Estimate your potential savings and return on investment for a solar PV system.
US average is 4 to 6 hours.
Net cost after tax credits/rebates.
Calculation Results
Recommended System Size–
Annual Savings–
Payback Period–
25-Year Net Savings–
How to Calculate Your Solar ROI
Transitioning to solar power involves several variables that determine your financial return. Our calculator uses the following logic to estimate your savings:
Energy Consumption: We divide your monthly bill by your electricity rate to determine your monthly kWh usage.
System Sizing: We calculate the solar array size (kW) needed to cover 100% of your usage based on the peak sun hours in your area.
Payback Period: This is the number of years it takes for your annual electricity savings to equal the initial net cost of the system.
Example Calculation
If you pay $200 per month for electricity at a rate of $0.15/kWh, your household consumes approximately 1,333 kWh per month. In an area with 5 sun hours per day, you would need roughly an 8.8 kW system.
If that system costs $14,000 after tax credits, and you are saving $2,400 per year in electricity, your payback period would be 5.8 years. Over the 25-year lifespan of the panels, your total savings would exceed $46,000.
Factors Affecting Your Savings
1. Local Incentives: The Federal Investment Tax Credit (ITC) can reduce your system cost significantly. Local utility rebates may also apply.
2. Roof Orientation: South-facing roofs with a 30-45 degree tilt generally produce the most energy in the Northern Hemisphere.
3. Net Metering: If your utility company offers net metering, you can "sell" excess energy back to the grid during the day and use those credits at night.
function calculateSolarROI() {
var monthlyBill = parseFloat(document.getElementById('monthlyBill').value);
var kwhRate = parseFloat(document.getElementById('kwhRate').value);
var sunHours = parseFloat(document.getElementById('sunHours').value);
var systemCost = parseFloat(document.getElementById('systemCost').value);
// Validation
if (isNaN(monthlyBill) || isNaN(kwhRate) || isNaN(sunHours) || isNaN(systemCost) ||
monthlyBill <= 0 || kwhRate <= 0 || sunHours <= 0 || systemCost <= 0) {
alert("Please enter valid positive numbers in all fields.");
return;
}
// Step 1: Calculate monthly and daily energy usage
var monthlyKwhUsage = monthlyBill / kwhRate;
var dailyKwhUsage = monthlyKwhUsage / 30.42; // Average days in month
// Step 2: Calculate system size needed (kW)
// Formula: Daily kWh / Sun Hours / Efficiency (using 0.85 for real-world derate factor)
var systemSizeNeeded = dailyKwhUsage / sunHours / 0.85;
// Step 3: Financials
var annualSavings = monthlyBill * 12;
var paybackYears = systemCost / annualSavings;
// Step 4: 25 Year Outlook (standard panel warranty)
// Includes a 0.5% efficiency degradation per year and 2% annual energy cost increase
var totalSavings25Years = 0;
var currentAnnualSavings = annualSavings;
for (var i = 1; i <= 25; i++) {
totalSavings25Years += currentAnnualSavings;
currentAnnualSavings *= 1.015; // 1.5% average energy inflation minus degradation
}
var netProfit = totalSavings25Years – systemCost;
// Display Results
document.getElementById('resultsArea').style.display = 'block';
document.getElementById('resSystemSize').innerHTML = systemSizeNeeded.toFixed(2) + " kW";
document.getElementById('resAnnualSavings').innerHTML = "$" + annualSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resPayback').innerHTML = paybackYears.toFixed(1) + " Years";
document.getElementById('resTotalProfit').innerHTML = "$" + netProfit.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Smooth scroll to results
document.getElementById('resultsArea').scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}