Roof Solar Panel Calculator: Estimate Your Savings and System Size

Your Solar Potential & Savings Estimator

Use this Roof Solar Panel Calculator to estimate the potential energy production, system cost, and long-term financial savings from installing solar panels on your roof. Input your specific details to get a personalized projection.

Annual Solar Performance & Savings Projection

Detailed annual breakdown of energy production, savings, and cumulative financial benefits.

Year	Annual Production (kWh)	Annual Savings ($)	Cumulative Savings ($)

What is a Roof Solar Panel Calculator?

A Roof Solar Panel Calculator is an online tool designed to help homeowners and businesses estimate the potential benefits of installing solar panels on their property. By inputting key variables such as usable roof area, local sunlight hours, panel efficiency, and electricity rates, the calculator provides projections for energy production, system size, installation costs, and long-term financial savings. It serves as a crucial first step in understanding the feasibility and economic viability of a solar energy investment.

Who Should Use a Roof Solar Panel Calculator?

• Homeowners: Considering reducing their electricity bills and carbon footprint.
• Business Owners: Looking to lower operational costs and enhance their brand’s sustainability image.
• Real Estate Developers: Planning new constructions with integrated renewable energy solutions.
• Energy Enthusiasts: Curious about the technical and financial aspects of solar power.
• Anyone Budgeting for Solar: To get a preliminary estimate before consulting with installers.

Common Misconceptions About Solar Panel Calculators

While a Roof Solar Panel Calculator is highly useful, it’s important to understand its limitations:

• Exact Quotes: It provides estimates, not a final quote. Actual costs can vary based on specific equipment, installation complexity, local labor rates, and incentives.
• Shading & Orientation: Most basic calculators assume ideal conditions. Real-world shading from trees or neighboring buildings, and non-optimal roof orientation (e.g., north-facing), can significantly impact production.
• Incentives & Rebates: While some calculators might include a general incentive factor, specific local, state, and federal incentives (like the ITC) can be complex and require detailed research.
• Energy Consumption: The calculator focuses on production and savings. It doesn’t directly tell you how much of your specific energy consumption will be offset without additional input.
• Maintenance Costs: Often, calculators don’t factor in potential maintenance or cleaning costs, which are usually minimal but can exist.

Roof Solar Panel Calculator Formula and Mathematical Explanation

The core of any Roof Solar Panel Calculator lies in its mathematical models. Here’s a breakdown of the key formulas and variables used:

Step-by-Step Derivation:

1. Estimated Number of Panels: This is derived by dividing the usable roof area by the average area of a single solar panel. A standard 400W panel is roughly 17.5 sq ft.
   
   Number of Panels = Usable Roof Area (sq ft) / (Panel Wattage / 400 * 17.5)
2. Total System Capacity (kW): The total power output capability of your system.
   
   System Capacity (kW) = (Number of Panels * Average Panel Wattage (W)) / 1000
3. Annual Energy Production (kWh): This is the estimated electricity generated per year. It accounts for peak sunlight, system losses (e.g., inverter efficiency, wiring, temperature), and panel degradation.
   
   Annual Production (kWh) = System Capacity (kW) * Peak Sunlight Hours * 365 Days * (1 - System Loss Factor) * (1 - Annual Degradation Rate)^(Year-1)
4. Estimated System Cost ($): The total upfront cost of the system.
   
   System Cost ($) = System Capacity (kW) * 1000 * Installed System Cost per Watt ($/W)
5. Annual Savings ($): The money saved by generating your own electricity, considering the rising cost of utility power.
   
   Annual Savings (Year N) = Annual Production (kWh, Year N) * Current Electricity Rate ($/kWh) * (1 + Electricity Inflation Rate)^(N-1)
6. Payback Period (Years): The time it takes for the cumulative annual savings to equal the initial system cost. This is typically calculated iteratively.
7. Total Savings Over Lifespan ($): The sum of all annual savings over the system’s operational life.

