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Saturday, April 27, 2013

Time for Gallons of Sunshine - Time of Use rate for EVs

How do electric vehicle (EV) charging, solar photovoltaic panels (PV), and time-of-use (TOU) electricity rates play together.


It is not possible to give a blanket answer to whether TOU will work for everyone, but I can use my example as a case study that may help you determine if it might work for you.

I live in Beaverton Oregon. My electric company is Portland General Electric (PGE), not to be confused with Pacific Gas & Electric (PG&E) of California. Portland General offers a time of use billing rate and they are encouraging EV drivers to use this plan. With standard service, you pay the same amount for a kilowatt-hour no matter what time of day it is. With time-of-use, there are three different rates depending on the time of day: Peak, Mid-peak, and Off-peak.

Electricity is relatively cheap here so I was not sure I could save much. Reading their website, they said if you can shift 50% or more of your use to off-peak, then you would generally save money. I didn't want to worry about what time it was when I turned on the TV or anything else. Electricity is a convenience, I don't want the inconvenience of waiting until 10PM to start the laundry. So if this was going to work, it had to work with the routine that my family and I have currently.

PGE's website had some good "usage shift" suggestions such as using a programmable thermostat for heating and cooling and using a timer on your water heater. We already have a Nest thermostat and our water heater is tankless, so none of these would help us shift our usage any more than we already have.

There were two items that I thought would help make TOU work for us: one, we have a 4kW solar array on roof and two, I drive an electric car that charges up overnight.

The solar panels produce electricity during the day, thereby reducing our peak demand. The electric car can be programmed to charge up at any time you'd like. I have it set to start charging at 3AM. This allows it to be fully charged by 6AM when the rates go up.

Note: of all my rate quotes, I am including any charge, tax, or fee that is scaled per kWh. All flat fees are ignored since they are fixed and must be paid (assuming I want electrical service).

Even with these two items, I was concerned. The standard rate for electricity is 6.778¢ per kilowatt-hour (kWh). With TOU, during peak, I would be paying 13.266¢. That is about twice as much! PGE had a clause that alleviated this concern. After one year on TOU, they would evaluate your past year of bills and if you did not save money with TOU, you would only have to pay, at most, 10% more than the standard rate.

This limited the risk and allowed me to sign up knowing that even if things went far differently than I expected, it wouldn't add much if any to our annual bill. We gave it a shot.

So here we are 12 months later. We have been on TOU for one year now. I received what I expected to be my year-in-review notice. However, I was disappointed to see that the letter, rather, just told me how to use their online calculator to do my own annual analysis. So I followed the directions, and 36 copy and pastes later each month's data was computed. I made my own spreadsheet of the results below:

Month Peak%Mid-Peak%Off-Peak%ToU Savings

April 201325%20%55%$2.63

March 201325%23%52%$1.64

Feb 201327%26%46%-$1.76

Jan 201322%30%49%$4.00

Dec 201221%30%49%$4.31

Nov 201219%34%47%$3.96

Oct 201214%33%54%$7.13

Sept 201219%40%41%$2.42

Aug 201215%36%49%$9.18

July 201214%33%53%$9.40

June 201212%31%57%$11.20

May 201213%28%59%$11.14

As you can see in the table, TOU saved us money nearly every month. The one exception was Feb 2013. Our solar panels don't make much in the winter months. The panels are west facing. Combine that with our location (north of the 45 parallel) and you'll see an exaggerated seasonal variation for our solar output.

This one outlier was more than compensated for by other months. The best months are in the spring when it is sunny, but not so hot as to require the air conditioner. We saved over $11 in each May and June.

For our one year on TOU, we saved a total of $65.24.

In the beginning, I asked: EV+PV+TOU=???

I can now tell you that for us, without changing any of our usage patterns, it equaled enough saving to fuel more than 3500 miles of EV driving.

Time-of-use allows our solar panels pay off faster because now they are offsetting a ~13¢ rate rather than a ~7¢ rate.

TOU also made it cheaper to charge up the car. The car is now being fueled with electricity at the off-peak rate of 4.422¢ per kWh rather than the standard 6.778¢ rate. That is a 35% reduction in fuel cost. I think most people would be happy with a 35% reduction in prices at the pump. I just happen to be using an electron pump. 

$65 annually is not a lot, but if the utility asked me if I would want an annual $65 reduction on my bill, the answer would be 'yes'. When we get a second plug-in vehicle, it will get even better. Now that I know we are going to stay on the TOU program, maybe I will go get a timer for our koi pond and take another look at the list of tips to shift energy usage.