The Solar Panel Cost Calculator estimates the system size needed to offset a monthly electricity bill, then calculates gross system cost, tax credit, net cost, annual bill savings, and simple payback.

Calculation method

The model converts your monthly bill into monthly energy use, estimates daily use, and sizes the system from sun hours and efficiency:

$\text{Monthly usage (kWh)}=\frac{\text{Monthly bill}}{\text{Electricity rate}}$ $\text{System size (kW)}=\frac{\text{Monthly usage}/30.42}{\text{Sun hours per day}\times\text{System efficiency}}$ $\text{Gross cost}=\text{System size (kW)}\times1{,}000\times\text{Cost per watt}$ $\text{Net cost}=\text{Gross cost}\times\left(1-\frac{\text{Tax credit}}{100}\right)$

Annual savings are modeled as monthly bill multiplied by 12, and simple payback is net cost divided by annual savings.

Worked example

For a $180 monthly bill,$ 0.30/kWh electricity, 4.5 sun-hours per day, $2.50 per watt, a 30% credit, and 80% efficiency:

Monthly usage: $180 / $0.30 = 600 kWh.
System size: (600 / 30.42) / (4.5 x 0.80) = 5.48 kW.
Gross cost: 5.48 x 1,000 x $2.50 = about $13,700.
Net cost after the modeled credit: about $9,590.

Questions

Does this size a system for zero grid usage?

No. It estimates average annual energy needed to offset the entered bill. Export limits, self-consumption, seasonal output, and tariffs can leave a remaining bill.

Is the tax credit guaranteed?

No. The credit is an input assumption. Eligibility and available incentives depend on jurisdiction, installation date, ownership, and current law.

Why does system efficiency matter?

Lower efficiency requires more nameplate capacity to produce the same modeled energy. Panel, inverter, temperature, shading, and installation losses are not separately modeled.

Limitations

This is a planning estimate, not a quote. It omits financing, battery storage, degradation, maintenance, export credits, time-of-use pricing, roof constraints, and installer-specific costs.

Solar Panel Cost Calculator