How to build a realistic time-of-use load-shifting worksheet
Use interval kWh and the actual tariff calendar to calculate peak share and test whether a practical schedule change saves money.
Build a load-shifting worksheet by assigning actual interval kWh to the tariff's time bands, then moving only the energy your household can realistically reschedule. Calculate the original and revised costs with the same rates and fees. This separates an achievable scheduling change from a theoretical ideal. Monthly kWh alone cannot show whether a time-of-use plan fits your home, and a cheap overnight rate does not establish the result without peak usage.
Prepare the interval data
Use the utility's official account portal to look for hourly or shorter-interval usage. Keep the original file unchanged and work from a copy. Note the units, whether timestamps identify the start or end of an interval, and the time zone. A one-hour error at the boundary can assign energy to the wrong price band. Missing intervals should be flagged rather than quietly treated as zero consumption.
Obtain the current tariff schedule for your account, including seasons, weekends, holidays, and special periods. Check that the interval dates align with the billing cycle you want to model. A calendar-month download may not match a meter-cycle bill. If the tariff changed during the period, divide the data into the applicable schedules before applying prices. The aim is a reproducible calculation, not a visually impressive chart with mismatched dates.
Calculate the baseline peak share
For each interval, multiply kWh by the applicable cents-per-kWh price divided by 100. Sum the energy and cost in each band, then add the fixed monthly charge. Peak share is total peak kWh divided by all billed kWh. If there are more than two bands, keep all of them; do not combine a shoulder band with off peak unless the price is actually the same.
Illustrative baseline: a home uses 800 kWh, including 320 peak kWh and 480 off-peak kWh. Peak share is 320 ÷ 800 = 40%. At invented prices of 30 cents and 10 cents, energy costs $96 + $48 = $144. Adding a $12 fixed fee produces $156. A flat 16-cent plan with the same fee would cost $140, so the time-based plan is $16 more in this example.
Identify a specific moveable load
Choose one realistic action and estimate the kWh involved. For example, an illustrative charging schedule might allow 80 kWh to move from peak to off peak during the month. Do not claim that every appliance running in the peak window can be moved. Refrigeration, essential equipment, and comfort needs can limit flexibility. Follow equipment instructions and avoid unsafe unattended operation.
| Illustrative case | Peak kWh | Off-peak kWh | Energy cost |
|---|---|---|---|
| Original pattern | 320 | 480 | $144 |
| Shift 80 kWh | 240 | 560 | $128 |
| Shift 160 kWh | 160 | 640 | $112 |
The first shift changes peak share to 30% and reaches equal cost with the illustrative flat rate. The second would reach 20%, but it is only a hypothetical case unless the household has enough practical flexibility. Total consumption remains 800 kWh in this table; if the new schedule changes consumption, update both quantities.
Test the full household schedule
Review morning preparation, work-from-home hours, dinner, laundry, charging, and cooling or heating. Ask everyone who uses the home which changes are sustainable. A timer can fail, a vehicle can arrive late, and a school or work schedule can change. Test a less successful scenario rather than assuming perfect compliance every day.
Consider whether the shifted task finishes before the expensive window begins. A charging session scheduled to start off peak can continue into peak hours. Estimate its duration and use measured charging energy if available. If one person must continually supervise the plan to achieve a small saving, include that burden in the decision. Savings calculations do not capture inconvenience automatically, but the household still experiences it.
Validate with a complete billing cycle
After a safe trial, compare actual interval data with the modeled schedule. Check whether energy moved, whether total consumption changed, and whether the utility used the time windows you expected. Look at a high-use season before making a year-round conclusion. A mild month's favorable result does not prove a summer cooling pattern will work equally well.
The time-of-use calculator accepts a two-band peak-share estimate and different fixed fees. It does not import interval files or model three bands, special events, or demand charges. If your tariff includes those features, retain the detailed worksheet or use the utility's official comparison tool after checking its assumptions. Do not compress a complex tariff into the site's simpler inputs merely to obtain an answer.
Record a failed trial too
If the intended load did not move as planned, keep that result in the worksheet. A missed timer, changed workday, or longer charging session is evidence about how practical the schedule is. Repeatedly deleting inconvenient days would make the model look cheaper without making the household bill cheaper. Use observed limitations to choose a sustainable scenario.
FAQ
How much usage must I shift?
It depends on the rate difference, fixed fees, starting peak share, and total kWh. Calculate an equal-cost threshold for your actual terms.
Does shifting always lower energy use?
No. It changes timing. Total kWh can stay the same, decrease, or increase depending on the task and strategy.
Can I use one week's data?
It can support an initial experiment but may not represent weather, holidays, and seasonal schedules. Review a broader period before drawing annual conclusions.
Related reading
Sources
- EIA: time-based utility programs — tariff types and data limits.
- DOE Energy Saver guide — household load shifting context.
