What's TOU (Time-of-Use) pricing and why does it matter?

TOU pricing means your utility charges different rates depending on time of day. Peak hours (typically 4-9pm weekdays) are 2-4× the off-peak overnight rate. Reason: utilities have to maintain enough generation capacity for peak demand, and peak power often comes from expensive natural-gas peaker plants. Shifting load to off-peak hours saves you money AND reduces grid stress. California has been most aggressive with TOU rollout (CA NEM 3.0 default-TOU); other states (NY, MA, TX free-market plans) increasingly offer optional TOU schedules. If you're not on TOU, switching to a TOU plan via your utility's rate-options page typically requires no install — just a billing-system change.

How does the calculator estimate manual-shift savings?

Three factors compound: (1) base flexibility tier — minimal 5%, moderate 10%, aggressive 18% — encodes how much of your monthly kWh is realistically shiftable to off-peak hours. (2) Willingness multiplier (0.3-1.5×) scales the base by your commitment — 0.5× at 5 hrs/wk is typical. (3) EV charging bonus (+12% if charging at peak and willing to shift) adds a discrete shift opportunity since EVs are 30% of household kWh. (4) Heating-type multiplier (1.0× for gas, 1.3× heat pump, 1.5× electric resistance). Total shift % × monthly kWh × TOU spread = monthly savings. Real-world variance ±25% based on actual schedule discipline.

What appliances are actually shiftable?

Highest leverage (delayed-start built-in): dishwasher (75-95% of modern dishwashers have delayed-start button), clothes dryer (most modern dryers, especially heat-pump dryers), clothes washer (high-efficiency front-loaders), electric water heater (timer module $50-150 retrofit). Medium leverage (smart-home control): EV charging (every modern EV has scheduled-charging in app), smart thermostat for heat pump / AC pre-cooling (Ecobee / Nest schedule TOU automatically). Low leverage / not shiftable: refrigerator (runs 24/7), lighting (controlled by occupancy not time), cooking (when you're hungry), TV / computers (when you're using them). Realistic shiftable share for a typical household: 5-25% depending on flexibility tier.

How do smart-home plugs / thermostats help?

Smart plugs ($15-30 each — Kasa, TP-Link, Wemo) let you schedule ANY 120V appliance. Smart thermostats ($150-300 — Ecobee, Nest) handle heating + cooling on TOU schedules natively. Smart EV chargers ($200-500 added cost over basic — Wallbox, ChargePoint) handle EV charging schedules. Total smart-home automation budget for full TOU optimization: $300-800 typical. Payback: usually under 2 years at moderate-or-higher TOU spreads. Implementation effort: 2-4 hours of setup; ongoing maintenance ~minimal once configured. The hardware lasts 5-10+ years.

Why does the calculator assume only 65% battery utilization?

Because batteries don't fully cycle every day. Real-world residential battery utilization data (NREL field studies, Tesla disclosure): ~65% average. Reasons: (1) weekends often don't hit the peak load profile (you're home more, evenly distributed); (2) mild weather days reduce HVAC demand; (3) vacations zero out usage; (4) battery management systems hold reserve capacity (10-20%) for backup-power buffer; (5) round-trip efficiency of lithium batteries is 90-95% — you lose 5-10% on every charge/discharge cycle. The 65% utilization assumption is industry-conservative; actual user experiences range 50-80%. To stress-test, multiply battery savings by 0.75-0.85 for a more conservative payback estimate.

Does the IRS Section 25D credit really apply to standalone batteries?

Yes, since 2023. Pre-2023 the federal residential clean energy credit only applied to batteries paired with solar. The Inflation Reduction Act extended the 30% credit to standalone residential battery storage (3+ kWh capacity) effective Jan 1, 2023, through Dec 31, 2032. Calculator nets 30% off gross battery cost: 10 kWh Powerwall ~$9K → $6.3K net; 20 kWh dual battery ~$16K → $11.2K net. Stack with state programs (CA SGIP gives $150-1,000/kWh for low-income households, $200-300/kWh standard). The federal credit is non-refundable but rolls forward up to 5 yrs. Claim on IRS Form 5695 in the tax year you commission the system.

What if my utility doesn't offer TOU?

