Why is my solar system producing less than expected?

Compare like with like. Illinois systems make far less in December than in July, so one bad month isn't proof of a problem. Use the full-year estimate from your contract or the Illinois Shines disclosure form, which has included an estimate of first-year production, and compare it with 12 months of actual output from your monitoring app or meter.

Weather varies too. A cloudier year than average means lower output, and NREL's PVWatts calculator lets you check what a system like yours should make at your address.

• Monitoring offline: the system may be fine, but the app stopped updating. Enphase says missing data in its app may mean the system is no longer connected to the internet.
• A tripped breaker or switched-off disconnect, often after an electrical job or a storm.
• A failed inverter or microinverter: with a string inverter, the whole system can stop; with microinverters, one panel drops out.
• New shade: trees grow, and on a string inverter, shade on one panel can pull down the output of the whole string.
• Snow, dirt or pollen covering the panels.
• Normal aging, a small loss each year.

Not much. NREL's 2024 study of about 8 gigawatts of U.S. commercial and utility-scale systems found a median loss of 0.75% a year, and 0.48% in cooler climates; home systems weren't part of that study. For a Chicago-area system we estimate at about 9,600 kWh in its first year, a 0.75% yearly loss would still leave about 8,900 kWh in year 11. A much bigger drop points to a fault, not age. See how long solar panels last.

Snow does, mostly in winter when output is already low. NREL's 2017 analysis found average yearly snow losses from zero to 16% across the lower 48 states, and the usual advice is to let it slide off rather than climb the roof. Pollen can matter more than people expect: NREL found in 2023 that rain doesn't rinse it off well, and output fell by up to 15% in its North Carolina tests. See solar in an Illinois winter.

Some installers and lease companies promise a minimum amount of production and pay you if the system falls short. EnergySage describes a typical example as a guarantee of 90% of a stated yearly figure. Not every installer offers one, there's no standard way to set the estimate, and it's separate from equipment warranties. Check your contract for one, and file a claim if your full-year output falls short. See solar warranties in Illinois.

Equipment warranties from the panel and inverter makers generally still apply, but the installer's workmanship warranty and any production guarantee usually go with it. Contact the manufacturer for a certified service company in your area, and ask whether work by a non-certified company affects your warranty. If you have a lease or PPA, check the contract: the company that owns the system is usually responsible for repairs.

1. 1

   Your installer

   Send them a year of production data compared with the estimate and ask for a site visit.

2. 2

   Illinois Shines

   The program's consumer complaint center takes complaints by phone at (877) 708-3456 or online, tries to mediate, and can warn or suspend vendors.

3. 3

   The Illinois Attorney General

   The Consumer Fraud Bureau takes complaints online and offers informal dispute resolution.

One Illinois-specific check: if your system's Illinois Shines production meter was made by SDSI, which shut down, automatic reporting ended April 30, 2026. Ask your installer or Illinois Shines whether your meter needs replacing so your production keeps being counted.