Solar / 12 kW system
12 kW solar system
A 12 kW array is 30 panels on about 525 square feet of roof. It produces 15,024 to 21,060 kilowatt-hours a year depending on where it stands, costs $25,440 to $35,760 after the incentives a buyer can actually claim in 2026, and covers a household paying roughly $244 to $576 a month. Payback runs from 6 yr in New Jersey to 12.9 yr in Arizona.
Every figure here is computed for a 12 kW system by the same engine that runs the calculator and the state pages, from the sources listed under each table. Statewide averages, 11 states, 2026 policy.
What it produces
Identical hardware, 40% apart. A kilowatt of panels in Arizona returns 1755 kilowatt-hours a year; in Connecticut it returns 1252. That single number, the specific yield, is the only thing on this page that is pure physics, and it is why a 12 kW quote means something different in two states.
First full year, before degradation. Modelled from the National Renewable Energy Laboratory PVWatts v8 (verified), for a well-oriented, unshaded array. Output falls about 0.5% a year thereafter, so year 25 is roughly 11% below year one.
Where this size sits
Four in five systems installed in the United States are smaller than this. At 12 kW you are into the top fifth of residential arrays, which usually means a large house, electric heating, a car, or a roof being sized for something that has not arrived yet.
The distribution is from the Lawrence Berkeley National Laboratory report Tracking the Sun, which reports a median installed size of 7.4 kW and a 20th-to-80th percentile band of 5 to 11 kW. It describes what has been installed, not what you should install: the right size is the one that matches your own use.
The household it covers, state by state
Read this table the other way round from a normal solar table. The system is fixed at 12 kW, so what changes is the household: the bill an array this size would cover, and what covering it is worth there.
| State | Covers a bill of | Produces | Net cost | Payback | 25-year net |
|---|---|---|---|---|---|
| New Jersey | $341/mo | 15,660 kWh | $30,960 | 6 yr | $107,108 |
| New York | $398/mo | 15,492 kWh | $28,120 | 6.2 yr | $110,392 |
| Massachusetts | $409/mo | 15,624 kWh | $33,920 | 6.9 yr | $112,873 |
| California | $576/mo | 20,124 kWh | $29,760 | 8.2 yr | $77,166 |
| Illinois | $263/mo | 15,696 kWh | $35,760 | 8.3 yr | $44,006 |
| Pennsylvania | $307/mo | 16,308 kWh | $30,960 | 8.4 yr | $76,762 |
| Maryland | $310/mo | 16,704 kWh | $31,440 | 8.5 yr | $77,378 |
| Florida | $244/mo | 18,528 kWh | $25,440 | 8.9 yr | $58,066 |
| Connecticut | $314/mo | 15,024 kWh | $32,640 | 10.1 yr | $63,664 |
| Texas | $251/mo | 18,072 kWh | $26,640 | 10.9 yr | $43,064 |
| Arizona | $282/mo | 21,060 kWh | $25,520 | 12.9 yr | $33,358 |
Ranked by payback, fastest first. Net cost is after the incentives a buyer can claim in 2026, which for the federal credit is nothing — that changed on 1 January. Installed cost is on the quoted basis; the reported basis runs about 60% higher and both are shown on the cost calculator. Rates: EIA 2026-07.
The cheapest place to buy this system is Florida at $25,440 and the dearest is Illinois at $35,760, a gap of $10,320 for the same kilowatts. Price is not what orders the table though: New Jersey pays back in 6 yr while Arizona takes 12.9 yr, and the two are only $5,440 apart on price. What separates them is the price of the electricity the array displaces, and what the utility pays for what it exports.
Does a bigger system pay back faster?