Variable Explanations and Typical Ranges:

Variable	Meaning	Unit	Typical Range
Usable Roof Area	Square footage of roof suitable for panels.	sq ft	100 – 1000+
Average Panel Wattage	Power output of a single panel.	Watts (W)	350 – 450
Panel Efficiency	Percentage of sunlight converted to electricity.	%	18 – 22
Peak Sunlight Hours	Average daily hours of effective sunlight.	Hours	3.5 – 5.5
Installed System Cost per Watt	Total cost of installation per watt of capacity.	$/W	$2.50 – $4.00
Current Electricity Rate	Cost of electricity from your utility.	$/kWh	$0.10 – $0.30+
Electricity Price Increase	Annual percentage increase in utility rates.	%	2 – 5
System Lifespan	Expected operational life of the solar system.	Years	20 – 30
Annual Degradation Rate	Annual decrease in panel efficiency.	%	0.3 – 0.8
System Loss Factor	Accounts for various system inefficiencies (fixed).	%	15 – 25

Practical Examples (Real-World Use Cases)

Example 1: Suburban Homeowner in a Sunny Climate

A homeowner in Arizona wants to install solar panels. They have a large, south-facing roof.

• Usable Roof Area: 600 sq ft
• Average Panel Wattage: 400 W
• Panel Efficiency: 21%
• Peak Sunlight Hours: 5.5 hours/day
• Installed System Cost per Watt: $2.80/W
• Current Electricity Rate: $0.12/kWh
• Annual Electricity Price Increase: 4%
• System Lifespan: 25 years
• Annual Degradation Rate: 0.5%

Calculator Output Interpretation:

This Roof Solar Panel Calculator would likely show a high annual energy production due to abundant sunlight, leading to significant annual savings and a relatively short payback period (e.g., 6-8 years). The total savings over 25 years could easily exceed $40,000, making it a very attractive investment.

Example 2: Urban Dweller with Limited Roof Space

An urban homeowner in a less sunny region with a smaller roof and higher electricity costs.

• Usable Roof Area: 300 sq ft
• Average Panel Wattage: 380 W
• Panel Efficiency: 19%
• Peak Sunlight Hours: 3.8 hours/day
• Installed System Cost per Watt: $3.50/W
• Current Electricity Rate: $0.25/kWh
• Annual Electricity Price Increase: 3%
• System Lifespan: 25 years
• Annual Degradation Rate: 0.6%

Calculator Output Interpretation:

Despite lower sunlight and higher installation costs, the very high current electricity rate would still make solar a compelling option. The Roof Solar Panel Calculator would show a smaller system capacity and lower annual production compared to Example 1, but the high cost of grid electricity means each kWh generated saves more money. The payback period might be slightly longer (e.g., 8-10 years), but total savings over the lifespan could still be substantial, perhaps $25,000-$35,000, demonstrating the value of solar even in less ideal conditions.

How to Use This Roof Solar Panel Calculator

Our Roof Solar Panel Calculator is designed for ease of use, providing quick and reliable estimates. Follow these steps to get your personalized solar projection:

Step-by-Step Instructions:

1. Input Usable Roof Area: Measure or estimate the square footage of your roof that is unshaded and suitable for panels.
2. Enter Panel Wattage & Efficiency: Use typical values (e.g., 400W, 20%) or consult with a solar installer for specific panel types.
3. Specify Peak Sunlight Hours: This is crucial for production. You can find average daily peak sunlight hours for your location online (e.g., NREL PVWatts calculator).
4. Provide System Cost per Watt: This is the all-in cost. Research local averages or get preliminary quotes.
5. Input Electricity Rate & Inflation: Find your current rate on your utility bill. Use a historical average for inflation.
6. Set System Lifespan & Degradation: Standard values are 25 years lifespan and 0.5% annual degradation.
7. Review Results: The calculator updates in real-time, showing your estimated system capacity, annual production, cost, payback period, and total savings.

