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 rebates = parseFloat(document.getElementById('rebates').value);
var kwhRate = parseFloat(document.getElementById('kwhRate').value);
if (isNaN(monthlyBill) || isNaN(systemSize) || isNaN(costPerWatt) || isNaN(sunHours)) {
alert('Please enter valid numerical values.');
return;
}
// Calculations
var grossCost = systemSize * 1000 * costPerWatt;
var netCost = grossCost – rebates;
// Annual Energy Production (kWh) = Size * sunHours * 365 * efficiency (0.78 factor for system losses)
var annualProduction = systemSize * sunHours * 365 * 0.78;
// Annual Savings ($)
var annualSavings = annualProduction * kwhRate;
// Ensure annual savings doesn't exceed current annual bill for ROI purposes (unless net metering pays back)
var annualBill = monthlyBill * 12;
var realAnnualSavings = Math.min(annualSavings, annualBill);
// Payback Period (Years)
var payback = netCost / realAnnualSavings;
// 25-Year Savings (Assuming 2.5% energy inflation and 0.5% panel degradation)
var totalSavings = 0;
var currentYearSavings = realAnnualSavings;
for (var i = 0; i < 25; i++) {
totalSavings += currentYearSavings;
currentYearSavings = currentYearSavings * 1.025 * 0.995;
}
var netProfit = totalSavings – netCost;
// Display results
document.getElementById('solarResult').style.display = 'block';
document.getElementById('resNetCost').innerText = '$' + netCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resPayback').innerText = payback.toFixed(1) + ' Years';
document.getElementById('resAnnualSavings').innerText = '$' + realAnnualSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resTotalSavings').innerText = '$' + netProfit.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
}
Understanding Your Solar Panel Return on Investment (ROI)
Switching to solar energy is one of the most significant financial and environmental decisions a homeowner can make. This Solar ROI Calculator helps you estimate how quickly your system will pay for itself and how much you stand to save over the 25-year lifespan of a typical photovoltaic (PV) system.
Key Factors in the Solar Payback Calculation
To determine your specific return on investment, several variables must be considered:
System Size: Measured in kilowatts (kW), this is the total power capacity of your panels. Most residential systems range from 5kW to 10kW.
Peak Sun Hours: This isn't just daylight; it's the amount of time the sun's intensity reaches 1,000 watts per square meter. Southwestern states usually have higher peak hours than the Northeast.
Federal Solar Tax Credit (ITC): As of current laws, the Residential Clean Energy Credit allows you to deduct 30% of your solar installation costs from your federal taxes.
Electricity Rates: The more you pay your utility company per kilowatt-hour (kWh), the more money you save by generating your own power.
Is Solar Worth It in 2024?
For most homeowners, the average solar payback period is between 6 and 10 years. Given that modern panels are warrantied for 25 years, this leaves 15 to 19 years of essentially "free" electricity. Furthermore, solar installations typically increase property value by an average of 4.1%, according to Zillow data.
Example Scenario:
A 6kW system costing $18,000 before a $5,400 federal tax credit results in a net cost of $12,600. If that system saves the homeowner $1,500 per year on electricity, the payback period is 8.4 years. Over 25 years, accounting for rising energy costs, the total net profit could exceed $40,000.
Maintenance and Longevity
Solar panels are remarkably durable because they have no moving parts. Most owners only need to perform basic cleaning once or twice a year. However, you should budget for an inverter replacement roughly every 10 to 15 years, which typically costs between $1,500 and $3,000 depending on the system type.