Peak sun hours in Idaho
Idaho averages 4.6 peak sun hours a day across the year, 21st of the 50 states. At that figure a 400-watt panel produces about 1.42 kWh a day after real-world losses, and covering the 900 kWh average US bill takes about 21 panels. Boise, the state's biggest city, runs slightly ahead of the statewide figure at 4.7 hours; treat 4.6 as the midpoint of a real spread rather than a local reading.
solid mid-pack sun: 4.6 of a possible ~6.5 hours
Panel counts for Idaho bills
Computed at Idaho's 4.6 hours with 400W panels and the 0.77 derate; the US-average column shows what the same bill takes at 4.5 hours, so you can see what your state's sun is worth in hardware.
| Monthly usage | Idaho | System size | US average |
|---|---|---|---|
| 500 kWh/mo | 12 panels | 4.8 kW | 12 panels |
| 750 kWh/mo | 18 panels | 7.2 kW | 18 panels |
| 900 kWh/mo | 21 panels | 8.4 kW | 22 panels |
| 1,000 kWh/mo | 24 panels | 9.6 kW | 24 panels |
| 1,500 kWh/mo | 35 panels | 14 kW | 36 panels |
| 2,000 kWh/mo | 47 panels | 18.8 kW | 48 panels |
What 4.6 hours means in practice
Idaho is mid-pack American sun: 21st of 50 at 4.6 peak sun hours, within 2% of the national average. The 900 kWh average bill lands at 21 panels against 22 nationally. At this tier the resource neither makes nor breaks the project, which is what the rate and the seasonal spread below are for.
How a Idaho year is shaped
The 4.6-hour figure is an annual average, and no month is average. These are the twelve monthly means for Idaho from NASA's 2001-2020 solar climatology, each as a share of the state's own annual mean, with that share applied to the 4.6-hour planning figure. July and December are marked.
| Month | Share of the annual average | Peak sun hours (est.) |
|---|---|---|
| January | 39% | 1.8 |
| February | 60% | 2.8 |
| March | 87% | 4.0 |
| April | 119% | 5.5 |
| May | 144% | 6.6 |
| June | 165% | 7.6 |
| July | 173% | 8.0 |
| August | 148% | 6.8 |
| September | 114% | 5.2 |
| October | 75% | 3.4 |
| November | 44% | 2.0 |
| December | 31% | 1.4 |
Idaho runs a short, hard solar year. July reaches 173% of the annual average and December falls to 31%, 5.7 to one, with 53% of the light arriving in four months. In hours that is 8.0 a day at the July top against roughly 1.4 in December. Sizing a Idaho array off the annual figure alone is fine on the grid and badly wrong off it.
Half the Idaho calendar sits above the annual average and half below: April through September are the six months that beat it, carrying 72% of the year's light. April is already worth about 5.5 hours a day, so the productive half of the year starts earlier than most people expect.
Bills here run above the national line. The average Idaho household used 944 kWh a month in 2024 against 863 nationally, 9% more, and covering that across a year takes 22 panels at Idaho's sun. Covering it from December sun alone would take 72, 3.3 times the array, which is the number that decides whether a battery plan is realistic.
Idaho is one of the states where a statewide number does the most damage: it has the 4th widest internal spread of the fifty. Across the 20 grid cells sampled here the south runs 27% sunnier than the northwest. Held against the 4.6-hour statewide figure that is roughly 5.2 hours at one end and 4.0 at the other, which is the difference between two quite different quotes. Nobody should size a Idaho roof off the state average without checking which end of the state it sits on.
What that sun is worth on a Idaho bill
| EIA, 2024 residential averages | Idaho | United States |
|---|---|---|
| Average home's monthly use | 944 kWh | 863 kWh |
| Price per kilowatt-hour | 11.52¢ | 16.48¢ |
| Average monthly bill | $108.73 | $142.26 |
| One 400W panel, a year's output | 517 kWh | 506 kWh |
| What that output displaces | $60 | $83 |
Idaho has some of the cheapest electricity in the United States, 11.52¢ a kilowatt-hour in 2024 against a national 16.48¢, 2nd cheapest of the fifty. That is 30% less value in every kilowatt-hour a panel produces: about $60 a year from one 400-watt panel where the national figure is $83. Sun is not this state's constraint on solar. The rate it displaces is.
Here the sun ranking flatters Idaho. 21st of fifty for sunlight, but only 48th for what a panel earns in a year, a drop of 27 places, and the reason is entirely the price of the electricity being replaced. Alabama gets the same sun (4.6 hours to Idaho's 4.6) and pays 15.18¢ against 11.52¢, so one panel is worth about $19 less a year in Idaho than in Alabama.
Two warnings on those dollar figures. They are displaced electricity and nothing else: no install cost, no incentive, no financing, and no assumption about how your utility settles a surplus, which is the single biggest unknown in the sum. And a state average hides the utility you are actually on; 11.52¢ is every Idaho residential customer averaged together, and neighbouring territories can differ by more than the gap between two states in the ranking.
Getting a number for your address
For a location-exact figure, run your address through NREL's free PVWatts; it uses measured weather for your grid cell and will also model roof tilt and direction, which statewide numbers cannot. Then compare its annual kWh against a quote's promise before you sign anything.
Questions people ask
How many solar panels do I need in Idaho?
About 21 400-watt panels (8.4 kW) for the 900 kWh a month an average US home uses, at Idaho's 4.6 peak sun hours. For the average Idaho home specifically, which EIA measured at 944 kWh a month in 2024, it is 22. Your own bill is the variable that matters, and the calculator takes any figure.
Is 4.6 peak sun hours good for solar?
It is solidly workable. Idaho sits near the national average of 4.5 hours, so panel counts here match the US-typical figures, and project economics turn on your utility's rates and net-metering terms rather than on the sun.
How much is one solar panel worth a year in Idaho?
About $60. One 400-watt panel at Idaho's 4.6 peak sun hours makes roughly 517 kWh a year after the 0.77 derate, and Idaho residential electricity averaged 11.52¢ a kilowatt-hour in 2024 (EIA), which puts Idaho 48th of the 50 states on this measure against 21st on sunlight alone. That figure is displaced electricity only. It says nothing about install cost, incentives, or how your utility settles a surplus.
Do peak sun hours change with the seasons in Idaho?
Yes, by a factor of 5.7 here. NASA's 2001-2020 climatology puts Idaho's July at 173% of the annual average and December at 31%, so the 4.6-hour figure on this page is the midpoint of a curve running from roughly 8.0 hours a day down to 1.4. Grid-tied homes bank the summer surplus as credit; off-grid designs have to size for the trough, and in Idaho that means 72 panels for an average local bill instead of 22.