The 28 plug-ins circulated between 140 different households for nine weeks each. Each time a new household was given a car, it was randomly assigned to have either an "unmanaged" (where drivers could charge up any time) or "managed" (where the cars came programmed to charge only between 10 pm and 6 am every day) charging profile. The households could change from one to the other whenever they wanted.
Here's where we learn something we suspected. The households were split roughly 50-50 into standard electricity rates and time-of-use electricity rates. CU found that, if the utility didn't offer incentives to charge the car, drivers didn't either. So, if you were were paying standard rates, you liked unmanaged charging. If you paid less at night, well, then you liked it when your car charged up at night. The "set it and forget it" mindset was popular.
Which brings up a more interesting finding. Even though sponsors Toyota and Xcel Energy offered online information about how each household was using electricity in their cars, "most were not interested in using it to control their vehicle charging," said Barbara Farhar, principal investigator, in a statement. Most here means "approximately 90 percent" that just barely used the websites, some never did.
AutoblogGreen asked Toyota representatives how this information could be used as the company tries to sell more Prius Plug-Ins around the US. Jaycie Chitwood said that starting the study took longer than anticipated, including installing smart meters and getting households through the screening process.
"We would have wanted this information a year ago, but we didn't, so we had to launch our first-generation plug-in hybrid without the benefit of some of this data," she said. Earlier Toyota research showed that people wanted more electric vehicle range for less money than is realistic – 30 to 50 miles of electric range for just $1,500 or $2,000 extra – and some of the CU data showed this as well. Toyota tested about 150 vehicles throughout the US, but the CU study was focused on "these greater questions about, if you give people the tools and the information and the price incentive, will they manage their charging energy and how do they feel about being managed and how does that impact how they feel about purchasing a vehicle. These are things that will help us moving forward, not just in the sales process. It's going to impact how people feel about the car."
You can find more information, including slides from the researchers who conducted the study, on Toyota's ESQ website here.
Households with plug-in hybrid vehicles, or PHVs, and smart meters actively managed how, when and where they charged their cars based on electricity rates but rarely took advantage of online feedback, a University of Colorado Boulder study found.
CU-Boulder's Renewable and Sustainable Energy Institute, or RASEI, today presented findings from the two-year study -- one of the only of its kind, combining both household and vehicle data in a smart-grid context.
"Although households had access to online feedback on electricity use, we were surprised that most were not interested in using it to control their vehicle charging," said Barbara Farhar, principal investigator and senior research associate at RASEI. "However, households still actively managed their charging in other ways."
The study was sponsored by Toyota Motor Sales U.S.A. Inc. with the integral partnership of Xcel Energy.
A total of 142 smart-metered households were randomly selected to participate from among early volunteers for Boulder's SmartGridCity project. Toyota loaned 28 Prius Plug-in Hybrid demonstration program vehicles to the study and Xcel Energy installed smart plugs in the garages of study households. Each household used the car for one nine-week period.
Households had access to two websites. One served as a nearly instantaneous meter of vehicle electricity consumption when the car was plugged in. The other website gave delayed feedback on overall household electricity use. Approximately 90 percent of the households looked at the websites only a few times or less. Some never looked at the websites.
Households created distinct methods of managing their vehicle charging based on personal preferences, pricing and convenience.
Initially, approximately half the households were randomly assigned to an "unmanaged" scenario, allowing PHV charging through their in-home smart plug at any time of day. The other half were randomly assigned to a "managed" scenario, which meant their smart plugs were initially programmed to charge only from 10 p.m. to 6 a.m. daily.
Households were shown how to change their charging scenarios from "managed" to "unmanaged" or vice versa and were free to alter the scenarios in any way they wanted. Approximately half of the households had standard and the other half had time-of-use electricity rates.
Most of those with standard electricity rates preferred the "unmanaged" scenario, and most of those with time-of-use rates preferred the "managed" scenario, many using a "set it and forget it" approach. Quite a few found the time constraints of the "managed" scenario inconvenient.
"Electricity pricing appeared to drive charging behavior and time cost or convenience was also very important," said Farhar. "People loved not having to go to the gas station."
Other findings of the study included a high level of satisfaction among households with the car, but a low level of satisfaction with its electric-only range, about 14 miles of cruising from a full charge, which took three hours in a regular 110-volt outlet.
The PHVs averaged 68 mpg on gasoline and were used for an average of 3.2 trips per day. Altogether, the cars used 27 megawatt-hours of electricity. It was less expensive to drive on electricity as a fuel than gasoline, even when paying higher on-peak electricity rates, according to an Xcel Energy analysis.
Some households charged at locations other than home. Using data from the vehicles, study investigators are continuing to look into where and when away-from-home charging took place.
The two-year study also allowed Toyota to test the PHVs in the Colorado environment including high altitudes, temperature extremes and mountainous terrain.
"The RASEI study demonstrates the importance of testing new technologies with real customers in everyday circumstances," said Bill Reinert, Toyota advanced technology vehicle national manager. "The results are often unexpected but help us understand the needs of potential customers and how to successfully introduce advanced technologies to the market."
Dragan Maksimovic, CU-Boulder professor of electrical, computer and energy engineering, was the study's co-principal investigator. Alison Peters, managing director of the Deming Center for Entrepreneurship at CU- Boulder's Leeds School of Business, was the senior manager.
RASEI is a joint venture with the U.S. Department of Energy's National Renewable Energy Laboratory. For more information visit http://rasei.colorado.edu/.