The amount of energy a solar panel system produces is measured in kilowatt-hours (kWh). This metric represents the power generated over time. A kilowatt-hour is equivalent to using one kilowatt (kW) of power for one hour.
How the Calculator Works
This calculator estimates the daily kWh output of your solar photovoltaic (PV) system based on several key factors:
Panel Peak Wattage (Wp): This is the maximum power a solar panel can produce under standard test conditions (STC). It's a rating, not an average daily output.
Number of Panels: The total count of solar panels in your array.
Peak Sun Hours per Day: This is a crucial factor representing the average number of hours per day when solar irradiance (sunlight intensity) reaches 1,000 watts per square meter. This is not the same as total daylight hours; it accounts for variations in sunlight intensity throughout the day and seasonal changes. Values typically range from 3 to 6 hours depending on geographic location and climate.
System Efficiency (Losses): Solar energy systems are not 100% efficient. Various factors contribute to energy loss, including:
Temperature: Panels become less efficient as they heat up.
Shading: Even partial shading on a single panel can impact the entire string.
Inverter Efficiency: Converting DC to AC power involves some loss.
Dirt and Soiling: Dust, dirt, and debris on panels reduce light absorption.
Wiring Losses: Resistance in the electrical connections.
Module Degradation: Panels gradually lose efficiency over time.
The "System Efficiency" input represents the percentage of energy that successfully makes it from the panels to usable AC power. A lower percentage indicates higher losses. For example, 0.80 means 80% efficiency (20% losses).
The Calculation Formula
The formula used by this calculator is a simplified representation:
Daily Energy (kWh) = (Panel Peak Wattage (Wp) × Number of Panels × Peak Sun Hours × System Efficiency) / 1000
We divide by 1000 to convert the result from Watt-hours (Wh) to Kilowatt-hours (kWh).
Example Calculation
Let's consider a system with:
Panel Peak Wattage: 350 Wp
Number of Panels: 12
Peak Sun Hours per Day: 4.8 hours
System Efficiency: 80% (or 0.80)
Calculation:
Daily Energy = (350 Wp × 12 panels × 4.8 hours × 0.80) / 1000Daily Energy = (20,160 Watt-hours) / 1000Daily Energy = 20.16 kWh
This system would therefore produce an estimated 20.16 kWh of energy per day on average.
Why This Matters
Understanding your system's potential daily kWh production is vital for:
Energy Bill Savings: Estimating how much electricity you'll offset from the grid.
System Sizing: Determining if your current system is adequate for your needs or if expansion is required.
Performance Monitoring: Comparing actual production to expected output to identify potential issues or maintenance needs.
Environmental Impact: Quantifying the amount of clean energy generated.
function calculateKWh() {
var panelWattage = parseFloat(document.getElementById("panelWattage").value);
var numberOfPanels = parseFloat(document.getElementById("numberOfPanels").value);
var peakSunHours = parseFloat(document.getElementById("peakSunHours").value);
var systemLosses = parseFloat(document.getElementById("systemLosses").value);
var resultValueElement = document.getElementById("result-value");
// Input validation
if (isNaN(panelWattage) || panelWattage <= 0) {
resultValueElement.innerHTML = "Invalid Panel Wattage";
return;
}
if (isNaN(numberOfPanels) || numberOfPanels <= 0) {
resultValueElement.innerHTML = "Invalid Number of Panels";
return;
}
if (isNaN(peakSunHours) || peakSunHours <= 0) {
resultValueElement.innerHTML = "Invalid Peak Sun Hours";
return;
}
if (isNaN(systemLosses) || systemLosses 1) {
resultValueElement.innerHTML = "Invalid System Efficiency";
return;
}
var totalWattage = panelWattage * numberOfPanels;
var dailyWattHours = totalWattage * peakSunHours * systemLosses;
var dailyKiloWattHours = dailyWattHours / 1000;
resultValueElement.innerHTML = dailyKiloWattHours.toFixed(2);
}