Off the Grid Solar Calculator

Off-Grid Solar System Sizing Calculator

function calculateSolar() { var dailyConsumptionWh = parseFloat(document.getElementById('dailyConsumptionWh').value); var peakSunHours = parseFloat(document.getElementById('peakSunHours').value); var systemVoltage = parseFloat(document.getElementById('systemVoltage').value); var batteryDoD = parseFloat(document.getElementById('batteryDoD').value); var daysAutonomy = parseFloat(document.getElementById('daysAutonomy').value); var panelDeratingFactor = parseFloat(document.getElementById('panelDeratingFactor').value); var batteryEfficiency = parseFloat(document.getElementById('batteryEfficiency').value); var inverterEfficiency = parseFloat(document.getElementById('inverterEfficiency').value); var resultDiv = document.getElementById('result'); resultDiv.style.color = '#155724'; // Reset color for valid results // Input validation if (isNaN(dailyConsumptionWh) || dailyConsumptionWh <= 0 || isNaN(peakSunHours) || peakSunHours <= 0 || isNaN(systemVoltage) || systemVoltage <= 0 || isNaN(batteryDoD) || batteryDoD 100 || isNaN(daysAutonomy) || daysAutonomy <= 0 || isNaN(panelDeratingFactor) || panelDeratingFactor 100 || isNaN(batteryEfficiency) || batteryEfficiency 100 || isNaN(inverterEfficiency) || inverterEfficiency 100) { resultDiv.innerHTML = 'Please enter valid positive numbers for all fields. Percentages should be between 1 and 100.'; return; } // Convert percentages to decimals var panelDeratingFactorDecimal = panelDeratingFactor / 100; var batteryEfficiencyDecimal = batteryEfficiency / 100; var inverterEfficiencyDecimal = inverterEfficiency / 100; var batteryDoDDecimal = batteryDoD / 100; // Step 1: Calculate effective daily energy demand considering inverter losses (DC energy needed from battery) var effectiveDailyDemandInverter = dailyConsumptionWh / inverterEfficiencyDecimal; // Step 2: Calculate effective daily energy demand considering battery losses (DC energy needed from solar panels) var effectiveDailyDemandBattery = effectiveDailyDemandInverter / batteryEfficiencyDecimal; // Step 3: Calculate Required Solar Panel Array Size (Watts) // This is the peak power rating of the solar array needed. var requiredPanelWatts = effectiveDailyDemandBattery / (peakSunHours * panelDeratingFactorDecimal); // Step 4: Calculate Required Battery Bank Capacity (Ah) // Total energy to be stored in the battery bank for autonomy days, considering usable capacity (DoD) var totalEnergyToStoreWh = effectiveDailyDemandInverter * daysAutonomy; var requiredUsableBatteryWh = totalEnergyToStoreWh / batteryDoDDecimal; var requiredBatteryAh = requiredUsableBatteryWh / systemVoltage; // Display results resultDiv.innerHTML = '

Estimated System Requirements:

' + 'Required Solar Panel Array Size: ' + requiredPanelWatts.toFixed(0) + ' Watts' + 'Required Battery Bank Capacity: ' + requiredBatteryAh.toFixed(0) + ' Ah (' + requiredUsableBatteryWh.toFixed(0) + ' Wh usable)' + 'Note: These are theoretical minimums. It\'s often recommended to add a buffer (e.g., 10-20%) for real-world variations.'; }

Understanding Your Off-Grid Solar System Needs

Going off-grid means disconnecting from the traditional utility power grid and generating all your electricity independently. This offers energy independence, reduced utility bills, and a smaller carbon footprint. However, it requires careful planning and sizing of your solar power system to ensure you have reliable power, especially during periods of low sunlight.

How the Off-Grid Solar Calculator Works

Our calculator helps you estimate the two most critical components of an off-grid system: the solar panel array size and the battery bank capacity. It takes into account various factors that influence real-world performance.

Key Inputs Explained:

• Daily Energy Consumption (Wh/day): This is the total amount of energy your appliances and devices consume in a 24-hour period. To estimate this, list all your electrical loads, their wattage, and how many hours per day each is used. Multiply wattage by hours for each item, then sum them up.
  Example:
  • LED Lights (10W x 5 hours x 4 lights) = 200 Wh
  • Laptop (60W x 6 hours) = 360 Wh
  • Refrigerator (150W x 8 hours run time) = 1200 Wh
  • Water Pump (750W x 0.5 hours) = 375 Wh
  • Total Daily Consumption = 2135 Wh/day
• Peak Sun Hours (hours/day): Also known as "Solar Insolation" or "Sun Hours," this represents the average number of hours per day that your location receives sunlight intense enough to generate peak power from your solar panels. This varies significantly by geographic location and season. You can find this data from solar maps or local weather resources. A common range is 3-7 hours.
• System Voltage (V): Common off-grid system voltages are 12V, 24V, and 48V. Higher voltages are generally more efficient for larger systems as they allow for thinner wiring and reduce power loss over distance.
• Battery Depth of Discharge (DoD %): This is the percentage of a battery's capacity that has been discharged relative to its total capacity. For lead-acid batteries, a DoD of 50% is often recommended to prolong battery life. For lithium-ion (LiFePO4) batteries, a DoD of 80-90% is typically safe and common.
• Days of Autonomy (days): This refers to the number of days your battery bank can power your home without any input from the solar panels (e.g., during extended cloudy periods). A common range is 1-5 days, depending on your climate and risk tolerance.
• Panel Derating Factor (%): Solar panels rarely perform at their theoretical maximum due to factors like temperature, dust, shading, wiring losses, and inverter inefficiencies. A derating factor accounts for these real-world losses. A typical value is 75-85%.
• Battery Efficiency (%): Batteries are not 100% efficient; some energy is lost during charging and discharging cycles. Lead-acid batteries typically have an efficiency of 80-90%, while lithium-ion batteries are generally 90-98% efficient.
• Inverter Efficiency (%): The inverter converts the DC (Direct Current) power from your batteries into AC (Alternating Current) power that most household appliances use. This conversion process involves some energy loss. High-quality inverters typically have efficiencies of 90-96%.

Interpreting Your Results

The calculator provides two main outputs:

• Required Solar Panel Array Size (Watts): This is the total peak power (in Watts) your solar panels should be rated for to meet your daily energy needs, considering all losses and available sun hours. You would then divide this by the wattage of individual panels to determine how many panels you need.
• Required Battery Bank Capacity (Ah): This is the total Amp-hour (Ah) capacity your battery bank needs to store enough energy to power your home for your specified days of autonomy, at your chosen system voltage, and within your desired depth of discharge limits. The Watt-hour (Wh) equivalent is also provided for easier comparison.

Remember, these calculations provide a strong starting point. It's always wise to consult with a professional solar installer who can perform a detailed site assessment and provide a customized system design tailored to your specific needs and local conditions.