ToolForage.
ENERGY CALCULATOR

Solar Energy Calculator

Make a first-pass solar generation estimate using array capacity and a peak-sun-hours assumption for a defined period.

Calculator

kW DC
h/day
Equivalent full-sun hours for this period and array orientation, not daylight hours.
%
Include temperature, inverter, wiring, shading, and other losses once.
%
YOUR RESULTS
Generation in the period480 kWh
Average daily generation
16 kWh
Generation used on site
336 kWh
Generation exported
144 kWh
Estimated energy value
74.40

Where the generated energy goes

  • Generation used on site336 kWh
  • Generation exported144 kWh

Both amounts are in kWh; the self-use share is supplied by you.

Understanding your result

Generation is split into energy used on site and energy exported. Energy value combines avoided imports and export credits at your entered prices. It is not a complete bill forecast or a return-on-investment calculation.

For an electric vehicle’s energy requirement, the EV Charging Calculator estimates charger-side kWh between two charge levels.

The formula

Daily kWh = array kW × peak sun hours × (1 − combined loss/100). Period kWh = daily kWh × days.

Peak sun hours express daily irradiation as an equivalent number of hours at reference full-sun intensity. The combined loss factor reduces the theoretical nameplate output once. Self-used and exported energy are then valued at their separate rates.

Worked example

A 5 kW array with four peak sun hours and 20% combined losses averages 16 kWh daily, or 480 kWh in thirty days. At 70% self-use, 336 kWh offsets imports and 144 kWh is exported. Prices of 0.20 and 0.05 give an estimated energy value of 74.40.

How to use this calculator

  1. Enter the DC nameplate capacity of the complete array.
  2. Supply peak sun hours appropriate to the location, orientation, and period.
  3. Set combined losses, self-use share, and the two energy prices.

Daylight hours are not peak sun hours

A long summer day does not provide full rated output for every daylight hour. Solar-resource data incorporates changing sunlight intensity. Orientation, shading, weather, and season all matter. Use a site-specific resource estimate for the relevant period rather than treating the example as a universal climate assumption.

When to use a detailed solar model

This calculation applies a single resource figure and one loss factor; it does not retrieve weather or model an inverter hour by hour. Tools such as PVWatts provide a more detailed location-based analysis. If multiple independent losses are known, combine their remaining fractions instead of blindly adding percentages. Include inverter effects only once when choosing the combined allowance here.

Assumptions & limitations

What this calculation assumes

  • The input resource and loss factors represent an average over the selected period.

What to keep in mind

  • No hourly clipping, battery dispatch, tariff tiers, installation cost, or guaranteed savings.

Common questions

Does the result include a battery?

No. The self-use percentage is entered directly. Storage losses, charging schedules, and battery capacity require a separate model.

Can I multiply one sunny month by twelve?

That can overstate annual generation. Use a representative annual-average resource value or calculate seasonal periods separately.

Sources & further reading