klepZ ArrayCare

Solar by state / Montana

Solar potential
in Montana.

Daily irradiance4.0kWh/m² average, 3.7–4.2 across the state
Per kW installed1,095kWh a year, south-facing at 0.80 PR
Strongest monthJuly7.1 kWh/m² a day
National rank33 / 51by sampled irradiance

Montana averages 4.0 kWh per square metre a day across the 8 grid cells sampled inside it — 33rd of 51 states by that measure. July is the strongest month at 7.1, December the weakest at 1.2.

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 1,095 kWh a year for every kW installed, or 7,665 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 Montana runs from 3.7 kWh/m²/day around Mineral County to 4.2 around Beaverhead County — 13% between the dimmest and sunniest sampled cells, or about 132 kWh a year per kW installed. That is a real difference, though a roof's orientation and shading will usually move the number further than its county does.

How precise this is

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

July runs 6.1× stronger than December. That is an extreme seasonal swing. Winter output is close to negligible, and an annual average badly misdescribes a year shaped like that.

MonthkWh/m² a daykWh per kW installed
January 1.5 36
February 2.5 54
March 3.6 85
April 4.8 108
May 5.8 135
June 6.5 148
July 7.1 166
August 5.9 138
September 4.3 98
October 2.7 64
November 1.6 37
December 1.2 27

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 pointkWh/m² a daykWh a year per kW
Beaverhead County4.21,158
Stillwater County4.11,133
Rosebud County4.11,126
Musselshell County4.11,113
Valley County4.01,090
Daniels County4.01,089
Mineral County3.71,026
Sanders County3.71,026

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.

States with similar sun

All 51 states ranked →