A 7 kW solar system costs about $18,200 to $23,100 and produces roughly 8,400 to 11,900 kWh per year. A 10 kW system costs about $26,000 to $33,000 and produces roughly 12,000 to 17,000 kWh. For most homes that use around 10,000 to 11,000 kWh a year, 7 kW is enough. A 10 kW system makes sense for larger homes, electric vehicles, heat pumps or pools.
This guide compares the two sizes side by side, shows what each saves under different electricity rates and explains how to pick the right size without paying for power you can’t use.
Key takeaways
- Cost: a 7 kW system runs about $18,200–$23,100; a 10 kW system runs $26,000–$33,000 before incentives (at $2.60–$3.30 per watt).
- Output: a 10 kW system produces about 43 % more electricity than a 7 kW one in the same location.
- Payback: if both are priced at the same cost per watt, their payback periods are almost identical. What matters is whether you can actually use or get credit for the extra power.
- Best fit: 7 kW suits an average home of 1,800–2,500 sq ft. 10 kW suits large homes, heavy air conditioning or electric heating, and households with one or more EVs.
- Watch out: a 10 kW system is more likely to need an electrical panel upgrade and may not fit on a small roof.
7 kW vs 10 kW at a glance
| 7 kW system | 10 kW system | |
|---|---|---|
| Typical installed cost (before incentives) | $18,200–$23,100 | $26,000–$33,000 |
| Number of panels (400 W each) | 17–18 | 25 |
| Roof space needed | 320–360 sq ft | 440–500 sq ft |
| Annual production (typical range) | 8,400–11,900 kWh | 12,000–17,000 kWh |
| Share of an average US home’s use (about 10,800 kWh) | 80–110 % | 110–155 % |
| Best for | Average homes, moderate use | Large homes, EVs, heat pumps, pools |
Panel counts assume 400-watt modules. Higher-wattage panels reduce the number of panels and the roof area required.
Cost: 7 kW vs 10 kW
At 2026 prices of $2.60 to $3.30 per watt, the difference between the two systems is about $7,800 to $9,900.
| System | Low ($2.60/W) | Mid ($2.95/W) | High ($3.30/W) |
|---|---|---|---|
| 7 kW | $18,200 | $20,650 | $23,100 |
| 10 kW | $26,000 | $29,500 | $33,000 |
Larger systems sometimes get a lower price per watt because fixed costs for design, permitting and travel are spread across more panels. In practice the saving is small, around $0.05–$0.20 per watt, so don’t expect the 10 kW system to be proportionally cheaper.
These prices don’t include batteries, roof repairs or an electrical panel upgrade. Because the federal homeowner tax credit ended for systems installed after 2025, the figures above are what you pay before any state or local incentives.
Output: how much electricity each system produces
The amount of electricity a system generates depends on your sun exposure, roof direction, tilt and shade. A rough rule is to multiply the system size by the annual production per kilowatt for your region.
| Region | Production per kW per year | 7 kW system | 10 kW system |
|---|---|---|---|
| Cloudier areas (Pacific Northwest, parts of the Northeast) | about 1,200 kWh | 8,400 kWh | 12,000 kWh |
| Average US location | about 1,450 kWh | 10,150 kWh | 14,500 kWh |
| Sunny areas (Southwest, parts of Florida) | about 1,700 kWh | 11,900 kWh | 17,000 kWh |
For comparison, the average US household uses roughly 10,800 kWh per year, though usage varies widely. A home with air conditioning in Texas or Florida may use 14,000 kWh or more. A small efficient home in a mild climate may use under 7,000 kWh.
Real output is a little lower than the numbers above if your roof is shaded, faces east or west, or has a low tilt. Ask every installer for a production estimate based on your exact roof, not a general regional number.
Savings: what each system saves per year
Annual savings equal the electricity your system produces, multiplied by what each kilowatt-hour is worth to you. The table below assumes an average location (1,450 kWh per kW) and that all production is used or credited at your retail rate. That is the best case, so your savings will be lower if your utility pays less for exported power.
| Electricity rate | 7 kW yearly savings | 10 kW yearly savings | Extra savings from the bigger system |
|---|---|---|---|
| 14 ¢/kWh | $1,421 | $2,030 | $609 |
| 20 ¢/kWh | $2,030 | $2,900 | $870 |
| 30 ¢/kWh | $3,045 | $4,350 | $1,305 |
Payback for each system
Using the mid price ($20,650 for 7 kW and $29,500 for 10 kW):
| Electricity rate | 7 kW simple payback | 10 kW simple payback |
|---|---|---|
| 14 ¢/kWh | 14.5 years | 14.5 years |
| 20 ¢/kWh | 10.2 years | 10.2 years |
| 30 ¢/kWh | 6.8 years | 6.8 years |
The paybacks are the same because the price per watt is the same in this example. This leads to an important conclusion: a bigger system is not a better or worse investment by itself. The question is whether the extra production replaces electricity you would otherwise buy.
