Solar panels in Downey, CA

Roofs in Downey get about 1,959 hours of usable sunlight a year — more than 94% 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 Downey → City averages are a starting point; your own roof's size, pitch and shading change the answer a lot.

What a typical Downey solar system costs

A 17-panel system (6.8 kW) is about right for an average Downey home using 10,800 kWh a year. It would produce roughly 11,323 kWh annually and offset 100% of that usage.

How we worked this out for Downey

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

Step 6 is where most calculators quietly overstate things. Only 33% of what a system this size produces in Downey is used the moment it is generated; the other 7,543 kWh is exported and credited at 20% of retail under net billing. Valuing every kWh at the full 31.2¢ retail rate — which many calculators do — would show a payback of 3.8 years instead of the 8.2 we show. That 4.4-year difference is the single biggest reason our figures look worse than other sites' for Downey.

Assumptions: 400W panels, 15% system losses (inverter, wiring, heat, soiling), $2.85/W installed, 10,800 kWh typical annual household use, 31.2¢/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 Downey gets 1,959 sun hours

That figure comes from Google's analysis of real rooftops across Downey — 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 Downey reaches about 2,020 hours, roughly 3% better than typical.

The numbers behind this page

When Downey actually produces

Annual totals hide the thing that catches people out: 34% of Downey's yearly sunlight arrives in May–July, and just 16% across November–January.

Output is unusually steady — only about 2.4× between Jun and Dec. Downey is close enough to the equator that seasonal variation is mild, which makes sizing a system considerably more predictable.

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

How Downey compares to the other 788 cities

What actually stands out about Downey:

• The case here is financial, not environmental. Downey's grid is already clean at 429 kg CO₂ per MWh, so the carbon saving from solar is modest. Judge this one on payback.
• Expensive electricity works in your favour. At 31.2¢/kWh, California is among the priciest places to buy power — which is exactly what makes generating your own pay back faster.

Cities with almost the same sunlight

These are the closest matches to Downey's 1,959 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 California → statewide sunlight, rates, incentives and every city we've measured.

Downey solar questions

Worth reading before you buy

Estimates only, generated 2026-08-22 from Google Solar API rooftop samples and average California 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.