⚡
EV Tim
Power Cost Calculator
@ev-tim

Power Cost Calculator

Upload your Detailed Consumption Data CSV, set your plan rates, see your actual power cost.

Step 1 — Upload CSV
📂
Drop your power CSV here, or click to browse
Step 2 — Configure Your Plan
Daily Supply Charge
EA Levy (Electricity Authority Levy)
Step 3 — Results
Compare Plans

Save your first calculation, then configure a second plan to compare side-by-side.

💡 Try It With Your Own Data

This calculator works with any NZ power company's half-hourly CSV export — not just Meridian. The only columns it needs are: a timestamp, and kWh used.

Want to test it with your data? Drop it into the tool and set your rates. If the column layout differs, let me know and I can add support for your network's format.

💬 Hit me up on YouTube with your CSV if you want help setting up the right plan config.

EV Tim · Open source, free to use
; document.getElementById('periodDays').textContent = dayCount; // Breakdown by period let breakdownHtml = '
Cost Breakdown
'; for (const [key, val] of Object.entries(byPeriodType)) { breakdownHtml += `
$${val.cost.toFixed(2)}
${key.toUpperCase()} · ${val.kwh.toFixed(1)} kWh
`; } if (feedInCredit > 0) { breakdownHtml += `
-$${feedInCredit.toFixed(2)}
FEED-IN CREDIT · ${totalFeedInKwh.toFixed(1)} kWh
`; } breakdownHtml += `
$${dailyChargeCost.toFixed(2)}
SUPPLY CHARGE · ${dayCount} days
`; if (eaLevyCost > 0) { breakdownHtml += `
$${eaLevyCost.toFixed(2)}
EA LEVY · ${totalKwh.toFixed(1)} kWh
`; } breakdownHtml += '
'; document.getElementById('breakdownSection').innerHTML = breakdownHtml; resultsSection.classList.remove('hidden'); // Save for comparison if (savedResult) showComparison(); } // ─── Compare ───────────────────────────────────────────────────────────────── document.getElementById('saveResult').addEventListener('click', () => { if (!resultsSection.classList.contains('hidden')) { savedResult = { name: document.getElementById('planName').value || 'Plan A', cost: document.getElementById('totalCost').textContent, kwh: document.getElementById('totalKwh').textContent, rate: document.getElementById('effectiveRate').textContent }; showComparison(); } }); document.getElementById('clearSaved').addEventListener('click', () => { savedResult = null; document.getElementById('comparisonSection').classList.add('hidden'); document.getElementById('comparisonSection').innerHTML = ''; }); function showComparison() { if (!savedResult) return; const currentCost = parseFloat(document.getElementById('totalCost').textContent.replace('$','')); const savedCost = parseFloat(savedResult.cost.replace('$','')); const diff = currentCost - savedCost; const sign = diff >= 0 ? '+' : ''; const comparison = document.getElementById('comparisonSection'); comparison.classList.remove('hidden'); comparison.innerHTML = `
${savedResult.cost}
${savedResult.name}
${document.getElementById('totalCost').textContent}
${document.getElementById('planName').value || 'Plan B'}
${sign}$${diff.toFixed(2)}
Difference