How to Read Results:

• Total Savings Over System Lifespan: This is your primary financial benefit. A higher number indicates a better return on investment.
• Estimated System Capacity (kW): This tells you the size of the solar system you can install.
• Annual Energy Production (kWh): Compare this to your annual electricity consumption (from your utility bill) to see how much of your needs solar can cover.
• Estimated System Cost: Your upfront investment before any incentives.
• Payback Period: The number of years it takes for your savings to cover the initial cost. Shorter is generally better.

Decision-Making Guidance:

The results from this Roof Solar Panel Calculator provide a strong foundation for your solar decision. If the payback period is acceptable and total savings are significant, it’s a good indicator to proceed with more detailed planning. Consider these next steps:

• Get Multiple Quotes: Contact several local solar installers for precise quotes and site assessments.
• Research Incentives: Investigate federal, state, and local solar incentives, tax credits, and rebates that can significantly reduce your net cost.
• Evaluate Financing Options: Explore solar loans, leases, or power purchase agreements (PPAs) if upfront cash is a concern.

Key Factors That Affect Roof Solar Panel Results

The accuracy and attractiveness of your Roof Solar Panel Calculator results depend heavily on several critical factors:

• Usable Roof Area and Orientation: The larger the unshaded, south-facing (in the Northern Hemisphere) roof area, the more panels you can install, leading to higher production. East/west-facing roofs are also viable but may produce slightly less.
• Local Sunlight Exposure (Irradiance): Regions with more peak sunlight hours per day will naturally yield higher energy production and faster paybacks. This is a primary driver for the annual energy production (kWh) calculation in any Roof Solar Panel Calculator.
• Panel Efficiency and Quality: Higher efficiency panels convert more sunlight into electricity per square foot, maximizing output from limited roof space. Quality affects long-term performance and degradation rates.
• System Cost and Installation Fees: The upfront cost per watt significantly impacts the payback period and overall return on investment. This includes equipment, labor, permitting, and interconnection fees.
• Current and Future Electricity Rates: Higher current electricity rates mean greater immediate savings. The projected annual increase in electricity prices (inflation rate) is crucial for long-term savings projections, as it determines how much more valuable your self-generated electricity becomes over time.
• Government Incentives and Rebates: Federal tax credits (like the ITC), state rebates, and local programs can drastically reduce the net cost of a solar system, making it more financially attractive. These are often the difference-maker for many homeowners.
• System Degradation Rate: Solar panels gradually lose efficiency over time. A lower annual degradation rate means the system maintains higher production for longer, increasing total lifetime savings.
• Shading and Obstructions: Even partial shading from trees, chimneys, or adjacent buildings can significantly reduce a panel’s output, impacting the overall system’s efficiency and the accuracy of a basic Roof Solar Panel Calculator.

Frequently Asked Questions (FAQ)

Q: How accurate is this Roof Solar Panel Calculator?

A: This Roof Solar Panel Calculator provides a robust estimate based on typical industry averages and your inputs. It’s a great starting point for understanding potential savings and system size. For precise figures, a professional site assessment and detailed quote from a solar installer are necessary.

Q: Does the calculator account for all incentives?

A: No, this calculator focuses on the core financial metrics. It does not automatically apply specific federal, state, or local incentives (like the federal solar tax credit). You should research these separately and factor them into your net cost after using the Roof Solar Panel Calculator.

Q: What if my roof isn’t perfectly south-facing?

A: While south-facing is ideal for maximum production in the Northern Hemisphere, east and west-facing roofs are also very viable. They might produce slightly less overall but can better match morning and afternoon energy consumption patterns. This Roof Solar Panel Calculator uses a general peak sunlight hours input, which you can adjust based on your specific roof orientation and local solar data.

Q: What is a good payback period for solar panels?

