Peak sun hours in Montana
Montana averages 4.3 peak sun hours a day across the year, 28th of the 50 states. At that figure a 400-watt panel produces about 1.32 kWh a day after real-world losses, and covering the 900 kWh average US bill takes about 23 panels. Billings, the state's biggest city, runs slightly ahead of the statewide figure at 4.5 hours; treat 4.3 as the midpoint of a real spread rather than a local reading.
modest sun: 4.3 of a possible ~6.5 hours
Panel counts for Montana bills
Computed at Montana's 4.3 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 | Montana | System size | US average |
|---|---|---|---|
| 500 kWh/mo | 13 panels | 5.2 kW | 12 panels |
| 750 kWh/mo | 19 panels | 7.6 kW | 18 panels |
| 900 kWh/mo | 23 panels | 9.2 kW | 22 panels |
| 1,000 kWh/mo | 25 panels | 10 kW | 24 panels |
| 1,500 kWh/mo | 38 panels | 15.2 kW | 36 panels |
| 2,000 kWh/mo | 50 panels | 20 kW | 48 panels |
What 4.3 hours means in practice
Montana runs 4% below the national solar average, 28th of 50 at 4.3 hours. That is workable sun, not bad sun: the 900 kWh bill takes 23 panels here versus 22 nationally, 1 more. Germany built the world's densest solar fleet on worse.
How a Montana year is shaped
The 4.3-hour figure is an annual average, and no month is average. These are the twelve monthly means for Montana from NASA's 2001-2020 solar climatology, each as a share of the state's own annual mean, with that share applied to the 4.3-hour planning figure. July and December are marked.
| Month | Share of the annual average | Peak sun hours (est.) |
|---|---|---|
| January | 39% | 1.7 |
| February | 64% | 2.8 |
| March | 92% | 4.0 |
| April | 120% | 5.2 |
| May | 144% | 6.2 |
| June | 164% | 7.1 |
| July | 178% | 7.6 |
| August | 147% | 6.3 |
| September | 108% | 4.7 |
| October | 69% | 3.0 |
| November | 42% | 1.8 |
| December | 30% | 1.3 |
Montana runs a short, hard solar year. July reaches 178% of the annual average and December falls to 30%, 5.9 to one, with 53% of the light arriving in four months. In hours that is 7.6 a day at the July top against roughly 1.3 in December. Sizing a Montana array off the annual figure alone is fine on the grid and badly wrong off it.
Half the Montana 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 5.2 hours a day, so the productive half of the year starts earlier than most people expect.
Montana's average home used 852 kWh a month in 2024 by EIA's count, within a few percent of the national 863, so the national panel counts on this page transfer here better than they do in most states. That average bill needs 22 panels across the year and 71 to be carried by December sun alone, a factor of 3.2.
Montana is one of the states where a statewide number does the most damage: it has the 9th widest internal spread of the fifty. Across the 20 grid cells sampled here the southwest runs 20% sunnier than the northwest. Held against the 4.3-hour statewide figure that is roughly 4.7 hours at one end and 3.9 at the other, which is the difference between two quite different quotes. Nobody should size a Montana roof off the state average without checking which end of the state it sits on.
What that sun is worth on a Montana bill
| EIA, 2024 residential averages | Montana | United States |
|---|---|---|
| Average home's monthly use | 852 kWh | 863 kWh |
| Price per kilowatt-hour | 12.66¢ | 16.48¢ |
| Average monthly bill | $107.91 | $142.26 |
| One 400W panel, a year's output | 483 kWh | 506 kWh |
| What that output displaces | $61 | $83 |
Cheap power cuts the other way. Montana residential electricity averaged 12.66¢ a kilowatt-hour in 2024, 23% under the national 16.48¢ and 11th cheapest in the country, so the same panel that offsets $83 a year at national rates offsets about $61 here. Nothing is wrong with the sun. There is just less money in each kilowatt-hour it makes.
Here the sun ranking flatters Montana. 28th of fifty for sunlight, but only 47th for what a panel earns in a year, a drop of 19 places, and the reason is entirely the price of the electricity being replaced. Maryland gets less sun (4.2 hours to Montana's 4.3) and pays 17.86¢ against 12.66¢, so one panel is worth about $23 less a year in Montana than in Maryland.
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; 12.66¢ is every Montana 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 Montana?
About 23 400-watt panels (9.2 kW) for the 900 kWh a month an average US home uses, at Montana's 4.3 peak sun hours. For the average Montana home specifically, which EIA measured at 852 kWh a month in 2024, it is 22. Your own bill is the variable that matters, and the calculator takes any figure.
Is 4.3 peak sun hours good for solar?
It is below the 4.5-hour national average but far from disqualifying. Panel counts run about 5% higher here for the same bill, and the December trough measured above deserves respect in any off-grid plan. Grid-tied systems ride through it on net metering.
How much is one solar panel worth a year in Montana?
About $61. One 400-watt panel at Montana's 4.3 peak sun hours makes roughly 483 kWh a year after the 0.77 derate, and Montana residential electricity averaged 12.66¢ a kilowatt-hour in 2024 (EIA), which puts Montana 47th of the 50 states on this measure against 28th 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 Montana?
Yes, by a factor of 5.9 here. NASA's 2001-2020 climatology puts Montana's July at 178% of the annual average and December at 30%, so the 4.3-hour figure on this page is the midpoint of a curve running from roughly 7.6 hours a day down to 1.3. Grid-tied homes bank the summer surplus as credit; off-grid designs have to size for the trough, and in Montana that means 71 panels for an average local bill instead of 22.