`; } // ─── Theme Toggle ─────────────────────────────────────────────────────────── const themeToggle = document.getElementById('themeToggle'); const themeIcon = document.getElementById('themeIcon'); function applyTheme(theme) { document.documentElement.setAttribute('data-theme', theme); themeIcon.textContent = theme === 'dark' ? 'Light mode' : 'Dark mode'; localStorage.setItem('evCalcTheme', theme); } themeToggle.addEventListener('click', () => { const current = document.documentElement.getAttribute('data-theme') || 'dark'; applyTheme(current === 'dark' ? 'light' : 'dark'); }); // Apply saved theme or default dark try { const savedTheme = localStorage.getItem('evCalcTheme') || 'dark'; applyTheme(savedTheme); } catch(e) { applyTheme('dark'); } // ─── TOU Overlap Validation ─────────────────────────────────────────────── function periodsOverlap(periods) { // Returns true if any two periods overlap in time-of-day. // Overnight periods (crossing midnight) are expanded to the next day for comparison. // e.g. 21:00→07:00 becomes 21:00→31:00 (where 31:00 = 07:00 next day) for (let i = 0; i < periods.length; i++) { for (let j = i + 1; j < periods.length; j++) { const a = periods[i]; const b = periods[j]; let aStart = timeToMinutes(a.start); let aEnd = timeToMinutes(a.end); let bStart = timeToMinutes(b.start); let bEnd = timeToMinutes(b.end); // Expand overnight periods to the next day (add 24h to end) if (aEnd < aStart) aEnd += 24 * 60; if (bEnd < bStart) bEnd += 24 * 60; // Now check if a and b overlap on the same timeline // a overlaps b if aStart < bEnd AND aEnd > bStart if (aStart < bEnd && aEnd > bStart) return true; } } return false; } function validatePeriods() { const type = planType.value; if (type !== 'tou') return true; const weekdayPeriods = getWeekdayPeriods(); const weekendMode = document.getElementById('weekendMode')?.value || 'same'; // Remove existing error const existing = document.getElementById('touOverlapError'); if (existing) existing.remove(); let errorMsg = ''; if (periodsOverlap(weekdayPeriods)) { errorMsg = '⚠️ Your weekday periods overlap. Each time period should be covered by only one rate.'; } else if (weekendMode === 'combined' && periodsOverlap(getWeekendPeriods())) { errorMsg = '⚠️ Your weekend periods overlap. Each time period should be covered by only one rate.'; } else if (weekendMode === 'separate') { if (periodsOverlap(getSaturdayPeriods())) { errorMsg = '⚠️ Your Saturday periods overlap. Each time period should be covered by only one rate.'; } else if (periodsOverlap(getSundayPeriods())) { errorMsg = '⚠️ Your Sunday periods overlap. Each time period should be covered by only one rate.'; } } if (errorMsg) { const div = document.createElement('div'); div.id = 'touOverlapError'; div.style.cssText = 'background:rgba(248,113,113,0.1);border:1px solid var(--red);border-radius:8px;padding:0.75rem 1rem;color:var(--red);font-size:0.85rem;margin-top:0.75rem'; div.textContent = errorMsg; document.getElementById('touConfig').appendChild(div); return false; } return true; } // Check periods whenever they change document.getElementById('weekdayPeriods')?.addEventListener('input', validatePeriods); document.getElementById('weekendPeriods')?.addEventListener('input', validatePeriods); document.getElementById('saturdayPeriods')?.addEventListener('input', validatePeriods); document.getElementById('sundayPeriods')?.addEventListener('input', validatePeriods); document.getElementById('addWeekdayPeriod')?.addEventListener('click', () => { setTimeout(validatePeriods, 0); }); // ─── Billy URL Import ───────────────────────────────────────────────────────── const planSourceSelect = document.getElementById('planSource'); const billyUrlSection = document.getElementById('billyUrlSection'); const billyFetchStatus = document.getElementById('billyFetchStatus'); const billyPlanSelector = document.getElementById('billyPlanSelector'); const