Estimate your annual savings and payback period based on your local sunlight and utility rates.
Daily Generation:0 kWh
Monthly Savings:$0.00
Annual Savings:$0.00
Estimated Payback Period:0 Years
25-Year Total Savings:$0.00
How Much Can You Really Save with Solar?
Switching to solar energy is one of the most effective ways to reduce your carbon footprint while locking in long-term financial benefits. Our Solar Panel Savings Calculator helps you determine the Return on Investment (ROI) by looking at four critical factors: your system size, local sunlight availability, current utility rates, and the initial installation cost.
Understanding the Metrics
System Size (kW): Most residential solar systems range from 5kW to 10kW. This is the peak power output your panels can produce under ideal conditions.
Peak Sun Hours: This isn't just daylight hours, but the intensity of the sun. Most areas in the US receive between 3.5 and 6 peak sun hours per day.
Utility Rate: The price you pay your electric company per kilowatt-hour (kWh). The higher your current rate, the more you save by generating your own power.
Payback Period: The number of years it takes for your cumulative energy savings to equal the initial cost of the solar installation.
Calculation Example
Let's look at a realistic scenario for a medium-sized home:
Factor
Typical Value
System Size
6 kW
Daily Sun Hours
5 Hours
Electricity Rate
$0.18 / kWh
Initial Cost (After Incentives)
$12,000
Resulting Payback
~6.3 Years
How the Math Works
To calculate your daily energy production, we use the formula:
Daily kWh = System Size (kW) × Peak Sun Hours × Efficiency Factor (0.78)
The efficiency factor accounts for real-world losses like inverter heat, wiring resistance, and panel soiling. We then multiply this by your utility rate to find your daily monetary savings. Over 25 years (the typical warranty life of a panel), these savings often exceed the original cost of the system by 300% or more.
Factors That Influence Your ROI
While the calculator provides a strong estimate, your actual savings may vary based on:
Roof Orientation: South-facing roofs generate the most power in the Northern Hemisphere.
Net Metering: Some states allow you to sell excess power back to the grid at retail rates, while others offer lower wholesale rates.
Tax Credits: The Federal Investment Tax Credit (ITC) can reduce your system cost by 30%, significantly shortening your payback period.
Shading: Trees or nearby buildings can reduce efficiency during specific times of the day.
function calculateSolarROI() {
var size = parseFloat(document.getElementById('solar_systemSize').value);
var sun = parseFloat(document.getElementById('solar_sunHours').value);
var rate = parseFloat(document.getElementById('solar_elecRate').value);
var cost = parseFloat(document.getElementById('solar_totalCost').value);
if (isNaN(size) || isNaN(sun) || isNaN(rate) || isNaN(cost) || size <= 0 || sun <= 0 || rate <= 0 || cost <= 0) {
alert("Please enter valid positive numbers for all fields.");
return;
}
// Efficiency derate factor (standard industry estimate 0.77 – 0.80)
var efficiency = 0.78;
// Daily Generation (kWh)
var dailyGen = size * sun * efficiency;
// Monthly Generation and Savings
var monthlyGen = dailyGen * 30.42;
var monthlySave = monthlyGen * rate;
// Annual Savings
var annualSave = monthlySave * 12;
// Payback Period (Years)
var payback = cost / annualSave;
// 25-Year Lifetime Savings (accounting for 0.5% annual panel degradation)
var lifetimeSavings = 0;
for (var i = 0; i < 25; i++) {
lifetimeSavings += annualSave * Math.pow(0.995, i);
}
// Update Display
document.getElementById('res_dailyGen').innerText = dailyGen.toFixed(2) + " kWh";
document.getElementById('res_monthlySave').innerText = "$" + monthlySave.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('res_annualSave').innerText = "$" + annualSave.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('res_payback').innerText = payback.toFixed(1) + " Years";
document.getElementById('res_lifetime').innerText = "$" + lifetimeSavings.toLocaleString(undefined, {minimumFractionDigits: 0, maximumFractionDigits: 0});
document.getElementById('solar_results').style.display = 'block';
}