Solar and Battery Savings Calculator
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Solar and Battery Savings Calculator
Estimated Annual Savings:
$0.00
Payback Period:
N/A
Total Savings Over Analysis Period:
$0.00
Return on Investment (ROI):
0.00%
Understanding Solar and Battery Savings
Investing in solar panels and battery storage can significantly reduce your electricity bills and provide energy independence. This calculator helps you estimate the potential financial benefits by considering key factors such as your energy consumption, system specifications, electricity costs, and system prices.
How the Calculator Works:
The calculator estimates your annual savings based on several interconnected calculations:
- Estimated Solar Generation: It first determines how much electricity your solar panels are likely to produce. This is influenced by the panel capacity (kWp), efficiency, and your location's solar irradiance (though simplified here by assuming a general efficiency factor). A basic formula for annual generation might look like:
Annual Solar Generation (kWh) = Solar Panel Capacity (kWp) * 1000 * System Performance Ratio * Annual Sunshine Hours
*Note: For simplicity in this calculator, we use a factor derived from capacity and efficiency, with an implicit performance ratio and average sunshine hours.* A more direct approach here would be:
Annual Solar Generation (kWh) = Solar Panel Capacity (kWp) * 8760 hours/year * (Solar Panel Efficiency / 100) * Average Solar Irradiance (kWh/m²/day) * Panel Area Factor
However, a common simplification is to estimate based on kWp and average local sunshine hours/yield. For this calculator, we simplify the generation estimation.
- Self-Consumption and Export: Not all solar energy is used immediately. The battery plays a crucial role here. The calculator estimates how much solar energy is consumed directly, how much is stored in the battery, and how much is exported to the grid.
- Electricity Bill Reduction: Savings from reduced grid consumption are calculated using your current grid electricity cost.
- Export Revenue: Any excess solar energy exported to the grid generates revenue based on the feed-in tariff.
- Battery Usage: The battery allows you to store excess solar energy (or cheaper off-peak grid electricity, if applicable, though not explicitly modeled here) for use when solar generation is low or grid prices are high. This further offsets your grid electricity costs. The effectiveness of the battery is influenced by its capacity and charge/discharge efficiencies.
- System Costs and Payback: The total upfront cost of the solar and battery systems is considered. The payback period is the time it takes for the cumulative savings to equal the total initial investment.
- Degradation: Solar panels and batteries degrade over time, meaning their performance reduces slightly each year. The calculator accounts for this annual degradation.
Key Factors Influencing Savings:
- Your Electricity Usage Pattern: How much electricity you use and when you use it is critical. High daytime usage aligns well with solar generation. Battery storage helps shift solar energy to evening usage.
- Local Climate and Solar Irradiance: More sunshine means higher solar generation.
- Electricity Prices: Higher grid electricity costs lead to greater savings from solar and battery.
- Feed-in Tariffs: The rate at which you are compensated for exported solar energy.
- System Size and Efficiency: A system sized appropriately for your needs and with efficient components will perform better.
- Battery Specifications: Capacity (how much energy it can store) and efficiency (how much energy is lost during charging/discharging) are vital.
Important Considerations:
This calculator provides an estimate. Actual savings can vary based on:
- Specific weather conditions year-to-year.
- Accurate measurement of your home's energy consumption patterns.
- Changes in electricity tariffs and feed-in rates.
- Installation quality and specific system components.
- Maintenance costs.
- Incentives and rebates (which are not included in this basic calculation).
It's always recommended to get personalized quotes from reputable solar installers who can provide a more precise analysis for your specific situation.
Mathematical Formulas Used (Simplified):
The calculation involves iterative simulation over the years.
