function calculateSolarROI() {
var size = parseFloat(document.getElementById("systemSize").value);
var cost = parseFloat(document.getElementById("totalCost").value);
var monthly = parseFloat(document.getElementById("monthlySavings").value);
var creditPercent = parseFloat(document.getElementById("taxCredit").value);
if (isNaN(size) || isNaN(cost) || isNaN(monthly) || isNaN(creditPercent)) {
alert("Please fill in all fields with valid numbers.");
return;
}
var netCost = cost – (cost * (creditPercent / 100));
var annualSavings = monthly * 12;
var paybackPeriod = netCost / annualSavings;
var lifetimeSavings = (annualSavings * 25) – netCost;
document.getElementById("resNetCost").innerText = "$" + netCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resAnnualSavings").innerText = "$" + annualSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resPayback").innerText = paybackPeriod.toFixed(1) + " Years";
document.getElementById("resLifetime").innerText = "$" + lifetimeSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("solar-result-area").style.display = "block";
}
Understanding Your Solar Investment Return (ROI)
Switching to solar power is more than just an environmental choice; it is a significant financial strategy. To accurately determine if solar panels are worth it for your home, you must look beyond the initial price tag and evaluate the Solar Return on Investment (ROI).
1. Calculating the Net System Cost
The "sticker price" of a solar installation is rarely what you actually pay. Thanks to the Federal Investment Tax Credit (ITC), homeowners in the United States can currently deduct 30% of the cost of installing a solar energy system from their federal taxes. Our calculator applies this credit automatically to show you the true net cost.
2. The Payback Period Explained
The payback period is the amount of time it takes for your cumulative energy bill savings to equal the net cost of the solar system. For most residential systems in high-sunlight areas, the payback period ranges between 6 to 10 years. Once you pass this "break-even" point, the electricity your panels generate is essentially free for the remainder of the system's life (usually 25–30 years).
3. Long-Term Financial Impact
Because utility rates tend to rise annually (historical averages suggest a 2-3% increase per year), your solar savings actually grow over time. This is often referred to as "locking in" your electricity rate. A standard 6kW system can save a homeowner anywhere from $20,000 to $50,000 over a 25-year period, depending on local utility rates and sun exposure.
Example Calculation:
Gross Cost: $20,000
30% Federal Tax Credit: -$6,000
Net Investment: $14,000
Monthly Savings: $150 ($1,800/year)
Payback Period: 7.7 Years
25-Year Profit: $31,000
Use the calculator above to input your specific quote data and utility bill information to get a customized breakdown of your potential solar savings.