Estimate your system size, financial savings, and payback period.
Recommended System0 kW
Annual Savings$0
Net Cost (After Credits)$0
Payback Period0 Years
Total 25-Year Net Profit$0
How Does Solar ROI Work?
Switching to solar power is a significant financial decision. To understand if it's worth it, you must look at the Return on Investment (ROI) and the "Payback Period." The payback period is the amount of time it takes for the electricity bill savings to cover the initial cost of the installation.
Key Variables in the Calculation
Sun Hours: This isn't just daylight; it's the number of hours the sun is strong enough to generate peak power. Most of the US averages between 3.5 to 6 hours.
System Size: Calculated based on your energy consumption. If you use 1,000 kWh per month, you need a system that can generate roughly 33 kWh per day.
Incentives: The Federal Solar Tax Credit (ITC) currently allows you to deduct 30% of your installation costs from your federal taxes.
Realistic Example:
Imagine a homeowner in Arizona with a $200 monthly bill paying $0.15/kWh. Their system costs $20,000. After the 30% federal tax credit, the net cost is $14,000. If their system saves them $2,400 a year, their payback period is just 5.8 years. Given that panels last 25+ years, the remaining 19 years provide pure profit.
Understanding Your Results
Our calculator uses a standard efficiency loss factor of 20% to account for inverter conversion, wiring, and environmental factors like dust or heat. If your Payback Period is under 10 years, solar is generally considered an excellent financial investment for your property.
function calculateSolarROI() {
var monthlyBill = parseFloat(document.getElementById("monthlyBill").value);
var elecRate = parseFloat(document.getElementById("elecRate").value);
var sunHours = parseFloat(document.getElementById("sunHours").value);
var systemCost = parseFloat(document.getElementById("systemCost").value);
var taxCredit = parseFloat(document.getElementById("taxCredit").value);
if (isNaN(monthlyBill) || isNaN(elecRate) || isNaN(sunHours) || isNaN(systemCost) || isNaN(taxCredit)) {
alert("Please enter valid numbers in all fields.");
return;
}
// 1. Calculate Monthly kWh usage
var monthlyKwh = monthlyBill / elecRate;
var dailyKwh = monthlyKwh / 30.42; // Average days in month
// 2. Calculate System Size needed (kW)
// Formula: (Daily kWh / Sun Hours) * 1.25 (to account for 80% efficiency)
var systemSizeNeeded = (dailyKwh / sunHours) * 1.25;
// 3. Annual Production (Estimate)
// System Size * Sun Hours * 365 * 0.8 (efficiency)
var annualProduction = systemSizeNeeded * sunHours * 365 * 0.8;
var annualSavings = annualProduction * elecRate;
// 4. Net Cost
var netCost = systemCost * (1 – (taxCredit / 100));
// 5. Payback Period
var paybackYears = netCost / annualSavings;
// 6. Lifetime Savings (25 years is standard warranty)
var lifetimeSavings = (annualSavings * 25) – netCost;
// Display Results
document.getElementById("resSystemSize").innerHTML = systemSizeNeeded.toFixed(2) + " kW";
document.getElementById("resAnnualSavings").innerHTML = "$" + annualSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resNetCost").innerHTML = "$" + netCost.toLocaleString();
document.getElementById("resPayback").innerHTML = paybackYears.toFixed(1) + " Years";
document.getElementById("resLifetime").innerHTML = "$" + lifetimeSavings.toLocaleString(undefined, {minimumFractionDigits: 0, maximumFractionDigits: 0});
document.getElementById("solarResults").style.display = "block";
}