- Annual Solar Generation Estimate:
Solar Generation (kWh/year) = Annual Energy Consumption (kWh) * (Solar Panel Capacity (kWp) * 1000 * (Solar Panel Efficiency / 100)) / (Annual Energy Consumption (kWh) / Assumed Solar Yield Factor)
*Note: This is a simplified estimation. A more robust model uses location-specific irradiance data. For this calculator, we simplify it as:Estimated Annual Solar Generation = Solar Panel Capacity (kWp) * 8760 * (Solar Panel Efficiency / 100) * SimplifiedIrradianceFactor. A common simplification is Solar Panel Capacity (kWp) * 1500 to Solar Panel Capacity (kWp) * 1800 kWh/year depending on location. We'll use a factor that scales with efficiency and capacity.*
Generation = solarPanelCapacity * 1000 * (solarPanelEfficiency / 100) * 1500; // Assuming 1500 kWh/kWp/year as a base, adjusted by efficiency
- Daily Energy Flow Simulation (Simplified):
At each hour (or day for simplicity):
- Solar Energy Produced =
Generation / 365 (daily)
- Energy Used from Grid = Max(0,
Daily Consumption – Solar Energy Produced)
- Excess Solar = Max(0,
Solar Energy Produced – Daily Consumption)
- Battery Charge = Min(
Excess Solar, Battery Capacity – Current Battery Level)
- Energy Exported =
Excess Solar – Battery Charge
- Grid Import for Battery Charging = 0 (in this simplified model focusing on solar export)
- Battery Discharge = Min(
Energy Used from Grid, Current Battery Level)
- Energy from Battery =
Battery Discharge
- Final Grid Import =
Energy Used from Grid – Energy from Battery
Current Battery Level = Current Battery Level + Battery Charge * (Battery Charge Efficiency / 100) – Battery Discharge
*Note: This requires a day-by-day or hour-by-hour simulation for accuracy. For this calculator, we'll simplify by calculating average daily flow and then apply efficiencies.*
- Simplified Annual Savings Calculation:
Solar Energy Exported (kWh/year) = (Generation * (1 - SelfConsumptionRatio)) * (1 - BatteryChargeEfficiency/100)
Solar Energy Self-Consumed (kWh/year) = Generation - Solar Energy Exported
Grid Energy Replaced by Solar & Battery (kWh/year) = Annual Energy Consumption - Solar Energy Self-Consumed
Savings from Grid Replacement ($/year) = Grid Energy Replaced by Solar & Battery (kWh/year) * Grid Electricity Cost ($/kWh)
Revenue from Exported Solar ($/year) = Solar Energy Exported (kWh/year) * Solar Feed-in Tariff ($/kWh)
Gross Annual Savings ($/year) = Savings from Grid Replacement + Revenue from Exported Solar
Net Annual Savings ($/year) = Gross Annual Savings - Annual System Degradation Cost
(Where degradation cost is complex, we'll simplify by reducing generation/efficiency over years)
- Total System Cost:
Total Cost = Solar Panel System Cost + Battery System Cost
- Payback Period (Years):
Payback Period = Total System Cost / Average Annual Net Savings
(This is an approximation; a more accurate calculation requires iterative summation of annual savings until the total exceeds the cost).
- Total Savings Over Analysis Period:
Sum of Net Annual Savings over
Years to Analyze, accounting for degradation.
- Return on Investment (ROI):
ROI = ((Total Savings Over Analysis Period - Total System Cost) / Total System Cost) * 100
function calculateSavings() {
// Input values
var annualEnergyConsumption = parseFloat(document.getElementById("annualEnergyConsumption").value);
var solarPanelCapacity = parseFloat(document.getElementById("solarPanelCapacity").value); // kWp
var solarPanelEfficiency = parseFloat(document.getElementById("solarPanelEfficiency").value); // %
var batteryCapacity = parseFloat(document.getElementById("batteryCapacity").value); // kWh
var batteryChargeEfficiency = parseFloat(document.getElementById("batteryChargeEfficiency").value); // %
var batteryDischargeEfficiency = parseFloat(document.getElementById("batteryDischargeEfficiency").value); // %
var gridElectricityCost = parseFloat(document.getElementById("gridElectricityCost").value); // $/kWh
var solarFeedInTariff = parseFloat(document.getElementById("solarFeedInTariff").value); // $/kWh
var solarPanelSystemCost = parseFloat(document.getElementById("solarPanelSystemCost").value); // $
var batterySystemCost = parseFloat(document.getElementById("batterySystemCost").value); // $
var annualSystemDegradation = parseFloat(document.getElementById("annualSystemDegradation").value); // %
var yearsToAnalyze = parseInt(document.getElementById("yearsToAnalyze").value);
// — Input Validation —
if (isNaN(annualEnergyConsumption) || annualEnergyConsumption <= 0 ||
isNaN(solarPanelCapacity) || solarPanelCapacity <= 0 ||
isNaN(solarPanelEfficiency) || solarPanelEfficiency 100 ||
isNaN(batteryCapacity) || batteryCapacity <= 0 ||
isNaN(batteryChargeEfficiency) || batteryChargeEfficiency 100 ||
isNaN(batteryDischargeEfficiency) || batteryDischargeEfficiency 100 ||
isNaN(gridElectricityCost) || gridElectricityCost < 0 ||
isNaN(solarFeedInTariff) || solarFeedInTariff < 0 ||
isNaN(solarPanelSystemCost) || solarPanelSystemCost < 0 ||
isNaN(batterySystemCost) || batterySystemCost < 0 ||
isNaN(annualSystemDegradation) || annualSystemDegradation = 100 ||
isNaN(yearsToAnalyze) || yearsToAnalyze <= 0) {
alert("Please enter valid positive numbers for all fields.");
return;
}
// — Calculations —
// Simplified Solar Generation Estimate (kWh/year)
// Using a common rule of thumb: 1 kWp produces ~1500 kWh/year, adjusted by efficiency.