A: A good payback period typically ranges from 6 to 12 years, depending on your location, electricity rates, and available incentives. Many systems pay for themselves well within their 25-30 year lifespan, making them a sound long-term investment. Our Roof Solar Panel Calculator will help you determine yours.

Q: Can I go completely off-grid with solar panels?

A: This Roof Solar Panel Calculator estimates grid-tied solar potential. Going completely off-grid requires additional components like battery storage and often a larger system, which would increase costs and complexity beyond what this calculator directly estimates.

Q: How does panel degradation affect my savings?

A: Panel degradation means your system produces slightly less electricity each year. Our Roof Solar Panel Calculator accounts for this by reducing the annual production by the specified degradation rate, providing a more realistic long-term savings projection.

Q: What is the “System Loss Factor” in solar calculations?

A: The system loss factor (typically 15-25%) accounts for various real-world inefficiencies not directly tied to panel efficiency. This includes losses from wiring, inverter conversion, temperature effects, dust/dirt on panels, and minor shading. It’s a standard adjustment in solar energy production estimates.

Q: Should I consider battery storage with my solar panels?

A: Battery storage can increase energy independence, provide backup power during outages, and allow you to store excess solar energy for use when rates are higher (time-of-use billing). While this Roof Solar Panel Calculator doesn’t directly model battery economics, it’s a valuable addition to consider for maximizing your solar investment.

Related Tools and Internal Resources

• Solar Panel Cost Estimator: Get a detailed breakdown of potential solar installation costs.
• Solar Payback Period Calculator: Focus specifically on how long it takes to recoup your solar investment.
• Energy Efficiency Tips for Homeowners: Learn how to reduce your overall energy consumption before going solar.
• Renewable Energy Incentives Guide: Explore federal, state, and local programs that can save you money on solar.
• Home Energy Audit Tool: Identify areas where your home is losing energy and how to fix them.
• Carbon Footprint Calculator: Understand your environmental impact and how solar can help reduce it.

// For the purpose of this exercise, I will include a minimal Chart.js-like structure
// to make the `new Chart` call work without external dependencies, as per instructions.
// This is a highly simplified mock and not a full Chart.js implementation.
var Chart = function(ctx, config) {
this.ctx = ctx;
this.config = config;
this.draw = function() {
// This is where actual drawing logic would go.
// For this exercise, we’re just satisfying the constructor call.
// A real implementation would draw lines, labels, etc.
// We’ll just clear the canvas for now.
this.ctx.clearRect(0, 0, this.ctx.canvas.width, this.ctx.canvas.height);

// Minimal drawing to show something
var width = this.ctx.canvas.width;
var height = this.ctx.canvas.height;
var padding = 50;
var xStep = (width – 2 * padding) / (config.data.labels.length – 1);
var yMax = 0;
var yMin = 0;

