Solar for large homes in Illinois

Our model caps home systems at 25 kW, so the largest bills get a system that covers most of their use, not all of it. Size matters more than square footage here: the federal Residential Energy Consumption Survey finds home size strongly tied to energy use, but pools, electric heat and EVs can make two homes of the same size use very different amounts. Size from your last 12 months of bills.

Usually. Permits, design, sales and setup cost about the same whatever the system's size, so they're spread over more watts on a big one. Berkeley Lab's Tracking the Sun found about a $1 per watt gap in median prices between the smallest and largest home systems installed in 2023.

A large system should come in below the typical price per watt. Check yours with our solar quote checker, and see what solar saves with a $250+ bill.

Small DG systems that the homeowner owns also qualify for a $20 per REC adder in 2026–27 if no federal tax credit is claimed, which is now the norm for purchased home systems. Under 2026–27 contracts, the Illinois Shines payment for small systems is paid half when the system is switched on and the rest over six years.

Our estimates use the up-to-10 kW REC price for every size, so they slightly overstate the Illinois Shines value for larger systems. Ask each installer to show the REC price and incentive amount on the program's disclosure form.

A 22.8 kW system needs roughly 1,200 square feet of usable roof in our estimates, and fire-code setbacks from ridges and edges take some of what you have. Large homes often have several roof planes; east- and west-facing ones produce less than south-facing but still work, and microinverters or optimizers handle mixed directions well. See premium panels for when higher efficiency helps squeeze more onto a roof.

On a larger lot, a ground-mounted array can face due south and grow without roof limits. See ground-mount vs. roof-mount solar.

Often. Under the electrical code's 120% rule, a standard 200-amp panel with a 200-amp main breaker can only take about 7.7 kW of solar through a breaker, well short of what a large home needs.

• Supply-side connection: the solar ties in ahead of the main breaker, avoiding the panel limit. Often the least expensive fix where the utility and town allow it.
• Main breaker derate or a larger busbar: a panel swap that raises the limit.
• 320- or 400-amp service: worth it if you're also adding EV chargers, heat pumps or a battery.

Ask each installer which option they're using and whether it's in the price. See adding solar to a new build or remodel for the panel math.