Solar by state / California
Solar potential
in California.
California averages 5.3 kWh per square metre a day across the 8 grid cells sampled inside it — 4th of 51 states by that measure. June is the strongest month at 8.3, December the weakest at 2.2.
What that means for an array
On the same assumptions the ArrayCare check uses — a south-facing array and a 0.80 performance ratio — that works out to roughly 1,458 kWh a year for every kW installed, or 10,206 kWh for a 7 kW system. Irradiance is what arrives; production is what a specific array, at a specific tilt, with specific shading and losses, converts. Those are different numbers and a real quote will use the second.
Where in the state
The spread inside California runs from 4.7 kWh/m²/day around Del Norte County to 5.9 around San Bernardino County — 25% between the dimmest and sunniest sampled cells, or about 320 kWh a year per kW installed. Where in the state a roof sits matters more than the state average does.
These figures come from NASA POWER's solar climatology, a grid of roughly 55 km cells. Two points 40 km apart return the same numbers, which is why this page covers a state and prints the range across 8 sampled cells rather than claiming a figure for a town or a ZIP code. Local terrain, coastal fog and elevation all move the real number at a given address, and none of them are visible at this scale.
Through the year
June runs 3.8× stronger than December. That is a steep seasonal swing: a winter month delivers well under half what a summer one does, and an array sized around the annual figure will run far below it for months at a time.
| Month | kWh/m² a day | kWh per kW installed | |
|---|---|---|---|
| January | 2.5 | 58 | |
| February | 3.5 | 74 | |
| March | 4.8 | 112 | |
| April | 6.3 | 141 | |
| May | 7.5 | 174 | |
| June | 8.3 | 187 | |
| July | 8.1 | 188 | |
| August | 7.3 | 170 | |
| September | 6.0 | 135 | |
| October | 4.4 | 102 | |
| November | 2.9 | 66 | |
| December | 2.2 | 51 |
Monthly means across the 8 sampled cells. The per-kW column applies a south-facing orientation and a 0.80 performance ratio to the irradiance beside it — the same arithmetic the array check uses.
The cells behind these numbers
Each row is one NASA POWER grid cell, named for the county its sample point falls in. Two counties in the same cell would return the same numbers, so only one of each appears.
| Sample point | kWh/m² a day | kWh a year per kW |
|---|---|---|
| San Bernardino County | 5.9 | 1,617 |
| San Diego County | 5.8 | 1,599 |
| Fresno County | 5.4 | 1,495 |
| Alameda County | 5.3 | 1,462 |
| Solano County | 5.2 | 1,436 |
| Sutter County | 5.1 | 1,405 |
| Tehama County | 5.0 | 1,362 |
| Del Norte County | 4.7 | 1,297 |
Against the rest of the country
For scale, Arizona leads the country at 5.8 kWh/m²/day and Alaska trails at 2.5. The national spread is narrower than most people expect — the sunniest state is not ten times the dimmest, it is about 2.3×.
Sunlight is only one input into whether solar pays somewhere. Electricity prices, net-metering rules, incentives, roof condition and shading routinely matter more than the difference between two neighbouring states, and none of them are on this page. ArrayCare is independent, sells nothing, and is not a quote.