Convert an entered annual shading-loss percentage into lost kWh and bill value, or explore a clearly simplified timing scenario.
Use an annual shading loss from an applicable solar model or a scenario you choose. The timing option is only an illustration; clock hours are not equivalent to solar energy.
Use a site-specific estimate or explicit scenario. No inverter recovery percentage is assumed.
Advanced options
1 means no additional adjustment. Change only to test an explicit assumption; selecting electronics does not establish a recovery factor.
Table of contents
How to use our Solar Panel Shading Loss Calculator
- Enter Unshaded yearly production (kWh) from a solar quote, monitoring app, or no-shade estimate.
- Enter Electric price ($ per kWh), Peak sun hours per day (hours), Shade time per day (hours), and Array covered by shade (percent).
- Open Advanced options if the shade is seasonal, happens only on some days, or your Panel electronics are not DC optimizers.
- Click Calculate and read Estimated yearly solar energy lost first, then compare the 1-hour less and 1-hour more cards to see how sensitive your estimate is.
- Sanity-check the result: if Estimated yearly production lost seems too high, recheck that Shade time per day counts only useful daylight and that Array covered by shade is for the whole array.
Definitions
Unshaded yearly production: The kWh your solar array is expected to make in a year with no shade.
kWh: A kilowatt-hour is energy equal to 1 kilowatt used or produced for 1 hour [2].
Electric price: The price you pay for each kWh of electricity. Fixed customer charges are not included.
Peak sun hours per day: The daily sunlight energy converted into an equal number of full-strength sun hours.
Shade time per day: The number of useful daylight hours when shade falls on the panels.
Array covered by shade: The percent of the entire solar array covered by shade during the shade window.
Panel electronics: The inverter or panel-level equipment setting used to adjust how much shade may affect nearby unshaded panels.
Common mistakes and quick fixes
Mistake: Entering nighttime or weak evening shade in Shade time per day.
Fix: Count only shade that hits the panels during useful daylight, then recalculate Estimated yearly solar energy lost.
Mistake: Using the shaded percent of one panel for Array covered by shade instead of the whole array.
Fix: Estimate the percent of all panels covered during the shade window.
Mistake: Leaving Months with this shade at 12 when the tree or building shade happens only in one season.
Fix: Enter the number of affected months so Average loss during shaded months and yearly loss stay realistic.
Mistake: Typing the full electric bill total into Electric price.
Fix: Use the energy price in $ per kWh and leave out fixed monthly charges.
Mistake: Assuming optimizers or microinverters recover a fixed fraction of all shading loss. Fix: Use an applicable system simulation for "Annual energy lost to shade (%)". In the timing illustration, "Panel electronics" records context and does not choose the multiplier.
Limitations & Key Assumptions / Boundary Conditions
- This is a planning estimate, not a site survey or a bankable solar production model.
- The calculator assumes the shade pattern is similar during the entered months and days.
- Real losses can differ because sun angle, panel tilt, azimuth, cloud cover, bypass diodes, wiring layout, and inverter behavior are not modeled in detail.
- No fixed loss or recovery factor is assigned to "Panel electronics". Actual performance depends on the shading pattern, module wiring, bypass diodes, and specific hardware.
- If Shade time per day is greater than Peak sun hours per day, the time part is capped at 100 percent of the daily usable sunlight.
- The yearly loss is capped at 100 percent of Unshaded yearly production, so Estimated yearly production after shade cannot go below zero.
- Estimated yearly bill value lost uses only Electric price ($ per kWh). It does not model net metering rules, demand charges, time-of-use rates, tax credits, or fixed fees.
Methodology
How the estimate is calculated
The default basis multiplies unshaded annual production by the entered annual loss percentage. The optional timing illustration uses the formula below with a user-supplied multiplier. It assumes uniform energy across the chosen time and season; it is not a site-specific shading simulation.
shade_factor = user_supplied_timing_scenario_multiplier
loss_percent = 100 * min(1, min(shade_hours_per_day / peak_sun_hours_per_day, 1) * array_shaded_percent / 100 * shaded_days_percent / 100 * months_with_shade / 12 * shade_factor)
annual_kwh_lost = unshaded_annual_kwh * loss_percent / 100
annual_dollar_loss = annual_kwh_lost * electric_rate_per_kwh
production_after_shade_kwh = unshaded_annual_kwh - annual_kwh_lost
average_loss_per_shaded_month_kwh = annual_kwh_lost / months_with_shade
One-hour shade-time check
The calculator repeats the same loss formula twice to show how much the answer changes if the observed Shade time per day is off by about 1 hour.
less_hours = max(shade_hours_per_day - 1, 0)
more_hours = min(shade_hours_per_day + 1, peak_sun_hours_per_day)
annual_loss_if_one_hour_less_kwh = loss formula using less_hours
annual_loss_if_one_hour_more_kwh = loss formula using more_hours
Mini example
For 12,000 kWh/year without shade and an entered 10% annual loss, 1,200 kWh is lost, 10,800 kWh remains, and lost bill value is $192 at $0.16/kWh. In the timing illustration, 2 hours out of 5, 25% of the array, year-round daily shade, and a multiplier of 1 also gives 10%; that agreement is scenario arithmetic, not validation of the timing model.