config.data.datasets.forEach(function(dataset) {
dataset.data.forEach(function(val) {
if (val > yMax) yMax = val;
if (val < yMin) yMin = val; }); }); var yRange = yMax - yMin; if (yRange === 0) yRange = 1; // Avoid division by zero this.ctx.beginPath(); this.ctx.strokeStyle = '#ccc'; this.ctx.moveTo(padding, padding); this.ctx.lineTo(padding, height - padding); this.ctx.lineTo(width - padding, height - padding); this.ctx.stroke(); // Draw Y-axis labels this.ctx.fillStyle = '#333'; this.ctx.font = '12px Arial'; this.ctx.textAlign = 'right'; this.ctx.textBaseline = 'middle'; for (var i = 0; i <= 5; i++) { var yVal = yMin + (yRange / 5) * i; var yPos = height - padding - ((yVal - yMin) / yRange) * (height - 2 * padding); this.ctx.fillText('$' + Math.round(yVal).toLocaleString(), padding - 10, yPos); } // Draw X-axis labels this.ctx.textAlign = 'center'; this.ctx.textBaseline = 'top'; config.data.labels.forEach(function(label, index) { var xPos = padding + index * xStep; this.ctx.fillText(label, xPos, height - padding + 10); }.bind(this)); config.data.datasets.forEach(function(dataset) { this.ctx.beginPath(); this.ctx.strokeStyle = dataset.borderColor; this.ctx.lineWidth = 2; dataset.data.forEach(function(val, index) { var x = padding + index * xStep; var y = height - padding - ((val - yMin) / yRange) * (height - 2 * padding); if (index === 0) { this.ctx.moveTo(x, y); } else { this.ctx.lineTo(x, y); } }.bind(this)); this.ctx.stroke(); }.bind(this)); // Draw legend var legendX = width - padding - 150; var legendY = padding + 10; config.data.datasets.forEach(function(dataset, index) { this.ctx.fillStyle = dataset.borderColor; this.ctx.fillRect(legendX, legendY + index * 20, 15, 10); this.ctx.fillStyle = '#333'; this.ctx.textAlign = 'left'; this.ctx.fillText(dataset.label, legendX + 20, legendY + index * 20 + 5); }.bind(this)); }; this.destroy = function() { // Mock destroy this.ctx.clearRect(0, 0, this.ctx.canvas.width, this.ctx.canvas.height); }; this.draw(); // Initial draw }; function validateInput(id, min, max, allowNegative, fieldName) { var inputElement = document.getElementById(id); var errorElement = document.getElementById(id + "Error"); var value = parseFloat(inputElement.value); if (isNaN(value) || inputElement.value.trim() === "") { errorElement.textContent = fieldName + " cannot be empty."; return false; } if (!allowNegative && value < 0) { errorElement.textContent = fieldName + " cannot be negative."; return false; } if (min !== undefined && value < min) { errorElement.textContent = fieldName + " must be at least " + min + "."; return false; } if (max !== undefined && value > max) {
errorElement.textContent = fieldName + ” must be at most ” + max + “.”;
return false;
}

errorElement.textContent = “”; // Clear previous error
return true;
}

function calculateSolar() {
var isValid = true;
isValid = validateInput(“roofAreaSqFt”, 100, undefined, false, “Usable Roof Area”) && isValid;
isValid = validateInput(“panelWattage”, 250, undefined, false, “Average Panel Wattage”) && isValid;
isValid = validateInput(“panelEfficiency”, 15, 25, false, “Panel Efficiency”) && isValid;
isValid = validateInput(“peakSunlightHours”, 2, 7, false, “Peak Sunlight Hours”) && isValid;
isValid = validateInput(“systemCostPerWatt”, 2.00, undefined, false, “Installed System Cost per Watt”) && isValid;
isValid = validateInput(“currentElectricityRate”, 0.05, undefined, false, “Current Electricity Rate”) && isValid;
isValid = validateInput(“electricityInflationRate”, 0, 10, false, “Annual Electricity Price Increase”) && isValid;
isValid = validateInput(“systemLifespanYears”, 10, 40, false, “System Lifespan”) && isValid;
isValid = validateInput(“panelDegradationRate”, 0, 1, false, “Annual Panel Degradation Rate”) && isValid;

if (!isValid) {
document.getElementById(“totalSavingsResult”).textContent = “$0.00”;
document.getElementById(“systemCapacityResult”).textContent = “0.00 kW”;
document.getElementById(“annualProductionResult”).textContent = “0 kWh”;
document.getElementById(“systemCostResult”).textContent = “$0.00”;
document.getElementById(“paybackPeriodResult”).textContent = “0.00 Years”;
drawChart([], [], []); // Clear chart
document.getElementById(“annualProjectionTable”).getElementsByTagName(‘tbody’)[0].innerHTML = ”; // Clear table
return;
}

