Question 1

How many solar panels does it take to power a house?

Accepted Answer

It depends on your electricity use, local sun, and panel wattage — not a fixed number. A typical US home using about 10,500 kWh a year needs roughly a 7–9 kW system, which is about 18–24 modern 400-watt panels at average sun. Sunnier regions need fewer; cloudier ones or higher usage need more. This calculator sizes it from your actual numbers.

Question 2

How is the number of panels calculated?

Accepted Answer

First the system size: annual usage × the share you want to offset, divided by (peak sun hours × 365 × a derate of ~0.8 for real-world losses). That gives the kW needed. Dividing by your panel wattage and rounding up gives the panel count. Roof area is estimated at about 19 watts per square foot of panel.

Question 3

What if I don't know my annual kWh?

Accepted Answer

Switch to "From my bill" and enter your average monthly bill and electricity rate (pick your state to fill the rate). The calculator converts that to annual kWh. For the most accurate result, use the actual kWh total from 12 months of utility bills, since rates and usage vary seasonally.

Question 4

Should I offset 100% of my usage?

Accepted Answer

Not always. Many homeowners size to 100% of annual use, but roof space, budget, shading, or utility net-metering rules can make a smaller system better. Oversizing past 100% rarely pays off unless you're adding loads like an EV or heat pump. Adjust the offset slider to see the trade-off.

How Many Solar Panels Do I Need?

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