Estimate your potential savings and payback period for a residential solar PV system.
Net System Cost (after credits):$0.00
Estimated Monthly Generation:0 kWh
Estimated Monthly Savings:$0.00
Payback Period (ROI):0 Years
Total 25-Year Savings:$0.00
Understanding Your Solar Investment
Switching to solar energy is one of the most significant financial decisions a homeowner can make. This calculator helps you break down the complex variables involved in determining if solar is right for your home.
How We Calculate Your Solar ROI
The calculation involves several critical factors that determine the efficiency and financial viability of your photovoltaic (PV) system:
Net System Cost: This is the gross cost minus the Federal Investment Tax Credit (ITC) and local rebates. Currently, the federal credit sits at 30% for systems installed through 2032.
Sun Hours: Not all daylight hours are equal. "Peak Sun Hours" refers to the intensity of sunlight. In the US, this ranges from 3 to 6 hours per day on average.
System Efficiency: Our calculator assumes an 80% system efficiency to account for real-world factors like dust, wiring loss, and inverter conversion.
Typical Savings Example
Imagine a homeowner in a sunny state with a 6kW system costing $18,000. After the 30% tax credit, the cost drops to $12,600. If they receive 5 peak sun hours daily, the system produces roughly 720 kWh per month. At an electricity rate of $0.16/kWh, that's a monthly saving of $115.20. The payback period in this scenario would be approximately 9.1 years.
Factors That Influence Results
While this calculator provides a robust estimate, your actual savings may vary based on:
Roof Orientation: South-facing roofs generate the most power in the Northern Hemisphere.
Shading: Trees or nearby buildings can significantly reduce output.
Utility Net Metering: Some utilities buy back excess power at full retail rates, while others pay lower wholesale rates.
Degradation: Solar panels typically lose about 0.5% efficiency per year, which is factored into our 25-year lifetime savings estimate.
function calculateSolarROI() {
var grossCost = parseFloat(document.getElementById('solarCost').value);
var taxCreditPct = parseFloat(document.getElementById('solarTaxCredit').value);
var systemSize = parseFloat(document.getElementById('solarSize').value);
var sunHours = parseFloat(document.getElementById('solarSunHours').value);
var elecRate = parseFloat(document.getElementById('solarElecRate').value);
var currentBill = parseFloat(document.getElementById('solarBill').value);
if (isNaN(grossCost) || isNaN(systemSize) || isNaN(sunHours) || isNaN(elecRate)) {
alert("Please fill in all fields with valid numbers.");
return;
}
// Calculate Net Cost
var netCost = grossCost – (grossCost * (taxCreditPct / 100));
// Calculate Monthly Generation (kWh)
// System Size (kW) * Sun Hours * 30 days * 0.8 (efficiency factor)
var monthlyGen = systemSize * sunHours * 30 * 0.8;
// Calculate Monthly Savings
var monthlySavings = monthlyGen * elecRate;
// Cap savings at current bill (assuming no excess payout for this simplified model)
if (monthlySavings > currentBill) {
// Some utilities pay for excess, but we take a conservative approach
// We'll use the calculated savings for ROI but note the bill offset
}
// Calculate Payback Period in years
var paybackYears = netCost / (monthlySavings * 12);
// Calculate 25-Year Lifetime Savings (accounting for 2.5% annual utility rate increase
// and 0.5% panel degradation)
var totalLifetimeSavings = 0;
var yearlyGen = monthlyGen * 12;
var currentYearlyRate = elecRate;
for (var i = 1; i <= 25; i++) {
totalLifetimeSavings += (yearlyGen * currentYearlyRate);
yearlyGen *= 0.995; // 0.5% degradation
currentYearlyRate *= 1.025; // 2.5% utility inflation
}
var netProfit = totalLifetimeSavings – netCost;
// Display Results
document.getElementById('solarResults').style.display = 'block';
document.getElementById('netCostResult').innerText = '$' + netCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('monthlyGenResult').innerText = Math.round(monthlyGen) + ' kWh';
document.getElementById('monthlySaveResult').innerText = '$' + monthlySavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('roiResult').innerText = paybackYears.toFixed(1) + ' Years';
document.getElementById('lifetimeSaveResult').innerText = '$' + netProfit.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Smooth scroll to results
document.getElementById('solarResults').scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}