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, beats the statewide figure at 4.5 hours, so the rest of the state leans the other way; treat 4.3 as the midpoint of a real spread.
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. What matters at this tier is the winter-summer swing; annual averages hide December, and December is where off-grid plans in Montana go wrong. Grid-tied with net metering, the year evens out.
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. Your bill is the variable that matters: the table on this page covers 500 to 2,000 kWh, 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-January trough deserves respect in any off-grid plan. Grid-tied systems ride through it on net metering.
Do peak sun hours change with the seasons in Montana?
Yes, everywhere: the figure on this page is the annual average of a curve that peaks in June and bottoms out in December. At Montana’s latitude and cloud cover the winter trough is deep, often a third of the summer figure or less. Grid-tied homes bank summer overproduction as credit; off-grid designs must size for the trough, not the average.