Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
System size (kW)
8.13
Net cost after tax credit
$17,080
Payback period (years)
7.9
First-year savings
$2,166.00
25-year net savings
$56,762
Approx. 400 W panels needed
21
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter monthly electricity use (kWh).
- 2Enter electricity rate ($/kWh).
- 3Enter peak sun hours per day.
- 4Enter installed cost ($/W).
- 5Enter tax credit (%).
- 6Enter target offset of usage (%).
- 7Enter annual utility rate increase (%).
- 8Read your system size (kw) on the right — it updates as you type.
- 9Hit Share to keep the scenario or send it to someone.
About this calculator
Payback depends on three things: your utility rate, sun hours, and the 30% federal tax credit. In high-rate states the break-even often lands under eight years.
Worked example
Using the values the calculator loads with:
Inputs
- Monthly electricity use: 950 kWh
- Electricity rate: 0.19 $/kWh
- Peak sun hours per day: 4.8
- Installed cost: 3 $/W
- Tax credit: 30 %
- Target offset of usage: 100 %
- Annual utility rate increase: 3 %
Results
- System size (kW): 8.13
- Net cost after tax credit: $17,080.48
- Payback period (years): 7.9
- First-year savings: $2,166.00
- 25-year net savings: $56,761.67
- Approx. 400 W panels needed: 21
What each field means
Inputs
- Monthly electricity use (kWh)
- The monthly electricity use used in the calculation, measured in kWh. Starts at 950 kWh so you have a working example on load.
- Electricity rate ($/kWh)
- The electricity rate used in the calculation, measured in $/kWh. Starts at 0.19 $/kWh so you have a working example on load. Accepted range: 0.05–1 $/kWh.
- Peak sun hours per day
- The peak sun hours per day used in the calculation. Starts at 4.8 so you have a working example on load. Accepted range: 2–7.
- Installed cost ($/W)
- The installed cost used in the calculation, measured in $/W. Starts at 3 $/W so you have a working example on load. Accepted range: 1–6 $/W.
- Tax credit (%)
- The tax credit used in the calculation, measured in %. Starts at 30 % so you have a working example on load. Accepted range: 0–50 %.
- Target offset of usage (%)
- The target offset of usage used in the calculation, measured in %. Starts at 100 % so you have a working example on load. Accepted range: 20–130 %.
- Annual utility rate increase (%)
- The annual utility rate increase used in the calculation, measured in %. Starts at 3 % so you have a working example on load. Accepted range: 0–10 %.
Results
- System size (kW)
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Net cost after tax credit
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Payback period (years)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- First-year savings
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- 25-year net savings
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Approx. 400 W panels needed
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the home solar savings calculator work?
Payback depends on three things: your utility rate, sun hours, and the 30% federal tax credit. In high-rate states the break-even often lands under eight years. The underlying maths is: Production = kW × sun hours × 365 × 0.8 derate; payback = net cost ÷ annual savings.
What do I need to enter?
7 values: monthly electricity use, electricity rate, peak sun hours per day, installed cost, tax credit, target offset of usage, and annual utility rate increase. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the system size (kw) result mean?
It is returned as a decimal number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Estimates assume standard, average conditions — local rules, pricing, and materials vary.
Who is this tool for?
It's built for anyone doing everyday planning maths — a quick estimate that would otherwise need four browser tabs and a calculator app.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Solar Savings Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/solar-savings
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/solar-savings" target="_blank" rel="noopener">Solar Savings Calculator — RevenueLab</a> (2026).</p>
Source: [Solar Savings Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/solar-savings) (2026).