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  • 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 work, security, communications.

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 . 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.


Proposed Back-up

Initial Cost

Total Cost After 1 Year

Total Cost After 2 Years

2kVA generatorGenerator

600 €

14,600 €

28,800 €

Battery systemSystem

4,800 €

9,300 €

13,900 €

Solar (covering 30% of energy needs)

6,500 €

9,600 €

12,900 €

          Simulation of the global cost during 24 months (fuel price = 1€/L)

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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).



  • Simple and cheap
  • Locally available
  • Limited nuisances

  • Short outages occur as the generator must be started when the grid go down
  • UPS and/or regulator necessary
  • Fuel supply and stock necessary
  • Maintenance required for the generator even if it is rarely used

Recommended for

  • Building connected to a public grid with long unpredictable outages
  • Building connected to a public electricity grid in a deteriorated security context
  • Building connected to a public electricity grid and used for a limited duration
  • Emergency back up when required

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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).



Well-known technology

  • Locally available
  • Limited initial costs

Permanent noise and maintenance hassle

  • High running cost
  • Short outage as generators are switched
  • UPS and/or regulator required
  • Fuel supply and stock required
  • Limited reliability and frequent maintenance
  • Time consuming
handling the system.
  • to manage

Recommended for

  • Isolated building with high energy needs
  • Isolated building used for a limited duration
  • Emergency back up when required

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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.



  • 24/7 electricity without outage and micro-outage
  • High reliability
  • Good electricity quality
  • Easy to add solar supply
  • Limited nuisances
  • Grid dependent
  • Local
  • procurement and maintenance not always possible
  • Battery room required
  • Higher initial cost than a generator
  • Back-up generator may still be necessary
  • Limited lifespan of the batteries (2 to 5 years) and possible environmental impact of batteries disposal

Recommended for

  • Building connected to a public grid with short and frequent outages
  • Building connected to a public grid with night outages
  • First step towards
  • solar system installation

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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. 



  • 24/7 electricity without outage or micro-outage
  • No nuisance during low consumption hours (night…)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


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.



  • 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 with a few years visibilityIsolated 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.


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.

Generator Power

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:







No derate


No derate





















(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.

Noise Level

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

50 dB(A)

Vacuum Cleaner at 5 m distance

60 dB(A)

Main road at 5 m distance

70 dB(A)

High traffic on an expressway at 25 m distance

80 dB(A)

Petrol Lawnmower

90 dB(A)

Jackhammer at 10 m distance

100 dB(A)


110 dB(A)

Threshold of pain

120 dB(A)


  • 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.


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