Is solar worth your money?

I built this calculator to help you think about buying solar for a home you own and live in. I couldn't find a quality, free tool that wasn't hidden behind a sales funnel, and I wanted the ability to tinker with the numbers. Think of it as an educational tool for weighing solar as a use of a lump sum. It models a cash purchase, so there's no financing yet, and no rental or business tax treatment — no depreciation, no taxable income, no basis. Enjoy!

Model a new system from scratch or a quote.
Model a second system, an expansion, or adding a battery.
See what changes when you add or subtract things in real time.
Export & share your final settings when you find what works!

Simplified Questionnaire → This feeds the calculator and is a great place to start. Open the calculator → Enter a quote and your utility rate, or start from the worked example and change one thing at a time.

What it actually models

The tool defaults to an actual quote for a system in the Bay Area of California. You'll see that many quotes and sources are California-centric, because that is what I know best — but I have tried hard to make it flexible enough to model most situations and jurisdictions, with links and hints pointing to where you can get the numbers you need to make the tool work for you.

It models how much of your production you can actually use or store, how your utility credits the rest, how fast retail rates climb, and what the same money would have earned elsewhere.

What it isn't: an accounting return. This is a comparison of cash flows — money out now against utility bills you don't pay later. Avoided bills aren't income, nothing here is GAAP ROI, and no household reports any of it on a tax return.

In a changing world, low-risk places to put your money are hard to find. If we're going to compare solar to other low-risk uses of the same cash, we need to make sure our numbers are genuinely low-risk projections. I've attempted to build this into the tool with guidance and an "analysis years" entry you can set. There is also a stress-test feature. Of course, these are just best guesses in an uncertain world!

Start here

Simplified questionnaireAnswer plain-language questions and land in the calculator, fully filled in. The calculatorThe full interactive tool, with a year-by-year schedule and a shareable link. How it worksThe model in plain language, plus every fixed assumption and its source. Solar vs. investingWhy the comparison is opportunity cost, and how to pick a fair return rate. Solar + EVWhat an electric car really changes about a solar investment, and what it doesn’t. FAQShort answers to the questions people ask before running the numbers. AboutWho builds this, why, and how to report something broken.

Independent and non-commercial. No account, no email, nothing stored on a server — every scenario lives in the link you share.