Switch first, optimize second. Most US utilities now offer optional TOU plans (sometimes called ‘Smart Saver’, ‘Time Advantage’, etc.). Find your utility's rate-options page and compare flat-rate vs TOU at your usage profile. Common pattern: TOU saves money for households with low daytime usage (work / school during the day, evening cooking + TV at off-peak); TOU costs money for households with heavy 4-9pm usage (stay-at-home + electric heat in winter evenings). Run this calculator with your utility's published TOU rates BEFORE switching to confirm net savings. Most utilities allow one rate-plan switch per year without penalty.

Should I install solar before adding a battery?

Almost always yes — but the optimal order depends on your net-metering policy. Under full retail net metering (legacy NEM 1.0 / 2.0 — many states), solar without battery is ideal because excess generation gets credited at retail; battery is unnecessary. Under partial / none net metering (CA NEM 3.0, Nevada, Texas), solar + battery is the right combo because battery captures excess generation for self-consumption at retail rates. Pure TOU optimization without solar (this calculator's scope) is a lower-stakes intervention — battery payback 8-14 yrs typical vs solar payback 6-12 yrs. Run the Solar ROI calc (L.5.1) first to see the bigger picture; battery economics layer on top.

How do I find my actual peak / off-peak rates?

Three places. (1) Your utility statement — usually near the bottom in a rate-summary table. Look for “Peak”, “Off-Peak”, “On-Peak” labels with $/kWh values. (2) Utility website — every utility publishes current rate schedules under “Rates” or “Tariffs”. PG&E: pge.com/tariffs. SCE: sce.com/regulatory. ConEd: coned.com/rates. (3) Bill apparenetly itemized — newer smart-meter bills show hourly usage × hourly rate × hourly cost broken out. If you're on flat-rate currently, look at the same utility's optional TOU schedule — that's the rate you'd pay if you switched. Plug those into the calculator. Avoid guessing — even a 10% error on rates throws the savings number 20% off.

What about pool pumps, EV chargers, and other large loads?

All optimizable. Pool pumps: 1-2 kW continuous load that often runs 4-8 hrs/day. Schedule for off-peak only (most pool controllers have built-in timers). Saves $20-50/mo at moderate TOU spreads. Hot tubs: similar profile. Aquariums (large): heater + pump can be timer-controlled. EV chargers: covered explicitly in the calculator's EV input — every modern EV has scheduled-charging built in (Tesla in-app, Ford / GM / VW apps, Wallbox / ChargePoint smart chargers). Electric vehicle = 250-400 kWh/mo of typically-shiftable load — single biggest optimizable load in most EV households. Calculator's EV bonus (+12%) reflects this; for 2-EV households or heavy-mileage drivers, mentally double the bonus.

What's the realistic best-case savings on this calculator?

At ideal inputs (high monthly kWh + wide TOU spread + aggressive flexibility + heat pump + 10+ hrs/wk willingness + EV charging shift): 30-40% bill reduction is achievable. Example: 1,500 kWh/mo at $0.50 peak / $0.13 off-peak (CA EV-2A) → $0.37 spread. Aggressive flex × max willingness × heat-pump (1.5×) × EV bonus = ~30% shift = 450 kWh × $0.37 = $166/mo savings. Add a 20 kWh battery: $11.2K net cost ÷ ($1,560 manual + $1,800 battery /yr) = 3.3 yr payback. Most users land at 5-15% bill reduction (modest TOU spread + moderate flexibility + 5 hrs/wk). Run with your real numbers; if savings are under $15/mo, the optimization isn't worth the friction at your specific rate schedule.

Climate & EnergyFree · No signup · 180K+/month

Electricity Bill Optimizer (TOU) — Manual Shift + Battery Arbitrage

Drop your monthly kWh, peak / off-peak TOU rates, EV charging time, appliance flexibility tier, heating type, willingness to shift hrs/wk, and battery option. Calculator computes manual-shift savings (moving load from peak → off-peak via thermostat scheduling, dishwasher / dryer / hot-water timing, EV charging window) and a separate battery-arbitrage scenario (battery charges off-peak, discharges peak — full TOU spread captured automatically). Recommends whether battery storage pays back at your specific TOU spread + bill size. Anchored to California NEM 3.0 + EV-2A rate schedules, DOE residential battery field studies, and IRS Section 25D 30% residential clean energy credit.

