Solar / 4 kW system
4 kW solar system
A 4 kW array is ten panels on about 175 square feet of roof. It produces 5,008 to 7,020 kilowatt-hours a year depending on where it stands, costs $7,840 to $11,920 after the incentives a buyer can actually claim in 2026, and covers a household paying roughly $89 to $200 a month. Payback runs from 5.8 yr in New York to 15.4 yr in Arizona.
Every figure here is computed for a 4 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 4 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 larger than this. A 4 kW array is not unusual, but it is a small one, and the price per watt of a small system runs above the published averages because permitting, design and a day of labour do not scale down.
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 4 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 York | $141/mo | 5,164 kWh | $8,280 | 5.8 yr | $34,190 |
| New Jersey | $122/mo | 5,220 kWh | $10,320 | 6.3 yr | $32,003 |
| Massachusetts | $144/mo | 5,208 kWh | $10,640 | 6.9 yr | $34,592 |
| California | $200/mo | 6,708 kWh | $9,920 | 8.9 yr | $22,022 |
| Pennsylvania | $110/mo | 5,436 kWh | $10,320 | 9.1 yr | $21,889 |
| Maryland | $111/mo | 5,568 kWh | $10,480 | 9.2 yr | $22,093 |
| Illinois | $96/mo | 5,232 kWh | $11,920 | 9.5 yr | $10,968 |
| Florida | $89/mo | 6,176 kWh | $8,480 | 9.8 yr | $15,657 |
| Connecticut | $113/mo | 5,008 kWh | $10,880 | 11 yr | $17,522 |
| Texas | $92/mo | 6,024 kWh | $8,880 | 14.3 yr | $10,654 |
| Arizona | $102/mo | 7,020 kWh | $7,840 | 15.4 yr | $8,086 |
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 Arizona at $7,840 and the dearest is Illinois at $11,920, a gap of $4,080 for the same kilowatts. Price is not what orders the table though: New York pays back in 5.8 yr while Arizona takes 15.4 yr, and the two are only $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 | 4 kW | 5 kW |
|---|---|---|
| New York | 5.8 yr | 5.7 yr |
| New Jersey | 6.3 yr | 6.2 yr |
| Massachusetts | 6.9 yr | 6.9 yr |
| California | 8.9 yr | 8.7 yr |
| Pennsylvania | 9.1 yr | 8.9 yr |
| Maryland | 9.2 yr | 9 yr |
| Illinois | 9.5 yr | 9.1 yr |
| Florida | 9.8 yr | 9.5 yr |
| Connecticut | 11 yr | 10.7 yr |
| Texas | 14.3 yr | 13.4 yr |
| Arizona | 15.4 yr | 14.6 yr |
Cash purchase, payback in years, each size on the household it covers in that state.
On this ladder every state we publish rewards the larger system, so what limits the size here is your roof, your budget and what your utility will interconnect — not the arithmetic.
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 175 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.
- 5 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 4 kW solar system?
- Ten panels of 400 watts each, needing roughly 175 square feet of unshaded roof. Panel wattage has risen steadily, so an older 4 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 4 kW system produce?
- Between 5,008 and 7,020 kilowatt-hours in its first full year, depending on where it stands: 7,020 in Arizona against 5,008 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 4 kW system suit?
- Not a house size, a bill. This array covers a household paying roughly $89 to $200 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 4 kW system worth it?
- In New York it repays its $8,280 net cost in 5.8 yr and returns $34,190 over 25 years. In Arizona the same hardware takes 15.4 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.
- 5 kW solar system
- 6 kW solar system
- 7 kW solar system
- 8 kW solar system
- 10 kW solar system
- 12 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