function calculateSolarROI() {
var monthlyBill = parseFloat(document.getElementById('monthlyBill').value);
var systemSize = parseFloat(document.getElementById('systemSize').value);
var costPerWatt = parseFloat(document.getElementById('costPerWatt').value);
var sunHours = parseFloat(document.getElementById('sunHours').value);
var incentive = parseFloat(document.getElementById('incentive').value) / 100;
if (isNaN(monthlyBill) || isNaN(systemSize) || isNaN(costPerWatt) || isNaN(sunHours)) {
alert("Please enter valid numbers in all fields.");
return;
}
// Calculation Logic
var grossCost = systemSize * 1000 * costPerWatt;
var netCost = grossCost * (1 – incentive);
// Assuming average electricity rate of $0.15/kWh for derived savings
// Or calculating based on production vs bill.
// Average solar production factor: system size * sun hours * 365 * 0.78 (derate factor)
var annualProduction = systemSize * sunHours * 365 * 0.78;
// Estimated electricity rate based on standard US averages ($0.15 – $0.25)
// If monthly bill is $150 and avg use is 900kWh, rate is $0.16
var estimatedRate = 0.16;
var annualSavings = annualProduction * estimatedRate;
// Cap savings to not exceed the actual bill significantly if system is oversized
var maxBillSavings = monthlyBill * 12;
if (annualSavings > maxBillSavings * 1.2) {
annualSavings = maxBillSavings * 1.2; // Account for net metering credits
}
var paybackPeriod = netCost / annualSavings;
var twentyFiveYearSavings = (annualSavings * 25) – netCost;
// Display Results
document.getElementById('netCost').innerText = '$' + netCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('annualSavings').innerText = '$' + annualSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('paybackPeriod').innerText = paybackPeriod.toFixed(1) + ' Years';
document.getElementById('totalProfit').innerText = '$' + twentyFiveYearSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('solar-results').style.display = 'block';
}
How to Calculate Solar Panel ROI
Investing in solar energy is one of the most effective ways for homeowners to reduce their carbon footprint while significantly lowering long-term utility costs. Understanding the Solar Return on Investment (ROI) is crucial before making the switch. This calculator helps you estimate how long it will take for the system to pay for itself and how much you can save over the life of the panels.
Key Factors in Solar Payback
Gross System Cost: This is the upfront price of panels, inverters, and labor. The industry standard is often measured in "dollars per watt."
Federal Tax Credit (ITC): As of 2024, the federal government offers a 30% tax credit on residential solar installations, which drastically reduces the net cost.
Sunlight Exposure: Houses in states like Arizona or California will see a faster ROI than those in cloudy regions because the panels generate more kilowatt-hours (kWh) per day.
Electricity Rates: The more your utility company charges per kWh, the more money you save by producing your own power.
Most residential solar systems in the United States reach the "break-even point" within 6 to 10 years. Since modern tier-1 solar panels are warrantied for 25 years, you can enjoy 15+ years of virtually free electricity.
Example Calculation
Imagine a homeowner with a $150 monthly electric bill who installs a 6kW system at $3.00/watt.
Gross Cost: 6,000 Watts * $3.00 = $18,000
After 30% Credit: $18,000 – $5,400 = $12,600
Annual Production: Approx 8,500 kWh (depending on location)
Annual Savings: 8,500 kWh * $0.16/kWh = $1,360
Payback Period: $12,600 / $1,360 = 9.2 Years
Maintenance and Longevity
Solar panels require very little maintenance. Occasional cleaning and ensuring that no large trees shade the array are usually sufficient. Inverters may need replacement every 12-15 years, but the panels themselves degrade very slowly (typically losing only 0.5% efficiency per year). This long lifespan makes solar one of the safest financial investments available to homeowners today.