billyPlanSelect = document.getElementById('billyPlanSelect'); const billyAutoFillWarning = document.getElementById('billyAutoFillWarning'); planSourceSelect.addEventListener('change', () => { const isImport = planSourceSelect.value === 'billy' || planSourceSelect.value === 'powerswitch'; billyUrlSection.classList.toggle('hidden', !isImport); if (!isImport) { billyFetchStatus.textContent = ''; billyPlanSelector.classList.add('hidden'); billyAutoFillWarning.classList.add('hidden'); billyPlanSelect.innerHTML = ''; } }); let billyPlansCache = []; // Upload a saved PowerSwitch comparison page (right-click → Save As → Webpage, Complete) document.getElementById('billyFileInput').addEventListener('change', (e) => { const file = e.target.files[0]; if (!file) return; billyFetchStatus.textContent = 'Parsing uploaded Billy page...'; billyPlanSelector.classList.add('hidden'); billyAutoFillWarning.classList.add('hidden'); billyPlansCache = []; const reader = new FileReader(); reader.onload = (ev) => { try { const html = ev.target.result; billyPlansCache = extractBillyPlans(html); if (billyPlansCache.length === 0) { const nameCount = (html.match(/data-slot="card-title"/g) || []).length; const psCount = (html.match(/TariffTable/g) || []).length; billyFetchStatus.textContent = `Could not find plans. Found ${nameCount} PowerSwitch tariff tables. Make sure you saved the full results page.`; return; } billyPlanSelect.innerHTML = '' + billyPlansCache.map((p, i) => ``).join(''); billyPlanSelector.classList.remove('hidden'); billyFetchStatus.textContent = `Found ${billyPlansCache.length} plans from file. Daily charge and rates will be filled when you select one.`; } catch(err) { billyFetchStatus.textContent = 'Error parsing file: ' + (err.message || 'unknown error'); } }; reader.readAsText(file); }); billyPlanSelect.addEventListener('change', () => { const idx = parseInt(billyPlanSelect.value); if (isNaN(idx)) { billyAutoFillWarning.classList.add('hidden'); return; } const plan = billyPlansCache[idx]; autoFillFromBillyPlan(plan); billyAutoFillWarning.classList.remove('hidden'); }); function extractBillyPlans(html) { // Try PowerSwitch format first (has TariffTable class) if (html.includes('TariffTable')) { return extractPowerSwitchPlans(html); } // Fall back to Billy format (data-slot attributes) const plans = []; const nameRegex = /data-slot="card-title"[^>]*>([^<]+)<\/div>/g; const descRegex = /data-slot="card-description"[^>]*>([^<]+)<\/div>/g; const priceRegex = /aria-label="Cost: \$(\d+)"/g; const names = []; const descs = []; const prices = []; let m; while ((m = nameRegex.exec(html)) !== null) names.push(m[1].trim()); while ((m = descRegex.exec(html)) !== null) descs.push(m[1].trim()); while ((m = priceRegex.exec(html)) !== null) prices.push(m[1]); // Prices may not be in saved HTML (loaded dynamically) let count = Math.min(names.length, descs.length); const hasPrices = prices.length > 0; if (hasPrices) count = Math.min(count, prices.length); for (let i = 0; i < count; i++) { plans.push({ name: names[i], description: descs[i] || '', price: hasPrices ? prices[i] : '', rates: {} }); } // If no prices found, still return what we have from names+descs if (plans.length === 0 && names.length > 0) { for (let i = 0; i < names.length; i++) { plans.push({ name: names[i], description: descs[i] || '', price: '', rates: {} }); } } return plans; } function extractPowerSwitchPlans(html) { // PowerSwitch format: plans are in

