function calculateSolarROI() {
var systemSize = parseFloat(document.getElementById('systemSize').value);
var totalCost = parseFloat(document.getElementById('totalCost').value);
var elecRate = parseFloat(document.getElementById('elecRate').value);
var sunHours = parseFloat(document.getElementById('sunHours').value);
var taxCredit = parseFloat(document.getElementById('taxCredit').value);
var efficiencyLoss = parseFloat(document.getElementById('efficiencyLoss').value);
if (isNaN(systemSize) || isNaN(totalCost) || isNaN(elecRate)) {
alert('Please enter valid numbers in all fields.');
return;
}
// Logic
var netCost = totalCost – (totalCost * (taxCredit / 100));
var efficiencyMultiplier = (100 – efficiencyLoss) / 100;
var annualProduction = systemSize * sunHours * 365 * efficiencyMultiplier;
var annualSavings = annualProduction * elecRate;
var paybackPeriod = netCost / annualSavings;
var lifetimeSavings = (annualSavings * 25) – netCost;
var roiPercentage = ((annualSavings * 25) / netCost) * 100;
// Display
document.getElementById('resNetCost').innerText = '$' + netCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resProduction').innerText = Math.round(annualProduction).toLocaleString();
document.getElementById('resAnnualSavings').innerText = '$' + annualSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resPayback').innerText = paybackPeriod.toFixed(1);
document.getElementById('resLifetime').innerText = '$' + lifetimeSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resROI').innerText = Math.round(roiPercentage) + '%';
document.getElementById('solar-results').style.display = 'block';
}
Understanding Your Solar Return on Investment (ROI)
Investing in solar energy is one of the most effective ways to increase your home's value while slashing monthly utility expenses. Our Solar ROI Calculator helps you determine exactly how long it will take for your system to pay for itself and how much profit you can expect over the 25-year warrantied life of the panels.
Key Variables in Solar Payback
The Federal ITC: The Investment Tax Credit (ITC) currently allows homeowners to deduct 30% of the cost of installing a solar energy system from their federal taxes. This drastically reduces the "Net Cost."
Peak Sun Hours: This isn't just daylight; it's the intensity of the sun. Most of the US averages between 3.5 and 5.5 peak sun hours per day.
Electricity Rates: The higher your local utility rate, the faster your solar panels pay for themselves. As utility prices rise (historically 2-3% annually), your solar savings actually increase.
A Realistic Example
Consider a standard 6kW system costing $18,000. With the 30% Federal Tax Credit, your out-of-pocket cost drops to $12,600. If you live in an area with 4.5 sun hours and pay $0.16 per kWh, your system produces roughly 8,300 kWh per year. This saves you approximately $1,328 annually. Your "break-even" point would be roughly 9.5 years. After that, the electricity generated is essentially free for the next 15+ years.
Long-term Financial Benefits
Beyond the monthly bill reduction, solar panels are considered a capital improvement. Unlike a new car, which depreciates the moment you drive it home, solar panels are an asset that generates revenue. Studies by Zillow have shown that homes with solar panels sell for approximately 4.1% more than comparable homes without them.