Understanding the numbers
How solar generation and electricity savings are estimated
Learn the difference between solar capacity, units generated, electricity used on site and estimated bill savings.
By Arkasri Energy
Capacity and units measure different things
System capacity is described in kW; electrical energy is measured in kWh. One kWh is one electricity unit. A 5 kW system does not produce five units continuously, and its panel capacity may differ from the inverter’s AC rating.
Use a stated annual generation assumption
A preliminary illustration might use 1,440 kWh per installed kWp per year. With that assumption, 5 kWp gives 7,200 units a year, or an annual-average 600 units a month. These are arithmetic illustrations, not an assessed forecast for a particular roof; individual months will differ. A site model should use location, orientation, shade and system losses.
Separate generation from bill savings
Savings depend on how the electricity is used and on the applicable tariff and settlement arrangement. Electricity used on site and electricity exported may have different values. Fixed and demand charges should be considered separately, and savings should not exceed the charges actually avoidable.
Read an estimate alongside its inputs
Ask which module capacity, annual yield, consumption pattern, tariff and export treatment were used. Our home calculator is an initial illustration. For a school, hospital or pharmaceutical plant, share bills and available load data so the proposal can reflect the facility’s operating pattern.
Further reading: PVWatts solar generation estimator ↗