Estimate the size and number of solar panels needed for your home.
Your Solar Estimate
Monthly Consumption:0 kWh
Recommended System Size:0 kW
Number of Panels Needed:0
Estimated Annual Production:0 kWh
Estimated Annual Savings:$0
Understanding Your Solar Calculation
Transitioning to solar energy is a significant step toward energy independence and sustainability. This solar calculator helps you determine the physical requirements of a photovoltaic (PV) system based on your current utility usage and local environmental factors.
Key Factors Explained
Monthly Consumption: This is calculated by dividing your total bill by your local utility rate. Most US households consume between 800 and 1,100 kWh per month.
Peak Sun Hours: This is not just the time between sunrise and sunset. It refers to the intensity of sunlight. Most regions in North America average between 3.5 and 6 peak sun hours per day.
System Losses: Our calculator assumes a standard 23% efficiency loss, which accounts for factors like inverter conversion, wiring resistance, and panel soiling (dust/dirt).
Panel Wattage: Modern residential panels typically range from 300W to 450W. Higher wattage means you need fewer physical panels on your roof.
Real-World Example
Suppose you live in a sunny area with a monthly bill of $200 and a rate of $0.15/kWh. Your monthly usage is approximately 1,333 kWh. If you have 5 peak sun hours daily, you would need a system size of roughly 11 kW. Using 400W panels, this would require about 28 panels to cover 100% of your electricity needs.
How to Optimize Your System
To get the most out of your solar investment, consider the orientation of your roof. South-facing roofs (in the northern hemisphere) capture the most energy. Additionally, reducing your base energy consumption through LED lighting and efficient appliances can decrease the number of panels required, lowering your initial installation cost.
function calculateSolarSystem() {
// Get Input Values
var bill = parseFloat(document.getElementById('monthlyBill').value);
var rate = parseFloat(document.getElementById('kwhRate').value);
var sun = parseFloat(document.getElementById('sunHours').value);
var watts = parseFloat(document.getElementById('panelWatts').value);
// Validate Inputs
if (isNaN(bill) || isNaN(rate) || isNaN(sun) || isNaN(watts) || rate <= 0 || sun <= 0 || watts <= 0) {
alert("Please enter valid positive numbers in all fields.");
return;
}
// 1. Calculate Monthly kWh consumption
var monthlyKwh = bill / rate;
// 2. Calculate Daily kWh needs
var dailyKwh = monthlyKwh / 30.42; // Average days in month
// 3. System Size calculation
// Formula: (Daily kWh / Sun Hours) * 1.25 (to account for 25% system losses/inefficiency)
var systemSizeKw = (dailyKwh / sun) * 1.25;
// 4. Number of Panels
// System Size in Watts / Panel Wattage
var totalPanels = Math.ceil((systemSizeKw * 1000) / watts);
// 5. Annual Production and Savings
var annualProduction = systemSizeKw * sun * 365 * 0.77; // 0.77 standard derate factor
var annualSavings = annualProduction * rate;
// Display Results
document.getElementById('resConsumption').innerText = monthlyKwh.toFixed(0) + " kWh";
document.getElementById('resSize').innerText = systemSizeKw.toFixed(2) + " kW";
document.getElementById('resPanels').innerText = totalPanels + " Panels";
document.getElementById('resAnnual').innerText = (systemSizeKw * sun * 365).toFixed(0) + " kWh";
document.getElementById('resSavings').innerText = "$" + annualSavings.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
// Show result box
document.getElementById('solarResult').style.display = 'block';
}