Solar Panel Savings Calculator
Estimate how much electricity your solar panels will generate versus what you currently pay, revealing your net annual savings. Use it when comparing solar quotes or deciding whether rooftop solar makes financial sense for your home.
About this calculator
Solar savings depend on how much energy your system generates compared with what you currently buy from the grid. The core formula is: Net Annual Savings ($) = round((systemSize (kW) × sunHours (hrs/day) × 365 × 0.15) − (monthlyBill ($) × 12), 2). Here, systemSize × sunHours × 365 gives annual kWh generated; multiplying by 0.15 converts that to dollar value at an assumed $0.15/kWh average retail electricity rate. Subtracting your current annual electricity spend (monthlyBill × 12) yields net savings — positive means the panels produce more value than you currently spend. System cost after incentives (systemCost × (1 − incentive/100)) divided by annual savings then gives the simple payback period in years. Panel degradation, net metering policies, and local utility rates will all influence real-world outcomes.
How to use
Say you have a 7 kW system, 5 daily sun hours, and a $150 monthly electricity bill. First, calculate annual generation value: 7 × 5 × 365 × 0.15 = 7 × 5 = 35; 35 × 365 = 12,775 kWh; 12,775 × 0.15 = $1,916.25. Then subtract current annual spend: $150 × 12 = $1,800. Net annual savings: $1,916.25 − $1,800 = $116.25. If the system costs $21,000 before a 30% federal tax credit, net cost = $14,700. Simple payback: $14,700 ÷ $116.25 ≈ 126 years — indicating the system is undersized or electricity rates are lower than average for this scenario.
Frequently asked questions
How many daily sun hours should I use for my solar panel calculation?
Daily sun hours (also called peak sun hours) measure the equivalent number of hours per day when sunlight intensity averages 1,000 W/m², the standard used to rate panel output. In the sunniest US regions like Arizona or Southern California, this figure is 5.5–6.5 hours; in the Pacific Northwest or New England, it may be as low as 3.5–4.0 hours. Your solar installer or the NREL PVWatts online tool can give a precise value for your exact address and roof orientation. Using an accurate local figure is one of the most important inputs for a realistic savings estimate.
What is a good payback period for a residential solar panel system?
Most financial advisors consider a solar payback period of 6–10 years to be attractive, given that quality panels carry 25-year performance warranties. At current equipment prices and the 30% US federal Investment Tax Credit, many US homeowners achieve payback in 7–9 years. After payback, the system generates essentially free electricity for the remaining 15+ years of its life, representing significant total savings. Short payback periods are more likely in states with high electricity rates, generous net metering, or additional state-level incentives on top of the federal credit.
How does the federal solar tax credit affect the total cost of installation?
The federal Residential Clean Energy Credit (commonly called the ITC) allows homeowners to deduct 30% of the total installed cost of a solar system from their federal income tax liability. On a $20,000 system, this equates to a $6,000 reduction in taxes owed, bringing the effective cost down to $14,000. The credit is non-refundable, meaning it can reduce your tax bill to zero but not generate a refund; any unused portion can be carried forward to the following tax year. Several states — including Massachusetts, New York, and California — layer additional credits or rebates on top of the federal incentive, further shortening payback.