tags followed by // Each row in the table is const plans = []; const h3Matches = html.matchAll(/]*>([^<]+)<\/h3>/g); for (const match of h3Matches) { const planName = match[1].trim(); if (planName === 'Filter your results' || planName === 'Plan details') continue; // Find the next tariff table after this h3 const afterH3 = html.substring(match.index); const tableStart = afterH3.indexOf('
LabelValue
([^<]+)<\/td><\/tr>/g); const rates = {}; for (const row of tariffRows) { const label = row[1].trim(); const value = row[2].trim(); rates[label] = value; } if (Object.keys(rates).length > 0) { // Parse rates into structured format const parsed = parsePowerSwitchRates(planName, rates); plans.push({ name: planName, description: '', price: rates['Daily costs'] || rates['Plan Fixed Charge'] || rates['Daily charge'] || '', rates: parsed }); } } return plans; } function parsePowerSwitchRates(planName, rates) { // Convert PowerSwitch rate table into calculator-friendly format const result = { type: 'flat', // default daily: 0, periods: [], freeHours: [] }; // Parse a rate value that may be in dollars ($0.30) or cents (0.30) // If it starts with $, it's dollars -> convert to cents by multiplying 100 // Otherwise it's already cents -> use as-is const parseRate = (val) => { if (!val) return 0; const str = String(val).trim(); const num = parseFloat(str.replace('$','')); if (isNaN(num)) return 0; return str.startsWith('$') ? num * 100 : num; }; // Extract daily charge (always in dollars, no *100) result.daily = parseFloat(rates['Daily costs']?.replace('$','') || rates['Plan Fixed Charge']?.replace('$','') || rates['Daily charge']?.replace('$','') || '0'); // Check for Free Hours plans const freeKeys = Object.keys(rates).filter(k => k.includes('Free:') || k.includes('Free:')); if (freeKeys.length > 0) { result.type = 'freehours'; freeKeys.forEach(fk => { const timeMatch = rates[fk].match(/(\d+(?::\d+)?)\s*(?:am|pm)?\s*-\s*(\d+(?::\d+)?)\s*(?:am|pm)?/i); if (timeMatch) { // Parse times - this is a simplified version result.freeHours.push({ period: fk.replace('Free:', '').trim(), rate: 0 }); } }); return result; } // Check for Peak/Off-Peak (TOU) const peakRate = rates['All Inclusive Plan variable charge Peak'] || rates['Peak - Controlled'] || rates['Peak']; const offPeakRate = rates['All Inclusive Plan variable charge Off Peak'] || rates['Off Peak - Controlled'] || rates['Off Peak']; if (peakRate && offPeakRate && peakRate !== offPeakRate) { result.type = 'tou'; // NZ default: off-peak/night is 9pm-7am, peak is everything else result.periods = [ { start: '21:00', end: '07:00', rate: parseRate(offPeakRate) }, // night/off-peak default 9pm-7am { start: '07:00', end: '21:00', rate: parseRate(peakRate) } // peak day 7am-9pm default ]; } else if (peakRate) { // Same rate for all day - could be flat or day/night with same rate result.type = 'flat'; result.periods = [{ start: '00:00', end: '00:00', rate: parseRate(peakRate) }]; } return result; } function parseBillyDescription(description) { // Parse plan description to extract rate periods and guess plan type const desc = (description || '').toLowerCase(); const result = { planType: 'tou', periods: [], weekendMode: 'same' }; // Free Sunday detection if (desc.includes('free sundays') || desc.includes('free sunday')) { result.planType = 'freehours'; result.freeRanges = [{ start: '00:00', end: '23:59' }]; // All day Sunday free return result; } // Night period detection const nightMatch = desc.match(/(\d+)\s*(?:pm|am)\s*[-–to]+\s*(\d+)\s*(?:pm|am)/); let nightStart = null, nightEnd = null; if (desc.includes('night') || desc.includes('overnight')) { // Try to extract night hours e.g. "9pm to 7am" const nightTimes = desc.match(/(?:9|10|11|12)\s*(?:pm|am)\s*(?:[-–to]\s*)?