5 kW vs 10 kW Solar System: Panels, Output and Roof Area

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Planning input	5 kW system	10 kW system
400W panel count	13 panels = 5.2 kW DC	25 panels = 10.0 kW DC
Module footprint	About 243 sq ft	About 468 sq ft
Annual output at 3.5 sun hours	About 5,110 kWh	About 10,220 kWh
Annual output at 4.5 sun hours	About 6,570 kWh	About 13,140 kWh
Annual output at 5.5 sun hours	About 8,030 kWh	About 16,060 kWh
Monthly average at 4.5 hours	About 548 kWh	About 1,095 kWh

Output rows use exact 5.0 and 10.0 kW reference capacities, 20% aggregate losses, and annual average peak sun hours. The 13-panel 400W example is 5.2 kW, so its actual modeled output would be slightly higher than the 5.0 kW reference row.

Generation formula

annual kWh = system kW x peak sun hours/day x 365 x 0.80

At 4.5 peak sun hours, 5 x 4.5 x 365 x 0.80 = 6,570 kWh/year. Doubling capacity to 10 kW gives 13,140 kWh/year under the same assumptions. Real output is not perfectly linear when roof directions, inverter clipping, shade, export limits, or curtailment differ between designs.

Which size is more appropriate?

5 kW is the stronger starting point whenannual use is near 5,000-8,000 kWh, roof area is limited, or local export compensation makes oversizing unattractive.

10 kW is the stronger starting point whenannual use is near 10,000-16,000 kWh, loads include an EV or electric heating, and roof plus utility rules support the capacity.

Neither number is enough alonewithout monthly electricity use, peak sun hours, roof fit, tariff/export rules, shading, and future-load assumptions.

Country and regional parameters to check

United States: utility interconnection limits, net metering/export rates, roof setbacks, incentives, and actual annual kWh.
Australia: distributor export limits, inverter capacity, phase configuration, high-sun yield, and daytime self-consumption.
United Kingdom: lower annual sun, roof orientation, export tariff, DNO requirements, and winter-heavy electricity loads.

Error boundary: installed capacity does not by itself determine savings. Electricity rates, self-consumption, export compensation, system price, incentives, degradation, maintenance, and financing change the financial result.

Check roof fit, then estimate savings

Each roof-fit link opens a reproducible 400W panel example. The result page can continue to Savings or Battery Sizing and can copy or print a Solar Project Summary.

Check 5 kW need vs fit Check 10 kW need vs fit Estimate 5 kW savings Estimate 10 kW savings Review the assumptions

Related planning evidence

Usage tableMap 500-3,000 kWh/month to panels

1,000 kWh answerSee a 9.2 kW worked example

EV chargingAdd an EV load before sizing

Last reviewed July 18, 2026. Planning estimate only; no production, savings, price, or installation result is promised.