Recasting Mortgage Calculator

Calculate your potential energy savings and payback period for a residential solar installation.

Typical US home uses 5kW – 10kW.

Total cost before incentives.

Peak hours vary by state (4-6 is common).

Find this on your utility bill.

The current ITC is 30%.

Average annual increase in energy prices.

Calculation Results

Net System Cost:

Estimated Annual Generation:

Year 1 Savings:

Payback Period:

25-Year Total Savings:

25-Year ROI:

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How Does the Solar ROI Calculator Work?

Switching to solar is a significant financial decision. To accurately estimate your return on investment, our calculator uses several key data points to simulate the financial lifecycle of a photovoltaic (PV) system.

Key Variables Explained

• System Size: Measured in kilowatts (kW), this is the total power capacity of your panels. A typical 6kW system can produce roughly 700-900 kWh per month depending on location.
• Sun Hours: Not all daylight hours are equal. "Peak sun hours" refer to when the intensity of the sun reaches 1,000 watts per square meter. In the US, this ranges from 3.5 in the Northeast to 6+ in the Southwest.
• The Solar Investment Tax Credit (ITC): Under the Inflation Reduction Act, homeowners can deduct 30% of the cost of installing a solar energy system from their federal taxes.

Understanding the Payback Period

The solar payback period is the time it takes for the cumulative energy bill savings to equal the initial net cost of the system. Most residential systems in the United States reach the "break-even" point between 6 and 10 years. After this point, the electricity generated is essentially free for the remainder of the system's 25-30 year lifespan.

Example Scenario

If you install a 7kW system for $21,000:

1. Federal Incentive: You receive a tax credit of $6,300 (30%), bringing your net cost to $14,700.
2. Production: In a state with 5 sun hours, you generate approx. 10,220 kWh annually.
3. Savings: At an electricity rate of $0.15/kWh, you save $1,533 in the first year.
4. Payback: Without considering utility rate hikes, your payback would be roughly 9.5 years. With a 3% annual rate hike, that payback drops to approx. 8.2 years.

function calculateSolarROI() { // Inputs var size = parseFloat(document.getElementById('systemSize').value); var cost = parseFloat(document.getElementById('installCost').value); var sun = parseFloat(document.getElementById('sunHours').value); var rate = parseFloat(document.getElementById('elecRate').value); var creditPercent = parseFloat(document.getElementById('taxCredit').value); var utilityHike = parseFloat(document.getElementById('utilityIncrease').value) / 100; // Validation if (isNaN(size) || isNaN(cost) || isNaN(sun) || isNaN(rate)) { alert("Please fill in all fields with valid numbers."); return; } // Calculation Logic // Efficiency factor (de-rating for inverter loss, wiring, soil) – standard is 0.78 var efficiencyFactor = 0.78; var dailyGen = size * sun * efficiencyFactor; var annualGen = dailyGen * 365; var netCost = cost – (cost * (creditPercent / 100)); var year1Savings = annualGen * rate; // Payback and 25-Year Projection var cumulativeSavings = 0; var currentRate = rate; var paybackYear = 0; var total25YearSavings = 0; var paybackFound = false; for (var year = 1; year = netCost) { paybackYear = year – 1 + ((netCost – (cumulativeSavings – annualSaving)) / annualSaving); paybackFound = true; } currentRate *= (1 + utilityHike); } var roi = ((total25YearSavings – netCost) / netCost) * 100; // Output formatting document.getElementById('resNetCost').innerText = "$" + netCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}); document.getElementById('resAnnualGen').innerText = annualGen.toLocaleString(undefined, {maximumFractionDigits: 0}) + " kWh"; document.getElementById('resYear1').innerText = "$" + year1Savings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}); document.getElementById('resPayback').innerText = (paybackFound ? paybackYear.toFixed(1) : "> 25″) + " Years"; document.getElementById('res25Year').innerText = "$" + total25YearSavings.toLocaleString(undefined, {maximumFractionDigits: 0}); document.getElementById('resROI').innerText = roi.toFixed(0) + "%"; // Show results document.getElementById('resultsArea').style.display = "block"; }