The steps below explain how to calculate the total Daily System Energy Requirement. This is the amount of energy that must be generated to meet the total daily load demand plus the extra energy required to overcome system losses.
The way you calculate the Daily Load Energy Demand in watt hours as explained below. This will enable you to establish your electricity generating requirements, and to provide any suppliers with that information. By rule of thumb, if your daily load energy demand is greater than 1 kW (kilowatt), then photovoltaics (PV) will not be your electricity energy source, and some other electricity generation, whether by generating set, wind, hydropower, biomass steam electric turbine, or other source will be needed.
Column A |
Column B |
Column C |
Column D |
Column E |
Lamp or appliance |
Voltage |
Power |
Daily use |
Daily Energy Use |
(list bellow) |
(volts) |
(watts) |
(hours) |
(watt hours) |
1. |
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2. |
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3. |
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4. |
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etc. |
The Daily Load Energy Demand is the amount of energy required each day to power the load (i.e. lamps and appliances). This is measured in watt hours and amp hours. It is calculated by totalling the energy that all the appliances and lamps used on an average day.
Column A: Individual load description. List all the lamps and appliances to be powered by the system here. When listing appliances, you should consider all the appliances to be powered by the system, even those that will be purchased in the future.
Column B: Individual lamp and appliance Voltage. List the voltage of each to the appliances and lamps. This will help determine if an inverter is needed.
Column C: Individual lamp and appliance Power. List the power in watts of each appliance and lamp. Usually, the manufacturer indicates the power rating on the appliance itself. Radios and cassette players are rated according to their maximum power, but they normally operate at much less than half the indicated power. (i.e. if a cassette player is rated at 30W, write down 15 watts in column C).
Column D: Individual lamp and appliance Daily Use (hours per day). List the estimated amount of hours per day that each lamp and appliance will be used. If the appliance is only to be used a few times per week (i.e. a sewing machine might only be used on weekends), estimate the number of hours it is used per week, divide by 7 and write the number of hours per day in column D.
Column E: Individual lamp and appliance Daily Energy Use (Wh/day). Multiply the power of each load (column C) by the number of hours it is used per day (column D) and write the figure in column E. This is the energy use in watt hours per day of each appliance.
Summary: Daily Load Energy Demand. Add all the numbers in column E, and write the total on a Summary Line below your table. This is the Daily Load Energy demand in watt hours. You should provide this information to any electricity generating equipment suppliers to help them size your electricity system.
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