How many solar panels do I need?
Most homes need 15 to 22 solar panels. The exact number is your annual electricity use in kWh divided by what one panel produces where you live — typically 429 kWh a year in cloudy regions and 657 kWh in sunny ones.
The formula
Panels needed = annual kWh used ÷ annual kWh produced per panel.
You'll find your annual usage on your electricity bill — most utilities print a 12-month total or a monthly average you can multiply by 12. The US average is about 10,800 kWh a year.
Production per panel depends on sunlight. A 400W panel in a location with
S usable sun hours per year produces about 0.4 × S × 0.85 kWh,
where 0.85 accounts for inverter losses, wiring, heat and dust.
Worked example
A home in Atlanta using 10,800 kWh a year, where roofs get about 1,545 usable sun hours:
- One panel produces 0.4 × 1,545 × 0.85 ≈ 525 kWh/year
- 10,800 ÷ 525 ≈ 21 panels
How location changes the answer
| City | Sun hrs/yr | kWh per panel | Panels for 10,800 kWh |
|---|---|---|---|
| Phoenix, AZ | 1,932 | 657 | 17 |
| Austin, TX | 1,688 | 574 | 19 |
| Denver, CO | 1,708 | 581 | 19 |
| Atlanta, GA | 1,545 | 525 | 21 |
| Chicago, IL | 1,469 | 499 | 22 |
| New York, NY | 1,488 | 506 | 22 |
| Seattle, WA | 1,262 | 429 | 26 |
| Vancouver, BC | 1,162 | 395 | 28 |
The limit most calculators ignore
What changes the number most
Two households in the same street can need very different arrays. The variable is almost never the house, it is what runs inside it.
| Situation | Adds per year | Effect on panel count |
|---|---|---|
| Electric vehicle | 2,000–3,000 kWh | Often doubles a modest array. Charge at midday and most of it comes off your own roof. |
| Heat pump | 2,500–6,000 kWh | Adds heavily, but in winter when output is lowest. Sizing for it means summer overproduction. |
| Pool pump | 2,000–3,000 kWh | Runs in summer, which lines up almost perfectly with peak solar. |
| Air conditioning | 1,000–3,000 kWh | Afternoon demand against afternoon generation. One of the best pairings there is. |
Notice which of these line up with when solar actually produces. A pool pump and air conditioning run hardest in summer daylight, so nearly every kWh they use can come straight off the roof. A heat pump does the opposite. Same annual kWh, very different value.
Sizing for the house you will have
Panels last 25 years. Whatever you plug in over the next decade is going onto the same array, and adding to it later means paying twice for scaffolding, a site visit and an electrician. If an EV or a heat pump is plausible within a few years, it is cheaper to size for it now than to extend later.
The counterweight is that oversizing costs money immediately for output you will export at a lower rate. The sensible middle is to size for current usage plus whatever you are genuinely likely to add, and no more.
Your roof may not fit them
All of the above assumes the panels physically fit. A 400W panel is roughly 1.9 × 1.1 m, and you need setbacks from roof edges, clearance around vents and chimneys, and unshaded orientation. Check your actual roof to see how many panels Google's imagery says will fit on it.
What this looks like in real cities
Measured rooftop data, spanning the range from fastest to slowest payback we have found:
| City | Sun hrs/yr | Rate | Payback |
|---|---|---|---|
| Honolulu, HI | 1,787 | 42.1¢ | 3.1 yrs |
| Eagle Pass, TX | 1,827 | 15.1¢ | 8.7 yrs |
| Spartanburg, SC | 1,562 | 14.2¢ | 10.8 yrs |
| Bristol, South West | 1,015 | 26.1¢ | 12.9 yrs |
| Gatineau, QC | 1,291 | 7.9¢ | 33.3 yrs |
Frequently asked
How many solar panels do I need for a 2,000 sq ft house?
Roof size does not determine panel count — your electricity usage does. A 2,000 sq ft home using 11,000 kWh a year typically needs 16 to 24 panels depending on local sunlight. Two identical houses in different cities can need very different arrays, because a panel in a sunny region produces far more each year.
How many solar panels to power a whole house?
Enough to match your annual kWh usage. For the average US home at 10,800 kWh that is about 15 to 22 panels, or roughly a 6 to 9 kW system. Pull twelve months of bills rather than guessing — heating type and EV charging shift the total more than house size does.
Do I need batteries too?
Not to save money on your bill. Batteries add backup power during outages and help where export rates are poor, but they typically lengthen payback rather than shorten it. Buy one for resilience, or because your utility pays little for exports — not on the assumption it improves the financial case.
Related guides
General information, updated 2026-08-22. Not financial, tax or engineering advice.