Estimate the potential savings and system size for your solar panel installation.
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$ per kWh
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$ per Watt
hours
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Estimated Solar System Details
Required System Size: — kW
Estimated System Cost: —
Estimated Annual Production: — kWh
Estimated Monthly Production: — kWh
Understanding Your Solar Electric System Calculation
This calculator helps you estimate the key parameters for a residential solar electric system. By inputting your current electricity usage and system costs, you can get an idea of the system size, cost, and potential energy production needed to offset your electricity consumption.
How the Calculation Works:
The calculator uses a series of formulas to convert your electricity bill into the requirements for a solar system. Here's a breakdown:
1. Annual Electricity Consumption (kWh):
First, we estimate your total annual electricity consumption. This is derived from your average monthly electricity bill and the cost of electricity per kilowatt-hour (kWh).
Monthly Bill = Average Monthly Electricity Bill ($)
Electricity Rate = Cost per kWh ($/kWh)
Monthly Consumption (kWh) = Monthly Bill / Electricity Rate
This determines the capacity of the solar panel system needed. It takes into account the target annual production, the average daily peak sun hours, and the overall system efficiency (which accounts for losses from panel temperature, shading, inverter efficiency, dust, etc.).
Average Peak Sun Hours per Day = The average number of hours per day when sunlight is strong enough for panels to produce at their rated capacity.
System Efficiency = The percentage of generated DC power that is converted to usable AC power (e.g., 85% means 15% loss).
Daily Production per kW of System Size (kWh/kW) = Average Peak Sun Hours per Day * (System Efficiency / 100)
Required System Size (kW) = Target Annual Production (kWh) / (Daily Production per kW of System Size (kWh/kW) * 365 days/year)
4. Estimated System Cost ($):
This is a straightforward calculation based on the required system size and the cost per watt (or kilowatt) of solar installations.
System Cost per Watt = The installed cost of solar per watt ($/Watt).
Required System Size (kW) = Calculated above.
Required System Size (Watts) = Required System Size (kW) * 1000 Watts/kW
Estimated System Cost ($) = Required System Size (Watts) * System Cost per Watt ($/Watt)
5. Estimated Annual and Monthly Production (kWh):
These values show you how much energy your estimated system size is expected to generate annually and monthly.
Estimated Annual Production (kWh) = Required System Size (kW) * Daily Production per kW of System Size (kWh/kW) * 365 days/year
Estimated Monthly Production (kWh) = Estimated Annual Production (kWh) / 12
Use Cases and Considerations:
System Sizing: Helps determine the appropriate size of a solar system based on your energy needs and budget.
Cost Estimation: Provides a ballpark figure for the investment required.
Incentive Planning: Can help you understand the potential return on investment when considering government incentives or net metering policies.
Roof Space: The required system size can also give you an idea of the physical space needed on your roof.
Disclaimer: This calculator provides estimates for informational purposes only. Actual system performance and costs may vary based on specific site conditions, equipment choices, installation quality, local weather patterns, and evolving utility rates and policies.
function calculateSolarSystem() {
var monthlyBill = parseFloat(document.getElementById("monthlyElectricityBill").value);
var electricityRate = parseFloat(document.getElementById("electricityRate").value);
var desiredOffset = parseFloat(document.getElementById("desiredOffset").value);
var systemCostPerWatt = parseFloat(document.getElementById("systemCostPerWatt").value);
var sunHoursPerDay = parseFloat(document.getElementById("sunHoursPerDay").value);
var systemEfficiencyPercent = parseFloat(document.getElementById("systemEfficiency").value);
var resultDiv = document.getElementById("result");
var requiredSystemSizeElem = document.getElementById("requiredSystemSize");
var estimatedSystemCostElem = document.getElementById("estimatedSystemCost");
var estimatedAnnualProductionElem = document.getElementById("estimatedAnnualProduction");
var estimatedMonthlyProductionElem = document.getElementById("estimatedMonthlyProduction");
// Clear previous results
requiredSystemSizeElem.innerText = "–";
estimatedSystemCostElem.innerText = "–";
estimatedAnnualProductionElem.innerText = "–";
estimatedMonthlyProductionElem.innerText = "–";
// Input validation
if (isNaN(monthlyBill) || isNaN(electricityRate) || isNaN(desiredOffset) || isNaN(systemCostPerWatt) || isNaN(sunHoursPerDay) || isNaN(systemEfficiencyPercent)) {
alert("Please enter valid numbers for all fields.");
return;
}
if (monthlyBill < 0 || electricityRate < 0 || desiredOffset 100 || systemCostPerWatt < 0 || sunHoursPerDay 24 || systemEfficiencyPercent 100) {
alert("Please enter valid values within the acceptable ranges.");
return;
}
var annualConsumptionKWh = (monthlyBill / electricityRate) * 12;
var targetAnnualProductionKWh = annualConsumptionKWh * (desiredOffset / 100);
var systemEfficiencyFactor = systemEfficiencyPercent / 100;
var dailyProductionPerKw = sunHoursPerDay * systemEfficiencyFactor;
var requiredSystemSizeKw = 0;
if (dailyProductionPerKw > 0) {
requiredSystemSizeKw = targetAnnualProductionKWh / (dailyProductionPerKw * 365);
}
var requiredSystemSizeWatts = requiredSystemSizeKw * 1000;
var estimatedSystemCost = requiredSystemSizeWatts * systemCostPerWatt;
var estimatedAnnualProductionKWh = 0;
if (dailyProductionPerKw > 0) {
estimatedAnnualProductionKWh = requiredSystemSizeKw * dailyProductionPerKw * 365;
}
var estimatedMonthlyProductionKWh = estimatedAnnualProductionKWh / 12;
// Display results
requiredSystemSizeElem.innerText = requiredSystemSizeKw.toFixed(2);
estimatedSystemCostElem.innerText = "$" + estimatedSystemCost.toFixed(2);
estimatedAnnualProductionElem.innerText = estimatedAnnualProductionKWh.toFixed(2);
estimatedMonthlyProductionElem.innerText = estimatedMonthlyProductionKWh.toFixed(2);
}