Calculators
Two different questions, and only one of them needs a calculator you cannot get anywhere else.
Sizing backup power: use the step-by-step guide
If you want to know what size solar generator your home needs, that is arithmetic you can do in five minutes, and we have written the method out in full:
How to size a solar generator for home backup →
It gives you a load table with the real watt-hours per day of a fridge, a furnace blower, a window air conditioner, a CPAP, a sump pump and a well pump, then walks through six steps: list what has to stay on, add up the daily watt-hours, decide how many days you must cover, check the output and the start-up surge, check whether you need 240V, and decide whether solar recharge changes the answer. It ends with three worked examples and a lookup table from daily watt-hours to the unit that covers them.
That is the calculation almost everyone arriving here actually wants, and doing it by hand takes less time than filling in a form.
If you would rather start from the recommendation and work backwards, the backup power buying guide names the five units we would buy and says who each one is for.
Rooftop solar costs and payback: use the state pages
For rooftop solar costs, incentives and payback, the numbers are state-specific and we publish them per state rather than behind a calculator:
Every state page lists the average system cost, the average cost after rebates where one applies, typical lifetime savings, the average payback period, the utilities that serve the state, and the incentives currently on the books. Bear in mind that the federal Residential Clean Energy Credit (Section 25D) was repealed for systems placed in service after 31 December 2025, so a payback figure that assumes a 30% federal credit is out of date. Always verify current incentives with the IRS, DSIRE and a tax professional before you commit.
Solar savings calculator: still to come
An interactive rooftop savings calculator is still on the list. It would let you estimate:
- The system size you need based on your average monthly electric bill
- Total system cost in your state
- Federal, state, and utility incentives you qualify for
- Estimated payback period and lifetime savings
- Whether owning or leasing makes more sense for your situation
We have not shipped it because the honest version of that tool depends on incentive rules that changed at the end of 2025 and are still settling, and a payback number that quietly assumes a credit you can no longer claim is worse than no number at all. The state pages carry the same figures with the assumptions written out where you can check them.
Want to be notified when the savings calculator launches?
Email us at [email protected] and we will let you know.