Instant result
Private — nothing saved
Works on any device
AI insight included

Reviewed by CalcBold EditorialLast verified May 4, 2026Methodology

Monthly electricity usage

Total monthly kWh from your utility statement (12-month average if available). EIA US average ~900 kWh/mo for residential; California ~570 kWh/mo (smaller homes + mild climate); Texas ~1,200 kWh/mo (large homes + heavy AC); EV households add 250-400 kWh/mo. Drives the absolute savings number — every percentage point of shift translates to monthlyKwh × spread × pct/100 dollars saved.

Peak rate

Highest rate on your TOU schedule, typically 4-9pm weekdays. CA NEM 3.0 peak: $0.45-0.50/kWh; PG&E EV-2A peak: $0.55+; standard CA TOU $0.30-0.40. Pull from your utility statement — should be on the rate-schedule line. If you're on flat-rate (no TOU), this calculator won't help — switch to a TOU plan first via your utility's rate-options page.

Off-peak rate

Lowest rate on your TOU schedule, typically overnight (12am-7am) and sometimes weekends. CA NEM 3.0 off-peak: $0.13-0.18; PG&E EV-2A overnight: $0.15-0.18; many utilities offer weekend off-peak tier. Wider spread (peak − off-peak) makes optimization more valuable — every $0.05 of additional spread roughly doubles the savings opportunity.

EV charging time

EV charging is typically 30% of monthly kWh for moderate driving (12K mi/yr). If currently charging during peak hours (sometimes default if you plug in at 6pm), the calculator surfaces a meaningful bonus shift — every kWh moved to off-peak saves the full TOU spread. Implementation: set a charging timer in Tesla app / Wallbox app / your charger's mobile app to start at 12am; or use utility's EV-specific TOU plan that auto-bills off-peak rate during scheduled hours.

Appliance flexibility

How many appliances you're willing to schedule via smart-home automation or manual delays. Minimal: just press ‘delayed start’ on dishwasher / dryer when running. Moderate: + EV charging timer + smart plug for high-draw devices. Aggressive: + smart thermostat (Ecobee / Nest) running pre-cooling schedule + hot-water-heater timer (electric water heater only). Aggressive requires modest capex ($300-800 in smart-home hardware, $500 typical).

Heating type (winter electricity load)

Heating drives a meaningful share of winter electricity load if you have heat pump or electric resistance. Calculator scales the manual-shift % accordingly — heat-pump owners can pre-heat the home during off-peak hours and coast through peak (smart thermostats Ecobee / Nest support this natively); electric-resistance + water-heater on timer can shift even more. Gas-furnace households see no heating-shift benefit (heating isn't on the electric bill).

Willingness to shift (hrs/wk attention)

How much weekly attention you'll give to shifting load. 0-3 hrs: manual delays only on weekends, no automation. 5 hrs: setting timers on dishwasher / dryer + EV charge schedule. 10 hrs: + smart-thermostat schedule + occasional manual peak-avoidance. 15+ hrs: full smart-home automation tuned + reviewed monthly. The willingness multiplier scales linearly: 0.3× (very low) to 1.5× (high) — most users land around 0.5-1.0× at 5-10 hrs/wk realistic commitment.

Battery storage option

Battery enables full TOU arbitrage automatically — charges off-peak (cheap), discharges peak (expensive), no behavior change required. Realistic 65% utilization assumed (battery doesn't fully cycle every day — weekends, mild weather, vacation reduce average). Best fit when TOU spread is wide ($0.20+) and you have steady evening peak load. Skip battery if your TOU spread is under $0.15 — payback stretches past warranty (10-12 yrs typical) and the math doesn't work.

