battery should be of equal length to ensure the same amount of cable resistance, allowing all batteries in the system working equally together.
Particular attention should also be paid to where the main system cables that are connected to the battery bank. All too often the system cables supplying the loads are connected to the first or “easiest” battery to get to, resulting in poor performance and service life reduction. These main system cables that run to the DC distribution (loads) should be connected across the whole battery bank. This ensures the whole battery bank is charged and discharged equally, providing optimal performance. The main system cables and the cables joining the batteries together should be of sufficient size (diameter) to handle the total system current. If there is a large battery charger or inverter it is important to be sure that the cables are capable of carrying the potentially large currents that are generated or consumed by these pieces of the connected equipment, as well as all the other loads.
- Isolate the battery system to decrease the risk of accident - such as acid leakage , or harmful gas emissions - and prevent non-authorised access.
- Ensure good operating conditions: a battery room must protect electronics against water and dust, and be well ventilated.
Batteries used for power back up and distribution need a specific place to be located, and must be well planned. It is convenient to have the battery room close to the main power supply or the distribution board, however the batteries must not be installed in the same room as the generator. High or fluctuating temperatures considerably affect the service life and batteries performance. It , and it is recommended to have a separate well ventilated battery room with a temperature as close as possible to 20ºC. If A dry and ventilated a cellar or underground room is a perfect location, provided the underground storage location will not flood or collapse.
Under no circumstances should battery storage locations be located in living or working spaces. A fully charged battery is highly energetic, and can spark, give off fumes, combust, or even explode. A faulty charger or an overcharged battery may display signs of distress, including swelling and smoking. An However, an overcharged battery may also display no signs and provide no waringwarning. A ruptured battery can propel shrapnel and throw very toxic chemicals, while the fumes may be extremely harmful or even lethal if breathed. If a battery shows any signs of warping, distress or overheating, the entire system should be shut off, and the battery should be disconnected if and when it is safe to do so. Do no not attempt to reuse damaged batteries – they should be disposed of safely, and in accordance with local laws and regulations.
To size a battery system, the following will be needed need to determinebe determined:
- The maximum power the inverter has to be able to deliver to the installation.
- The amount of energy that must be stored in the battery to cover your needs.
- In some case, the power the charger can deliver to the batteries.
Please reference he the section on energy management on how to calculate the power and energy the system has to deliver.
To manually calculate manually the maximum power of the installation:
- List all electric appliances fed by the installation.
- Find the maximum power of each electrical appliance. For appliances including an electrical motor the maximum power is approximately three times the nominal power. For example, a 300W water pump will need around 1kW to start.
- Add all power together.
To manually calculate manually the energy consumption of the installation:
Take into consideration the hours that the battery system is intended to deliver electricity and plan accordingly. A battery configuration won’t be the same if the system will deliver power only during night or be use used as a full day twenty-four-hour backup. If it is possible, plan to run a generator during peak energy consumption hours, decreasing the number of batteries required and reducing the full cost of the system.
The power of the battery charger will determine how long recharging will take. A high-power charger that can charge batteries rapidly are is useful if the main power supply is very expensive – a big generator with high consumption - or if the electricity from the main power supply is only available during short duration - public grid available only few hours per day.
- If 12V charger is used, the charge current must be: 2,150 / 12 = 180A..
- If 48V charger is used, the charge current must be: 2,150 / 48 = 45A.
- The minimum duration to charge battery is 4 hours. Faster charging may damage batteries, and some batteries may have limitations longer than 4 hours.
- Even with a powerful battery charger powerful enough, the charge may be longer due to the limited power available from the main power supply - with 5kW generator, buying a 10kW charger is pointless.
- For chargers that have advanced settings, the charge algorithm may extend charge duration to save battery life. Some chargers automatically decreases the charge power when the battery is close to 100%.
Wiring batteries together in series will increase the voltage while keeping the amp hour capacity the same. In this configuration, batteries are coupled in series to gain higher voltage, for instance 24 or even 48 Volt. The positive pole of each battery is connected to the negative pole of the following one, with the negative pole of the first battery and the positive pole of the last battery connected to the system.
For example; 2 x 6V 150Ah batteries wired in series will give 12V, but only 150Ah capacity. 2 x 12V 150Ah batteries wired in series will give 24V, but still only 150Ah.
