Estimate your production and payback
Calculator Inputs
Formula used
This estimator models first-year energy production with an effective multiplier that captures system performance and losses.
-
Annual Energy (kWh):
kW×PeakSunHours×365×EffectiveMultiplier -
Effective Multiplier:
PR×Tilt×Shading×Inverter× (1 −OtherLosses%) -
First-year value:
AnnualkWh×Rate×NetMetering% -
Simple payback (years):
NetCost÷ (Value−O&M) - NPV: discounted cashflows across the analysis period, with degradation and growth rates applied annually.
Monthly production uses a seasonal profile that sums to the annual estimate.
How to use this calculator
- Enter your system size and peak sun hours.
- Adjust performance and loss factors for realism.
- Add electricity price, costs, and incentives.
- Set long-run assumptions for NPV and ROI.
- Click Calculate Solar Output to view results above.
- Use CSV or PDF buttons to export the report.
Example data table
| Scenario | System (kW) | Sun hours | Multiplier | Annual kWh | Rate | Annual value | Simple payback |
|---|---|---|---|---|---|---|---|
| Apartment backup | 2.0 | 4.5 | 0.72 | 2,365 | 0.16 | 378 | N/A |
| Typical home | 5.0 | 5.0 | 0.70 | 6,388 | 0.16 | 1,022 | 11.7 yrs |
| Small business | 20.0 | 5.5 | 0.75 | 30,113 | 0.18 | 5,420 | 6.8 yrs |
Production drivers and realistic ranges
Peak sun hours typically range from 3.5 to 6.5 per day, depending on location and season. A performance ratio near 0.75–0.85 is common for well-designed systems. Tilt and shading factors translate site conditions into output changes, so a 0.90 shading factor means about 10% less energy annually. In many markets, installers quote production in kWh per kW-year, often 1,200–1,800.
Loss modeling and effective multiplier
The effective multiplier combines PR, tilt, shading, inverter efficiency, and other losses. If PR=0.80, tilt=1.00, shading=0.95, inverter=0.96, and other losses=8%, the multiplier is 0.80×1.00×0.95×0.96×0.92 ≈ 0.67. This single number explains why nameplate kW rarely matches delivered kWh. Small changes compound: improving shading from 0.90 to 0.95 increases output by about 5.6%.
Energy yield benchmarks
Annual kWh is calculated as kW × peak sun hours × 365 × multiplier. For a 5 kW array, 5.0 hours, and 0.67 multiplier, annual production is about 6,114 kWh. Capacity factor is annual kWh ÷ (kW×8,760) and often lands near 15–25% for rooftop solar. A 10 kW system at the same assumptions produces roughly 12,228 kWh, scaling almost linearly.
Financial value and payback context
First-year bill value uses your electricity rate and net metering credit. With $0.16/kWh and 100% credit, 6,114 kWh yields roughly $978. If annual O&M is $150, net savings are $828. A $12,000 net cost would imply a simple payback near 14.5 years, before price growth effects. If net metering is 70%, the same output values at about $685, materially extending payback.
Lifetime view, NPV, and emissions
Degradation (often 0.3–0.8% per year) reduces energy over time, while electricity inflation can increase value. NPV discounts future savings using your chosen rate, commonly 4–8%, helping compare solar to other investments. Plan for periodic costs such as cleaning or inverter replacement in long horizons. Emissions offsets are annual kWh × grid factor; at 0.45 kg/kWh, 6,114 kWh avoids about 2,751 kg CO₂ yearly. Use the charts to stress-test assumptions and document your decision for stakeholders internally.
FAQs
What are peak sun hours?
Peak sun hours convert sunlight into an equivalent number of full-sun hours per day. Use solar resource maps, utility studies, or installer proposals. Small changes strongly affect annual kWh, so use a conservative average.
How do I set the performance ratio?
Performance ratio reflects real-world output after temperature, wiring, and operational impacts. For quality rooftop systems, 0.75–0.85 is typical. Use lower values for very hot roofs, older equipment, or limited ventilation.
How much does shading affect production?
Shading reduces energy and can amplify losses if it hits strings of panels. A shading factor of 0.90 implies roughly 10% less annual kWh. If your site has morning or winter shade, model it explicitly.
What does net metering credit (%) represent?
It estimates how much of each kWh produced offsets your bill. At 100%, exported energy is credited at the full retail rate. Lower credits apply when exports earn less than retail, or when self-consumption is limited.
Why use NPV in addition to simple payback?
Payback ignores timing and long-run changes. NPV discounts future cashflows and can include price growth, maintenance growth, and degradation. It helps compare solar to other uses of capital at a consistent discount rate.
How should I interpret the CO₂ offset result?
CO₂ offset equals annual kWh multiplied by your grid emissions factor. Use a local factor when available. It is a planning estimate, not a certified carbon claim, because grid intensity varies by hour and season.