Simanaitis Says

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ONE HUNDRED and forty two families in Boulder, Colorado, received Toyota Prius Plug-in hybrids for 9-week stints. Scads of data collected over two years on recharge strategies, trip length, user feedback and other parameters gave researchers at the University of Colorado at Boulder a better understanding of PHEV use in a smart-grid environment.

Attendees at Toyota’s 2012 Future Mobility Seminar got a first look at results presented by Dr. Barbara Farhar, sociologist at the university’s Renewable and Sustainable Energy Institute, a joint effort with the National Renewable Energy Laboratory; and Dr. Dragan Maksimovic, professor of electrical, computer and energy engineering at the university.

Boulder demographics, it can be noted, aren’t exactly U.S. average: highly educated, very liberal politically and extremely environmentally active (to the point of the city establishing its own cap-and-trade emissions program).

All of the participating households were smart-metered, with access to two websites offering data. One had nearly real-time feedback on PHEV recharge; the other, with lagged information of total household electrical use.

Participants were initially placed in this 2×2 matrix defining their characterisitics of PHEV recharging and home electric metering. They were free to modify strategies at will.

The “Managed” scenario had smart plugs programmed to charge only from 10 p.m. until 6 a.m. daily. “Unmanaged” participants could recharge their PHEV anytime and anywhere. A Prius PHEV needn’t be plugged in at all, of course, because it can operate, albeit less efficiently, in the manner of its conventional HEV sibling.

Approximately half of the households paid standard rates recorded through electric meters without Time-Of-Use monitoring. Those with TOU meters got lower electrical rates during off-peak hours countered by higher ones during peak times.

Most with standard electricity rates eventually settled into the Unmanaged scenario. Most with TOU metering preferred Managed, many opting for a set-and-forget approach.

Generally, no one bothered with the interactive options of the websites. Approximately 90 percent of all four categories looked at the websites only a few times. Some never looked at all.

Toyota Prius Plug-in hybrids were given to participants for 9-week stints. The program included 28 cars and 142 households over two years.

Over the two-year study, the Prius PHEVs averaged 68 mpg in their gasoline usage. The cost of their plug-in electricity (as opposed to that of the Prius PHEV’s own generation) was figured to be less than that of gasoline, even in households recharging at peak electricity rates. The Boulder sample spent 42 percent of its driving in EV mode; the national average for Prius PHEV use is 27 percent.

An important aspect of the study was testing the Prius PHEV in Boulder conditions, high altitude, mountainous terrain and extremes of temperature. For instance, researchers reported range degradation of around 11 percent in cold-weather driving and as much as 21 percent in hot conditions. Boulder is known for its climate extremes, with -25 and +105 degrees Fahrenheit on the books.

Another aspect was analyzing the means and location of remote recharge. At not inconsiderable cost (figured at around $10,000 per hookup), Boulder has a fair number of public-access nominal-220-volt Level 2 charge units. Some of these proved to be inconveniently located; others with fees for charging were perceived as expensive. Researchers are in the process of analyzing where and when away-from-home charging took place.

This is the second of several pieces gleaned from the 2012 Toyota Future Mobility Seminar in Denver, Colorado, Oct. 16-17. See also, and others to follow. ds

© Dennis Simanaitis,, 2012

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