Determining the right size for your solar panel system is crucial for maximizing your energy savings and achieving energy independence. This calculator helps you estimate the total direct current (DC) power capacity your solar array needs to generate your desired amount of electricity.
How the Calculation Works
The calculator uses the following principles:
Daily Energy Needs: This is the amount of electricity (in kilowatt-hours, kWh) your household consumes on an average day. You can find this information on your electricity bills.
Peak Sun Hours: This represents the average number of hours per day when the sun's intensity is strong enough for solar panels to operate at their rated capacity. This varies significantly by geographic location and season. It's not the same as the total hours of daylight.
System Losses: No solar system is 100% efficient. Energy is lost due to factors like shading, dirt on panels, inverter inefficiency, temperature effects, and wiring resistance. A typical loss factor ranges from 15% to 20%.
Panel Wattage: This is the rated power output of a single solar panel under standard test conditions (STC).
The core formula to estimate the required system capacity (in kWp) is derived from your daily energy needs, accounting for sun hours and system inefficiencies:
Required DC System Size (kW) = (Average Daily Energy Usage (kWh) / Peak Sun Hours per Day) / (1 - System Losses) / 1000
The division by 1000 converts the result from Watt-hours (Wh) to Kilowatt-hours (kWh) if intermediate calculations are done in Wh, or directly converts Watts to Kilowatts for the final DC capacity. In our calculation, we directly aim for the DC capacity in kW.
The number of panels required can then be estimated:
Number of Panels = (Required DC System Size (kW) * 1000) / Individual Panel Wattage (W)
The calculator focuses on providing the system size in kilowatts-peak (kWp), which is a standard unit for solar system capacity.
Factors to Consider:
Roof Space: Ensure you have enough suitable roof area to install the estimated number of panels. The calculator also provides an estimate of the physical space needed.
Shading: Significant shading will reduce energy production and may necessitate a larger system or different panel technology.
Budget: System cost is often tied to its capacity.
Future Needs: Consider potential increases in electricity consumption (e.g., electric vehicles, new appliances).
Local Regulations: Some areas have limits on the size of residential solar systems that can be connected to the grid.
This calculator provides an estimate. For an accurate assessment, consult with a professional solar installer who can perform a site-specific evaluation.
function calculateSolarPanelSize() {
var dailyEnergy = parseFloat(document.getElementById("dailyEnergy").value);
var peakSunHours = parseFloat(document.getElementById("peakSunHours").value);
var systemLoss = parseFloat(document.getElementById("systemLoss").value);
var panelWattage = parseFloat(document.getElementById("panelWattage").value);
var panelArea = parseFloat(document.getElementById("panelArea").value);
var resultValueElement = document.getElementById("result-value");
var resultUnitElement = document.getElementById("result-unit");
// Input validation
if (isNaN(dailyEnergy) || dailyEnergy <= 0) {
alert("Please enter a valid average daily electricity usage.");
return;
}
if (isNaN(peakSunHours) || peakSunHours <= 0) {
alert("Please enter a valid number of peak sun hours.");
return;
}
if (isNaN(systemLoss) || systemLoss = 1) {
alert("Please enter a valid system loss percentage (e.g., 0.15 for 15%).");
return;
}
if (isNaN(panelWattage) || panelWattage <= 0) {
alert("Please enter a valid individual panel wattage.");
return;
}
if (isNaN(panelArea) || panelArea <= 0) {
alert("Please enter a valid area per panel.");
return;
}
// Calculation
// Required AC output in kW to meet daily needs
var requiredAcKw = dailyEnergy / peakSunHours;
// Required DC input in kW, accounting for system losses
// DC_kW = AC_kW / (1 – losses)
var requiredDcKw = requiredAcKw / (1 – systemLoss);
// Convert panel wattage from W to kW
var panelWattageKw = panelWattage / 1000;
// Calculate the number of panels needed
var numberOfPanels = requiredDcKw / panelWattageKw;
// Calculate total system area
var totalSystemArea = numberOfPanels * panelArea;
resultValueElement.innerText = requiredDcKw.toFixed(2);
resultUnitElement.innerText = "kWp (DC)";
// Optional: Display number of panels and total area if desired
// You could add more elements to the HTML to show these.
// For now, we stick to the primary request of system size.
}