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What are Time of Use Rates, & When Is Electricity Cheapest?

Avatar for Ben Zientara
Published on 04/27/2020 in
Updated 04/27/2020
Time of use rates on electric bill

Time of use rates are a kind of electricity billing arrangement in which the price of electricity changes based on the time of day. Also called “TOU rates,” they make electricity more expensive during “peak hours,” when there is high demand, and less expensive during hours of low-demand.

Time of use rates are intended to encourage people to switch their electricity consumption to times when demand is low. In most places around the country, TOU rates are optional, but people who install solar in California are now required to accept a time of use billing arrangement. The rest of the state’s residents will ultimately be shifted to time of use sometime in the future.

Time of use plans can get quite complicated and confusing, which might sound like the opposite of what you want in an electric bill. But there can be advantages to choosing a TOU rate over a flat rate.

If you have the choice between a flat or TOU rate plan, this article will tell you what you need to know about which option is right for you and how you can use time of use rates to save money on your electric bills.

Why do utility companies use Time of Use Rates?

Simply put, utility companies like time of use rates because they help curb demand when lots of people are using electricity. Reducing that “peak” usage saves the utility money because each kWh of electricity costs a lot more to make during peak times. Here’s why:

Utilities have a really good idea about the minimum amount of electricity they need to serve their customers at all times. This is called “baseload power,” and it’s really cheap, because the power plants that make it stay operational at all times and maintain high efficiency.

But power usage fluctuates based on weather conditions, temperature, and more. The utilities “book” this fluctuating level of electricity on a weekly and daily basis, and they end up paying a little more for it than baseload power, because starting up extra power plants costs more money.

Finally, during hours of “peak” usage, utilities need to purchase extra energy on shorter time frames: 1 hour ahead, 15 minutes ahead, and even 5 minutes ahead. This is the most expensive kind of electricity.

Under a rate structure where every user pays a flat amount for electricity, the utility makes less of a profit when lots of people use electricity during peak times, because its average cost per kWh goes up while its revenue stays flat. That’s why utilities invented time of use rates.

The differences between Time of Use and Standard Rates

Most people have a pretty simple electric bill. All month long, they use appliances, electronics, light bulbs, water heaters and air conditioners, all of which adds up as total kilowatt-hours (kWh) of usage. At the end of the month, the utility company sends a bill with a simple calculation: usage times price.

For example, if you use 1,000 kWh of electricity in a month and your rate is $.15/kWh, you get a bill for $150, plus whatever flat fee your utility charges to connect to the grid—usually something like $5 or $10. Under TOU rates, you get billed different amounts for usage at different times of day.

What is the cheapest time of day to use electricity?

The hours of the day when a lot of people are using electricity are called “peak” or “on-peak” times, and the rest are called “off-peak.” Some utility companies also add a “super off-peak” category for hours with the very least demand.

Here’s a screenshot from SDG&E’s website:

SDG&E's time of use example rates

Wow, that’s a lot of numbers, and they’re used just for illustration purposes. SDG&E’s actual rates vary widely and are generally more expensive than the example above.

Basically, the image shows that up until 130% of your “baseline” allowed kWh usage per month, you’ll pay $.25.kWh for “Super Off-Peak” electricity from midnight to 6 am, $.26/kWh from 6 am to 4 pm (except in March and April, which include a second Super Off-Peak period from 10 am to 2 pm), and $.27/kWh from 4 pm to 9 pm. Then if you exceed that baseline, add 7 cents to all those prices. What a mess.

The gist of that imagem though, is that it’s cheapest to use electricity late at night, from midnight to 6 am, when most people are asleep. If you can shift your clothes-washing and drying and electric vehicle charging to the late-night hours, you’ll save some money.

How Time of Use rates change with the seasons

Electricity usage patterns change from summer to winter, so some utilities offer different rates based on the time of year. For example, Southern California Edison offers the same rate from 9pm to 4pm the next day during the summer, but raises the price of nighttime electricity in the winter. Here are two screenshots of the SCE website that show the difference:

Southern California Edison Winter Time of Use rates Southern California Edison Summer Time of Use rates

You may notice from the picture that electricity from 9 pm to 8 am is more expensive than in the summer, and electricity from 8 am to 4 pm is less expensive. This is because people tend to heat their homes more in the winter when they’re home. In this case, it makes sense to shift most of your wintertime electricity usage to the hours between 8 am and 4 pm if you can.

Is time of use metering worth it?

What makes time of use metering a good idea? The answer is it depends on whether you as an individual consumer can shift enough of your electricity to off-peak times.

Here’s an example: at the time we wrote this article, SDG&E’s actual time of use rates were about $.25, $.30, and $.35/kWh for Super Off-Peak, Off-Peak, and On-Peak, respectively. Their flat rate for residential customers was a little less than $.29/kWh.

If a homeowner used 1,000 kWh per month, they’d be billed $290 on the flat rate. If instead they chose time of use billing and used 1/3 of their energy equally on each of the periods, they’d be billed $300. In order to save a couple dollars over the flat rate, they could shift their energy usage so about half occurred during the Super Off-Peak pricing period.

Seems like a hassle, right? It gets even more complicated when you consider the changes in the cost of electricity when you exceed your baseline usage. Those changes can make TOU more attractive, because the TOU rate goes up by 7.5 cents/kWh after you exceed your baseline, whereas the flat rate goes up by 8.5 cents/kWh.

If you’re a heavy user of electricity compared to other people in your area, a time of use rate may save you more money. The key is to check your local utility rates and estimate how much electricity you use during each of the periods. Something that can help with that last step is the Sense Energy Monitor (or similar), which tracks your electrical consumption and can help you decide how to shift your usage or improve energy efficiency.

Do solar panels make time of use cheaper?

In the past several years, residential solar systems have popped up on roofs all over the country. Clean energy is a great benefit to our environment and neighbors, but it can also help save its owners lots of money.

Solar panels don’t specifically make time of use rates cheaper, because they tend to generate the most electricity during off-peak periods, when the sun is high in the sky and people are at work instead of using all the appliances in their homes.

That said, adding solar panels to a west-facing roof can benefit people on time of use rates, because these types of solar installations generate more energy in the late afternoon and early evening, provided they aren’t shaded by trees or other obstructions. The solar energy generated goes directly to reducing you consumption of the most expensive electricity, and kWh sold back to the grid during peak times are worth more if you have a good net metering agreement.

Time of use rates and home batteries

Perhaps the smartest way to save money with time of use rates is to add a home battery. The battery can be charged with electricity overnight during off-peak times, then be used to power your home during peak times, completely eliminating your usage of the most expensive electricity.

Some utilities even have special time of use rate plans for battery owners, like Southern California Edison, whose “TOU PRIME” rates are just $.15 for off-peak, which is 5 cents/kWh less than their other plans’ cheapest prices. In this example, a homeowner using 1,000 kWh per month could save as much as $50/month on electricity by adding a battery to their home, with or without solar.

Of course, combining solar panels with batteries gives you both benefits. Your solar panels make electricity far cheaper than buying it from the utility. Your batteries store the energy for later use. You can save a lot of money this way.

Last modified: April 27, 2020

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