Photovoltaic Panels Calculator

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Photovoltaic (PV) System Calculator

Determine the number of solar panels and system size required for your home.

Calculation Results

Required System Size

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Number of Panels

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Estimated Annual Production

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Daily Production

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How to Calculate Your Photovoltaic System Requirements

Switching to solar energy is a major step toward sustainability and energy independence. To determine the size of the photovoltaic (PV) system you need, you must evaluate three primary variables: your average energy consumption, the geographical solar potential of your location, and the efficiency of the hardware you choose.

1. Understanding Monthly Consumption

The first step is looking at your utility bills. We measure consumption in Kilowatt-hours (kWh). A typical household might consume between 800 and 1,200 kWh per month depending on heating, cooling, and appliance usage. Our calculator uses this figure to determine the daily energy target your solar panels must meet.

2. Peak Sun Hours vs. Daylight Hours

It is important to distinguish between "daylight hours" and "peak sun hours." Peak sun hours refer to the intensity of sunlight. One peak sun hour is defined as an hour where the intensity of sunlight reaches an average of 1,000 watts per square meter. Most locations in the continental US range from 3.5 to 6.0 peak sun hours per day.

3. Accounting for Efficiency Losses

No solar system is 100% efficient. Energy is lost through DC-to-AC conversion (inverters), wiring resistance, panel temperature, and accumulated dust or shading. A standard "derate factor" or efficiency rating of 75% to 80% is commonly used by engineers to provide a realistic estimate of actual output.

Example Calculation

If your monthly bill shows 900 kWh and you live in an area with 5 peak sun hours:

  • Daily Consumption: 900 kWh / 30 days = 30 kWh/day.
  • Required System Output: 30 kWh / (5 sun hours * 0.75 efficiency) = 8.0 kW system.
  • Number of Panels: If using 400W panels, 8,000W / 400W = 20 panels.

Why System Size Matters

Installing a system that is too small won't cover your bill, while an oversized system may lead to unnecessarily high upfront costs, especially if your local utility does not offer "Net Metering" (paying you for the excess energy you pump back into the grid). Use this calculator as a starting point to discuss your project with a certified installer.

function calculateSolar() { var monthlyKwh = parseFloat(document.getElementById('monthlyConsumption').value); var sunHrs = parseFloat(document.getElementById('sunHours').value); var panelW = parseFloat(document.getElementById('panelWattage').value); var eff = parseFloat(document.getElementById('efficiency').value); // Validation if (isNaN(monthlyKwh) || isNaN(sunHrs) || isNaN(panelW) || isNaN(eff) || monthlyKwh <= 0 || sunHrs <= 0 || panelW <= 0) { alert("Please enter valid positive numbers for all fields."); return; } // Convert efficiency percentage to decimal var effDecimal = eff / 100; // 1. Daily energy target var dailyTargetKwh = monthlyKwh / 30; // 2. Required System Size in kW // Formula: (Daily kWh) / (Sun Hours * Efficiency) var systemSizeKw = dailyTargetKwh / (sunHrs * effDecimal); // 3. Number of Panels // Formula: (System Size in Watts) / (Panel Wattage) var totalWatts = systemSizeKw * 1000; var panelCount = Math.ceil(totalWatts / panelW); // 4. Annual Generation var annualKwh = systemSizeKw * sunHrs * effDecimal * 365; // Display Results document.getElementById('resSystemSize').innerText = systemSizeKw.toFixed(2) + " kW"; document.getElementById('resPanels').innerText = panelCount + " Panels"; document.getElementById('resAnnualKwh').innerText = Math.round(annualKwh).toLocaleString() + " kWh"; document.getElementById('resDailyKwh').innerText = dailyTargetKwh.toFixed(2) + " kWh"; document.getElementById('solar-results').style.display = 'block'; }

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