Calculate Solar Panels

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Solar Panel Calculator

Estimate the number of solar panels needed for your home based on energy consumption.

Required System Size: 0 kW
Number of Panels Needed: 0 Panels
Estimated Roof Space Required: 0 sq ft
Daily Energy Production: 0 kWh

How to Calculate Your Solar Panel Needs

Transitioning to renewable energy requires precise planning. To determine how many solar panels your home needs, we must analyze your monthly consumption, the solar potential of your geographic location, and the efficiency of the equipment used.

The Core Calculation Formula

To calculate the required system size manually, we use the following methodology:

  1. Daily Energy Need: Monthly kWh usage / 30 days.
  2. Raw Solar Array Size: Daily Energy Need / Peak Sun Hours.
  3. Corrected System Size: Raw Size / System Efficiency (typically 0.75 to 0.80 to account for inverter losses and shading).
  4. Number of Panels: System Size (in Watts) / Panel Individual Wattage.

Key Factors Explained

Peak Sun Hours: This is not the total daylight duration. It refers to the intensity of sunlight. For example, while a day may have 12 hours of light, it may only receive 4.5 "peak sun hours" of 1,000 Watts per square meter intensity.

Panel Wattage: Modern residential panels typically range from 300W to 450W. Higher wattage panels mean you need fewer physical units on your roof, which is ideal for limited spaces.

Example Calculation

If your home consumes 1,200 kWh per month and you live in an area with 5 peak sun hours:

  • Daily Need: 1,200 / 30 = 40 kWh/day
  • Target Output: 40 kWh / 5 hours = 8 kW raw system
  • Adjusted for 75% efficiency: 8 kW / 0.75 = 10.6 kW system
  • If using 400W panels: 10,600 / 400 = 27 Panels

Space Requirements

On average, a residential solar panel is approximately 17.5 square feet. A 20-panel system would require roughly 350 square feet of clear, unshaded roof space facing the correct direction (South in the Northern Hemisphere).

function calculateSolarPanels() { var monthlyKwh = parseFloat(document.getElementById("monthlyKwh").value); var sunHours = parseFloat(document.getElementById("sunHours").value); var panelWattage = parseFloat(document.getElementById("panelWattage").value); var systemEfficiency = parseFloat(document.getElementById("systemEfficiency").value) / 100; if (isNaN(monthlyKwh) || isNaN(sunHours) || isNaN(panelWattage) || isNaN(systemEfficiency) || sunHours <= 0 || panelWattage <= 0) { alert("Please enter valid positive numbers for all fields."); return; } // Daily consumption in kWh var dailyKwh = monthlyKwh / 30; // Required System Size in kW // Formula: (Daily kWh / Sun Hours) / Efficiency var systemSizeKw = (dailyKwh / sunHours) / systemEfficiency; // Number of panels // System Size in Watts / Panel Wattage var totalWattsNeeded = systemSizeKw * 1000; var panelCount = Math.ceil(totalWattsNeeded / panelWattage); // Roof Space: Approx 17.5 sq ft per panel var roofSpace = panelCount * 17.5; // Daily Production estimation var dailyProduction = (panelCount * panelWattage * sunHours * systemEfficiency) / 1000; // Display Results document.getElementById("resSystemSize").innerText = systemSizeKw.toFixed(2) + " kW"; document.getElementById("resPanelCount").innerText = panelCount + " Panels"; document.getElementById("resRoofSpace").innerText = roofSpace.toFixed(0) + " sq ft"; document.getElementById("resDailyProd").innerText = dailyProduction.toFixed(2) + " kWh"; document.getElementById("solarResult").style.display = "block"; }

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