Sizing Guide

Sizing Solar by Your Actual Usage, Not a Rule of Thumb

"The average home needs X panels" is a starting point at best. Your actual usage is a far better one.

Averages hide enormous variation

A national average monthly usage figure blends tiny apartments with large air-conditioned homes in hot climates — the range across real households is enormous. Sizing off your own actual kWh usage, not a generic average, is the difference between a system that offsets your real bill and one that's meaningfully over- or under-sized.

System size (kW) = Annual kWh ÷ (Sun hours/day × 365 × Derate factor)

Find your real number, even without a bill handy

Your utility bill's usage section is the most accurate source. If you don't have one handy, the kWh usage from bill calculator can reverse-engineer a reasonable estimate from just your total dollar amount and rate.

We've pre-built common usage tiers

To make this concrete, we've built dedicated sizing pages for common monthly usage levels — from 500 kWh/month up through 3,000 kWh/month. Find the tier closest to your actual usage as a fast starting estimate, then refine with your exact number in the full solar panel calculator.

Don't forget seasonal swings

Annual sizing math smooths over the fact that production (and often usage) varies significantly by season — a system sized around annual averages can still leave you short in the depths of winter if you're off-grid or want maximum self-sufficiency. See the seasonal output calculator for how much that swing typically looks like at your latitude.

Electrification changes your number too. If you're planning to add an EV, heat pump, or other major electric load, size around your projected future usage, not just your current bill — retrofitting a too-small system later is more expensive than sizing correctly the first time.

Frequently asked questions

Should I size solar for my current usage or future usage?

If you're planning known future electric loads — an EV, heat pump conversion, pool — size around that projected usage rather than just your current bill, since expanding a system later typically costs more per watt than sizing correctly upfront.

What if my usage varies a lot month to month?

Use your annual total divided by 12 for a monthly average baseline, since solar sizing is fundamentally an annual calculation — a few unusually high or low months matter less than your yearly total under net metering.

Written by the Solargrin team. Estimates only — verify specifics for your own equipment and utility before making a purchase decision.
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Tools mentioned in this guide

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