Solar Panel Calculator

Solar panels have become one of the best long-term investments for homeowners with sunny rooftops and expensive electricity. This calculator estimates the system size you need to offset your electric bill, the number of standard 400W panels required, and the payback period after factoring in federal tax credits and state incentives.

The math: your annual electricity use (in kWh) divided by your location's daily peak sun hours × 365 gives the kilowatt system size you need. Sunlight hours range from about 3.5 (Pacific Northwest) to 6+ (Southwest US). System cost has dropped dramatically — typical residential installs now run $2.50–$3.50 per watt before incentives. The federal solar tax credit covers 30% (through 2032).

Payback periods of 6–10 years are typical in sunny states with high electricity rates. After payback, you essentially get free electricity for the remaining 15–20 years of the panels' useful life. Quality panels are warrantied for 25 years and continue producing at 80%+ efficiency past that.

Beyond cost: solar increases home value (typically by the system's net cost), hedges against future electricity rate increases, and dramatically cuts your carbon footprint. Net metering lets you sell excess power back to the grid in many states. Get quotes from at least three local installers — pricing varies significantly.

Residential solar installation costs averaged about $3.00 per watt in 2024 before federal incentives, or roughly $25,000 for a typical 8 kW system. The federal Investment Tax Credit (ITC) covers 30% of system cost through 2032. Many states add their own rebates, property-tax exemptions or sales-tax exemptions. Payback periods range from 6–12 years depending on local electricity rates, solar resource and incentive stack.

Net metering is the policy that lets solar customers sell excess electricity back to the grid at the retail rate. Several states have weakened or replaced net metering with less favourable "net billing" or "avoided cost" tariffs that pay much less for exported energy. Check your state's current rules — they materially affect the economics, especially for systems sized larger than household consumption.

Battery storage paired with solar provides backup power during outages and lets you arbitrage time-of-use rates. Tesla Powerwall, Enphase IQ Battery and Franklin Home Power are the leading residential options, costing $10,000–$20,000 installed. The ITC now covers standalone batteries as well as those paired with solar. Without batteries, a grid-tied solar system shuts off during outages for safety — many homeowners are surprised by this.

Roof condition and shading determine whether solar makes sense. Asphalt-shingle roofs typically last 20–25 years; install solar only if your roof has at least 15 years of life left, otherwise you will pay to remove and reinstall panels mid-life. Shading from trees, chimneys or neighbouring buildings can cut output 20–50%. A reputable installer will use shade-analysis tools (Solmetric SunEye, Aurora Solar) and walk you through the year-round impact before quoting.