Solar Systems Sized Bigger Than You Need
Let's go with 10 kW so you're covered for the future. The extra power gets sold back to the utility, so it pays for itself.
What's actually true
Panels beyond what your home uses often earn far less than retail, especially under net billing, where exports may be credited at a few cents per kWh. Extra capacity raises the price faster than it raises savings.
A solar system sized well beyond your electricity use usually costs more than it saves. The first panels offset power you’d otherwise buy at full retail price. Extra panels mostly send power to the grid, and in many places that power earns much less. Since sales reps are commonly paid more for bigger systems, it’s worth checking whether your quote matches your usage.
Why salespeople do it
Bigger systems mean a bigger contract, and commissions often scale with size. “Cover your future needs” sounds prudent and is hard to argue with. And if the production estimate is also inflated, the size can look justified on paper.
Why extra panels earn less
Under full retail net metering, surplus might be credited at close to retail, though many utilities pay a lower rate for any yearly surplus at true-up. Under net billing, exports earn much less. California’s current Net Billing Tariff, for example, credits exports at hourly avoided-cost values that work out to a few cents per kWh on average, versus retail prices many times higher. Illinois, Idaho, Duke Energy in North Carolina and others have also moved away from full retail credit. Check your state on our net metering page.
A worked example
Your home used 9,000 kWh in the last 12 months. Assume about 1,300 kWh per kW per year and $3.00 per watt (illustrative figures).
| Right-sized | Oversized | |
|---|---|---|
| System size | 7 kW | 10 kW |
| Price at $3.00/W | $21,000 | $30,000 |
| Yearly production | about 9,100 kWh | about 13,000 kWh |
| Extra beyond your usage | about 100 kWh | about 4,000 kWh |
| Value of extra at 4¢ export credit | about $4 | about $160 a year |
The extra 3 kW cost $9,000 and adds roughly $160 a year in credits. That’s a payback of over 50 years on the added panels, longer than they will last. Financed with a dealer-fee loan at $4.50 per watt, the extra panels would cost about $13,500.
When a bigger system does make sense
- You’re buying an EV soon. A typical EV can add a few thousand kWh a year depending on miles driven. See solar and EV charging.
- You’re switching to a heat pump or electric water heater.
- Your utility credits exports at or near full retail and is expected to keep doing so for your system.
- Adding panels later would cost much more (some roofs, some permitting situations).
Even then, size for the specific load, not a vague “future.”
How it shows up in a quote
- “Offset: 140%” or similar
- Usage listed as an estimate or one month times 12
- No monthly usage vs. production chart
- A single size option
Questions to ask
- “What annual usage did you size this system to? Where did that number come from?”
- “What percent of production will I export, and what does my utility pay for it?”
- “What would a system sized to 90% to 100% of my usage cost?”
- “What’s the price per watt at each size?”
What to do next
Get your real usage, then use the system size calculator and compare options to price two sizes side by side. Our guide on how many solar panels you need explains sizing. If your bill is high from waste, efficiency first may shrink the system you need.
Bottom line: Size to the electricity you use now, plus specific loads you’re sure are coming. Not more.
Where to report it
Oversizing alone isn’t illegal. If the rep misrepresented your usage or what the utility pays for exports, report it to your state attorney general or the FTC at reportfraud.ftc.gov.
Related red flags
Inflated Solar Production Estimates
Production depends on your location, roof direction, tilt, shading and system losses. Estimates that ignore shading, skip degradation or use optimistic losses can overstate output, and every savings number built on it, by a wide margin.
Home Batteries Sold on Exaggerated Savings
At about $1,130 per kWh installed, a 13.5 kWh battery costs roughly $15,000. Bill savings depend on your rate plan and export rules, and in many places they are a few hundred dollars a year. Backup power has real value, but it isn't bill savings.
"Your Electric Bill Will Be $0"
Most homes with solar still get a utility bill every month. Fixed customer charges, minimum bills, low export credits under net billing, and winter months with less sun mean a $0 bill is rare.
"Net Metering Is Guaranteed Forever"
Net metering is set by state law and utility regulators, and it changes often. Grandfathering usually lasts a fixed number of years, and many states and utilities have already moved new customers to net billing, where exported power earns far less than retail.
Quotes That Show Only a Monthly Payment
A monthly payment hides the total price, the system size, the price per watt and any dealer fee built into the loan. Two quotes with similar payments can differ by thousands of dollars in total cost.