Edison Rates by Time of Day: How the Windows Work

Switching does not discount the load you move — it reprices every kilowatt-hour the house uses, which is why the answer is in your own interval data.

A time-of-day rate replaces one price per kilowatt-hour with several,
depending on when the energy is used. For a household with a car charger and a
predictable evening routine that can be worth real money. For one that is home
all day with resistance heating it can be the opposite, and the difference is
not a matter of opinion — it is in your own usage data.

Edison Rates by Time of Day: How the Windows Work

The structure is consistent even though the numbers are not. The day is
divided into defined periods — typically a peak window and everything else —
and each carries its own price. Those definitions and prices live in the
utility’s filed rate schedule, which is a public document, and they are revised
on their own schedule. So the honest position of any article is that the
mechanism is stable and every figure belongs to the tariff.

Three things about the structure are worth knowing before you look one
up.

• The windows are seasonal. The peak period is defined
  differently in the warm months than in the rest of the year, because the system
  peak itself moves.
• Weekends and holidays are usually treated differently from
  weekdays, which materially changes the arithmetic for households whose heavy use
  is at the weekend.
• Supply and delivery can each vary by time. The bill has two
  sides, and a time-varying element on one does not imply it on the other. Reading
  your own bill’s structure first, as in
  a Con Edison bill read line by line,
  makes the tariff much easier to interpret.

Why the utility offers it at all

The cost of running an electricity system is driven disproportionately by its
peak. Capacity has to exist for the worst hour of the year even though it sits
idle most of the time, so energy used during those hours genuinely costs more to
deliver than energy used at three in the morning. A time-of-day rate passes that
structure through to the customer, and the customer who can move load gets paid
for doing it. Who that helps and who it does not is set out in
who benefits from a time-of-use rate.

What actually moves, and what does not

Car charging is the standout because it is both large and completely
indifferent to timing, which is why the arithmetic in
cost per mile to charge
splits into two numbers on this kind of rate. Heating is the harder case, since
a heat pump running through a cold snap runs when it is cold rather than when
it is cheap — worked through in
running a heat pump on a time-of-use rate.

The trap: it reprices everything

This is the point most people miss. Switching does not add a discount to the
load you shift; it applies a different price structure to every kilowatt-hour
the house uses. A household that moves its charging overnight but keeps all its
other consumption in the peak window may still finish worse off, because the
shifted load was never the majority of the bill.

So the question is not “can I move my car charging” but “what share of my
total consumption falls in the peak window, and how much of that share can
actually move”.

Answering it with your own data rather than your intuition

1. Get the peak and off-peak definitions for your service class out of the
   filed rate schedule, including how the seasons and weekends are treated.
2. Get your own interval usage from your utility account. A smart meter records
   it, and most utilities make it downloadable — the same account page behind
   finding your monthly kilowatt-hours.
3. Classify each interval into the tariff’s windows and total each bucket.
4. Price both buckets under the time-of-day schedule, and price the total under
   your current one.
5. Then, separately, model what changes if the loads you can genuinely shift
   move. Two numbers: as you live now, and as you would live.
6. Ask your utility whether it publishes a rate comparison tool that does this
   for you, because several do and it saves the arithmetic.

Use a full year if you can. Consumption is strongly seasonal and a summer-only
sample flatters or punishes the comparison depending on which month you took —
the shape described in
why a year of bills looks the way it does.

Storage changes the answer completely

A battery makes a time-of-day rate work without anyone changing their
behaviour: it charges when energy is inexpensive and discharges during the peak,
so the household’s consumption pattern becomes irrelevant to its billing
pattern. That is the clearest use case for storage on this kind of rate and it
is set out in
battery storage on a time of use rate.

If you also export solar, the interaction between what you export and how it
is credited is a separate question from the rate itself, and it is worth
settling before switching —
how Con Edison net metering credits work.

Before you switch

• Confirm the rate is available for your service class, not just for
  residential customers generally.
• Ask whether there is a minimum period before you can switch back.
• Confirm when a switch takes effect — normally on a meter read rather than
  on request.
• Check whether the change interacts with any programme or credit you already
  receive.
• Re-run the comparison after a year, because both your usage and the tariff
  will have moved.

Done that way this is a straightforward decision with a defensible answer.
Done on intuition it is a guess, and it is a guess that reprices the whole
house.

Frequently Asked Questions

How do time-of-day rates work?

The day is divided into defined periods, typically a peak window and everything else, with a different price for each. The definitions and prices live in the utility’s filed rate schedule, which is public and is revised on its own schedule, so read the tariff rather than any secondary summary for the current hours and figures.

Are the peak hours the same all year?

No. The peak period is normally defined differently in the warm months than in the rest of the year, because the system peak itself moves seasonally. Weekends and holidays are also usually treated differently from weekdays, which changes the arithmetic considerably for households whose heavy use falls at the weekend.

Which household loads can actually be shifted?

Car charging almost completely, because the car sits still overnight. Water heating substantially, because a tank stores heat. Dishwashers and laundry, with a delay timer. Battery discharge entirely and automatically. Cooking, lighting and electronics essentially not at all, and heating and cooling only at the edges through pre-conditioning.

Will switching save me money if I charge my car overnight?

Not necessarily, and this is the most common mistake. Switching does not discount the load you move; it reprices every kilowatt-hour the house uses. If most of your other consumption still falls in the peak window, the shifted charging may not be enough to offset it. The question is what share of total usage is in the peak, not whether one load can move.

How do I work out whether it is worth it?

Get the window definitions from the filed rate schedule, download your own interval usage from your utility account, classify each interval into the windows and price both buckets under each rate. Then model separately what changes if the loads you can genuinely shift move. Use a full year, because consumption is strongly seasonal.

Does a home battery change the calculation?

Completely. A battery charges when energy is inexpensive and discharges during the peak, so the household’s consumption pattern stops mattering to its billing pattern. That decoupling is the clearest argument for storage on this kind of rate, and it works without anyone changing their daily habits.

Can I switch back if it does not work out?

Usually, but ask first whether a minimum period applies before you can change again, and confirm when a switch takes effect — normally on a meter read rather than on the day you request it. It is also worth checking whether the change interacts with any programme or credit you already receive.