Solar
Solar Savings Calculator
Solar savings equal the lesser of annual production and annual usage multiplied by the visible electricity rate. Long-term values apply the entered rate change and production degradation assumptions.
Estimate annual solar production, first-year bill offset, and long-term simple savings from visible usage, system, rate, and degradation inputs.
Calculated result
Solar production estimate
Calculating…
Calculated locally in your browser
Planning math only. Verify equipment specifications and installation requirements separately.
Layer B · economics
Economics estimate
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State averages are editable prefills, not utility tariffs. This section is not tax, financial, or investment advice.
Data provenance: NLR PVWatts v8 grid awaiting its first private-key refresh; the visible peak-sun-hours fallback is active. EIA residential state averages updated 2026-08-13. ZIP centroids use the 2025 Census Gazetteer. No ZIP or calculator input is sent to those sources. Read the solar data provenance and limitations.
What this calculator returns
Retail-rate offset is not the same as a utility bill forecast. Fixed charges, time-of-use periods, export tariffs, and minimum bills are excluded.
Use savings to test bill-offset assumptions
This page answers how much of the entered electricity spending could be offset under a simple retail-rate scenario. It focuses on energy value rather than the date the system recovers its cost.
- Energy eligible for offset
- The model values no more solar energy than the entered annual household use, preventing excess production from automatically receiving a retail value.
- Rate basis
- The editable electricity rate is the value applied to eligible energy; a state average is not a substitute for a utility tariff.
- Bill items left outside
- Fixed charges, demand charges, minimum bills, time-of-use periods, taxes, and export compensation can make the actual bill change different from this result.
Formula and variables
The calculation runs entirely in your browser. Static formulas, definitions, examples, and tables remain readable without JavaScript.
Annual production = array kW × adjusted kWh/kW; annual bill offset = lesser of production and use × electricity rate.
- S1
- First-year simple bill offset from eligible solar energy and the entered electricity rate.
- Eoffset
- The lesser of modeled annual solar production and entered annual household use.
- r0
- Editable starting electricity value per kilowatt-hour, not a complete utility tariff.
- g
- User-selected annual rate-change scenario applied to future eligible energy value.
- d
- Entered annual production degradation used to reduce modeled energy in later years.
The production result remains available without economics; savings use visible rate, cost, rate-change, and degradation assumptions.
Worked example
| Input | Value |
|---|---|
| Solar array size | 8 kW DC |
| Monthly energy use | 900 kWh |
| ZIP Code | 80202 |
| Peak sun hours fallback | 4.5 h/day |
An 8 kW array is first converted to annual kWh; savings then apply the visible editable rate only to energy that does not exceed annual household use.
Reference table
| Bill component | Calculator treatment | What to verify |
|---|---|---|
| Eligible solar energy | Capped at entered annual use | Self-consumption and export quantities |
| Energy rate | One editable value per kWh | Time-of-use and tiered prices |
| Fixed and minimum charges | Excluded | Charges that remain after solar |
| Exported energy | No automatic export credit | Current utility compensation rule |
Frequently asked questions
Why is production capped at household use for bill offset?
The simple model values only production up to entered annual use and does not assume an export-compensation rate.
Does this predict my utility bill?
No. Fixed charges, time-of-use pricing, export rules, taxes, minimum bills, and demand charges are outside the model.
Why can actual bill savings be lower?
Exports, fixed charges, time-of-use prices, minimum bills, taxes, and utility rules can value solar energy differently from a simple retail-rate offset.
Assumptions and limitations
- Not tax, financial, or investment advice.
- EIA values are state averages, not utility tariffs.
- Actual production varies with weather, soiling, shading, degradation, and equipment.
- Obtain a licensed installer site assessment.
Method and sources
Review the solar data sources, calculation methodology, and electrical formulas for the references most relevant to this calculation. The broader technical sources index records source scope and verification. Last reviewed .