"How many panels" is the industry's favorite question to answer badly, because the honest answer starts with your utility bills and the dishonest one starts with how much roof they can sell you. Sizing is arithmetic: your annual kilowatt-hours, your region's production per installed kilowatt, and, the step most calculators skip, your state's export rules deciding whether surplus power is treasure or waste. Here is the whole method.
The one-sentence version: divide your annual kWh by your region's production per kW to get system size, then adjust the offset target to your state's export policy, near-retail netting rewards ~100%, weak export rates reward sizing to self-consumption.
Step one: your real usage
Pull twelve months of bills and total the kilowatt-hours, twelve months because seasons lie individually: summer AC in Florida, winter heat pumps in Vermont. Typical American households land near 10,000-12,000 kWh annually, but electrified homes (heat pumps, EVs) run far higher and deserve sizing for the household you are becoming, not the one you were.
Step two: production per kilowatt, by region
| Region | Approx. annual kWh per installed kW |
|---|---|
| Florida / Southeast | 1,350 - 1,500 |
| Colorado / Southwest | 1,450 - 1,650 |
| New England / New York | 1,150 - 1,300 |
Divide annual usage by your region's figure: a 11,000 kWh Massachusetts home needs roughly 9 kW; the same usage in Tampa, closer to 8 kW. At today's 400-450W panels, that is the familiar 16-22 panel band, before the policy adjustment that follows.
Step three: the export-policy adjustment
Here is where identical houses in different states deserve different systems. Strong-netting states, Massachusetts, New Hampshire, Vermont, credit exports near retail, so sizing to ~100% of annual usage lets summer bank against winter. Weak-export states flip the logic: where surplus earns a fraction of retail (Georgia being the teaching example), the last panels produce the cheapest electrons, and sizing to daytime self-consumption, often 60-80% of usage, protects the math. Any quote that names a size without naming your export regime skipped the step that matters.
Roof reality and honest compromises
Roofs vote too: azimuth, shade, and usable faces cap capacity, and the honest response is optimization, higher-wattage panels, the best-producing faces, realistic offset expectations, not cramming. Partial offset at high rates outperforms full offset at cheap ones, which is why a 60% Massachusetts solution can beat a 100% one further south. Run your address through our calculator, then let a real quote defend its sizing against your actual bills, the only defense that counts.
Frequently asked questions
How many panels does an average home need?
Most homes land between 15 and 25 panels: a typical household using around 10,000-12,000 kWh annually needs roughly a 7-9 kW system, and at today's common 400-450W panels that is 16-22 of them. Your twelve months of bills, not averages, produce your real number.
Should I size my system to cover 100% of my usage?
Where exports earn near-retail (strong netting states), sizing to about 100% of annual usage is the sweet spot. Where exports earn a fraction of retail, sizing to daytime self-consumption, often 60-80% of usage, protects your economics. State policy, not ambition, sets the target.
Do I need more panels in New England than Florida?
Somewhat: the same annual production requires modestly more capacity under northern sun, though cool temperatures partially compensate (panels run more efficiently cold). Production modeling handles this; rules of thumb across states mislead.
What if my roof cannot fit enough panels?
Partial offset still pays where rates are high: covering 60% of a Massachusetts or New Hampshire bill beats covering 100% of a cheap-power bill. Higher-wattage panels, better azimuth choices, and honest expectations beat cramming a compromised layout.
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