Payback for the extra 3 kW
The 3 kW difference costs $7,800 to $9,900 and produces about 4,350 more kWh per year. Its payback depends heavily on your rate:
- At 14 ¢/kWh: about 13 to 16 years
- At 20 ¢/kWh: about 9 to 11 years
- At 30 ¢/kWh: about 6 to 8 years
If your utility pays little for exported power, the extra panels only pay off when you consume the additional electricity yourself.
How to choose the right system size
Step 1: Find your annual usage
Add up the kilowatt-hours on your last 12 electric bills. If you have lived in the home less than a year, ask the utility for the previous owner’s usage or use a similar home as a guide.
Step 2: Estimate future changes
Electric loads you add later can push usage up quickly:
- An electric vehicle: about 3,000–4,000 kWh per year for a typical 12,000 miles
- A heat pump or electric heating: about 3,000–6,000 kWh per year, depending on climate
- A pool pump or heater: 1,500–4,000 kWh per year
- A hot tub, workshop or home office: 500–2,500 kWh per year
Step 3: Use the sizing formula
System size (kW) = annual usage (kWh) ÷ production per kW per year
Example: A home uses 11,000 kWh a year in an average location (1,450 kWh per kW). The system size is 11,000 ÷ 1,450 = 7.6 kW. If the owners also buy an EV (3,500 kWh), the usage rises to 14,500 kWh and the size becomes 10 kW.
Step 4: Check your limits
The final size also depends on your roof space, shade, electrical panel, utility policy and budget.
Roof space and electrical limits
Roof space
A 7 kW system needs about 320–360 square feet of unshaded roof. A 10 kW system needs 440–500 square feet. Hips, vents, skylights, chimneys and setbacks required by fire codes reduce the usable area. If your roof is small, high-efficiency panels let you fit more power in the same space, at a higher price.
Electrical panel
Many homes have a 200-amp main panel. Electrical rules limit how much solar current can connect to the panel, and a 10 kW system often approaches or exceeds that limit. In that case, the installer may need to upgrade the panel, move the connection to the utility side of the meter or reduce the inverter size. A panel upgrade typically costs $1,500–$4,000. A 7 kW system rarely triggers this issue. Ask any installer how they would connect the system and whether the quote includes the upgrade.
Utility limits
Some utilities cap system size at 100–110 % of your past usage, and some limit credit for excess production. Check the rules before you order a system larger than you need.
When a 7 kW system is the better choice
- Your annual usage is under about 11,000 kWh and you don’t plan big new loads.
- Your home is average in size and located in a moderately sunny area.
- Your roof space is limited.
- Your utility pays little for exported power.
- You want the lowest upfront cost and the least risk of oversizing.
When a 10 kW system is the better choice
- Your annual usage is above about 13,000–14,000 kWh.
- You own or plan to buy one or more EVs or install a heat pump.
- You have a large home, a pool or other heavy electrical loads.
- Your electricity rate is high (above about 25 ¢/kWh) and your utility credits exports at or near the retail rate.
- You have enough unshaded roof space and your electrical panel can handle the system.
What about 8 kW or 9 kW?
Systems aren’t limited to 7 and 10 kW. If your usage sits between the two, an 8 kW or 9 kW system may match better. Ask installers to quote two or three sizes so you can see the cost and savings of each step. Smaller increments let you pay only for what you need.
Frequently asked questions
Is a 10 kW solar system too big for a house?
Not if your home uses 13,000 kWh or more per year, or if you plan to add an EV or a heat pump. For a home that uses 8,000 kWh, a 10 kW system would be oversized and likely wouldn’t pay off.
How many panels do I need for 7 kW and 10 kW?
With 400-watt panels, a 7 kW system needs about 17 to 18 panels and a 10 kW system needs 25.
Can a 7 kW system run a whole house?
It can cover most or all of the annual electricity of an average home, but solar alone doesn’t keep power on during an outage. For backup power you need a battery and the right inverter.
Is it cheaper per watt to install a bigger system?
Slightly. Fixed costs are spread across more watts, so the price per watt may drop by $0.05 to $0.20. The total cost is still higher.
Should I size my system to cover 100 % of my usage?
Usually that is a good target if your utility credits exports well. If exports are paid poorly, aim for 70–90 % of your usage so that most of the energy you produce replaces power you would buy.
Bottom line
A 7 kW system is the practical choice for most average homes. A 10 kW system is worth the extra $7,800–$9,900 when your usage is high, you plan to electrify more of your home or your utility pays well for exports. Size your system to your usage, not to the biggest number a salesperson will quote.
The next step is to gather your last 12 months of bills, estimate any new loads and ask installers to quote two sizes side by side.