Calculator research

What makes a solar calculator accurate?

A useful solar calculator is not just a form. It should expose the assumptions that move the result: sunlight, bill usage, utility rate, export policy, installed price, financing, incentives, and degradation.

Quick answer

The best solar calculator is the one that lets you inspect and change the assumptions, uses local production data, separates cash price from financing, and reflects current 2026 incentive law.

Reviewed 2026-07-26

Best for: Homeowners comparing calculator outputs or checking why two solar estimates disagree.
Inputs needed: annual kWh, local electric rate, system size, installed cost, export credit
Formula used: Savings = self-consumed solar value + export credit value - ownership and financing costs.
Source checked: NREL PVWatts, DSIRE, public utility tariffs, Wattcrunch methodology

Accuracy factor	Why it matters
Production model	Does the calculator use local solar resource data such as NREL PVWatts instead of a flat national production factor?
Rate model	Can the user change import rates, export credits, and time-of-use assumptions?
Current incentives	Does the calculator reflect the 2026 end of the homeowner 25D federal credit?
Quote pressure test	Can the user compare a real proposal against state planning benchmarks?
Privacy	Can a homeowner run numbers without a lead form or account wall?
Explainability	Are formulas, assumptions, sources, and limitations visible?

Where Wattcrunch is intentionally different

Wattcrunch is built for pre-sales due diligence. It does not require an email address, does not sell installer rankings, and keeps the default assumptions visible so a homeowner can challenge a proposal line by line.

The main tradeoff is that Wattcrunch is not a marketplace with live installer bids. Use it to understand the numbers before requesting bids, then compare real quotes with the quote checker.

Start with the solar savings calculator, then pressure-test proposals in the quote fairness checker.