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Calculator · Updated August 2026
Solar offset percentage calculator
Offset is not bill reduction. Here is the difference, with your own numbers.
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The calculator
What share of your usage would a system cover?
Offset is not the same as bill reduction. You keep a customer charge, and exported power is often worth less than power you use as it is made.
This is an estimate, not a savings guarantee.
It uses published utility rates, NREL regional sun data and a standard system derate. It does not know your roof orientation, your shading, your usage pattern or what your utility will charge next year. No solar company can honestly guarantee savings, and any that does is describing a model rather than making a promise.
Offset is not bill reduction
A 100% offset system does not produce a $0 bill. Three things remain: the customer charge, which you pay whether you produce anything or not; the gap between what exports are credited at and what imports cost; and any minimum bill or demand-related rider your utility applies.
Anyone promising a zero bill is describing offset and calling it savings.
Why 100% is often the wrong target
It is the number people reach for and it is frequently a mistake. Where your state credits exports below retail — California under net billing, Ohio at the generation rate, Illinois on supply-only since January 2025 — the surplus you build to reach 100% is worth far less than the power you consume as it is produced. In those states an array sized to your daytime load, sometimes with storage, beats one sized to your annual total.
Where net metering is 1:1 at retail — Pennsylvania, New Jersey, Virginia, Maine — sizing to 100% is defensible, because an exported kilowatt-hour and a consumed one are worth the same.
What caps offset in practice
Usable roof area
Not roof area. Fire code setbacks, vents, chimneys, skylights and dormers typically remove 20–30% before a panel is placed. A roof that looks large often supports a much smaller array.
Orientation and shading
South-facing is the reference. East and west lose roughly a fifth. The shading selector above applies a flat derate, which is a simplification — midday shading costs far more than early-morning shading because those hours carry most of the production.
Utility interconnection limits
Many utilities cap residential systems, commonly at 25 kW, and some cap at a percentage of your historical usage specifically to prevent oversizing.
Where to find your real usage
Your utility's online account has twelve months of kilowatt-hours. Use that rather than estimating from a dollar amount — dollars move with rates, kilowatt-hours are the actual quantity. A home with electric heat or an EV will be badly served by extrapolating one summer month.
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Who you would be working with
SolarAmerica
We design your system and manage the project; installation is performed by vetted licensed partners in your area. SolarAmerica is not itself the installing contractor.
Questions
The things people actually ask
What percentage of my bill will solar cover?
Offset and bill reduction are different. This shows the share of your kilowatt-hours a system would produce. Your bill also carries a customer charge, and exported power is often credited below retail.
Should I aim for 100% offset?
Only where exports are credited at the retail rate. Where export credit is well below retail, an array sized to your daytime load produces a better result.
Can I install a system bigger than my usage?
Often not. Many utilities cap residential systems at a percentage of historical usage, and most cap absolute size around 25 kW.
Get the number for your actual roof
About 60 seconds. No cost, no obligation, and we will tell you if solar does not make sense for your home.
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