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Short for Alternating Current.


Short for Direct Current.


Small charged particles that exist as part of the molecular structure of materials.

Free electron

An electron that is easily separated from the nucleus of the atom to which it belongs.


Bodies that possess free electrons (metals, for example, but also the human body and the earth).


Bodies that do not possess free electrons (e.g., glass, plastic and wood).

Voltage (U)

The difference in charge between two points.

Current (I)

The rate at which charge is flowing.

Resistance (R)

A material's tendency to resist the flow of charge (current).


A closed loop that allows charge to move from one place to another.


Any material that allows electrical energy to be converted to thermal energy.


Additional power available for a short amount of time.

VRLA Battery

Short for Valve Regulated Lead Acid Battery.

Absorption voltage rangeRange

The level of charge that can be applied without overheating the battery.

Float voltage rangeRange

The voltage at which a battery is maintained after being fully charged.

Distribution Panel:

This is a circuit breaker and contains many electrical circuits. Using this, a circuit can be turned on or off.

Circuit breakers Breakers and Fuses:

These protect wires from overheating and are found in the distribution panel box. When there is an overload, that is, too much current flowing, the fuses will blow or the circuit breakers will trip. Fuses and circuit breakers are rated so therefore at a particular current, they will be damaged by the circuit will be off. 


Switches can energise circuits, that is, they allow a current to flow through. If carelessly used, these can cause damage to a person and to equipment. Receptacles connect the appliances to a circuit.


connecting metal parts of electric appliances to earth.

(W)Short for Watt, the Power unit measure.
(Wh) Short for Watt-hour, the Energy unit measure
(V) Short for Volts, the Voltage unit measure
(A)A Short for Ampere, the Electrical Current unit measure




2-way lighting, switch

Switch 3-way lighting, switch



Distribution board

Distribution panel, breaker panel

Earth, earthing

Ground, grounding



Residual current device (RCD)

Ground fault circuit interrupter (GFCI)

Skirting board




In general, the word energy refers to a concept that can be paraphrased defined as anything that has "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. Energy is a conserved quantity, meaning that it cannot be created or destroyed, but only converted from one form into another; for instance, a battery converts chemical energy into electrical energy.

The aim of this is guide is to provide an idea about guide users on how to transform and use the electric energy in to electric power where electric current is used to energise the and electric power used for equipment and devices needed in the humanitarian interventions. Understanding the , including; understand basic electric concepts, knowing how to properly size the installationinstallations, and how to efficiently manage it with all the safety and precautions measures in placeelectrical installations.

Electrical Basics

An electric current is a flow of electric charge in a circuit ; in other words, the flow of a free electron electrons between two points in a conductor. The energy of these These free electrons in motion is what constitutes electrical energy. Electricity production consists of forcing the electrons to move together in a conducting material by creating an electron deficit on one side of the conductor, and a surplus on the other.


When a load is connected to the generator’s terminals, the generator pushes electrons: it absorbs the + charges positive charged particles and sends back the negatively charged particles. In the a circuit, the electrons circulate from the – terminal to the + terminal.

To be able to use electrical equipment properly and safely it is important to understand electricity works.  It is vital to start by understanding the basics of voltage, current, and resistance - the understand the three basic building blocks required to manipulate and utilise electricity - voltage, current, and resistance - and how the three relate to each other.


















Diameter (mm)














Cross Section (mm2)














Colour Code

Colour Coding

While is possible to use the same cables 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. 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.


The lower the resistance, the better 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.


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.

Short Circuit

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 by a weak overcurrent occurring over a long duration. Overloads can be caused by a current that is too high to be conducted through the relative diameter of the conducting cable.


  • 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

Insulation faults are caused by damage to the insulation of one or more phase conductors. These 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.


This image depicts an electrical current as it flows through the human body.

The arrows indicates indicate 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 ExposureReaction

More than 3 mA

Painful shock

More than 10 mA

Muscle contraction – “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

Safety Equipment

To avoid or reduce the damaging effects current can have in a human body, is highly recommended to use protective equipment and take precautions when handling electrified circuits and equipment. 


  • 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 who's use can be postponed, such as those for comfort or non-urgent tasks, and differentiate those used or for work, security, communications.


There are multiple options for a back-up system, including batteries, solar or smaller generators. There are other things to take in to into account when selecting a back-up system, including what and how reliable the main source is.


In many contexts, the main power supply is the electricity provided by the local power company. A back-up is a generator should be able to cover all electricity needs of the installation excluding appliance marked as non-essential. (See energy demand management).


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 supplies the installation during low consumption hours. 



