FixerCalc

Solar Savings Calculator

Solar sales decks often hide the assumptions. This calculator uses your kWh, rate, kW, sun hours, derate, and an incentive percent you type—so you can reproduce the math on a napkin.

Last reviewed 2026-08-25. How we calculate

Results update as you type. Units stay imperial inside the math.

Bills

Average a full year of bills if you can. One mild month will understate use.

Include delivery charges if that is how you actually pay. Do not use the generation-only line if you pay more.

System

Lower 48 planning values often fall roughly in the 3.5–6.5 range. A site survey beats a map.

Inverter, soiling, temperature, wiring. 0.75–0.85 is a common planning band.

Money

Enter 0 if you are not sure you can use a credit. Do not copy a sales flyer blindly.

If 0, 20-year savings is 20 × year-1 savings. If you set 2%, we compound the rate for a what-if only—not a forecast.

Results

  • Estimated annual production

    10,512 kWh

  • Year-1 bill savings (production × rate)

    $1,682

  • Simple payback on net cost

    13.3 years

  • Net system cost after your incentive %

    $22,400

  • Production vs. annual use

    97%

Annual household use
10,800 kWh
Gross installed cost
$22,400
20-year undiscounted savings (what-if)
$33,638
Assumption
Every produced kWh is worth your all-in rate. Check your tariff.
  • This is not a shade study, interconnection application, or finance offer. Net metering rules can make bill savings much lower than production × retail rate.
  • Enter incentive percent yourself. We do not invent a federal or state credit from your location.

How this calculation works

  1. Annual production (kWh) ≈ kW × peak sun hours × 365 × derate.
  2. Year-1 savings ≈ production × $/kWh. That assumes you get retail-like value for every kWh, which is not true under all tariffs.
  3. Gross cost = kW × 1000 × $/W. Net cost applies your incentive percent. Simple payback = net cost / year-1 savings (if savings > 0).

kWh/yr = kW × sunHours × 365 × derate; net$ = kW×1000×$/W × (1 − incentive%); payback = net$ / (kWh/yr × rate)

What to do next

  • Compare this production to a PVWatts or designer report for the same kW and address.
  • Read your utility’s net metering or net billing rider. Export credits may be far below retail.
  • If payback uses a 30% credit you cannot take this year, rerun with 0% or a realistic percent.

FAQ

Why is the default incentive 0%?
Because eligibility and rates change, and a tax credit is not cash at closing for every household. Typing the percent you actually expect is more honest than a hardcoded marketing number.
Does this include battery storage?
No. Add battery cost into a higher $/W or treat it as a separate project. Backup value is not the same as kWh savings.

Sources

  • Annual kWh ≈ system kW × peak sun hours/day × 365 × derate. Simple payback = net cost / annual $ savings

Cost defaults are typical US planning bands, last reviewed 2026-08-25. Edit the price fields on this page rather than treating them as a local market index.