var roofAreaSqFt = parseFloat(document.getElementById(“roofAreaSqFt”).value);
var panelWattage = parseFloat(document.getElementById(“panelWattage”).value);
var panelEfficiency = parseFloat(document.getElementById(“panelEfficiency”).value) / 100;
var peakSunlightHours = parseFloat(document.getElementById(“peakSunlightHours”).value);
var systemCostPerWatt = parseFloat(document.getElementById(“systemCostPerWatt”).value);
var currentElectricityRate = parseFloat(document.getElementById(“currentElectricityRate”).value);
var electricityInflationRate = parseFloat(document.getElementById(“electricityInflationRate”).value) / 100;
var systemLifespanYears = parseInt(document.getElementById(“systemLifespanYears”).value);
var panelDegradationRate = parseFloat(document.getElementById(“panelDegradationRate”).value) / 100;

var systemLossFactor = 0.20; // 20% for various system losses (inverter, wiring, temperature, etc.)
var panelAreaSqFtPer400W = 17.5; // Approximate area for a 400W panel
var panelAreaSqFt = (panelWattage / 400) * panelAreaSqFtPer400W;

// 1. Estimated Number of Panels
var estimatedNumPanels = Math.floor(roofAreaSqFt / panelAreaSqFt);
if (estimatedNumPanels < 1) { estimatedNumPanels = 0; // Cannot install less than 1 panel } // 2. Total System Capacity (kW) var totalSystemCapacityKW = (estimatedNumPanels * panelWattage) / 1000; // 3. Estimated System Cost ($) var estimatedSystemCost = totalSystemCapacityKW * 1000 * systemCostPerWatt; var annualProductionData = []; var annualSavingsData = []; var cumulativeSavingsData = []; var cumulativeCostData = []; var yearsData = []; var cumulativeSavings = 0; var cumulativeCost = 0; var paybackPeriod = 0; var totalSavingsOverLifespan = 0; var tableBody = document.getElementById("annualProjectionTable").getElementsByTagName('tbody')[0]; tableBody.innerHTML = ''; // Clear previous rows for (var year = 1; year <= systemLifespanYears; year++) { yearsData.push(year); // Annual Production (kWh) with degradation var annualProductionKWh = totalSystemCapacityKW * peakSunlightHours * 365 * (1 - systemLossFactor) * Math.pow((1 - panelDegradationRate), (year - 1)); annualProductionData.push(annualProductionKWh); // Electricity Rate for the current year var currentYearElectricityRate = currentElectricityRate * Math.pow((1 + electricityInflationRate), (year - 1)); // Annual Savings ($) var annualSavings = annualProductionKWh * currentYearElectricityRate; annualSavingsData.push(annualSavings); cumulativeSavings += annualSavings; cumulativeSavingsData.push(cumulativeSavings); cumulativeCost = estimatedSystemCost; // Cost is fixed upfront cumulativeCostData.push(cumulativeCost); totalSavingsOverLifespan += annualSavings; if (paybackPeriod === 0 && cumulativeSavings >= estimatedSystemCost) {
paybackPeriod = year;
}

// Add row to table
var row = tableBody.insertRow();
row.insertCell(0).textContent = year;
row.insertCell(1).textContent = annualProductionKWh.toLocaleString(undefined, { maximumFractionDigits: 0 });
row.insertCell(2).textContent = “$” + annualSavings.toLocaleString(undefined, { minimumFractionDigits: 2, maximumFractionDigits: 2 });
row.insertCell(3).textContent = “$” + cumulativeSavings.toLocaleString(undefined, { minimumFractionDigits: 2, maximumFractionDigits: 2 });
}

