Explore how shade timing and inverter assumptions affect solar production. Compare illustrative losses and verify roof shading with an installer design survey.
Quick answer
Illustrative loss = shaded-area fraction x time weighting x obstruction factor x inverter assumption.
Notes updated 2026-10-06
- Best for
- Homeowners pressure-testing solar proposals before signing.
- Inputs needed
- electric usage, local rate, system size or quote assumptions
- Formula used
- Illustrative loss = shaded-area fraction x time weighting x obstruction factor x inverter assumption.
- Method references
- PVEducation shading physics, NREL PVWatts production model
Can roof area tell me annual shading loss?
A shaded-area percentage is only a rough starting point. A winter morning shadow and a summer midday shadow affect different amounts of energy. Use a roof shade survey and production design to validate the estimate.
Will a microinverter recover every shading loss?
No inverter can restore sunlight that is blocked. Module-level electronics may reduce mismatch losses, but the recovery depends on wiring, bypass diodes, geometry and equipment. The percentages here are sensitivity assumptions.
How does this solar shading loss estimate work?
Illustrative loss = shaded-area fraction x time weighting x obstruction factor x inverter assumption.
A worked example with explicit assumptions
A design producing 10,000 kWh before shade with a measured 8% annual shade loss loses 800 kWh. At $0.20/kWh retail self-use, that is $160/year; exported energy may have a lower value.
What should I verify before using the result?
Area shaded is not annual energy lost. Bypass diodes, array layout and sun position matter; this sensitivity model cannot replace a shade survey.
Use your bill or written equipment quote, run a conservative scenario, and compare the result with the same inputs in another model.
References and next steps
Calculation notes updated 2026-10-06. Reference links explain the method; they do not establish a current utility tariff or installer price.
Read the full methodology or save and compare your solar plan.
Am I applying system losses twice?
A site production ratio calculated from PVWatts AC annual output already includes its modeled losses. Do not apply the same loss percentage again.
Worked example: For 12,000 kWh demand and a modeled 1,400 kWh/kW-year AC yield, divide by 1,400 directly; do not derate that yield by a second 14% factor.
What to verify: A new shade assumption can still be a separate scenario if it was not represented in the original model.
Method reference (not verification of example prices)Planning notes updated October 12, 2026. Example assumptions are not a local tariff.
Pressure-test the estimate
Treat the result as a planning range, not a promise. Re-run it with a lower and higher production estimate, your actual utility tariff, and the written installer quote.
- Check roof shade, orientation, tilt, and equipment losses.
- Separate cash price, financing fees, battery cost, and roof work.
- Verify export credits, fixed charges, and interconnection rules.
- Confirm incentive eligibility, deadlines, and tax treatment.
Sources behind this estimate
Use the method references below to check the formula and its limitations. Input defaults and illustrative scenarios are not current tariffs, guaranteed output or live installer quotes.
Utility export rates, eligibility rules, and installer pricing can change. Confirm the applicable tariff, interconnection requirements, and tax treatment before making a purchase decision.
Frequently asked questions
How do I use the solar shading loss calculator?+
Start with your actual usage, equipment or quote inputs, keep the displayed units, and change one assumption at a time. Area shaded is not annual energy lost. Bypass diodes, array layout and sun position matter; this sensitivity model cannot replace a shade survey.
What calculation does this tool use?+
Illustrative loss = shaded-area fraction x time weighting x obstruction factor x inverter assumption.
Can I check the arithmetic with an example?+
A design producing 10,000 kWh before shade with a measured 8% annual shade loss loses 800 kWh. At $0.20/kWh retail self-use, that is $160/year; exported energy may have a lower value.
What could change the accuracy of my result?+
Area shaded is not annual energy lost. Bypass diodes, array layout and sun position matter; this sensitivity model cannot replace a shade survey.
Can I use the estimate outside the United States?+
Physical kW and kWh calculations use the same units internationally. Dollar results, regional defaults, emissions factors, incentives and utility guidance are US-oriented. Replace rate and production assumptions with local values; do not apply US tax or export rules abroad.
Can I print or save results without registering?+
Use Print / PDF to save this page from your browser without an email address. The solar plan stores supported scenario inputs in your browser; private files should be checked and redacted before uploading for extraction.
Compare the decision, not just the number
Compare cash, loan, lease, and battery scenarios using the same production, rate, and quote assumptions before choosing a financing path.
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