Embed builderDrop the Bill Optimizer on your site →Free widget · 3 sizes · custom theme · auto-resizes · no signupGet embed code

What This Calculator Does

The Electricity Bill Optimizer answers the question every TOU-rate customer asks but few actually run the numbers on: how much can I actually save by shifting dishwasher / dryer / EV charging / hot-water / heating to off-peak hours, and is a Tesla Powerwall worth it for full automated TOU arbitrage? Drop your monthly kWh, peak / off-peak TOU rates, EV charging time, appliance flexibility tier, heating type, willingness to shift hrs/wk, and battery option. The calculator computes manual- shift savings (no battery, just behavior + smart-home automation) and a separate battery- arbitrage scenario (battery charges off-peak, discharges peak — full TOU spread captured automatically). Recommends whether battery storage pays back at your specific TOU spread + bill size.

Most online TOU calculators are utility- marketing tools that show optimistic savings without acknowledging the friction (smart-home hardware setup, ongoing schedule maintenance, actual behavior change required). CalcBold’s version is honest: the willingness multiplier scales savings based on how much weekly attention you’ll realistically give it, and the battery scenario surfaces a clear payback verdict (excellent / borderline / too long) instead of just claiming “Powerwall pays for itself.” Anchored to California NEM 3.0 + EV-2A rate schedules, DOE residential battery field studies (65% utilization realistic), and IRS Section 25D 30% residential clean energy credit on standalone batteries.

The Math — Manual Shift + Battery Arbitrage

Three layers compound the manual-shift result. Base flexibility encodes how much of your monthly kWh is realistically shiftable: minimal 5% (just dishwasher / dryer), moderate 10% (+ EV charge timing), aggressive 18% (+ AC pre-cooling + hot water on timer). Willingness multiplierscales the base by how much attention you’ll give it weekly — 0 hrs/wk = 0.3× (very low), 5 hrs = 0.5×, 10 hrs = 1.0× (industry default), 15+ hrs = 1.5× (smart-home enthusiast). EV bonus (+12% × willingness) adds when you have an EV charging at peak hours — moving EV charging to off-peak is the single biggest TOU lever for EV households (EV = ~30% of monthly kWh). Heating multiplier scales again for thermal-load households: gas furnace 1.0× (no electric heat shift), heat pump 1.3× (thermostat scheduling pre-heats off-peak), electric resistance 1.5× (hot-water + heating both shiftable significantly).

Battery arbitrageis a separate layer that doesn’t require behavior change. The battery charges from the grid during off-peak hours (cheap), discharges during peak hours (expensive). Realistic 65% utilization is assumed (battery doesn’t cycle fully every day — weekends, mild weather, vacation reduce average). 10 kWh Powerwall-class battery shifts ~6.5 kWh/day = 195 kWh/mo; 20 kWh dual battery shifts ~13 kWh/day = 390 kWh/mo. Multiply by TOU spread × 12 = annual savings; divide net battery cost (gross × 70% after IRS Section 25D 30% credit) by annual savings = payback period. Industry rule of thumb: under 8 yrs is excellent, 8-12 yrs borderline (must be inside warranty — Tesla 10-yr / Enphase 12-yr typical), 12+ yrs is too long.

A Worked Example — “California Household with EV”

Suppose a California household on a TOU rate schedule: 900 kWh/mo, $0.40/kWh peak, $0.15/kWh off-peak ($0.25 spread), EV currently charging during peak (default Tesla schedule when plugging in at 6pm), moderate appliance flexibility, gas furnace (no electric heat shift), 5 hrs/wk willingness, considering a 10 kWh Powerwall. The calculator builds:

TOU spread: $0.40 − $0.15 = $0.25/kWh (typical CA NEM 3.0 range)
Willingness multiplier: 5/10 = 0.5×
Base shift: 10% × 0.5 = 5%
EV bonus: 12% × 0.5 = 6% (EV charging at peak + willing to shift schedule)
Heating multiplier: 1.0× (gas furnace)
Total shift: (5% + 6%) × 1.0 = 11% of 900 kWh = 99 kWh/mo shifted
Manual monthly savings: 99 × $0.25 = $24.75/mo (~$297/yr)
Battery monthly arbitrage: 6.5 kWh/day × 30 × $0.25 = $48.75/mo (~$585/yr)
Battery net cost: $9,000 gross × 70% after ITC = $6,300
Battery payback: $6,300 ÷ $585 = ~10.8 yrs (borderline) — within Tesla 10-yr warranty but tight
Combined optimization: $24.75 + $48.75 = $73.50/mo total ($882/yr) if battery installed; $24.75/mo ($297/yr) if manual-shift only

The verdict: meaningful manual-shift savings ($25/mo, $300/yr) at zero capex — just scheduling the EV charger and dishwasher / dryer for off-peak. Battery decision is borderline at 10.8 yrs payback (within warranty but tight). At wider TOU spreads (CA NEM 3.0 standard $0.30+, EV-2A peak $0.55+), battery payback compresses to 6-9 yrs and becomes an obvious yes. At narrower spreads ($0.15-0.20), payback stretches to 12-15 yrs and battery isn’t worth it.