  • 24/7 electricity without outage or micro-outage
  • No nuisance during low consumption hours 
  • Good electricity quality
  • Better reliability and service-life of the generator
  • More flexibility on power consumption
  • Easy to add solar supply

  • Fuel supply and stock required
  • Minimum daily running duration for the generator to reload batteries
  • Local purchase and maintenance may not be possible
  • Battery room required
  • Higher initial cost than generator alone
  • Back-up generator may still be necessary
  • Limited lifespan of the batteries (2 to 5 years) and possible environmental impact of battery disposal

Recommended for

  • Isolated office or compound
  • First step towards Solar system installation

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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 all sources and supplies the installation when they are off.



  • Same as “grid/generator + battery”
  • Lower nuisances
  • Fuel saving, best cost/efficiency ratio on the long run for isolated building
  • Very reliable back-up power supply

  • Could require some time to be installed.
  • Local purchase and maintenance may not be possible
  • Battery room and a large open surface required
  • High initial cost
  • Limited lifespan of the batteries (2 to 5 years) and possible environmental impact of battery disposal

Recommended for

  • Isolated guest-house
  • Isolated building with limited energy needs
  • Isolated building in area where fuel supply is very difficult and/or very expensive
  • Building where security context impose a very reliable and totally autonomous back-up power supply, such as places with possible hibernation requirements.

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Generators Sets

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.


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.


  1. Make sure that the generator circuit breaker is open (if the generator does not have a circuit breaker: make sure that the installation main breaker is open).
  2. Check the oil level.
  3. Check the fuel level.
  4. Check the water level (for water-cooled generators only).
  5. Make sure that there is no leakage (no oil or fuel under the generator).
  6. Start the generator.
  7. Wait 2 minutes.
  8. Close the circuit to the main circuit of the office or compound.
  9. Record time of start on the associated log booklogbook.

Standard stopping procedure:

  1. Warn users that the power will be cut.
  2. Open the generator circuit breaker (if the generator does not have a circuit breaker: open the installation main breaker).
  3. Wait 2 minutes and.
  4. Stop the generator.
  5. Record time of stoppage on the associated log booklogbook.
  6. 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

General Inspection

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.


Intensive Usage

Occasional Usage

Starting generator

As often as required

At least once a week

150 hours maintenance

Every month

Every 4 months

250 hours maintenance

Every 3 month

Every year

500 hours maintenanceEvery 6 monthsEvery 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 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.

Safety Considerations

  • 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.


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:


Flooded cell batteries are the most common conventional battery used in internal combustion vehicles. Flooded cell batteries are referred to in several ways:

  • Flooded Battery.
  • Welt Wet Cell Battery.
  • Spillable Lead Acid Battery.
  • Resealable Lead Acid Battery.

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 increase with  
  • Temperature: 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 need to be needed to determinedetermined:

  • 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:

  1. List all electric appliances fed by the installation.
  2. 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.
  3. 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.

Additional considerations:

  • 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%.


Series Connection

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.

Parallel Connection

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.

Series/Parallel Connection

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 absorption 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

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 .





Charge Method

3 stage


Battery Charge

Multi-Stage MPPT

Conversion Rate

Turn solar Solar to electricityElectricity



Ampere Rate

30A -100A



small Small solar system

Product Range


Large power system


Average Price

  • PWM Regulators have a longer and proven history.
  • PWM Regulators are a more simple have simpler structure and are more cost-effective.
  • Easily deployed.
  • Maximum power point tracking algorithm increases power conversion rate up to 99%.
  • 4 stage charging is better for batteries.
  • Scalable for large off-grid power system.
  • Available for solar systems up to 100 Amps.
  • Available for solar input up to 200V.
  • Offer flexibility when system growth required.
  • Equipped with multiple protection devices.
  • Low conversion rate.
  • Input voltage must match battery bank voltage.
  • Less scalability for system growth.
  • Lower output.
  • Less protection.
  • High cost, usually twice a PWNPWM.
  • Larger Size than a PWM regulator.

Panel Installation

This section will focus on connecting batteries to the solar system. Please reference the section on battery installation

For a proper installation of a solar array, ideally the 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 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.

Installation Sizing

PV Modules

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:

  • A planned power need of 12,880Wh
  • An annual average daily production is 4.32kWh per 1kWp
  • During the worst month, an average daily production of 2.62kWh per 1kWp

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:

  • 12 x 130Wp panels (1.56kWp)
  • 9 x 180Wp panels (1.62kWc)
  • 6 x 260Wp panels (1.56kWc)

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.


Information about Batteries sizing can be found in the section on installing a battery system.


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.