Estimate your payback period and long-term savings from solar energy.
Net Investment (After Incentives):$0.00
Estimated Year 1 Savings:$0.00
Simple Payback Period:0 Years
25-Year Total Savings:$0.00
Annual Return on Investment (ROI):0%
How Solar ROI is Calculated
Calculating the Return on Investment (ROI) for solar panels involves comparing the upfront costs of the installation against the cumulative savings on your electricity bill over the life of the system. A typical residential solar panel system lasts 25 to 30 years.
The Formula:
Net Cost = Total Installation Cost – (Federal Tax Credits + State Rebates)
Annual Production = System Size (kW) × Daily Sun Hours × 365 Days × Efficiency Factor (0.78 approx)
Annual Savings = Annual Production × Utility Rate per kWh
Understanding Your Results
Net Investment: This is the "out-of-pocket" cost. In the United States, the Federal Solar Tax Credit (ITC) currently allows you to deduct 30% of your installation costs from your federal taxes.
Payback Period: This is the amount of time it takes for the electricity savings to equal the initial cost of the system. Most homeowners see a payback period between 6 and 10 years, depending on local electricity rates and sunlight availability.
25-Year Total Savings: Solar panels are a long-term asset. Because utility rates generally increase by 2-3% every year, your solar panels become more valuable over time. The total savings account for these rising costs and the consistent production of your panels.
Factors That Influence Your ROI
Geographic Location: States like Arizona or California produce more energy per panel than states with less direct sunlight.
Roof Orientation: South-facing roofs at a 30-45 degree angle typically yield the highest efficiency.
Local Utility Rates: The more you pay for electricity now, the faster your solar panels will pay for themselves.
Maintenance: Solar panels require minimal maintenance, but occasional cleaning and eventual inverter replacement (usually around year 12-15) should be factored in.
function calculateSolarROI() {
// Inputs
var systemCost = parseFloat(document.getElementById("systemCost").value);
var taxCredit = parseFloat(document.getElementById("taxCredit").value);
var systemSize = parseFloat(document.getElementById("systemSize").value);
var sunHours = parseFloat(document.getElementById("sunHours").value);
var elecRate = parseFloat(document.getElementById("elecRate").value);
var annualIncrease = parseFloat(document.getElementById("annualIncrease").value) / 100;
// Validation
if (isNaN(systemCost) || isNaN(systemSize) || isNaN(elecRate) || systemCost <= 0) {
alert("Please enter valid positive numbers for cost, size, and rates.");
return;
}
// Calculations
var netCost = systemCost – taxCredit;
if (netCost < 0) netCost = 0;
// Standard efficiency loss factor (derate factor) of 0.78 accounts for inverter loss, wiring, and dirt
var annualkWhProduction = systemSize * sunHours * 365 * 0.78;
var yearOneSavings = annualkWhProduction * elecRate;
// Payback Period (simple calculation)
var payback = netCost / yearOneSavings;
// 25 Year Cumulative Savings (with utility inflation)
var totalSavings = 0;
var currentYearRate = elecRate;
for (var i = 1; i <= 25; i++) {
totalSavings += annualkWhProduction * currentYearRate;
currentYearRate *= (1 + annualIncrease);
}
// ROI Percentage (Year 1)
var roi = (yearOneSavings / netCost) * 100;
// Display Results
document.getElementById("netCost").innerText = "$" + netCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("yearOneSavings").innerText = "$" + yearOneSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("paybackPeriod").innerText = payback.toFixed(1) + " Years";
document.getElementById("totalSavings").innerText = "$" + totalSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("roiPercentage").innerText = roi.toFixed(2) + "%";
// Show result div
document.getElementById("solarResult").style.display = "block";
}