Wiring batteries together in parallel has the effect of doubling capacity while keeping the voltage the same. Parallel coupling involves connecting the positive poles and negative poles of multiple batteries to each other. The positive of the first battery and the negative of the last battery are then connected to the system.
For example; 2 x 12V 150Ah batteries wired in parallel will give only 12V, but increases capacity to 300Ah.
A series/parallel connection is combines the combination of the above methods and is used for 2V, 6V or 12V batteries to achieve both a higher system voltage and capacity. A parallel connection is required if increased capacity is needed. The battery should then be cross-wired to the system using the positive pole of the first and the negative pole of the last battery.
For example; 4 x 6V 150Ah batteries wired in series/parallel will give 12V at 300Ah. 4 x 12V 150Ah batteries can be wired in series /parallel to give you 24V with 300Ah capacity.
Sunlight and the Photovoltaic Effect
The photovoltaic effect , is the process of using sunlight to produce DC electricity in a silent, clean, and autonomous way. The equipment required to produce this electricity is commonly called a “solar panel,” and are modular and require minimum maintenance. Combined with their long durability solar systems are increasing in popularity in remote areas or when an installation is expected to last.
Solar panels are devices able to transform light radiation into electricity through a process of trapping the photons and using them to excite P-type and N-Type semiconductors to move free electrons. Modern photovoltaic panels can generally convert around 15-20% of energy directly into electricity. There are panels that are more efficient, but they are very costly and , easy to damage, and are generally not accessible in places where humanitarian organisations might work.
Light enters the device through an anti-reflective coating that minimises the loss of light by reflection; it . The device then effectively traps the light striking the solar cell by promoting its transmission to the three energy-conversion layers below.
- N-Type Silicon layer; Provides extra electrons (negative).
- P-N junction layer. The absorber The absorbion layer, which constitutes the core of the device orienting the electrons in one direction.
- P-Type Silicon layer; Creates vacancy of electrons (positive).
Most solar cells are a few square centimetres in area and are protected from the environment by a thin coating of glass or transparent plastic. Because a typical 10cm×10cm (4 inch × 4 inch) solar cell generates only about two Watts of electrical power, cells are usually combined in series to boost the voltage or in parallel to increase the current. A solar, or photovoltaic (PV), module generally consists of 36 or more interconnected cells laminated to glass within an aluminium frame.
One or more of these PV modules may be wired and framed together to form a solar panel, and multiple panels can be combined to form a solar array, together supplying power as a single unit.
All solar cells - and by extension solar panels - degrade over time. While solar systems draw energy from the sun, the sun also slowly breaks down the components of solar cells. Most commercially available solar panels degrade at an average rate of 2% per year of usage. The duration of use of an installation must be factored for planning and budgeting purposes. For example, a solar array installed in direct sunlight degrading at 2% a year means that after 10 years, the panels will only be roughly 80% as efficient as they were at the time of installation. Less efficiency means less Wattage output from the array, meaning longer periods of of time to charge batteries and less optimal charging times throughout the day. Humanitarian agencies planning to use solar arrays longer than 10 years in a single location may want to consider budgeting for the replacement of panels after 12-15 years if the the overall output is no longer meeting the needs of the location.
A complete photovoltaic system may consist of one solar module or many – solar panel or array - , depending on the power needed. While batteries can be used as back-up of any main power supply, solar systems need a battery system to storage store the energy produced. Therefore, a solar system always includes some form of battery system, either small or big. These batteries are specifically designed to deliver limited current over long period of time.
A power system can accommodate different electrical loads by regulating the voltage and/or current coming from the solar panels going to the battery to prevent overcharging. Most "12 volt" panels can put out about 16 to 20 volts in optimal conditions, so if there is no regulation the batteries can and will be damaged from overcharging. Most batteries need around 14 to 14.5 volts to get become fully charged. Like any other electrical system, proper assessment and cabling is are required.
A solar system is usually composed by:
Solar systems can accommodate almost any specific need because they are modular in nature. This makes it possible connect PV modules directly do many devices, such as submersible pumps or standalone freezer units, or as a complete solar power plants arrays able to produce energy for distribution purposesentire offices or compounds.