EV Charging Is the Single Biggest TOU Lever

EV charging is typically 30% of monthly kWh for moderate-mileage drivers (12K mi/yr × 0.3 kWh/mi = 3,600 kWh/yr = 300 kWh/mo). When plugging in at 6pm (default behavior for many EV owners arriving home from work), the EV charges through peak hours at the highest rates. Setting a charging-start timer for 12am moves the entire EV load to off-peak — single behavior change, no smart-home hardware required, fully reversible.

How to enable on common EVs:

Tesla:in-app schedule setting; pick “Off-Peak Charging” and set departure time. Car auto-schedules to finish charging by morning.
Ford / GM / Hyundai / VW: mobile app charging schedule. Some cars also support utility-direct programs that bill off-peak rate during scheduled hours.
Smart EV chargers (Wallbox, ChargePoint, JuiceBox): built-in time-of-use scheduling; some integrate with utility plans.
Utility EV-specific TOU plans (PG&E EV-2A, ConEd EV plan, etc.): auto-bills off-peak rate during designated hours regardless of when you charge — set and forget.

Savings impact: at $0.25 TOU spread + 300 kWh EV charging shifted off-peak = $75/mo savings on the EV alone. For households with two EVs or heavy mileage (15K+ mi/yr), the savings scale linearly. The calculator’s 12% EV bonus reflects this opportunity scaled by willingness multiplier; for heavy-EV users (2 cars, 25K+ mi/yr combined), mentally double the bonus when interpreting results.

When Battery Storage Actually Pays Back

Battery economics depend on the intersection of TOU spread and battery cost. Decision framework:

Wide TOU spread ($0.30+/kWh): battery typically pays back 6-9 yrs. Examples: CA NEM 3.0, PG&E EV-2A, SoCal Edison TOU-D-Prime. Clear winner if you have steady evening peak load + plan to stay 10+ yrs.
Medium TOU spread ($0.15-0.25/kWh): battery pays back 8-12 yrs (borderline). Examples: most other CA TOU plans, NYC ConEd TOU. Within Tesla 10-yr / Enphase 12-yr warranty but tight — secondary value (backup-power resilience) often closes the gap.
Narrow TOU spread (under $0.15/kWh): battery pays back 12-18 yrs (too long — past warranty). Examples: most TX free- market plans, Midwest TOU. Skip battery; stick with manual-shift optimization.
Flat-rate (no TOU): battery doesn’t pay back via arbitrage at all. Battery’s only value is backup-power. Switch to a TOU rate first, OR pair battery with solar (different economics — see Solar ROI calc).

Battery’s secondary value: backup-power resilience. A 10 kWh Powerwall covers 8-24 hrs of essential loads (lights, refrigerator, modem, basic AC) during grid outages. If grid reliability is poor in your area (frequent outages, hurricane country, wildfire-PSPS zones in CA), battery has insurance value not modeled in this calculator — many CA homeowners buy Powerwall primarily for outage protection, with TOU arbitrage as bonus.

