8 kW solar system: cost, output and payback
A 8 kW solar system is 20 panels and costs about $22,800 installed, or $15,960 after the US federal tax credit. Across 673 measured cities it produces a median of 10,513 kWh a year and pays back in about 9.9 years.
Check whether 20 panels fit your actual roof → These are medians across real cities; your roof's size, pitch and shading change the answer.
Is a 8 kW system the right size?
This is about right for an average household. A 8 kW array covers roughly 97% of a typical home's 10,800 kWh a year, which is the size range where solar generally pays back fastest — you use most of what you generate instead of exporting it cheaply.
What a 8 kW system produces where you live
Output depends almost entirely on local sunlight. The same 8 kW of hardware produces 14,382 kWh a year in Palmdale and 6,487 kWh in Fairbanks — a 2.2× spread across 673 cities we have measured from Google's rooftop imagery.
Where a 8 kW system pays back fastest
Payback is driven more by electricity price than by sunshine. Honolulu, HI tops the list at 3.4 years on 42.1¢/kWh, while Gatineau, QC takes 32.9 years on just 7.9¢/kWh. That is identical hardware producing 28% less electricity, but taking 9.7× as long to pay for itself — because the power it displaces is worth 5.3× less.
| City | kWh/yr | Rate | Payback |
|---|---|---|---|
| Honolulu, HI | 12,152 | 42.1¢ | 3.4 yrs |
| Lihue, HI | 12,084 | 42.1¢ | 3.4 yrs |
| Kahului, HI | 11,064 | 42.1¢ | 3.5 yrs |
| Hilo, HI | 10,268 | 42.1¢ | 3.7 yrs |
| Kailua-Kona, HI | 8,520 | 42.1¢ | 4.4 yrs |
| Quincy, MA | 10,343 | 30.1¢ | 5.1 yrs |
| Boston, MA | 9,833 | 30.1¢ | 5.4 yrs |
| Worcester, MA | 9,812 | 30.1¢ | 5.4 yrs |
| Warwick, RI | 10,322 | 28.3¢ | 5.5 yrs |
| New Haven, CT | 10,010 | 29.2¢ | 5.5 yrs |
| Fall River, MA | 9,717 | 30.1¢ | 5.5 yrs |
| Lowell, MA | 9,670 | 30.1¢ | 5.5 yrs |
| Somerville, MA | 9,642 | 30.1¢ | 5.5 yrs |
| Pawtucket, RI | 9,996 | 28.3¢ | 5.6 yrs |
| Cambridge, MA | 9,547 | 30.1¢ | 5.6 yrs |
Where it pays back slowest
| City | kWh/yr | Rate | Payback |
|---|---|---|---|
| Gatineau, QC | 8,779 | 7.9¢ | 32.9 yrs |
| Levis, QC | 9,017 | 7.9¢ | 32 yrs |
| Trois-Rivières, QC | 9,160 | 7.9¢ | 31.5 yrs |
| Longueuil, QC | 9,296 | 7.9¢ | 31 yrs |
| Drummondville, QC | 9,323 | 7.9¢ | 31 yrs |
| Terrebonne, QC | 9,384 | 7.9¢ | 30.8 yrs |
| Montreal, QC | 9,411 | 7.9¢ | 30.7 yrs |
| Laval, QC | 9,418 | 7.9¢ | 30.6 yrs |
| Quebec City, QC | 9,574 | 7.9¢ | 30.1 yrs |
| Coquitlam, BC | 7,466 | 12.4¢ | 24.6 yrs |
Other system sizes
8 kW solar questions
How many panels is a 8 kW solar system?
A 8 kW system is 20 panels at 400W each, the standard residential size in 2026. It needs roughly 40 m² (about 430 sq ft) of usable roof, and more in practice once you allow for edge setbacks, vents and access paths.
How much does a 8 kW solar system cost?
About $22,800 installed before incentives at $2.85 per watt, or roughly $15,960 after the 30% US federal tax credit. Quotes for the same 8 kW system routinely differ by thousands, because labour, margin and equipment vary far more than hardware cost does.
How much power does a 8 kW solar system produce?
Across the 673 cities we have measured, a 8 kW array produces a median of 10,513 kWh a year. The range runs from about 6,487 kWh in Fairbanks to 14,382 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.