Solargrin is a free library of solar planning calculators — built for the person staring at a utility bill trying to figure out if solar actually makes sense for their roof.
Most solar calculators online exist to collect a phone number for an installer's sales team. You put in your address, and instead of a number, you get a call three minutes later. We wanted the opposite: instant, honest math, with the ability to see exactly which assumption changed the answer — no address, no phone number, no forced quote request.
Every calculator uses transparent, published formulas — the kind an installer or electrical engineer would sanity-check a proposal with. Country-level defaults (electricity rates, average sun hours, typical install cost) come from public utility and market data and are refreshed periodically; every default is visible and editable, never hidden inside the math.
We're upfront about the limits: these are planning-stage estimates. Shading, roof condition, panel orientation and local permitting will all move the real number. Use Solargrin to shortlist and sanity-check, then get a proper site survey before signing anything.
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