Determining the right size for your solar panel system is crucial for maximizing energy savings and ensuring your power needs are met. This calculator helps estimate the number of solar panels and the total system capacity (in kWp) required based on your energy consumption, local sunlight availability, and system efficiency.
How the Calculator Works
The calculation involves several key steps, considering your daily electricity usage, the amount of usable sunlight in your area, and the efficiency of the solar system.
Calculate Required Daily Production: The calculator first determines how much energy your solar system needs to produce daily to meet your specified coverage percentage. This is calculated as:
Required Daily Production (kWh) = Average Daily Electricity Usage (kWh) * (Desired Coverage (%) / 100)
Calculate Required DC System Size (kWp): This is the core sizing calculation. It accounts for the peak sun hours and the system's overall efficiency (including losses due to temperature, soiling, wiring, and inverter efficiency). The formula is:
Required DC System Size (kWp) = Required Daily Production (kWh) / (Peak Sun Hours per Day * System Loss Factor) Note: The result is typically in kWp (kilowatt-peak), which is the rated power output of the solar panels under standard test conditions.
Calculate Number of Panels: Finally, the calculator determines how many individual solar panels you'll need by dividing the total required DC system size by the wattage of a single panel.
Number of Panels = (Required DC System Size (kWp) * 1000) / Panel Wattage (Wp) We multiply kWp by 1000 to convert kilowatts to watts, ensuring consistent units. The result is then rounded up to the nearest whole number, as you can't install fractions of panels.
Key Input Factors Explained:
Average Daily Electricity Usage (kWh): This is the amount of electricity your household or business consumes on an average day, measured in kilowatt-hours. You can find this on your electricity bills.
Peak Sun Hours per Day: This refers to the average number of hours per day when the sun's intensity is at least 1000 watts per square meter. This varies significantly by geographic location and season. Online resources or local solar installers can provide this data for your area.
System Loss Factor: Solar panel systems are not 100% efficient. Factors like temperature, dirt on panels (soiling), shading, wiring resistance, and inverter inefficiency reduce the actual energy output. A typical loss factor ranges from 0.75 to 0.90 (representing 75% to 90% efficiency). A common value is 0.85.
Solar Panel Wattage (Wp): This is the power output rating of a single solar panel, usually expressed in Watts-peak (Wp). Common panel wattages range from 300Wp to 450Wp or more.
Desired Energy Coverage (%): This percentage indicates how much of your total electricity consumption you aim to cover with solar energy. 100% means generating enough energy to offset your entire electricity bill.
Why Size Your System Correctly?
An undersized system might not meet your energy goals, leaving you with high electricity bills. An oversized system, while potentially generating more electricity, can be more expensive upfront and may not be necessary or even allowed by utility net metering policies in some regions. This calculator provides a good starting point for system design.
Disclaimer: This calculator provides an estimate for educational purposes. Actual system design should be performed by a qualified solar professional who can conduct a site assessment and consider all site-specific factors and local regulations.
function calculateSolarSize() {
var avgDailyUsage = parseFloat(document.getElementById("averageDailyUsage").value);
var peakSunHours = parseFloat(document.getElementById("peakSunHours").value);
var systemLossFactor = parseFloat(document.getElementById("systemLossFactor").value);
var panelWattage = parseFloat(document.getElementById("panelWattage").value);
var desiredCoverage = parseFloat(document.getElementById("desiredCoverage").value);
var resultDiv = document.getElementById("result");
// Input validation
if (isNaN(avgDailyUsage) || avgDailyUsage <= 0 ||
isNaN(peakSunHours) || peakSunHours <= 0 ||
isNaN(systemLossFactor) || systemLossFactor 1 ||
isNaN(panelWattage) || panelWattage <= 0 ||
isNaN(desiredCoverage) || desiredCoverage 100) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields. System loss factor should be between 0 and 1, and coverage between 0 and 100.";
return;
}
// Calculation Steps
var requiredDailyProduction = avgDailyUsage * (desiredCoverage / 100);
var requiredDcSystemSizeKw = requiredDailyProduction / (peakSunHours * systemLossFactor);
var numberOfPanels = Math.ceil((requiredDcSystemSizeKw * 1000) / panelWattage);
// Ensure number of panels is not zero if inputs are valid but result is very small
if (numberOfPanels === 0 && requiredDcSystemSizeKw > 0) {
numberOfPanels = 1;
} else if (numberOfPanels < 0) { // Handle potential negative results from edge cases, though unlikely with current validation
numberOfPanels = 0;
}
var resultHtml = "
Estimated System Size:
";
resultHtml += "Required DC System Capacity: " + requiredDcSystemSizeKw.toFixed(2) + " kWp";
resultHtml += "Number of Panels Needed: " + numberOfPanels + "";
resultHtml += "(Based on " + panelWattage + " Wp panels)";
resultDiv.innerHTML = resultHtml;
}