.solar-calc-container {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 20px auto;
padding: 25px;
border: 1px solid #e0e0e0;
border-radius: 12px;
background-color: #ffffff;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
}
.solar-calc-header {
text-align: center;
margin-bottom: 30px;
}
.solar-calc-header h2 {
color: #2c3e50;
margin-bottom: 10px;
}
.solar-calc-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
}
.solar-input-group {
margin-bottom: 15px;
}
.solar-input-group label {
display: block;
font-weight: 600;
margin-bottom: 8px;
color: #34495e;
font-size: 14px;
}
.solar-input-group input {
width: 100%;
padding: 12px;
border: 1px solid #ccc;
border-radius: 6px;
font-size: 16px;
box-sizing: border-box;
}
.solar-calc-btn {
grid-column: span 2;
background-color: #27ae60;
color: white;
padding: 15px;
border: none;
border-radius: 6px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background-color 0.3s;
margin-top: 10px;
}
.solar-calc-btn:hover {
background-color: #219150;
}
.solar-results {
margin-top: 30px;
padding: 20px;
background-color: #f9f9f9;
border-radius: 8px;
display: none;
}
.solar-result-item {
display: flex;
justify-content: space-between;
padding: 10px 0;
border-bottom: 1px solid #eee;
}
.solar-result-item:last-child {
border-bottom: none;
}
.solar-result-label {
font-weight: 500;
color: #7f8c8d;
}
.solar-result-value {
font-weight: bold;
color: #2c3e50;
font-size: 18px;
}
.solar-highlight {
color: #27ae60 !important;
}
.solar-article {
margin-top: 40px;
line-height: 1.6;
color: #333;
}
.solar-article h3 {
color: #2c3e50;
margin-top: 25px;
}
@media (max-width: 600px) {
.solar-calc-grid {
grid-template-columns: 1fr;
}
.solar-calc-btn {
grid-column: span 1;
}
}
Gross System Cost ($)
Federal Tax Credit (%)
Avg. Monthly Electric Bill ($)
Electricity Rate ($/kWh)
System Size (kW)
Daily Peak Sun Hours
Calculate Savings & ROI
Net System Cost (after credits):
$0
Estimated Annual Savings:
$0
Payback Period (Years):
0 Years
25-Year Net Profit:
$0
25-Year ROI Percentage:
0%
How Solar ROI is Calculated
Investing in solar panels is a long-term financial decision. To determine the Return on Investment (ROI), we look at several key factors: the upfront net cost, the annual energy production, and the local utility rates. Most homeowners in the United States see a solar payback period between 6 and 10 years.
Key Factors Influencing Your Savings
Federal Solar Tax Credit (ITC): Currently set at 30%, this is the largest incentive available, significantly reducing the "Net Cost" of your system.Peak Sun Hours: Not all daylight is created equal. "Peak sun hours" refers to the intensity of sunlight. For instance, Arizona receives more peak hours than Washington, resulting in faster ROI.Electricity Rates: The more your utility company charges per kilowatt-hour (kWh), the more money you save by producing your own power.System Degradation: Solar panels typically lose about 0.5% efficiency per year. Our 25-year calculation accounts for this minor loss in production.
Example Calculation
If you purchase a 7kW system for $21,000:
Tax Credit: $21,000 * 30% = $6,300 credit. Net cost = $14,700.Production: A 7kW system in a region with 4.5 sun hours produces roughly 11,500 kWh per year.Savings: At $0.16 per kWh, that is $1,840 in annual savings.Payback: $14,700 / $1,840 = ~8 years .
After the 8th year, all electricity generated by the panels is essentially free profit for the remainder of the system's 25+ year lifespan.
function calculateSolarROI() {
var grossCost = parseFloat(document.getElementById('solar_system_cost').value);
var taxCreditPct = parseFloat(document.getElementById('solar_tax_credit').value);
var monthlyBill = parseFloat(document.getElementById('solar_bill').value);
var rate = parseFloat(document.getElementById('solar_rate').value);
var systemSize = parseFloat(document.getElementById('solar_size').value);
var sunHours = parseFloat(document.getElementById('solar_sun').value);
if (isNaN(grossCost) || isNaN(taxCreditPct) || isNaN(rate) || isNaN(systemSize) || isNaN(sunHours)) {
alert("Please enter valid numbers in all fields.");
return;
}
// 1. Calculate Net Cost
var netCost = grossCost – (grossCost * (taxCreditPct / 100));
// 2. Calculate Annual Production and Savings
// Formula: kW * Daily Sun Hours * 365 days
var annualKwh = systemSize * sunHours * 365;
var annualSavings = annualKwh * rate;
// If the calculated savings exceed the current bill, we cap it (unless net metering pays cash, but usually it's a credit)
var maxBillSavings = monthlyBill * 12;
if (annualSavings > maxBillSavings) {
annualSavings = maxBillSavings;
}
// 3. Payback Period
var payback = netCost / annualSavings;
// 4. 25-Year Forecast (assuming 0.5% degradation per year)
var total25Savings = 0;
for (var i = 0; i < 25; i++) {
total25Savings += annualSavings * Math.pow(0.995, i);
}
var netProfit25 = total25Savings – netCost;
var roiPct = (netProfit25 / netCost) * 100;
// Update UI
document.getElementById('res_net_cost').innerText = '$' + netCost.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('res_annual_savings').innerText = '$' + annualSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('res_payback').innerText = payback.toFixed(1) + ' Years';
document.getElementById('res_25_profit').innerText = '$' + netProfit25.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('res_roi_pct').innerText = roiPct.toFixed(1) + '%';
document.getElementById('solar_results').style.display = 'block';
}