Smart Lighting Payback and ROI Calculator

ANA›Life Services Authority›National Calculator Authority›Smart Lighting Payback and ROI Calculator

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Smart Lighting Payback and ROI Calculator

Estimate how quickly your smart lighting upgrade pays for itself and the total return on investment over the system's lifetime.

### Current Lighting System

Number of Fixtures

Wattage per Fixture (W)

Operating Hours per Day (hrs)

Operating Days per Year

Electricity Rate ($/kWh)

Annual Maintenance Cost – Current ($)

### Smart LED Upgrade

New Wattage per Fixture (W)

Dimming / Occupancy Savings (%)

Cost per Smart Fixture ($)

Total Installation Cost ($)

Utility Rebate / Incentive ($)

Annual Maintenance Cost – Smart ($)

System Lifetime (years)

Discount Rate / WACC (%)

Calculate

function smaCalc() { var errors = [];

var numFixtures = parseFloat(document.getElementById('sma-num-fixtures').value); var oldWatts = parseFloat(document.getElementById('sma-old-watts').value); var hoursDay = parseFloat(document.getElementById('sma-hours-day').value); var daysYear = parseFloat(document.getElementById('sma-days-year').value); var elecRate = parseFloat(document.getElementById('sma-electricity-rate').value); var oldMaint = parseFloat(document.getElementById('sma-old-maint-cost').value); var newWatts = parseFloat(document.getElementById('sma-new-watts').value); var dimmingSav = parseFloat(document.getElementById('sma-dimming-savings').value); var fixtureCost = parseFloat(document.getElementById('sma-fixture-cost').value); var installCost = parseFloat(document.getElementById('sma-install-cost').value); var rebate = parseFloat(document.getElementById('sma-rebate').value); var newMaint = parseFloat(document.getElementById('sma-new-maint-cost').value); var sysLife = parseFloat(document.getElementById('sma-system-life').value); var discountRate = parseFloat(document.getElementById('sma-discount-rate').value);

if (isNaN(numFixtures) || numFixtures 0."); if (isNaN(hoursDay) || hoursDay 24) errors.push("Operating hours per day must be between 0.1 and 24."); if (isNaN(daysYear) || daysYear 365) errors.push("Operating days per year must be between 1 and 365."); if (isNaN(elecRate) || elecRate 0."); if (isNaN(oldMaint) || oldMaint 0."); if (isNaN(dimmingSav) || dimmingSav 60) errors.push("Dimming/occupancy savings must be between 0% and 60%."); if (isNaN(fixtureCost) || fixtureCost = oldWatts) { errors.push("New wattage per fixture should be less than current wattage for energy savings."); } if (!isNaN(rebate) && !isNaN(fixtureCost) && !isNaN(numFixtures) && !isNaN(installCost)) { var totalInv = fixtureCost * numFixtures + installCost; if (rebate > totalInv) errors.push("Rebate cannot exceed total investment cost."); }

var resultDiv = document.getElementById('sma-result'); if (errors.length > 0) { resultDiv.innerHTML = 'Please fix the following:' + errors.map(function(e){ return ''; }).join('') + ''; return; }

// ── Energy calculations ────────────────────────────────────────────────── // Annual operating hours var annualHours = hoursDay * daysYear;

// Annual energy consumption (kWh) var oldEnergyKwh = (oldWatts * numFixtures * annualHours) / 1000; var newEnergyBase = (newWatts * numFixtures * annualHours) / 1000;

// Apply dimming/occupancy savings on top of wattage reduction var dimmingFactor = 1 - (dimmingSav / 100); var newEnergyKwh = newEnergyBase * dimmingFactor;

// Annual energy savings (kWh) var energySavingsKwh = oldEnergyKwh - newEnergyKwh;

// Annual cost savings var annualEnergySavings = energySavingsKwh * elecRate; var annualMaintSavings = oldMaint - newMaint; var totalAnnualSavings = annualEnergySavings + annualMaintSavings;

// ── Investment ─────────────────────────────────────────────────────────── // Net investment = (fixture cost × fixtures + installation) − rebate var grossInvestment = (fixtureCost * numFixtures) + installCost; var netInvestment = grossInvestment - rebate;

// ── Simple Payback Period ──────────────────────────────────────────────── // SPP (years) = Net Investment / Total Annual Savings var simplePayback = (totalAnnualSavings > 0) ? (netInvestment / totalAnnualSavings) : Infinity;

// ── NPV & Discounted Payback ───────────────────────────────────────────── // NPV = -NetInvestment + Σ [TotalAnnualSavings / (1 + r)^t] for t = 1..sysLife var r = discountRate / 100; var npv = -netInvestment; var discountedPayback = Infinity; var cumulativeDiscounted = 0;

for (var t = 1; t = netInvestment) { // Interpolate within the year var prevCumulative = cumulativeDiscounted - discountedCF; var fraction = (netInvestment - prevCumulative) / discountedCF; discountedPayback = (t - 1) + fraction; } }

