Estimate your long-term energy savings and solar investment ROI.
Estimated Financial Returns
Net System Cost (after incentives):$0.00
Estimated Annual Production:0 kWh
Estimated Annual Savings:$0.00
Payback Period (Break-even):0 Years
Total 25-Year Savings:$0.00
Understanding Your Solar Investment
Switching to solar energy is one of the most significant financial and environmental decisions a homeowner can make. This calculator helps you understand the Return on Investment (ROI) by looking at the upfront costs, government incentives, and daily energy production.
How to Calculate Solar Savings
To determine how much you will save, we look at several key metrics:
Net Cost: This is your total quote minus the Federal Solar Tax Credit (currently 30% in the US) and any local rebates.
Annual Production: Calculated as: System Size (kW) × Peak Sun Hours × 365 days × 0.82 (efficiency factor).
Payback Period: The amount of time it takes for your cumulative energy savings to equal the net cost of the system.
Example Calculation
Let's say you install a 7 kW system for $20,000. If you qualify for the 30% tax credit, your net cost is $14,000. If the system generates 10,000 kWh per year and your electricity rate is $0.15/kWh, you save $1,500 annually. Your payback period would be roughly 9.3 years.
Key Factors Affecting ROI
Several variables can shift your results:
Roof Orientation: South-facing roofs in the northern hemisphere produce the most energy.
Local Utility Rates: The higher your current electricity bill, the faster your solar panels pay for themselves.
Net Metering: Some utilities pay you for the excess energy you send back to the grid, accelerating your savings.
Degradation: Most panels lose about 0.5% efficiency per year, which we account for in long-term projections.
function calculateSolarROI() {
var cost = parseFloat(document.getElementById('solar_cost').value);
var size = parseFloat(document.getElementById('solar_size').value);
var incentive = parseFloat(document.getElementById('solar_incentive').value);
var rate = parseFloat(document.getElementById('solar_rate').value);
var sunHours = parseFloat(document.getElementById('solar_sun').value);
var monthlyBill = parseFloat(document.getElementById('solar_bill').value);
if (isNaN(cost) || isNaN(size) || isNaN(incentive) || isNaN(rate) || isNaN(sunHours)) {
alert("Please enter valid numbers in all fields.");
return;
}
// 1. Calculate Net Cost
var netCost = cost – (cost * (incentive / 100));
// 2. Calculate Annual Production (kWh)
// Formula: Size * Daily Sun Hours * Days * Efficiency Loss (standard 0.82)
var annualProduction = size * sunHours * 365 * 0.82;
// 3. Calculate Annual Savings ($)
var annualSavings = annualProduction * rate;
// Safety check: annual savings shouldn't realistically exceed the actual bill by massive margins
// depending on net metering, but we use the production value here.
// 4. Payback Period
var paybackYears = netCost / annualSavings;
// 5. 25-Year Savings (accounting for 0.5% degradation annually)
var totalSavings = 0;
var currentYearProduction = annualProduction;
for (var i = 1; i <= 25; i++) {
totalSavings += (currentYearProduction * rate);
currentYearProduction *= 0.995; // 0.5% degradation
}
var netProfit = totalSavings – netCost;
// Display Results
document.getElementById('res_net_cost').innerText = "$" + netCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('res_annual_kwh').innerText = Math.round(annualProduction).toLocaleString() + " kWh";
document.getElementById('res_annual_savings').innerText = "$" + annualSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('res_payback').innerText = paybackYears.toFixed(1) + " Years";
document.getElementById('res_total_savings').innerText = "$" + netProfit.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('solar_results').style.display = 'block';
}