Common Mistakes That Distort the Answer

Not actually being on a TOU plan. Many users assume they’re on TOU when they’re actually on flat-rate. Check your bill or utility rate-options page. Switching to TOU is usually a billing-system change requiring no install — but most utilities allow only one rate-plan switch per year.
Optimistic willingness estimate. Most users overestimate how much weekly attention they’ll give to schedule maintenance. Realistic willingness for smart-home-novice households: 3-5 hrs/wk. Smart-home-enthusiast households: 8-12 hrs/wk. Set conservative; you can always increase later if you’re actually following through.
Ignoring smart-home hardware capex. Aggressive flexibility tier requires smart plugs ($15-30 each), smart thermostat ($150-300), maybe a smart EV charger (extra $200-500). Total capex $300-800 typical. Calculator doesn’t model this; subtract from year-1 savings if modeling fairly. Hardware payback is usually under 2 yrs at moderate-or-higher TOU spreads.
Buying battery without checking TOU spread. Battery economics scale linearly with spread. At $0.30 spread, 10 kWh Powerwall pays back in 6-7 yrs (clear winner). At $0.15 spread, same battery stretches to 14-16 yrs (skip). Many CA customers buy battery on the assumption of NEM 3.0 spread, but if their utility uses different TOU rates, the math changes. Run with your specific rates, not estimates.
Forgetting battery warranty horizon. Tesla Powerwall: 10-yr warranty (70% capacity retained). Enphase IQ: 12-yr. LG Chem RESU: 10-yr. If your payback is longer than warranty, you’re betting on the unit lasting beyond warranty — possible but adds risk. Aim for payback under 80% of warranty horizon.
Skipping the solar comparison. Solar past payback gives near-zero marginal-cost electricity, making TOU optimization much less impactful (you produce your own peak-hour electricity). If you’re solar-eligible (decent roof, good orientation), run the Solar ROI calc first — solar usually beats TOU optimization on dollar-savings terms, and combining solar + battery (under partial / no net metering) is the highest-leverage residential energy play available.
Stress-testing only one scenario. Run the calculator multiple times: once with current behavior + no battery (baseline); once with optimized behavior + no battery (realistic optimization); once with optimized behavior + battery (full investment scenario). The first two show whether the friction is worth it; the third shows the marginal value of battery on top of behavior change.

Related Calculators

Pair the Electricity Bill Optimizer with the Solar ROI Calculator — solar past payback gives near-zero marginal-cost electricity, making TOU optimization moot (you produce your own peak- hour electricity, no utility purchase needed). Run solar first to see whether panels make sense; if so, solar usually beats TOU optimization on dollar-savings terms, and combining solar + battery (under partial / no net metering) is the highest-leverage residential energy play available. Pair with the EV vs ICE TCO Calculator — EV charging is 30% of monthly kWh and the single biggest TOU lever (+12% bonus shift if currently charging at peak). Run EV TCO with your post-TOU-optimization rate to see whether EV economics still pencil — most EV decisions are unaffected by TOU optimization since the EV is already a winner, but TOU can flip borderline cases to clear winners. Pair with the Heat Pump Payback Calculator — heat pump on TOU saves an additional 20-30% via off-peak pre-conditioning (smart thermostat schedules pre-heat home during off-peak, coast through peak). Run heat-pump calc with your TOU off-peak rate rather than blended rate to see optimized economics. And run the Carbon Footprint True Cost Calculator to see TOU optimization in context — off- peak electricity often has lower carbon intensity (overnight wind in TX / Midwest, hydro flowing for cheap in PNW), so shifting load typically cuts home electricity emissions 5-15% beyond the dollar savings.

How to Read the Verdict

Two scenarios run in parallel: manual shift (free, behavior-only) and battery arbitrage (capital cost, automated). Compare the manual savings against the battery-incremental savings; the gap has to clear the battery’s 10-year amortized cost for the hardware to make sense.

Manual shift saves $300+/yr. Do it before spending a dollar on hardware — programmable thermostat, EV charger schedule, dishwasher/dryer timers cover 80% of the gain.
Battery payback under 8 years AND peak-offpeak spread > $0.20/kWh. Strong battery case (CA NEM 3.0, HI, NYC, parts of MA). Add a Powerwall-class unit and let the system arbitrage automatically.
Battery payback 8-15 years. Wait for cheaper storage or pair the purchase with solar + outage protection (where battery doubles as backup, the resilience value stacks).
Flat-rate utility (no TOU). Skip both — your savings are conservation, not arbitrage. Run the insulation calc instead for higher-leverage moves.

Frequently Asked Questions

The most common questions we get about this calculator — each answer is kept under 60 words so you can scan.