Solar modules are rated in Watt-peak, represented as nominal peak power (P max), derived from multiplying peak power voltage (Vmp) with its peak power current (Imp):
A 100Wp solar panel produces 100W under standards standard test conditions (STC). The STC exist only in laboratories, applying a solar irradiance to panels of 1,000W/m2 with a cell temperature of 25ºC. In a real installation, the actual production of electricity is usually far lower than the peak-power, but however the measures remain useful as qualitative reference to compare sizes and capacities as every panel is rated under those the same conditions.
Example: Label that Comes with Solar Panel
Daily Irradiance: The quantity of energy provided by the sun in one day is the most important parameter. Areas closes close to the equator have the best average irradiance, however this parameter general rule may vary greatly from one place to the other and from one season to the other. Average The average performance of a PV system expressed in KwH/m2/day can be referenced in the chart below.
Long Term Average Daily Sum
Long Term Average Yearly Sum
Shade, haze and haze, and cloudy weather: any obstacle blocking sun radiation light will decrease the energy production of the module. In addition, if a solar panel is partially shaded, the electricity production may stop as the shaded cells will consume the energy produced by the rest of the panel. In some cases, a phenomenon called “hot spot heating” occurs when the shaded portions of a single panel rapidly heat up as they consume electricity from the an unshaded part, and can rapidly destroy the panel. This can be prevented by using by-pass diodes which are commonly included in PV modules, but it is highly recommended to check on this feature.
Panel orientation: a poorly oriented panel - from for example facing the north in the northern hemisphere - will produce far less energy than the panel is rated for, or even no energy at all.
Temperature: Temperature above 25oC also can decrease the amount of energy produced by a solar panel.
Daylight Hourshours: Solar panels produce more electricity when the vertical rays of sunlight are closer together, providing more energy per square cm. By result, solar panels will produce less electricity as the sun is near the horizon than it will when the sun is directly overhead. A simple way to think about this: I practical terms, a solar panel near the equator that is outside for a 12 hour day will only produce the equivalent of 6 hours worth of peak electricity, and this is only under optimal conditions. Changes to the seasons or bad weather will drop this production even further.
WPV modules combined to create solar panels, and solar panels combined mounted together to create solar arrays are possible using standard junction boxes - MC3/MC4 type - that are waterproof and easy to connect. Like batteries, panel arrays should only use solar modules with the same characteristics, the same model, and as far a possible the same history.
Solar trackers - devices that orient panels towards the sun - are complex, expensive and not recommended outside of industrial uses and/or high latitudes where the sun moves considerably. Some mounts are designed to allow seasonal adjustment, giving the ability to switch manually between 2 two positions during the year, which should be more than enough to orient the modulesfor most installations.
There are essentially 2 two types of solar mounts available: Ground and Roof mounts. Ground mounted solar panels are easier to install and maintain than roof mounted systems. Roof mounted systems are difficult or impossible to adjust and can cause structural damage due to weight and wind pressure. However, ground mounts have their own problems; they occupy usable space, are more prone shade, and run the risk of accidental damage from cars and people. Mounting decisions should be made depending on the location and infrastructure available.
While more expensive upfront, the MPPT Charge Controller will give more power (and potentially reduce the size of the PV module) and extend the lifespan of the batteries connected to it. Certain controllers even allow to connect it connection to smart devices for remote control and monitoring.
Pulse Width Modulation (PWM): PWM charge controllers can be considered an electric switch between the solar panel and battery packs, programmed to only allow a pre-determined current into the battery. The controller slowly reduces the amount of power going into the battery as they the batteries approach maximum capacity. PWM Charge Controllers do not adjust voltage, meaning the batteries and panels must have compatible voltages in order to operate properly. This makes this type of charge controller suitable for smaller solar applications, or for installations that feature lower voltage panels and limited size battery banks. PWMs are a more affordable option but will result in a lower power production from the PV .
Turn solar Solar to electricityElectricity
small Small solar system
Large power system
This section will focus on connecting batteries to the solar system. Please reference the section on battery installation.
The storage location of the solar array connected batteries should be identified before sizing and purchasing the any equipment. Not only should the space be large enough to mount the required panels, the distance and cable length from the battery storage location will impact the calculated power requirements. Please reference the section on battery installation.
A good spot location to install a solar array will have the following characteristics:
- Inside the Be inside a compound and not visible from the outside. Ground mounted solar panels ideally should be protected by a wall or fence, so sufficient ground space is important.
- Arrays should be Be as close as possible to the battery system.
- Be away from shadingshade, such as trees or buildings.
