Estimate how long it takes for your solar investment to pay for itself.
Your Solar Investment Summary
Net System Cost (after incentives):$0.00
Annual Energy Production:0 kWh
Estimated Year 1 Savings:$0.00
Estimated Payback Period:0 Years
25-Year Total Savings:$0.00
Understanding Solar Panel ROI
Investing in solar panels is one of the most effective ways to reduce your carbon footprint while locking in low energy costs for decades. However, understanding the "Payback Period"—the time it takes for the energy savings to equal the initial cost—is crucial for any homeowner.
Key Factors in Your Calculation
Gross System Cost: This is the sticker price from your installer including equipment, labor, and permitting.
Federal Investment Tax Credit (ITC): In many regions, you can deduct a significant percentage (currently 30% in the US) of your solar costs from your federal taxes.
Solar Peak Sun Hours: This isn't just daylight; it's the amount of time sun intensity is strong enough to produce maximum power. This varies by your geographic location.
Utility Rate Inflation: Energy prices typically rise 2-3% annually. Solar protects you from these hikes by allowing you to produce your own power.
What is a "Good" Payback Period?
In the United States, an average solar payback period is between 6 to 10 years. Since most solar panels are warrantied for 25 years, you can expect 15 to 19 years of essentially "free" electricity after the system has paid for itself. Factors such as local SRECs (Solar Renewable Energy Certificates) and net-metering policies can shorten this period even further.
Maintenance and Longevity
Solar systems are remarkably durable because they have no moving parts. Aside from occasionally rinsing off dust or debris and replacing the inverter (usually once every 12-15 years), your maintenance costs remain very low, ensuring your calculated ROI stays on track.
function calculateSolarROI() {
var cost = parseFloat(document.getElementById("systemCost").value);
var taxCreditPercent = parseFloat(document.getElementById("taxCredit").value);
var sizeKW = parseFloat(document.getElementById("systemSize").value);
var sunHours = parseFloat(document.getElementById("sunHours").value);
var rate = parseFloat(document.getElementById("elecRate").value);
var inflation = parseFloat(document.getElementById("elecIncrease").value) / 100;
if (isNaN(cost) || isNaN(sizeKW) || isNaN(sunHours) || isNaN(rate)) {
alert("Please enter valid numbers in all fields.");
return;
}
// Calculations
var netCost = cost – (cost * (taxCreditPercent / 100));
// Annual Production (kWh) = Size * Sun Hours * 365 * Derate Factor (standard is ~0.78 for real-world losses)
var annualKwh = sizeKW * sunHours * 365 * 0.78;
var year1Savings = annualKwh * rate;
// Payback Period Calculation with compounding utility rates
var cumulativeSavings = 0;
var currentRate = rate;
var years = 0;
var total25YearSavings = 0;
for (var i = 1; i <= 25; i++) {
var yearlySavings = annualKwh * currentRate;
cumulativeSavings += yearlySavings;
total25YearSavings += yearlySavings;
if (cumulativeSavings = netCost) {
var finalFullYearSavings = annualKwh * Math.pow(1 + inflation, years);
var remainingCost = netCost – (cumulativeSavings – (annualKwh * Math.pow(1 + inflation, 24))); // Simple linear approximation for the specific payback year
// Re-calculating more simply for UI clarity
var simplePayback = netCost / year1Savings;
// Adjust for inflation impact roughly
var estimatedYears = (Math.log(1 + (netCost * inflation) / year1Savings) / Math.log(1 + inflation)).toFixed(1);
} else {
var estimatedYears = "More than 25";
}
// Update UI
document.getElementById("resNetCost").innerHTML = "$" + netCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resProduction").innerHTML = Math.round(annualKwh).toLocaleString() + " kWh / year";
document.getElementById("resYear1").innerHTML = "$" + year1Savings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resPayback").innerHTML = estimatedYears + " Years";
document.getElementById("resTotalSavings").innerHTML = "$" + total25YearSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("solarResult").style.display = "block";
}