kWh and MWh calculator

Three small tools: the unit ladder, plant energy from size and yield, and battery duration. Use a decimal point and no thousands separator (commas as thousands separators are read correctly). Defaults are the page's invented example. A design aid, not a guarantee basis.

1. Unit ladder

Energy value

Unit

- Wh

- kWh

- MWh

- GWh

- TWh

- MJ, - GJ

- Btu

Prefixes step by 1,000. 1 kWh = 3.6 MJ exactly (NIST SP 811) and 3,412 Btu (EIA, a rounded figure), so Btu results are approximate.

2. Plant energy from size and yield

Array size (DC, at STC)

Size unit

Specific yield, kWh/kWp a year (same as MWh/MWp)

Annual energy: - MWh (- kWh, - GWh)

Average power: - MW over 8,760 hours. Average day: - MWh

The default yield of 1,450 is invented. Use your own simulation result and say which energy boundary it uses.

3. Battery duration: MW against MWh

Power rating, MW

Energy rating (nameplate), MWh

Nameplate duration: - hours

Duration = energy rating divided by power rating (the EIA definition of nameplate duration). For usable and delivered energy, see the kWh page.