Estimate your potential energy savings and system payback period.
Net System Cost (after credits):$0.00
Est. Annual Generation (kWh):0 kWh
Est. Annual Savings:$0.00
Estimated Payback Period:0 Years
25-Year Total Savings:$0.00
How to Calculate Your Solar Return on Investment (ROI)
Switching to solar energy is one of the most significant financial decisions a homeowner can make. To accurately determine if solar is worth it, you must look beyond the initial sticker price and evaluate the long-term energy offset.
Key Metrics Explained
Peak Sun Hours: This isn't just daylight; it's the intensity of sunlight equivalent to 1,000 watts per square meter. Most US regions average between 3.5 to 5.5 hours.
System Size: Measured in kilowatts (kW), this is the maximum capacity of your panels. A typical residential system ranges from 5kW to 10kW.
The 30% Tax Credit: The Federal Investment Tax Credit (ITC) currently allows you to deduct 30% of your installation costs from your federal taxes.
Example Calculation
Imagine a homeowner in Arizona with a $200 monthly bill. If they install an 8kW system costing $20,000:
Net Cost: $20,000 – 30% ($6,000) = $14,000.
Production: An 8kW system with 5 sun hours produces roughly 40kWh per day, or 14,600 kWh annually.
Savings: If electricity costs $0.14/kWh, the annual savings equals $2,044.
Payback: $14,000 / $2,044 ≈ 6.8 years.
Is Solar Worth It for You?
The "break-even" point usually occurs between year 6 and year 10. Since modern Tier-1 solar panels are warrantied for 25 years, you can expect 15+ years of virtually free electricity after the system has paid for itself. Factors such as roof orientation (South-facing is best), local utility net-metering policies, and shading from trees will impact these results.
function calculateSolarROI() {
var bill = parseFloat(document.getElementById("monthlyBill").value);
var rate = parseFloat(document.getElementById("electricityRate").value);
var size = parseFloat(document.getElementById("systemSize").value);
var sun = parseFloat(document.getElementById("sunHours").value);
var cost = parseFloat(document.getElementById("installCost").value);
var credit = parseFloat(document.getElementById("taxCredit").value);
if (isNaN(bill) || isNaN(rate) || isNaN(size) || isNaN(sun) || isNaN(cost) || isNaN(credit)) {
alert("Please enter valid numbers in all fields.");
return;
}
// 1. Calculate Net Cost
var netCost = cost – (cost * (credit / 100));
// 2. Calculate Annual Generation
// Size (kW) * Sun Hours * 365 days * efficiency factor (0.85 typical)
var annualGeneration = size * sun * 365 * 0.85;
// 3. Calculate Annual Savings
// We assume the user uses all they produce or gets 1:1 net metering
var annualSavings = annualGeneration * rate;
// 4. Calculate Payback Period
var payback = netCost / annualSavings;
// 5. 25-Year Savings (accounting for 2.5% energy inflation and 0.5% panel degradation)
var totalSavings = 0;
var currentYearSavings = annualSavings;
for (var i = 1; i 0) {
document.getElementById("resPayback").innerHTML = payback.toFixed(1) + " Years";
} else {
document.getElementById("resPayback").innerHTML = "Infinite";
}
document.getElementById("resTotalSavings").innerHTML = "$" + netProfit.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("solar-result-box").style.display = "block";
}