Sometimes it is difficult to completely avoid shadesshaded areas. The priority should be to avoid shades shade during the sunny hours the sunniest hours of the day (generally 10am to 16pm). Remember that the positions position and sizes of shadows change with the seasons.
Solar Panel Position
To optimise energy production, solar panels must be carefully oriented to take full advantage of sunlight exposure. Solar panel pointing includes.
- Orientation - Orientation is the angle of the solar panel with relative to the north-south axis. solar Solar panels must face the south in the northern hemisphere and the north in the southern hemisphere.
- Tilt - Tilt is the angle of the solar panel with relative to the horizontal plan. Tilt is more difficult to optimizeoptimise. Latitude can be used as an approximation of the optimal tilt angle, as referenced in the guide below for panels with fixed angels. However, even on the equator panels should have a minimum tilt angle of 5 to 10° to avoid accumulation of water and dust on the panel.
The output of the solar panels is connected to the solar regulator, while the output of the solar regulator is connected to the batteries. The solar panel mounting frame is connected to the ground, and a grounding/earthing connection may be required is highly recommended for the regulator and surge protector as well.
Depending on the power or energy required, the panels can follow three different schemes that will give different power and current results. Connect the modules Modules connected in series, parallel, or a combination of both will give different power and energy outputs.
A Below is a simple method of sizing installations so that it produces they produce 30% of the daily energy needs during the worst month.months of the year:
Example: To cover 30% of the energy needs of an installation, how many solar panels will be needed for:
The total actual power production needed per day is: 12.88 x 0.3 = 3.87kWh
At an average daily production of 2.62kWh per 1kWp of module, the total daily need is: 3.87 / 2.62 = 1.48kWp
The actual number of solar panels required will depend on the peak-power of each individual panel. The configuration could be:
As there is an annual average daily production is 4.32kWh per 1kWp, 1.48kWp installation will produce 4.32 x 1.48 = 6.39kWh per day in yearly average, adding to the overall increased energy costs savings.
The solar regulator must be sized according to the number and type of solar modules used. Regulator sizing includes:
- The voltage should be the highest possible according to the number of solar modules in the systems.
- Maximum current should be equal to the short-circuit current (ISC) of your solar array. Short circuit current for one individual panel can be found on the identification tag of the panel or in the manufacturer manual. To calculate the short-circuit current of an entire array, combine the short-circuit currents of all panels connected in parallel.
Whenever persons must handle a PV solar panels , they must wear the proper protective clothing and equipment at all times.
More importantly - PV solar panels produce an electrical current, even when they are not connected to any other device! As long as a panel is partially exposed to light, it will be producing some form of current and can still pose a risk. A panel producing electricity will not make a noise or vibrate, and may not even be warm to the touch. Usually PV solar panels have no form of indicator light that they are producing electricity at all. For this reason, PV solar panels tend to look safe to the touch, while even when they may not be.
When installing, removing, or simply adjusting solar panels, they should be completely covered. If possible, work can also be done at night time. When carrying or handling solar panels, handlers should note all electrical connector outputs on the side, avoiding making accidental contact with them. Consider all wires coming from a solar panel as the same as a live wire coming from a powered grid or live generator.
PV Solar panels should always be in a secure location, just like generators and batteries. The orientation of buildings and vegetation may make this a difficult task, but planners should consider access control.
- If possible, install panels on roofs of buildings, and in areas where persons do not frequently visit - avoid roof top terraces or resting areas.
- Install solar arrays inside of compound spaces, inside the safety of a perimeter wall wherever possible. Even if arrays are inside a compound wall, there should be some form of signage and barrier fencing to prevent visitors or casual labour from accessing the area.
- If solar arrays are installed in the open or in remote locations, then a separate security fence or wall will need to be built around the outside. The equipment is expensive, but it can also harm humans and animals passing by. Persons unfamiliar with solar panels may be drawn close out of curiosity, so signage must be posted in the appropriate local language.
Sites and Resources
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- ACTION CONTRE LA FAIM, (2020). Solar pumping, Electrical design and installation.
- INTERNATIONAL COMITEE OF THE RED CROSS and MEDICINS SANS FRONTIERS, (2016). Electrical installation and equipment in the field, Rules and Tools.
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- MEDICINS SANS FRONTIERS, (2012) Electrical safety guidelines