What's TOU (Time-of-Use) pricing and why does it matter?
TOU pricing means your utility charges different rates depending on time of day. Peak hours (typically 4-9pm weekdays) are 2-4× the off-peak overnight rate. Reason: utilities have to maintain enough generation capacity for peak demand, and peak power often comes from expensive natural-gas peaker plants. Shifting load to off-peak hours saves you money AND reduces grid stress. California has been most aggressive with TOU rollout (CA NEM 3.0 default-TOU); other states (NY, MA, TX free-market plans) increasingly offer optional TOU schedules. If you're not on TOU, switching to a TOU plan via your utility's rate-options page typically requires no install — just a billing-system change.
How does the calculator estimate manual-shift savings?
Three factors compound: (1) base flexibility tier — minimal 5%, moderate 10%, aggressive 18% — encodes how much of your monthly kWh is realistically shiftable to off-peak hours. (2) Willingness multiplier (0.3-1.5×) scales the base by your commitment — 0.5× at 5 hrs/wk is typical. (3) EV charging bonus (+12% if charging at peak and willing to shift) adds a discrete shift opportunity since EVs are 30% of household kWh. (4) Heating-type multiplier (1.0× for gas, 1.3× heat pump, 1.5× electric resistance). Total shift % × monthly kWh × TOU spread = monthly savings. Real-world variance ±25% based on actual schedule discipline.
Is a Tesla Powerwall worth it?
Depends on your TOU spread + bill size + grid reliability. At CA NEM 3.0 spreads ($0.30+/kWh peak vs off-peak), a 10 kWh Powerwall pays back in 8-11 yrs (borderline — within warranty but tight). At standard TOU spreads ($0.15-0.20/kWh), payback stretches to 12-18 yrs (too long — past warranty). Battery's secondary value: backup-power resilience. If grid reliability is poor (frequent outages, hurricane country, wildfire-PSPS zones in CA), battery has additional insurance value not captured in pure-savings payback — many CA homeowners buy Powerwall primarily for outage protection, with TOU arbitrage as bonus. Run calc with realistic spread first; if pure-savings payback is over 10 yrs and grid is reliable, skip battery.
What appliances are actually shiftable?
Highest leverage (delayed-start built-in): dishwasher (75-95% of modern dishwashers have delayed-start button), clothes dryer (most modern dryers, especially heat-pump dryers), clothes washer (high-efficiency front-loaders), electric water heater (timer module $50-150 retrofit). Medium leverage (smart-home control): EV charging (every modern EV has scheduled-charging in app), smart thermostat for heat pump / AC pre-cooling (Ecobee / Nest schedule TOU automatically). Low leverage / not shiftable: refrigerator (runs 24/7), lighting (controlled by occupancy not time), cooking (when you're hungry), TV / computers (when you're using them). Realistic shiftable share for a typical household: 5-25% depending on flexibility tier.
How do smart-home plugs / thermostats help?
Smart plugs ($15-30 each — Kasa, TP-Link, Wemo) let you schedule ANY 120V appliance. Smart thermostats ($150-300 — Ecobee, Nest) handle heating + cooling on TOU schedules natively. Smart EV chargers ($200-500 added cost over basic — Wallbox, ChargePoint) handle EV charging schedules. Total smart-home automation budget for full TOU optimization: $300-800 typical. Payback: usually under 2 years at moderate-or-higher TOU spreads. Implementation effort: 2-4 hours of setup; ongoing maintenance ~minimal once configured. The hardware lasts 5-10+ years.
Why does the calculator assume only 65% battery utilization?
Because batteries don't fully cycle every day. Real-world residential battery utilization data (NREL field studies, Tesla disclosure): ~65% average. Reasons: (1) weekends often don't hit the peak load profile (you're home more, evenly distributed); (2) mild weather days reduce HVAC demand; (3) vacations zero out usage; (4) battery management systems hold reserve capacity (10-20%) for backup-power buffer; (5) round-trip efficiency of lithium batteries is 90-95% — you lose 5-10% on every charge/discharge cycle. The 65% utilization assumption is industry-conservative; actual user experiences range 50-80%. To stress-test, multiply battery savings by 0.75-0.85 for a more conservative payback estimate.