Usually yes, for an unglamorous reason: several costs do not grow with the array. The fixed monthly charge on your bill, the $150 a year of maintenance and the inverter replacement in year 12 are much the same on a small system as on a large one, so a bigger array spreads them over more kilowatt-hours.
| State | 10 kW | 12 kW | 15 kW |
|---|---|---|---|
| New Jersey | 6 yr | 6 yr | 5.9 yr |
| New York | 6 yr | 6.2 yr | 6.3 yr |
| Massachusetts | 6.9 yr | 6.9 yr | 6.9 yr |
| California | 8.3 yr | 8.2 yr | 8.1 yr |
| Illinois | 8.4 yr | 8.3 yr | 8.2 yr |
| Pennsylvania | 8.5 yr | 8.4 yr | 8.4 yr |
| Maryland | 8.5 yr | 8.5 yr | 8.4 yr |
| Florida | 9 yr | 8.9 yr | 8.8 yr |
| Connecticut | 10.2 yr | 10.1 yr | 10 yr |
| Texas | 11 yr | 10.9 yr | 10.8 yr |
| Arizona | 13.1 yr | 12.9 yr | 12.7 yr |
Cash purchase, payback in years, each size on the household it covers in that state.
One state runs the other way. In New York (6 yr at 10 kW against 6.3 yr at 15 kW), a bigger system pays back more slowly, and the reason is in the tariff rather than in the panels: a charge billed per kilowatt of capacity every month, and a state credit that stops at its cap, so the extra kilowatts earn nothing.
That is the kind of thing a rule of thumb hides, and a reason to read your own utility tariff before sizing up. A charge levied on capacity is paid every month whether the sun shines or not.
What a size alone cannot tell you
A kilowatt figure is a specification, not a decision. Four things this page does not know, any of which can matter more than the step between one size and the next:
- Whether it matches your bill
- This page derives the household from the system; you need it the other way round. Put your own bill in and the same engine returns the size that fits it, which is very unlikely to be a whole number of kilowatts.
- Whether your roof takes it
- Those 525 square feet assume clear, well-oriented roof. Shade, a chimney, a hip roof, setback rules and an ageing covering all reduce what actually fits, and none of them are modelled here. Only a site survey settles it.
- Whether your utility will connect it
- Some utilities cap the system they will interconnect at your historic annual use. Where that applies, an array sized beyond your consumption is a permitting problem before it is an economic one.
- What you will actually be quoted
- Installed prices here are state averages on the quoted basis. A small system carries a higher price per watt than a large one, because permitting, design and a day of labour do not scale down, and the spread between three quotes for one roof is routinely wider than the spread between states in the table above.
If you are choosing between two sizes
- Size a system from your own bill
The same engine, run the way you actually need it.
- 10 kW solar system
One step down: 6 yr payback in New Jersey against 6 yr here.
- 15 kW solar system
One step up, on the households that size covers.
- Is solar worth it in 2026?
The ranking above, explained: why sunshine is not what decides it.
Questions
- How many panels is a 12 kW solar system?
- 30 panels of 400 watts each, needing roughly 525 square feet of unshaded roof. Panel wattage has risen steadily, so an older 12 kW array will have more panels than a new one and a future one will have fewer. The kilowatts are what matter, not the count.
- How much electricity does a 12 kW system produce?
- Between 15,024 and 21,060 kilowatt-hours in its first full year, depending on where it stands: 21,060 in Arizona against 15,024 in Connecticut. That is a spread of 40% for identical hardware, and it comes from the sun rather than from anything a salesperson can change. Output then falls about 0.5% a year.
- What size house does a 12 kW system suit?
- Not a house size, a bill. This array covers a household paying roughly $244 to $576 a month, again depending on the state, because the same kilowatt-hours cost very different amounts in different places. If your bill is well below that range, this system is larger than you need, and the surplus is exported at whatever your utility pays for exports.
- Is a 12 kW system worth it?
- In New Jersey it repays its $30,960 net cost in 6 yr and returns $107,108 over 25 years. In Arizona the same hardware takes 12.9 yr. The size is not what decides that: the price of electricity, what the utility pays for exports, and the local installed cost are.
The other sizes
Every one of these runs the same engine on the same data, with one number changed. Where they differ is what that change buys.
- 4 kW solar system
- 5 kW solar system
- 6 kW solar system
- 7 kW solar system
- 8 kW solar system
- 10 kW solar system
- 15 kW solar system
A screening estimate from published data, not a quote and not tax or financial advice. Every input is listed with the source it came from and the date it was read; the formulas are on the methodology page. Confirm against real quotes, and with a professional, before relying on any figure here.
Published 6 September 2026. Data last verified 6 September 2026. Rates: EIA 2026-07. Found a figure that looks wrong? Tell us — we publish corrections. About the author