// This is a simplification; actual generation depends heavily on location (irradiance, angle, shading).
var simplifiedSolarYieldFactor = 1500; // kWh/kWp/year baseline
var estimatedAnnualSolarGeneration = solarPanelCapacity * simplifiedSolarYieldFactor * (solarPanelEfficiency / 100);
// Self-consumption ratio estimation (simplified). Assumes battery helps increase it.
// A typical unassisted solar self-consumption might be 30-50%. Battery significantly increases this.
// Let's estimate based on battery capacity relative to daily usage.
var dailyEnergyConsumption = annualEnergyConsumption / 365;
// Rough estimate: Higher battery capacity relative to daily usage implies higher self-consumption.
// Maximum possible self-consumption is capped by generation.
var estimatedSelfConsumptionRatio = Math.min(0.95, 0.3 + (batteryCapacity / dailyEnergyConsumption) * 0.4); // Capped at 95%
var solarEnergySelfConsumed = estimatedAnnualSolarGeneration * estimatedSelfConsumptionRatio;
var solarEnergyExported = estimatedAnnualSolarGeneration – solarEnergySelfConsumed;
// Adjust exported energy by battery charge efficiency
var effectiveExportedSolar = solarEnergyExported * (batteryChargeEfficiency / 100);
// Energy drawn from grid that is replaced by solar/battery
var gridEnergyReplaced = Math.min(annualEnergyConsumption, solarEnergySelfConsumed); // Cannot replace more than consumed
// Savings from reduced grid consumption
var savingsFromGridReplacement = gridEnergyReplaced * gridElectricityCost;
// Revenue from exported solar
var revenueFromExportedSolar = effectiveExportedSolar * solarFeedInTariff;
// Gross Annual Savings (before degradation)
var grossAnnualSavings = savingsFromGridReplacement + revenueFromExportedSolar;
// — Iterative Calculation for Degradation, Payback, and Total Savings —
var totalCost = solarPanelSystemCost + batterySystemCost;
var cumulativeSavings = 0;
var currentYearGenerationMultiplier = 1.0;
var year = 0;
var netAnnualSavings = 0;
var yearlySavingsArray = [];
for (year = 0; year = totalCost && year 0) ? yearlySavingsArray.slice(0, year).reduce((a, b) => a + b, 0) : 0;
var remainingCost = totalCost – previousCumulativeSavings;
var paybackPeriod = year + (remainingCost / netAnnualSavings);
document.getElementById("paybackPeriod").innerText = paybackPeriod.toFixed(1) + " years";
break; // Exit loop once payback is reached
}
if (year === yearsToAnalyze – 1 && cumulativeSavings < totalCost) {
document.getElementById("paybackPeriod").innerText = "Longer than " + yearsToAnalyze + " years";
}
}
// Calculate average annual savings over the analysis period
var averageAnnualSavings = cumulativeSavings / yearsToAnalyze;
// Calculate ROI
var roi = ((cumulativeSavings – totalCost) / totalCost) * 100;
if (isNaN(roi)) roi = 0; // Handle division by zero if totalCost is 0
// Display results
document.getElementById("annualSavings").innerText = "$" + averageAnnualSavings.toFixed(2);
document.getElementById("totalSavings").innerText = "$" + cumulativeSavings.toFixed(2);
document.getElementById("roi").innerText = roi.toFixed(2) + "%";
// Ensure Payback Period is set if loop finished without reaching payback
if (year === yearsToAnalyze && cumulativeSavings < totalCost) {
document.getElementById("paybackPeriod").innerText = "Longer than " + yearsToAnalyze + " years";
}
}