Quick answer
Usually yes, and in dollars it's where solar pays best. For a Chicago-area home with a $300 monthly ComEd bill, we estimate a 16.8 kW system costs about $22,700 after the utility rebate and Illinois Shines, saves about $2,722 in year one and about $92,800 over 25 years, with payback around 8.3 years.
How much does solar save with a big electric bill?
| Monthly bill | System | Cost after incentives | First-year savings | Payback | 25-year savings |
|---|---|---|---|---|---|
| $150 | 8.0 kW (20 panels) | $10,800 | $1,296 | 8.3 yrs | $44,200 |
| $250 | 14.0 kW (35 panels) | $18,800 | $2,268 | 8.3 yrs | $77,300 |
| $300 | 16.8 kW (42 panels) | $22,700 | $2,722 | 8.3 yrs | $92,800 |
| $400 | 22.8 kW (57 panels) | $30,800 | $3,694 | 8.3 yrs | $125,900 |
| $500 | 25.0 kW (63 panels) | $33,700 | $4,050 | 8.3 yrs | $138,100 |
| Monthly bill | System | Cost after incentives | First-year savings | Payback | 25-year savings |
|---|---|---|---|---|---|
| $150 | 7.6 kW (19 panels) | $11,400 | $1,272 | 9 yrs | $43,400 |
| $250 | 13.2 kW (33 panels) | $19,600 | $2,210 | 8.9 yrs | $75,300 |
| $300 | 16.4 kW (41 panels) | $24,400 | $2,745 | 8.9 yrs | $93,600 |
| $400 | 22.0 kW (55 panels) | $32,800 | $3,683 | 8.9 yrs | $125,600 |
| $500 | 25.0 kW (63 panels) | $37,300 | $4,185 | 8.9 yrs | $142,700 |
Estimates assume a cash purchase on an unshaded, south-facing roof at $3.10 per watt. Our model caps home systems at 25 kW, so a $500 bill gets a system that covers most, not all, of its use. See how we estimate, or enter your own bill in the calculator.
Why do high-usage homes get the biggest solar savings?
Payback stays around 8 to 9 years at every bill size, because the $300/kW utility rebate and the Illinois Shines REC payment both grow with the system. What grows is the dollar amount: a $500 bill can save about $138,100 over 25 years, roughly three times what a $150 bill saves.
Large homes often use more of their solar as it's produced, too. Daytime air conditioning, a pool pump or a home office soak up midday output that would otherwise be exported at the lower supply-rate credit. Our estimates assume half of production is used at home; a home that uses more of it saves more.
Installed prices per watt also tend to fall on bigger systems, because permits, design and labor don't double when the system does. Our estimates use one flat price, so a well-priced quote for a large system can beat them.
Will a big solar system fit on my roof?
A system sized for a $300 ComEd bill needs about 42 panels and roughly 880 square feet of usable roof. Large homes usually have it, but shade, dormers, skylights and vents shrink the usable area, and north-facing planes produce much less.
If the roof falls short, a ground-mounted array on a larger lot is often the answer, and it can face due south at the ideal tilt. See ground-mount vs. roof-mount solar.
Large systems sometimes need an electrical panel or service upgrade so the house can safely take in that much solar. Ask each installer whether yours does and whether the cost is in the quote.
Should I lower my usage before going solar?
Cheap fixes first: LED lighting, a smart thermostat and sealing obvious drafts cost little and shrink the system you need. Beyond that, size for the home you'll have: if an electric car, a heat pump or a pool is coming, include that load now, because adding panels later costs more per watt than including them up front. See adding solar for an EV or heat pump.
What should high-usage homes ask solar installers?
- 1
Size it from 12 months of bills
A single summer bill overstates use and a spring bill understates it. Give installers a full year of usage.
- 2
Ask for the price per watt
Large systems should come in at a lower price per watt. Check any quote with our solar quote checker.
- 3
Confirm the electrical work
Ask whether a panel or service upgrade is needed and whether it's included.
- 4
Ask about a battery
With a large system you'll export more at midday. A battery stores it for the evening and qualifies for the utility storage rebate.
Sources
- Illinois Shines: Final 2026–27 REC prices for the program year starting June 1, 2026
- Illinois Shines: Small distributed generation
- Citizens Utility Board: Solar and storage rebates (ComEd and Ameren)
- ComEd: Distributed generation rebate
- Illinois Shines: FAQs related to changes in net metering in Illinois
- NREL PVWatts Calculator
- U.S. EIA: Average retail price of electricity by state (Electric Power Monthly, Table 5.6.A)
This guide is general information, not tax, legal or financial advice. Incentive programs change, so confirm current terms with your installer, your utility and a tax professional.