Most cost guides quote a single average that fits almost nobody. What matters is the cost of the size your house needs — and since the federal credit ended, these are the full out-of-pocket figures with nothing subtracted.
Cost by system size, both routes
DIY at $1.00-1.80 per watt including permits and an electrician for the tie-in; professional at $2.50-3.50 per watt installed.
| Size | 400W panels | DIY total | Professional total | You save with DIY |
|---|---|---|---|---|
| 4 kW | 10 | $4,000 – $7,200 | $10,000 – $14,000 | ~$6,000 – $7,000 |
| 6 kW | 15 | $6,000 – $10,800 | $15,000 – $21,000 | ~$9,000 – $10,000 |
| 8 kW | 20 | $8,000 – $14,400 | $20,000 – $28,000 | ~$12,000 – $14,000 |
| 10 kW | 25 | $10,000 – $18,000 | $25,000 – $35,000 | ~$15,000 – $17,000 |
| 12 kW | 30 | $12,000 – $21,600 | $30,000 – $42,000 | ~$18,000 – $20,000 |
In 2025 every professional figure in that table would have been 30% lower after the federal credit. That is the single biggest change in residential solar pricing in a decade, and it is why the DIY column now deserves serious consideration from people who would previously have dismissed it.
What each size produces and covers
| Size | Annual production* | Covers a household using | Typical fit |
|---|---|---|---|
| 4 kW | ~5,300 kWh | 440 kWh/month | Small home, gas heat, 1-2 people |
| 6 kW | ~7,900 kWh | 660 kWh/month | Average small-to-mid home |
| 8 kW | ~10,500 kWh | 875 kWh/month | The U.S. average home |
| 10 kW | ~13,100 kWh | 1,090 kWh/month | Larger home, or one EV |
| 12 kW | ~15,800 kWh | 1,315 kWh/month | Large home, electric heat, or EV plus pool |
*At 4.5 peak sun hours with a 0.8 derate. In the Southwest add roughly 25%; in the Pacific Northwest subtract roughly 30%. Location moves these figures more than any equipment choice — the regional table is in how many solar panels do I need to run my house.
Why bigger systems cost less per watt
Permits, the design and engineering package, the electrician's site visit, the interconnection application and the inverter are largely fixed costs. Spreading them across 12 kW instead of 4 kW meaningfully lowers the per-watt figure — which is why a 4 kW system rarely costs half a 8 kW system, and why very small grid-tied installations often have disappointing economics.
This cuts against a common instinct after losing the credit, which is to start small and expand later. Adding a second array in three years means paying most of those fixed costs twice, plus possibly a second inverter. If you are confident about the size you need, buying it once is usually cheaper.
The ceiling nobody mentions until it is too late
On a standard 200 amp service, interconnection rules typically cap backfed inverter output around 7.6 kW. That means the 10 kW and 12 kW rows above frequently require a main breaker derate, a supply-side tap, or a service upgrade costing $3,000-8,000 — none of which appear in a per-watt quote. Check this before falling in love with a larger system: solar panel sizing for a 200 amp service covers the math and the workarounds.
What is not in these numbers
- Battery storage — add roughly $8,000-15,000 installed for a whole-home battery, or $4,000-6,000 for a smaller unit
- Roof replacement — if the roof has under ten years left, do it first
- Service panel upgrades — $200-600 for a derate, $3,000-8,000 for a full upgrade
- Tree removal for shading, which can run into thousands
- State and utility incentives, which subtract from these totals — see what still exists in 2026
Once you have a size and a price, run it through the payback calculation using your own export rate. Two identical 8 kW systems in different utility territories can differ by six years in break-even, and that spread matters more than shopping the equipment.