(?:7|6|5|4|3|2|1)\s*(?:am|pm)/); // Heuristic: common night periods if (desc.includes('9pm') && desc.includes('7am')) { nightStart = '21:00'; nightEnd = '07:00'; } else if (desc.includes('10pm') && desc.includes('7am')) { nightStart = '22:00'; nightEnd = '07:00'; } else if (desc.includes('11pm') && desc.includes('7am')) { nightStart = '23:00'; nightEnd = '07:00'; } } // Peak/off-peak detection const hasPeak = desc.includes('peak') || desc.includes('day rate') || desc.includes('peak rate'); const hasOffPeak = desc.includes('off-peak') || desc.includes('night rate') || desc.includes('shoulder'); if (nightStart && nightEnd) { if (hasPeak || hasOffPeak) { result.planType = 'tou'; result.periods = [ { start: nightStart, end: nightEnd, rate: 18.0, label: 'Night' }, { start: nightEnd, end: nightStart, rate: 28.5, label: 'Day' } ]; } else { result.planType = 'daynight'; result.nightStart = nightStart; result.nightEnd = nightEnd; result.dayRate = 28.5; result.nightRate = 18.0; } } else if (hasPeak && hasOffPeak) { result.planType = 'tou'; result.periods = [ { start: '07:00', end: '23:00', rate: 28.5, label: 'Peak' }, { start: '23:00', end: '07:00', rate: 18.0, label: 'Off-peak' } ]; } return result; } function autoFillFromBillyPlan(plan) { // plan can come from either Billy (has description) or PowerSwitch (has rates) // Check which format we have if (plan.rates && Object.keys(plan.rates).length > 0) { // PowerSwitch format - plan has parsed rates autoFillFromPowerSwitchPlan(plan); } else { // Billy format - plan has description const parsed = parseBillyDescription(plan.description); planType.value = parsed.planType; planType.dispatchEvent(new Event('change')); if (parsed.planType === 'daynight' && parsed.nightStart) { document.getElementById('dayRate').value = parsed.dayRate; document.getElementById('nightRate').value = parsed.nightRate; document.getElementById('nightStart').value = parsed.nightStart; document.getElementById('nightEnd').value = parsed.nightEnd; } else if (parsed.planType === 'tou' && parsed.periods.length > 0) { const wContainer = document.getElementById('weekdayPeriods'); wContainer.innerHTML = ''; parsed.periods.forEach(p => addWeekdayPeriod(p.start, p.end, p.rate)); document.getElementById('addWeekdayPeriod').onclick = () => addWeekdayPeriod('00:00', '00:00', 0); } } // Also fill in daily charge if available if (plan.price) { // Price might be "$2.67/day" or just "$2.67" const dailyMatch = plan.price.match(/\$?([\d.]+)/); if (dailyMatch) { document.getElementById('dailyCharge').value = dailyMatch[1]; } } } function autoFillFromPowerSwitchPlan(plan) { // PowerSwitch has already parsed the rates - fill them in const rates = plan.rates; // Set plan type planType.value = rates.type || 'flat'; planType.dispatchEvent(new Event('change')); // Set daily charge if (rates.daily > 0) { document.getElementById('dailyCharge').value = rates.daily.toFixed(2); } if (rates.type === 'flat') { // Flat rate - use the single period rate if (rates.periods && rates.periods.length > 0) { document.getElementById('flatRate').value = (rates.periods[0].rate / 100).toFixed(2); } } else if (rates.type === 'tou') { // TOU - fill in the periods const wContainer = document.getElementById('weekdayPeriods'); wContainer.innerHTML = ''; if (rates.periods) { rates.periods.forEach(p => { addWeekdayPeriod(p.start, p.end, p.rate / 100); }); } document.getElementById('addWeekdayPeriod').onclick = () => addWeekdayPeriod('00:00', '00:00', 0); } else if (rates.type === 'freehours') { // Free hours planType.value = 'freehours'; planType.dispatchEvent(new Event('change')); // Free hours would need more parsing - for now, just set plan type } } function debounce(fn, ms) { let t; return (...args) => { clearTimeout(t); t = setTimeout(() => fn(...args), ms); }; } // ─── Init ───────────────────────────────────────────────────────────────────── initTOU(); initFreeHours(); // Load from localStorage try { const saved = localStorage.getItem('evCalcConfig'); if (saved) { const cfg = JSON.parse(saved); // restore basic values if present } } catch(e) {} window.addEventListener('beforeunload', () => { // could save config to localStorage here });