Solar Installation Calculator

Solar Installation Cost & Savings Calculator

function calculateSolarInstallation() { // Get input values var avgMonthlyKWH = parseFloat(document.getElementById("avgMonthlyKWH").value); var offsetPercentage = parseFloat(document.getElementById("offsetPercentage").value); var dailySunlightHours = parseFloat(document.getElementById("dailySunlightHours").value); var costPerWatt = parseFloat(document.getElementById("costPerWatt").value); var currentKWHPrice = parseFloat(document.getElementById("currentKWHPrice").value); var federalTaxCredit = parseFloat(document.getElementById("federalTaxCredit").value); var stateLocalIncentives = parseFloat(document.getElementById("stateLocalIncentives").value); var systemDegradation = parseFloat(document.getElementById("systemDegradation").value); var electricityInflation = parseFloat(document.getElementById("electricityInflation").value); // Validate inputs if (isNaN(avgMonthlyKWH) || avgMonthlyKWH <= 0 || isNaN(offsetPercentage) || offsetPercentage 100 || isNaN(dailySunlightHours) || dailySunlightHours <= 0 || isNaN(costPerWatt) || costPerWatt <= 0 || isNaN(currentKWHPrice) || currentKWHPrice <= 0 || isNaN(federalTaxCredit) || federalTaxCredit 100 || isNaN(stateLocalIncentives) || stateLocalIncentives < 0 || isNaN(systemDegradation) || systemDegradation < 0 || isNaN(electricityInflation) || electricityInflation < 0) { alert("Please enter valid positive numbers for all fields. Percentage values should be between 0 and 100."); return; } // Constants for calculation var systemEfficiencyFactor = 0.75; // Accounts for losses (inverter, wiring, temperature, dust) // 1. Calculate Desired Annual Production (kWh) var desiredAnnualProductionKWH = (avgMonthlyKWH * 12) * (offsetPercentage / 100); // 2. Calculate Estimated System Size (kW) // System Size (kW) = Desired Annual Production (kWh) / (Average Daily Sunlight Hours * 365 * System Efficiency Factor) var systemSizeKW = desiredAnnualProductionKWH / (dailySunlightHours * 365 * systemEfficiencyFactor); var systemSizeWatts = systemSizeKW * 1000; // 3. Calculate Estimated Total System Cost var totalSystemCost = systemSizeWatts * costPerWatt; // 4. Calculate Net Cost After Incentives var federalTaxCreditAmount = totalSystemCost * (federalTaxCredit / 100); var netCost = totalSystemCost – federalTaxCreditAmount – stateLocalIncentives; if (netCost < 0) netCost = 0; // Ensure net cost doesn't go negative due to excessive incentives // 5. Estimated Annual Electricity Production (kWh) – This is the desired production var annualElectricityProduction = desiredAnnualProductionKWH; // 6. Estimated Annual Savings (Year 1) var annualSavingsYear1 = annualElectricityProduction * currentKWHPrice; // 7. Calculate Payback Period var currentInvestment = netCost; var currentAnnualSavings = annualSavingsYear1; var years = 0; var paybackPeriod = "N/A (over 50 years)"; // Default if not paid back within reasonable time // Cap at 50 years to prevent infinite loop for systems that never pay back for (var i = 0; i < 50; i++) { if (currentInvestment <= 0) { paybackPeriod = i.toFixed(1) + " years"; break; } currentInvestment -= currentAnnualSavings; // Adjust savings for next year based on inflation and degradation currentAnnualSavings *= (1 + electricityInflation / 100) * (1 – systemDegradation / 100); } // 8. Calculate 25-Year Savings var totalSavings25Years = 0; var currentYearSavingsFor25Years = annualSavingsYear1; for (var i = 0; i < 25; i++) { totalSavings25Years += currentYearSavingsFor25Years; // Adjust savings for next year based on inflation and degradation currentYearSavingsFor25Years *= (1 + electricityInflation / 100) * (1 – systemDegradation / 100); } totalSavings25Years -= netCost; // Subtract initial investment from total savings // Display results document.getElementById("systemSizeOutput").innerText = systemSizeKW.toFixed(2) + " kW"; document.getElementById("totalCostOutput").innerText = "$" + totalSystemCost.toFixed(2); document.getElementById("netCostOutput").innerText = "$" + netCost.toFixed(2); document.getElementById("annualProductionOutput").innerText = annualElectricityProduction.toFixed(0) + " kWh"; document.getElementById("annualSavingsOutput").innerText = "$" + annualSavingsYear1.toFixed(2); document.getElementById("paybackPeriodOutput").innerText = paybackPeriod; document.getElementById("twentyFiveYearSavingsOutput").innerText = "$" + totalSavings25Years.toFixed(2); } // Run calculation on page load with default values window.onload = calculateSolarInstallation;

