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Solar Panel ROI & Savings Calculator

Calculation Results:

Total System Cost:

Annual Generation: kWh

Estimated Yearly Savings:

Payback Period: Years

25-Year Net Profit:

function calculateSolarROI() { var bill = parseFloat(document.getElementById('monthlyBill').value); var size = parseFloat(document.getElementById('systemSize').value); var costKw = parseFloat(document.getElementById('costPerKw').value); var sunHours = parseFloat(document.getElementById('sunHours').value); // Validation if (isNaN(bill) || isNaN(size) || isNaN(costKw) || isNaN(sunHours) || bill <= 0 || size <= 0) { alert("Please enter valid positive numbers in all fields."); return; } // Constants var electricityRate = 0.16; // Average US residential rate per kWh var efficiencyLoss = 0.78; // Standard derate factor (inverter, wiring, etc) var federalTaxCredit = 0.30; // 30% Federal Investment Tax Credit // Math Logic var totalGrossCost = size * costKw; var netCost = totalGrossCost * (1 – federalTaxCredit); // Annual generation (Size * Sun Hours * 365 * Efficiency) var annualKwhGenerated = size * sunHours * 365 * efficiencyLoss; // Yearly savings based on avoided utility costs var yearlySavings = annualKwhGenerated * electricityRate; // Payback period (Net Cost / Yearly Savings) var paybackYears = netCost / yearlySavings; // 25 Year Profit (Assuming 2.5% energy inflation and 0.5% panel degradation) var totalSavings25Years = 0; var currentYearlySavings = yearlySavings; for (var i = 1; i <= 25; i++) { totalSavings25Years += currentYearlySavings; currentYearlySavings *= 1.025; // Energy price increase currentYearlySavings *= 0.995; // Panel degradation } var netProfit = totalSavings25Years – netCost; // Display Results document.getElementById('resTotalCost').innerText = "$" + netCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}) + " (After 30% Tax Credit)"; document.getElementById('resAnnualGen').innerText = Math.round(annualKwhGenerated).toLocaleString(); document.getElementById('resYearlySavings').innerText = "$" + yearlySavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}); document.getElementById('resPayback').innerText = paybackYears.toFixed(1); document.getElementById('resProfit').innerText = "$" + netProfit.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}); document.getElementById('solar-results').style.display = "block"; }

How to Use the Solar Panel Savings Calculator

Switching to renewable energy is one of the most significant financial decisions a homeowner can make. This calculator helps you determine the Return on Investment (ROI) by analyzing your current utility costs and local solar potential. To get the most accurate estimate, follow these steps:

  • Monthly Electricity Bill: Look at your utility bills for the past 12 months and find your average monthly cost.
  • System Size (kW): A typical residential system ranges from 5kW to 10kW. An average US home needs about 6kW to 8kW to cover 100% of its energy needs.
  • Cost per kW: The national average is approximately $2,500 to $3,500 per kW installed. This varies by your location and the quality of the panels (Monocrystalline vs. Polycrystalline).
  • Daily Sunlight Hours: This refers to "peak sun hours," not just daylight. For example, Arizona averages 6+ hours, while Washington state averages around 3.5 to 4 hours.

Understanding Your Results

Our calculator accounts for the 30% Federal Investment Tax Credit (ITC), which significantly lowers the upfront cost of your installation. The Payback Period indicates the point at which your cumulative electricity savings equal the net cost of the solar system. Most homeowners see a payback period between 6 and 10 years.

Key Factors Influencing Your ROI

While the calculator provides a strong baseline, several external factors can impact your real-world savings:

  1. Net Metering Policies: Some states allow you to sell excess energy back to the grid at retail rates, while others offer lower wholesale rates.
  2. Roof Orientation: South-facing roofs in the Northern Hemisphere maximize energy production. West-facing roofs are also effective, especially if your utility uses "Time of Use" pricing.
  3. Energy Inflation: As utility companies raise rates (historically 2-3% per year), your solar savings actually increase over time.
  4. Local Rebates: Many states and local municipalities offer additional cash rebates or SREC (Solar Renewable Energy Certificate) credits on top of federal incentives.

Expert Note: Solar panels are usually warrantied for 25 years but often produce power for 30-40 years. Even if your payback is 8 years, you are essentially "pre-paying" for 20+ years of free electricity.

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