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Solar Panel ROI Calculator
Calculate My Savings
Net Installation Cost:
$0
Est. Annual Generation:
0 kWh
Year 1 Savings:
$0
Payback Period:
0 Years
25-Year Total Profit:
$0
How to Calculate Solar Panel ROI
Switching to solar energy is a major financial decision. To determine if it's worth it, you need to calculate the Solar Return on Investment (ROI) and the Payback Period . The payback period is the time it takes for your cumulative energy savings to equal the net cost of the system.
Our calculator uses several key variables to provide a realistic estimate:
Net Cost: This is your gross system price minus the Federal Solar Tax Credit (currently 30% in the US) and any local utility rebates.Production Efficiency: We apply a standard 78% derate factor to account for inverter losses, wiring, and panel soiling.Energy Value: Every kWh your panels produce is a kWh you don't buy from the grid at your current utility rate.
Real-World Example
Imagine you install a 7 kW system in a region with 5 peak sun hours per day. Your local electricity rate is $0.18 per kWh . The total cost is $21,000 .
Net Cost: $21,000 – 30% Tax Credit = $14,700.Annual Production: 7 kW * 5 hours * 365 days * 0.78 efficiency = ~9,964 kWh/year.Year 1 Savings: 9,964 kWh * $0.18 = $1,793.Simple Payback: $14,700 / $1,793 = 8.2 Years .
Factors That Impact Your ROI
Several external factors can speed up or slow down your solar payback:
Roof Orientation: South-facing roofs in the northern hemisphere produce the most energy. East/West roofs may see a 15-20% drop in efficiency.Shading: Trees or nearby buildings can significantly reduce output, even if only one panel is shaded.Net Metering Policies: Some utilities credit you 1-to-1 for excess energy sent back to the grid, while others pay a lower "wholesale" rate.Maintenance: Solar panels are low-maintenance, but you should budget for an inverter replacement around year 12-15.
function calculateSolarROI() {
// Get Input Values
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 elecIncrease = parseFloat(document.getElementById('elecIncrease').value) / 100;
// Validation
if (isNaN(systemCost) || isNaN(systemSize) || isNaN(sunHours) || isNaN(elecRate)) {
alert("Please enter valid numerical values for all required fields.");
return;
}
// 1. Calculate Net Cost
var netCost = systemCost * (1 – (taxCredit / 100));
// 2. Calculate Annual Production (kWh)
// Formula: Size (kW) * Sun Hours * 365 days * Derate Factor (0.78 typical)
var annualProduction = systemSize * sunHours * 365 * 0.78;
// 3. Year 1 Savings
var yearOneSavings = annualProduction * elecRate;
// 4. Payback Period and 25-Year Profit (Accounting for rate increases)
var cumulativeSavings = 0;
var currentYearSavings = yearOneSavings;
var paybackYears = 0;
var foundPayback = false;
var totalLifeSavings = 0;
for (var year = 1; year = netCost) {
// Linear interpolation for more accurate payback year
var prevSavings = cumulativeSavings – currentYearSavings;
var needed = netCost – prevSavings;
paybackYears = (year – 1) + (needed / currentYearSavings);
foundPayback = true;
}
totalLifeSavings = cumulativeSavings;
// Increase electricity rate for next year
currentYearSavings = currentYearSavings * (1 + elecIncrease);
}
var totalProfit = totalLifeSavings – netCost;
// Display Results
document.getElementById('solarResults').style.display = 'block';
document.getElementById('netCostDisplay').innerHTML = '$' + netCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('annualGenDisplay').innerHTML = Math.round(annualProduction).toLocaleString() + ' kWh';
document.getElementById('yearOneSavings').innerHTML = '$' + yearOneSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
if (foundPayback) {
document.getElementById('paybackDisplay').innerHTML = paybackYears.toFixed(1) + ' Years';
} else {
document.getElementById('paybackDisplay').innerHTML = 'Over 25 Years';
}
document.getElementById('totalProfitDisplay').innerHTML = '$' + totalProfit.toLocaleString(undefined, {minimumFractionDigits: 0, maximumFractionDigits: 0});
// Scroll to results on mobile
document.getElementById('solarResults').scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}