// ── ROI ────────────────────────────────────────────────────────────────── // ROI (%) = (Total Lifetime Savings − Net Investment) / Net Investment × 100 var totalLifetimeSavings = totalAnnualSavings * sysLife; var roi = (netInvestment > 0) ? ((totalLifetimeSavings - netInvestment) / netInvestment * 100) : Infinity;

// ── IRR (Newton-Raphson) ───────────────────────────────────────────────── // Solve: 0 = -NetInvestment + Σ [TotalAnnualSavings / (1+IRR)^t] var irr = NaN; if (totalAnnualSavings > 0 && netInvestment > 0) { var irrGuess = 0.1; for (var iter = 0; iter -1) irr = irrGuess * 100; }

// ── CO₂ savings ────────────────────────────────────────────────────────── // US average grid emission factor: 0.386 kg CO₂/kWh (EPA eGRID 2022) var co2Factor = 0.386; var annualCo2Savings = energySavingsKwh * co2Factor; var lifetimeCo2Savings = annualCo2Savings * sysLife;

// ── Energy reduction % ─────────────────────────────────────────────────── var energyReductionPct = (oldEnergyKwh > 0) ? (energySavingsKwh / oldEnergyKwh * 100) : 0;

// ── Helpers ─────────────────────────────────────────────────────────────── function fmt(n, dec) { if (!isFinite(n)) return 'N/A'; return n.toLocaleString('en-US', {minimumFractionDigits: dec, maximumFractionDigits: dec}); } function fmtCur(n) { if (!isFinite(n)) return 'N/A'; return '$' + n.toLocaleString('en-US', {minimumFractionDigits: 2, maximumFractionDigits: 2}); }

var paybackStr = isFinite(simplePayback)

? fmt(simplePayback, 1) + ' years'

'Never (no net savings)';
var discPaybackStr = isFinite(discountedPayback)
? fmt(discountedPayback, 1) + ' years': 'Beyond system life'; var irrStr = isNaN(irr) ? 'N/A' : fmt(irr, 1) + '%';

resultDiv.innerHTML = '### Results ' + '' +

'' + 'Simple Payback Period' + '' + paybackStr + '' + '' +

'' + 'Lifetime ROI' + '' + fmt(roi, 1) + '%' + '' +

'' + 'Net Investment (after rebate)' + '' + fmtCur(netInvestment) + '' + '' +

'' + 'Annual Energy Savings' + '' + fmtCur(annualEnergySavings) + '' + '' +

'' + 'Annual Maintenance Savings' + '' + fmtCur(annualMaintSavings) + '' + '' +

'' + 'Total Annual Savings' + '' + fmtCur(totalAnnualSavings) + '' + '' +

'' + 'Total Lifetime Savings (' + fmt(sysLife,0) + ' yrs)' + '' + fmtCur(totalLifetimeSavings) + '' + '' +

'' + 'Net Present Value (NPV)' + '' + fmtCur(npv) + '' + '' +

'' + 'Discounted Payback Period' + '' + discPaybackStr + '' + '' +

'' + 'Internal Rate of Return (IRR)' + '' + irrStr + '' + '' +

'' + 'Energy Reduction' + '' + fmt(energyReductionPct, 1) + '% (' + fmt(energySavingsKwh, 0) + ' kWh/yr)' + '' +

'' + 'Annual CO₂ Avoided' + '' + fmt(annualCo2Savings / 1000, 2) + ' tonnes' + '' +

'' + 'Lifetime CO₂ Avoided' + '' + fmt(lifetimeCo2Savings / 1000, 2) + ' tonnes' + '' +

''; }

#### Formulas Used

Annual Energy (kWh) Old = (Wold × N × Hannual) / 1000 New = (Wnew × N × Hannual) / 1000 × (1 − Dimming%/100) where Hannual = Hours/Day × Days/Year

Net Investment Net Investment = (Cost/Fixture × N + Installation Cost) − Rebate

Total Annual Savings = (Energy Saved kWh × $/kWh) + (Old Maintenance − New Maintenance)

Simple Payback Period (SPP) SPP = Net Investment / Total Annual Savings

Net Present Value (NPV) NPV = −Net Investment + Σt=1n [Annual Savings / (1 + r)t]

Discounted Payback Period Year at which cumulative discounted cash flows ≥ Net Investment (interpolated)

Lifetime ROI ROI (%) = (Total Lifetime Savings − Net Investment) / Net Investment × 100

IRR Solve: 0 = −Net Investment + Σt=1n [Annual Savings / (1 + IRR)t] (Newton-Raphson iteration)

CO₂ Avoided Annual CO₂ (kg) = Energy Saved (kWh) × 0.386 kg CO₂/kWh

#### Assumptions & References

US average grid emission factor of 0.386 kg CO₂/kWh (EPA eGRID 2022 national average).
Utility rebates vary by region; check the DSIRE database for current incentives.

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References

The law belongs to the people. Georgia v. Public.Resource.Org, 590 U.S. (2020)

Smart Lighting Payback and ROI Calculator

Smart Lighting Payback and ROI Calculator

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References

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