Solar potential
in Massachusetts.

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 1,053 kWh a year for every kW installed, or 7,371 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 Massachusetts runs from 3.7 kWh/m²/day around Berkshire County to 3.9 around Dukes County — 5% between the dimmest and sunniest sampled cells, or about 48 kWh a year per kW installed. The state reads close to uniform at this resolution, so the average describes it about as well as any local figure would.

Through the year

July runs 4.2× 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.

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.

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.