What that is equal to
🏠 170
homes powered for a year
at the US average of 10,500 kWh per household
🌍 662 t
CO₂ avoided annually
displacing grid power at 0.371 kg CO₂e/kWh (EPA eGRID)
🚗 144
cars taken off the road
an average passenger vehicle emits 4.6 t CO₂e a year
⚡ 5.1 million
electric vehicle miles
at roughly 0.35 kWh per mile
The pay-off
It pays for itself here. A panel on this roof delivers electricity at 8.9¢ a kWh against a local price of 14.7¢ — 39% cheaper than local power. The install is repaid after 14.8 years, inside the panel's 25-year life.
8.9¢ vs 14.7¢
cost per kWh: this panel vs the grid
levelised over 25 years including 0.5%/yr degradation
$3.75 million
to fit every building here
4,165 panels at $900 installed each
14.8 years
to break even
saving $262 thousand a year area-wide at today's price
Assumes $900 to install one 325 W panel — hardware, mounting,
microinverter, electrical work, labour and permitting — repaid only by the electricity it
avoids buying. No subsidies, tax credits, net-metering premium, financing cost or future
price rises are counted, and the figure is undiscounted. Electricity price is the
MT residential average (EIA, May 2026). A single panel is unusually expensive per watt because it
carries a whole array's fixed costs, which is why these numbers look worse than rooftop
solar generally does.
How this is calculated
| Buildings with roofs | 4,165 |
| × Panel rating | 325 W |
| × Annual yield per panel here | 428.7 kWh |
| Annual generation | 1,785,488 kWh |
Assumptions and limitations
- Yield is specific to this location: 428.7 kWh per panel per
year, from NASA POWER climatology transposed onto a tilted roof plane.
The same panel makes roughly 596 kWh in Phoenix and 265 kWh in Anchorage.
- Assumes a south-facing roof at a typical residential pitch, with a
~22% total system loss for soiling, shading, wiring, inverter, and heat.
- Counts every above-ground structure with a footprint of at least 20 m²,
so garages and outbuildings are excluded but barns and sheds of real
size are not. Building data is machine-derived and imperfect.
- No account is taken of roof orientation, obstructions, structural
condition, or whether the owner wants a panel.
Places like McCone County