Solar panels in Decatur, IL

Roofs in Decatur get about 1,497 hours of usable sunlight a year — less than 51% of the cities we've measured. Here's what that means in cost, savings and payback, using real rooftop data rather than a national average.

Check your specific roof in Decatur → City averages are a starting point; your own roof's size, pitch and shading change the answer a lot.

What a typical Decatur solar system costs

A 22-panel system (8.8 kW) is about right for an average Decatur home using 10,800 kWh a year. It would produce roughly 11,198 kWh annually and offset 100% of that usage.

How we worked this out for Decatur

Every number on this page comes from these seven steps. Nothing is a national average — the sunlight figure is measured from Decatur rooftops.

Step 6 matters more than it looks. Only 34% of what a system this size produces in Decatur is used the moment it is generated; the other 7,418 kWh is exported and credited one-for-one under net metering. Because exports here are credited at or near retail, that split changes the payback very little — 9.6 years against the 9.9 we show. In places where exports pay a fraction of retail the same split moves payback by years, which is why we model it explicitly rather than assuming.

Assumptions: 400W panels, 15% system losses (inverter, wiring, heat, soiling), $2.85/W installed, 10,800 kWh typical annual household use, 16.3¢/kWh electricity. Change any of those and every figure above moves — which is exactly why a single national "solar costs X" number is misleading.

Notice that payback barely improves as systems get bigger, and eventually gets worse. That's because you can only save money on electricity you were going to buy anyway. Once a system covers your usage, extra panels mostly generate exports at a much lower rate.

Why Decatur gets 1,497 sun hours

That figure comes from Google's analysis of real rooftops across Decatur — it already accounts for shading from trees, chimneys and neighbouring buildings, which is why it's lower than the raw "hours of daylight" figures you'll see elsewhere. An unusually open, unshaded roof in Decatur reaches about 1,610 hours, roughly 8% better than typical.

The numbers behind this page

When Decatur actually produces

Annual totals hide the thing that catches people out: 36% of Decatur's yearly sunlight arrives in May–July, and just 13% across November–January.

Decatur produces about 3.0× as much in Jun as in Dec — a normal mid-latitude swing. Expect real winter shortfall and summer surplus rather than steady year-round output.

The annual total is measured from Google's rooftop imagery. Its split across months is calculated from solar geometry at Decatur's latitude, not separately measured, so treat the monthly figures as the shape of a typical year rather than a forecast.

How Decatur compares to the other 788 cities

What actually stands out about Decatur:

• Every kWh counts more here. The grid serving Decatur emits 892 kg CO₂ per MWh, among the highest of the 788 cities measured — so the same panels displace more emissions than they would elsewhere.

Cities with almost the same sunlight

These are the closest matches to Decatur's 1,497 usable sun hours from other states and provinces. Same sunlight, different electricity prices — which is usually what decides whether solar is worth it.

Nearby cities

See all of Illinois → statewide sunlight, rates, incentives and every city we've measured.

Decatur solar questions

Worth reading before you buy

Estimates only, generated 2026-08-22 from Google Solar API rooftop samples and average Illinois electricity rates. Not a quote and not financial advice. Your roof, usage, utility plan and local incentives will change these numbers — get real quotes before buying.