Does the IRS Section 25D credit really apply to standalone batteries?
Yes, since 2023. Pre-2023 the federal residential clean energy credit only applied to batteries paired with solar. The Inflation Reduction Act extended the 30% credit to standalone residential battery storage (3+ kWh capacity) effective Jan 1, 2023, through Dec 31, 2032. Calculator nets 30% off gross battery cost: 10 kWh Powerwall ~$9K → $6.3K net; 20 kWh dual battery ~$16K → $11.2K net. Stack with state programs (CA SGIP gives $150-1,000/kWh for low-income households, $200-300/kWh standard). The federal credit is non-refundable but rolls forward up to 5 yrs. Claim on IRS Form 5695 in the tax year you commission the system.
What if my utility doesn't offer TOU?
Switch first, optimize second. Most US utilities now offer optional TOU plans (sometimes called ‘Smart Saver’, ‘Time Advantage’, etc.). Find your utility's rate-options page and compare flat-rate vs TOU at your usage profile. Common pattern: TOU saves money for households with low daytime usage (work / school during the day, evening cooking + TV at off-peak); TOU costs money for households with heavy 4-9pm usage (stay-at-home + electric heat in winter evenings). Run this calculator with your utility's published TOU rates BEFORE switching to confirm net savings. Most utilities allow one rate-plan switch per year without penalty.
Should I install solar before adding a battery?
Almost always yes — but the optimal order depends on your net-metering policy. Under full retail net metering (legacy NEM 1.0 / 2.0 — many states), solar without battery is ideal because excess generation gets credited at retail; battery is unnecessary. Under partial / none net metering (CA NEM 3.0, Nevada, Texas), solar + battery is the right combo because battery captures excess generation for self-consumption at retail rates. Pure TOU optimization without solar (this calculator's scope) is a lower-stakes intervention — battery payback 8-14 yrs typical vs solar payback 6-12 yrs. Run the Solar ROI calc (L.5.1) first to see the bigger picture; battery economics layer on top.
How do I find my actual peak / off-peak rates?
Three places. (1) Your utility statement — usually near the bottom in a rate-summary table. Look for “Peak”, “Off-Peak”, “On-Peak” labels with $/kWh values. (2) Utility website — every utility publishes current rate schedules under “Rates” or “Tariffs”. PG&E: pge.com/tariffs. SCE: sce.com/regulatory. ConEd: coned.com/rates. (3) Bill apparenetly itemized — newer smart-meter bills show hourly usage × hourly rate × hourly cost broken out. If you're on flat-rate currently, look at the same utility's optional TOU schedule — that's the rate you'd pay if you switched. Plug those into the calculator. Avoid guessing — even a 10% error on rates throws the savings number 20% off.
What about pool pumps, EV chargers, and other large loads?
All optimizable. Pool pumps: 1-2 kW continuous load that often runs 4-8 hrs/day. Schedule for off-peak only (most pool controllers have built-in timers). Saves $20-50/mo at moderate TOU spreads. Hot tubs: similar profile. Aquariums (large): heater + pump can be timer-controlled. EV chargers: covered explicitly in the calculator's EV input — every modern EV has scheduled-charging built in (Tesla in-app, Ford / GM / VW apps, Wallbox / ChargePoint smart chargers). Electric vehicle = 250-400 kWh/mo of typically-shiftable load — single biggest optimizable load in most EV households. Calculator's EV bonus (+12%) reflects this; for 2-EV households or heavy-mileage drivers, mentally double the bonus.
What's the realistic best-case savings on this calculator?
At ideal inputs (high monthly kWh + wide TOU spread + aggressive flexibility + heat pump + 10+ hrs/wk willingness + EV charging shift): 30-40% bill reduction is achievable. Example: 1,500 kWh/mo at $0.50 peak / $0.13 off-peak (CA EV-2A) → $0.37 spread. Aggressive flex × max willingness × heat-pump (1.5×) × EV bonus = ~30% shift = 450 kWh × $0.37 = $166/mo savings. Add a 20 kWh battery: $11.2K net cost ÷ ($1,560 manual + $1,800 battery /yr) = 3.3 yr payback. Most users land at 5-15% bill reduction (modest TOU spread + moderate flexibility + 5 hrs/wk). Run with your real numbers; if savings are under $15/mo, the optimization isn't worth the friction at your specific rate schedule.