Solar Panel Calculator
Find out exactly how many solar panels your home needs. Enter your monthly electricity usage and state — get system size, number of panels, installed cost after the IRA 30% federal tax credit, payback period, and 25-year net savings. NREL PVWatts v8 sun hours for all 50 states.
Usage & location
Find on your electricity bill
Panel & battery
| Monthly usage | 900 kWh |
| Annual usage | 10,800 kWh |
| Peak sun hrs/day | 5.8 hrs |
| System size | 5.93 kW-DC |
| Panels needed | 15 |
| Panel area total | 323 sq ft |
| Annual production | 10,924 kWh |
| Offset | 100% |
| CO₂ offset | 9,340 lbs/yr |
| Equivalent trees | 195 trees/yr |
Page types — explore all 5 axes
How to calculate solar panel system size
Start with your annual kWh usage (monthly bill × 12). Divide by your state's peak sun hours per day (from NREL PVWatts v8) × 365 days × 0.86 system derate factor. That gives you the required system size in kW-DC. Divide by your panel's rated watts and round up to get panel count. For example, a 900 kWh/month home in California (5.8 sun hrs/day) needs: (900 × 12) ÷ (5.8 × 365 × 0.86) = 6.1 kW → 16 × 400W panels.
What is the IRA 30% solar tax credit?
The Inflation Reduction Act (2022) provides a 30% federal Investment Tax Credit (ITC) on the full installed cost of a residential solar system, including battery storage. This credit applies through 2032 and reduces dollar-for-dollar what you owe in federal income taxes. It is not a rebate — you must have sufficient tax liability to use it. Systems installed in 2024–2032 qualify at the full 30%.
Frequently asked questions
How many solar panels do I need for a 1,000 kWh/month home?▾
It depends on your state's sun hours. In California (5.8 hrs/day): 6.5 kW system → 17 × 400W panels. In New York (4.0 hrs/day): 9.3 kW → 24 panels. In Arizona (6.5 hrs/day): 5.8 kW → 15 panels. This calculator handles all 50 states automatically.
What is the average cost of a solar system in 2024?▾
Based on LBNL Tracking the Sun 2023 data, residential solar costs $2.50–$3.50/watt installed before incentives. A typical 8 kW system costs $20,000–$28,000 gross, or $14,000–$19,600 after the 30% ITC. Prices vary by installer, panel brand, and region.
How long is the solar payback period?▾
Average US payback is 7–12 years. States with high electricity rates (California $0.30/kWh, Hawaii $0.44/kWh, Massachusetts $0.29/kWh) have shorter paybacks of 5–8 years. Low-rate states (Wyoming $0.11/kWh, Idaho $0.11/kWh) run 10–14 years.
What is a good solar panel efficiency?▾
Standard monocrystalline panels run 19–22% efficiency. Polycrystalline is 16–18%. Premium panels (SunPower, REC Alpha) reach 22–23%. Higher efficiency means fewer panels needed for the same output — important when roof space is limited.
Do I need battery storage?▾
Battery storage (e.g., Tesla Powerwall at 13.5 kWh) adds $10,000–$15,000 but qualifies for the same 30% ITC when installed with solar. It's most valuable in Hawaii (self-supply required), Florida (hurricane backup), and states moving away from net metering.