Estimate the ideal size for your solar panel system based on your energy needs and location.
kWh
hours
(Decimal: 0.7 to 0.9)
Watts (W)
Understanding Your Solar Array Size Calculation
Determining the right size for your solar photovoltaic (PV) system is crucial for maximizing energy production and ensuring it meets your household's electricity demands. This calculator helps you estimate the required DC (Direct Current) capacity of your solar array.
The Math Behind the Calculation:
The core idea is to figure out how much energy your solar panels need to produce daily and then work backward to determine the total system size.
Daily Energy Requirement (kWh): This is the total amount of electricity your home consumes on an average day, measured in kilowatt-hours (kWh). You can find this information on your electricity bills.
Peak Sun Hours: This isn't the total number of daylight hours, but rather the equivalent number of hours per day when solar irradiance averages 1,000 watts per square meter. This value varies significantly by geographic location and season. Higher values mean more energy generation per panel.
System Losses (Efficiency Factor): Solar energy systems are not 100% efficient. Energy is lost due to factors like panel degradation over time, shading from trees or buildings, dust and dirt on panels, inverter efficiency (converting DC to AC), wiring resistance, and temperature effects. This is represented as a decimal between 0 and 1 (e.g., 0.85 means 85% efficiency, or 15% loss).
Solar Panel Wattage: This is the rated power output of a single solar panel under Standard Test Conditions (STC). Common panel wattages range from 300W to 450W or more.
The calculation follows these steps:
Calculate Required Daily DC Energy Production: Required Daily DC Energy = Average Daily Electricity Usage (kWh) / System Losses Factor
This accounts for the energy that will be lost in the system, meaning you need to generate more DC power initially to compensate.
Calculate Required System DC Capacity (kW): Required System DC Capacity (kW) = Required Daily DC Energy (kWh) / Peak Sun Hours (hours)
This tells you the total DC power your system needs to generate on average each day, given the available sunlight.
Convert System Capacity to Watts (W): Required System DC Capacity (W) = Required System DC Capacity (kW) * 1000
Calculate Number of Panels: Number of Panels = Required System DC Capacity (W) / Solar Panel Wattage (W)
This gives you an estimate of how many individual panels of your chosen wattage you'll need. You might round this up to the nearest whole number.
Calculate Total Array Size (kWp): Total Array Size (kWp) = Required System DC Capacity (kW)
The final output often refers to the system's DC capacity in kilowatts-peak (kWp).
Use Cases & Considerations:
Homeowners: To estimate the size of a solar system needed to offset a significant portion or all of their electricity bill.
System Designers/Installers: As a preliminary tool to quickly gauge system requirements.
Budgeting: Helps in understanding the scale of the project, which is a primary factor in cost.
Important Note: This calculator provides an estimate. Actual system design should be performed by a qualified solar professional who will consider factors like roof space, orientation, shading analysis, local regulations, and specific equipment performance. The "Peak Sun Hours" value is a critical input that requires accurate local data.
function calculateSolarArraySize() {
var dailyKwh = parseFloat(document.getElementById("dailyKwh").value);
var peakSunHours = parseFloat(document.getElementById("peakSunHours").value);
var systemLossFactor = parseFloat(document.getElementById("systemLossFactor").value);
var panelWattage = parseFloat(document.getElementById("panelWattage").value);
var resultDiv = document.getElementById("result");
// Input validation
if (isNaN(dailyKwh) || dailyKwh <= 0) {
resultDiv.textContent = "Please enter a valid average daily electricity usage (kWh).";
resultDiv.style.backgroundColor = "#dc3545"; // Error red
return;
}
if (isNaN(peakSunHours) || peakSunHours <= 0) {
resultDiv.textContent = "Please enter a valid number of peak sun hours per day.";
resultDiv.style.backgroundColor = "#dc3545"; // Error red
return;
}
if (isNaN(systemLossFactor) || systemLossFactor 1) {
resultDiv.textContent = "Please enter a valid system loss factor (decimal between 0 and 1).";
resultDiv.style.backgroundColor = "#dc3545"; // Error red
return;
}
if (isNaN(panelWattage) || panelWattage <= 0) {
resultDiv.textContent = "Please enter a valid solar panel wattage.";
resultDiv.style.backgroundColor = "#dc3545"; // Error red
return;
}
// Calculations
var requiredDailyDcEnergy = dailyKwh / systemLossFactor;
var requiredSystemCapacityKw = requiredDailyDcEnergy / peakSunHours;
var requiredSystemCapacityWatts = requiredSystemCapacityKw * 1000;
var numberOfPanels = Math.ceil(requiredSystemCapacityWatts / panelWattage); // Round up to nearest whole panel
var totalArraySizeKw = requiredSystemCapacityKw; // This is the final kWp rating
resultDiv.textContent = "Estimated Solar Array Size: " + totalArraySizeKw.toFixed(2) + " kWp\n" +
"Estimated Number of Panels: " + numberOfPanels + " panels";
resultDiv.style.backgroundColor = "var(–success-green)"; // Success green
}