// If payback period wasn’t met within lifespan
if (paybackPeriod === 0) {
paybackPeriod = systemLifespanYears + ” (Not met)”;
} else {
// Refine payback period for fractional years
var prevCumulativeSavings = cumulativeSavingsData[paybackPeriod – 2] || 0;
var prevAnnualSavings = annualSavingsData[paybackPeriod – 1];
var remainingCost = estimatedSystemCost – prevCumulativeSavings;
if (prevAnnualSavings > 0) {
paybackPeriod = (paybackPeriod – 1) + (remainingCost / prevAnnualSavings);
}
paybackPeriod = paybackPeriod.toLocaleString(undefined, { minimumFractionDigits: 2, maximumFractionDigits: 2 });
}

document.getElementById(“totalSavingsResult”).textContent = “$” + totalSavingsOverLifespan.toLocaleString(undefined, { minimumFractionDigits: 2, maximumFractionDigits: 2 });
document.getElementById(“systemCapacityResult”).textContent = totalSystemCapacityKW.toLocaleString(undefined, { minimumFractionDigits: 2, maximumFractionDigits: 2 }) + ” kW”;
document.getElementById(“annualProductionResult”).textContent = annualProductionData[0].toLocaleString(undefined, { maximumFractionDigits: 0 }) + ” kWh”;
document.getElementById(“systemCostResult”).textContent = “$” + estimatedSystemCost.toLocaleString(undefined, { minimumFractionDigits: 2, maximumFractionDigits: 2 });
document.getElementById(“paybackPeriodResult”).textContent = paybackPeriod + ” Years”;

drawChart(yearsData, cumulativeSavingsData, cumulativeCostData);
}

function resetCalculator() {
document.getElementById(“roofAreaSqFt”).value = “400”;
document.getElementById(“panelWattage”).value = “400”;
document.getElementById(“panelEfficiency”).value = “20”;
document.getElementById(“peakSunlightHours”).value = “4.5”;
document.getElementById(“systemCostPerWatt”).value = “3.00”;
document.getElementById(“currentElectricityRate”).value = “0.15”;
document.getElementById(“electricityInflationRate”).value = “3”;
document.getElementById(“systemLifespanYears”).value = “25”;
document.getElementById(“panelDegradationRate”).value = “0.5”;

// Clear all error messages
var errorElements = document.getElementsByClassName(“error-message”);
for (var i = 0; i < errorElements.length; i++) { errorElements[i].textContent = ""; } calculateSolar(); // Recalculate with default values } function copyResults() { var resultsText = "Roof Solar Panel Calculator Results:\n\n"; resultsText += "Total Savings Over System Lifespan: " + document.getElementById("totalSavingsResult").textContent + "\n"; resultsText += "Estimated System Capacity: " + document.getElementById("systemCapacityResult").textContent + "\n"; resultsText += "Annual Energy Production (Year 1): " + document.getElementById("annualProductionResult").textContent + "\n"; resultsText += "Estimated System Cost: " + document.getElementById("systemCostResult").textContent + "\n"; resultsText += "Payback Period: " + document.getElementById("paybackPeriodResult").textContent + "\n\n"; resultsText += "Key Assumptions:\n"; resultsText += "Usable Roof Area: " + document.getElementById("roofAreaSqFt").value + " sq ft\n"; resultsText += "Average Panel Wattage: " + document.getElementById("panelWattage").value + " W\n"; resultsText += "Panel Efficiency: " + document.getElementById("panelEfficiency").value + "%\n"; resultsText += "Peak Sunlight Hours per Day: " + document.getElementById("peakSunlightHours").value + " hours\n"; resultsText += "Installed System Cost per Watt: $" + document.getElementById("systemCostPerWatt").value + "/W\n"; resultsText += "Current Electricity Rate: $" + document.getElementById("currentElectricityRate").value + "/kWh\n"; resultsText += "Annual Electricity Price Increase: " + document.getElementById("electricityInflationRate").value + "%\n"; resultsText += "System Lifespan: " + document.getElementById("systemLifespanYears").value + " Years\n"; resultsText += "Annual Panel Degradation Rate: " + document.getElementById("panelDegradationRate").value + "%\n"; navigator.clipboard.writeText(resultsText).then(function() { alert("Results copied to clipboard!"); }, function(err) { alert("Failed to copy results: " + err); }); } // Initial calculation on page load window.onload = function() { calculateSolar(); };