20 kW solar system: cost, output and payback
A 20 kW solar system is 50 panels and costs about $57,000 installed, or $39,900 after the US federal tax credit. Across 673 measured cities it produces a median of 26,282 kWh a year and pays back in about 17.6 years.
Check whether 50 panels fit your actual roof → These are medians across real cities; your roof's size, pitch and shading change the answer.
Is a 20 kW system the right size?
This is more than most households need. A 20 kW array covers roughly 243% of an average home's 10,800 kWh a year, so unless you have electric heating, an EV, a pool or unusually high usage, you would be exporting a large share of it — usually at well below the retail rate you paid to install the panels.
What a 20 kW system produces where you live
Output depends almost entirely on local sunlight. The same 20 kW of hardware produces 35,955 kWh a year in Palmdale and 16,218 kWh in Fairbanks — a 2.2× spread across 673 cities we have measured from Google's rooftop imagery.
Where a 20 kW system pays back fastest
Payback is driven more by electricity price than by sunshine. Honolulu, HI tops the list at 6 years on 42.1¢/kWh, while Gatineau, QC takes 53.1 years on just 7.9¢/kWh. That is identical hardware producing 28% less electricity, but taking 8.8× as long to pay for itself — because the power it displaces is worth 5.3× less.
| City | kWh/yr | Rate | Payback |
|---|---|---|---|
| Honolulu, HI | 30,379 | 42.1¢ | 6 yrs |
| Lihue, HI | 30,209 | 42.1¢ | 6.1 yrs |
| Kahului, HI | 27,659 | 42.1¢ | 6.3 yrs |
| Hilo, HI | 25,670 | 42.1¢ | 6.5 yrs |
| Kailua-Kona, HI | 21,301 | 42.1¢ | 7.1 yrs |
| Quincy, MA | 25,857 | 30.1¢ | 9.1 yrs |
| Boston, MA | 24,582 | 30.1¢ | 9.3 yrs |
| Worcester, MA | 24,531 | 30.1¢ | 9.3 yrs |
| Fall River, MA | 24,293 | 30.1¢ | 9.4 yrs |
| Lowell, MA | 24,174 | 30.1¢ | 9.4 yrs |
| Somerville, MA | 24,106 | 30.1¢ | 9.4 yrs |
| Cambridge, MA | 23,868 | 30.1¢ | 9.4 yrs |
| New Haven, CT | 25,024 | 29.2¢ | 9.5 yrs |
| Lynn, MA | 23,664 | 30.1¢ | 9.5 yrs |
| Newton, MA | 23,375 | 30.1¢ | 9.5 yrs |
Where it pays back slowest
| City | kWh/yr | Rate | Payback |
|---|---|---|---|
| Gatineau, QC | 21,947 | 7.9¢ | 53.1 yrs |
| Levis, QC | 22,542 | 7.9¢ | 52.5 yrs |
| Trois-Rivières, QC | 22,899 | 7.9¢ | 52.2 yrs |
| Longueuil, QC | 23,239 | 7.9¢ | 51.9 yrs |
| Drummondville, QC | 23,307 | 7.9¢ | 51.8 yrs |
| Terrebonne, QC | 23,460 | 7.9¢ | 51.7 yrs |
| Montreal, QC | 23,528 | 7.9¢ | 51.6 yrs |
| Laval, QC | 23,545 | 7.9¢ | 51.6 yrs |
| Quebec City, QC | 23,936 | 7.9¢ | 51.2 yrs |
| Winnipeg, MB | 23,613 | 10.1¢ | 40.3 yrs |
Other system sizes
20 kW solar questions
How many panels is a 20 kW solar system?
A 20 kW system is 50 panels at 400W each, the standard residential size in 2026. It needs roughly 100 m² (about 1,076 sq ft) of usable roof, and more in practice once you allow for edge setbacks, vents and access paths.
How much does a 20 kW solar system cost?
About $57,000 installed before incentives at $2.85 per watt, or roughly $39,900 after the 30% US federal tax credit. Quotes for the same 20 kW system routinely differ by thousands, because labour, margin and equipment vary far more than hardware cost does.
How much power does a 20 kW solar system produce?
Across the 673 cities we have measured, a 20 kW array produces a median of 26,282 kWh a year. The range runs from about 16,218 kWh in Fairbanks to 35,955 kWh in Palmdale — the same hardware, differing by 122% purely on local sunlight.
See the full dataset → every city, with sunlight, shading, roof size and rates.
Estimates generated 2026-08-22 from Google Solar API rooftop samples across 673 cities. Not a quote and not financial advice.