Understanding Your Solar Installation Costs and Savings

Going solar is a significant investment that can lead to substantial long-term savings and environmental benefits. Our Solar Installation Cost & Savings Calculator helps you estimate the potential costs, system size, and financial returns of installing solar panels on your home or business.

How the Calculator Works

This tool uses several key inputs to provide a comprehensive estimate. Here's a breakdown of what each input means and why it's important:

• Average Monthly Electricity Consumption (kWh): This is the amount of electricity your household uses each month, typically found on your utility bill. It's crucial for determining how much solar power you need.
• Desired Electricity Offset (%): Do you want to cover 100% of your electricity needs with solar, or a smaller percentage? This input allows you to customize your goal.
• Average Daily Peak Sunlight Hours: This refers to the average number of hours per day your solar panels receive direct, effective sunlight. This varies significantly by geographic location and season. You can often find this data for your specific area online.
• Average Cost per Watt for Installation ($): This is the typical cost to install solar panels, per watt of capacity, in your region. It includes equipment, labor, permits, and other fees. National averages typically range from $2.50 to $3.50 per watt.
• Current Electricity Price per kWh ($): Your current cost for electricity from your utility company. This is essential for calculating your potential savings.
• Federal Solar Tax Credit (%): The Investment Tax Credit (ITC) allows homeowners to deduct a percentage of the cost of installing a solar energy system from their federal taxes. As of 2023, this is 30%.
• State/Local Incentives (flat $): Many states and local municipalities offer additional rebates, grants, or tax credits to encourage solar adoption. Enter any known flat dollar amount incentives here.
• Annual System Degradation Rate (%): Solar panels gradually lose a small amount of efficiency over time. A typical degradation rate is around 0.5% to 1% per year.
• Annual Electricity Price Inflation Rate (%): Utility electricity prices tend to increase over time. This input helps project future savings more accurately.

Understanding Your Results

Once you hit "Calculate," the tool provides several key outputs:

• Estimated System Size (kW): The total power output capacity your solar system would need to meet your desired offset.
• Estimated Total System Cost: The upfront cost of your solar system before any incentives.
• Net Cost After Incentives: Your out-of-pocket cost after applying the federal tax credit and any state/local incentives.
• Estimated Annual Electricity Production (kWh): The amount of electricity your system is expected to generate in a year.
• Estimated Annual Savings (Year 1): The money you'd save on your electricity bill in the first year of operation.
• Estimated Payback Period: The number of years it will take for your energy savings to equal your net investment in the solar system.
• Estimated 25-Year Savings: The total projected financial benefit over the typical lifespan of a solar panel system, accounting for degradation and electricity price inflation.

Example Scenario:

Let's consider a homeowner in a sunny region:

• Average Monthly Electricity Consumption: 900 kWh
• Desired Electricity Offset: 100%
• Average Daily Peak Sunlight Hours: 5 hours
• Average Cost per Watt: $3.00
• Current Electricity Price: $0.15/kWh
• Federal Solar Tax Credit: 30%
• State/Local Incentives: $0
• Annual System Degradation Rate: 0.5%
• Annual Electricity Price Inflation Rate: 3%

Based on these inputs, the calculator would estimate:

• Estimated System Size: Approximately 6.58 kW
• Estimated Total System Cost: Around $19,740
• Net Cost After Incentives: Approximately $13,818 (after 30% federal tax credit)
• Estimated Annual Electricity Production: 10,800 kWh
• Estimated Annual Savings (Year 1): $1,620
• Estimated Payback Period: Around 9-10 years
• Estimated 25-Year Savings: Over $30,000

This example demonstrates how a solar investment can pay for itself and then generate significant savings over its lifetime.

Important Considerations:

While this calculator provides a strong estimate, actual costs and savings can vary. Factors like roof condition, shading, specific equipment choices, financing options, and local utility net metering policies can all influence the final outcome. Always consult with multiple qualified solar installers for precise quotes and a detailed financial analysis tailored to your specific situation.