Switching to solar power is one of the most effective ways to reduce your carbon footprint while locking in long-term financial savings. However, understanding the true return on investment (ROI) requires more than just looking at the price of panels. This calculator helps you bridge the gap between installation costs and long-term utility bill reductions.
Key Variables Explained
System Size (kW): This is the total power capacity of your solar array. A typical residential system ranges from 5kW to 10kW.
Sun Hours: This isn't just daylight; it's the number of hours where the sun's intensity reaches 1,000 watts per square meter. In the US, this typically ranges from 3 to 6 hours depending on your state.
Efficiency Loss: Our calculator assumes a standard 25% system loss due to inverter efficiency, wiring, and panel degradation (using a 0.75 derate factor).
Calculation Example
If you install a 6kW system in a region with 5 sun hours per day, and your utility charges $0.16 per kWh:
To ensure the fastest payback period, consider the federal solar tax credit (ITC), which currently allows you to deduct a significant percentage of the installation costs from your federal taxes. Additionally, check with your local utility for net metering programs, which allow you to sell excess energy back to the grid during the day.
function calculateSolarSavings() {
var size = parseFloat(document.getElementById('systemSize').value);
var sunHours = parseFloat(document.getElementById('sunHours').value);
var rate = parseFloat(document.getElementById('elecRate').value);
var cost = parseFloat(document.getElementById('totalCost').value);
var resultsDiv = document.getElementById('solar-results');
if (isNaN(size) || isNaN(sunHours) || isNaN(rate) || isNaN(cost) || size <= 0 || sunHours <= 0) {
alert("Please enter valid positive numbers for all fields.");
return;
}
// Standard Solar Equation: Size * Sun Hours * Derate Factor (0.75) * Days
var dailyProd = size * sunHours * 0.75;
var monthlyProd = dailyProd * 30.42; // Average days in month
var monthlySavings = monthlyProd * rate;
var annualSavings = monthlySavings * 12;
var paybackYears = cost / annualSavings;
// Update DOM
document.getElementById('resProduction').innerHTML = monthlyProd.toFixed(2) + " kWh";
document.getElementById('resMonthlySavings').innerHTML = "$" + monthlySavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resAnnualSavings').innerHTML = "$" + annualSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
if (isFinite(paybackYears)) {
document.getElementById('resPayback').innerHTML = paybackYears.toFixed(1) + " Years";
} else {
document.getElementById('resPayback').innerHTML = "N/A";
}
resultsDiv.style.display = 'block';
resultsDiv.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}