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Solar Panel Savings & ROI Calculator

Estimated Results

Monthly Energy Gen.

Estimated Monthly Savings

Payback Period (Years)

25-Year Net Profit

function calculateSolarSavings() { var monthlyBill = parseFloat(document.getElementById("monthlyBill").value); var kwhRate = parseFloat(document.getElementById("kwhRate").value); var systemSize = parseFloat(document.getElementById("systemSize").value); var sunHours = parseFloat(document.getElementById("sunHours").value); var installCost = parseFloat(document.getElementById("installCost").value); if (isNaN(monthlyBill) || isNaN(kwhRate) || isNaN(systemSize) || isNaN(sunHours) || isNaN(installCost)) { alert("Please enter valid numbers in all fields."); return; } // Calculation Logic // Efficiency factor (de-rating factor) typically around 0.75 – 0.80 var efficiency = 0.77; var monthlyKwhGen = systemSize * sunHours * 30 * efficiency; var monthlySavingsVal = monthlyKwhGen * kwhRate; // Monthly savings cannot exceed the actual bill (assuming no net-metering payout for surplus) var actualSavings = Math.min(monthlySavingsVal, monthlyBill); var paybackVal = installCost / (actualSavings * 12); var profit25yr = (actualSavings * 12 * 25) – installCost; // Display Results document.getElementById("monthlyGen").innerHTML = monthlyKwhGen.toFixed(2) + " kWh"; document.getElementById("estSavings").innerHTML = "$" + actualSavings.toFixed(2); document.getElementById("paybackYears").innerHTML = paybackVal.toFixed(1) + " Years"; document.getElementById("longTermProfit").innerHTML = "$" + profit25yr.toLocaleString(undefined, {minimumFractionDigits: 0, maximumFractionDigits: 0}); document.getElementById("solar-results").style.display = "block"; }

How to Use the Solar Panel Savings Calculator

Switching to solar energy is a significant investment. This calculator helps homeowners and business owners estimate the Return on Investment (ROI) of a photovoltaic (PV) system. By entering your current energy usage and the specifications of your potential solar setup, you can visualize how much you stand to save over the system's 25-year lifespan.

Key Variables Explained

  • System Size (kW): This is the rated power of your solar array. A standard residential system usually ranges from 5kW to 10kW.
  • Daily Sunlight Hours: This is not just "daylight" but "peak sun hours"—the intensity of sunlight equivalent to 1,000 watts per square meter. In the US, this typically ranges from 3 to 6 hours depending on your state.
  • Electricity Rate ($/kWh): The amount your utility company charges you for every kilowatt-hour used. This determines the value of every unit of energy your panels produce.
  • Installation Cost: The total out-of-pocket cost after federal tax credits (ITC) and local rebates.

The Math Behind the Savings

Our calculator uses the standard industry formula for energy production:

Monthly Production (kWh) = System Size × Sun Hours × 30 Days × Efficiency Factor (0.77)

The efficiency factor accounts for real-world losses like wiring resistance, inverter heat, and panel soiling (dust/dirt). By comparing this production to your current utility rate, we determine your monthly bill reduction.

Example Scenario

Let's look at a realistic example for a homeowner in a sunny location:

  • Monthly Bill: $180
  • System Size: 7 kW
  • Sun Hours: 5.5 hours
  • Net Cost: $14,000

A 7kW system in these conditions generates approximately 889 kWh per month. At a rate of $0.16/kWh, this generates roughly $142 in monthly savings. The payback period would be approximately 8.2 years, after which the electricity produced is essentially free for the remainder of the panels' life (usually 25-30 years).

Maximizing Your Solar ROI

To ensure you reach your payback period as quickly as possible, consider these factors:

  1. Roof Orientation: South-facing roofs in the northern hemisphere capture the most sunlight.
  2. Net Metering: Check if your utility provider offers net metering, allowing you to sell excess energy back to the grid at retail rates.
  3. Maintenance: Keep panels clear of debris and check inverter performance annually to maintain the 0.77 efficiency rating used in our calculations.

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