Grid-Connected Cars and Renewables: Understanding the Potential
09 July 2006
From Renewable Energy Access
The prospect of having millions of vehicles plugging in to the nation's
electric grid in the coming decade has never been better. The car-buying
public has firmly demonstrated the commercial viability of hybrid electric
vehicles (HEV), with HEVs reaching 1% of new car sales in 2005. Most vehicle
manufacturers are betting on this trend accelerating in the coming years, and
are rushing to bring hybrid vehicles to their dealer's showrooms. The
evolution of HEVs to allow charging from the electric gird is assumed by many
as desirable, and I would argue inevitable. The underlying economic and
national security advantages of displacing gasoline with electricity are
"As the vehicle fleet moves toward at least partial electric drive and grid
charging, this creates the opportunity for renewables -- beyond biofuels -- to
serve as a source of energy for the transport sector."
- Steven Letendre, The Prometheus Institute for Sustainable Development
While the renewable energy community is generally supportive of PHEVs, they
have yet to fully appreciate the new opportunity that this would create for
their industry. As the vehicle fleet moves toward at least partial electric
drive and grid charging, this creates the opportunity for renewables -- beyond
biofuels -- to serve as a source of energy for the transport sector.
Although solar photovoltaics (PV) is not viewed as cost-effective without
significant subsidy when compared to grid power, it begins to look interesting
when compared to the price of gasoline for transportation. Furthermore, the
opportunity that solar hybrids offer is exciting, whereby a new generation of
solar PV technology is developed specifically for vehicle integrated (VIPV)
applications (see Solar Today, May/June 2006, Letendre, Perez, and Herig).
Growth in VIPV applications could one day mimic the current explosion in new
product development for building integrated PV applications. While PV may serve
just a small part of a vehicle's overall energy needs, the modest additional
costs from a 500 watt VIPV system may be well worth the investment. VIPV should
be considered as an avenue to enhance a PHEV's overall efficiency, similar to
It is generally understood that PHEVs would charge during the evening and early
morning hours when electricity demand is low and there is significant excess
capacity available on the network. In some areas, wind resources are strongest
at night, thus allowing wind power to serve as an energy source for vehicles.
With smart charging, the rate of charging could be adjusted to match the power
production from a distant wind farm. I can envision interesting marketing
schemes whereby PHEVs are sold in conjunction with a wind power supply contract
further enhancing the vehicle's "green" attributes.
The potential of grid connected cars is even more exciting when the notion of
vehicle to grid (V2G) is considered. The emerging V2G concept envisions grid
connected cars with bi-directional chargers that both accept power from the grid
and deliver power to serve different ancillary services markets. Initial
economic analyses suggest that V2G capable vehicles could generate significant
revenue for vehicle owners by providing specialty grid services such as
regulation (frequency response) and spinning reserves. Ratepayers pay over $1
billion for these services each year.
The battery wear and tear from providing these services would be minimal given
that regulation services would include both charging and discharging energy from
the vehicle's battery pack in response to signals from a grid operator striving
to maintain grid frequency at 60 Hz. Spinning reserves is another ancillary
service needed to maintain grid reliability; these reserves are infrequently
called upon, and when they are dispatched, are only used for a short duration
and thus would have minimal impact on the vehicle battery pack.
While a small number of PHEVs have been built and are being tested, there are
still hurdles to be overcome, the most important of which is the batteries. The
U.S. Department of Energy recently convened experts from across the country to
discuss the potential of PHEVs. While batteries were identified as a key
technical challenge, the general consensus was that this barrier can be
overcome. Additional research and development funding should be directed toward
developing advanced batteries for PHEV applications. There is general agreement
among electro chemical engineers about the potential that lithium-ion (Li-ion)
batteries offer in serving the hybrid vehicle market. In fact, several battery
companies are currently developing Li-ion battery packs for vehicle
A more distant potential that grid-connected cars may offer is their role in
serving as storage to allow greater penetration of intermittent resources on to
the nation's electric grid. I envision a future with millions of vehicles
connected to the electric grid providing storage to allow large amounts of wind
and solar to become seamlessly integrated in to the electric grid ushering in a
truly sustainable energy future. In addition, PHEVs would require less liquid
fuels making it more likely that biofuels could meet the challenge of displacing
100% of petroleum as a transport fuel.
While the renewable energy community must address a number of issues, I would
urge renewable energy industry associations and advocacy organizations to join
the growing chorus directed at the major automobile manufacturers to commit to
bringing PHEVs to the market place. Grid-connected cars offer many fascinating
opportunities to allow renewables to play a greater role in fueling society's
About the author...
Steven Letendre serves as the Director of Research at the Prometheus
Institute for Sustainable Development, located in Cambridge, MA. Dr. Letendre
has over ten years of research experience in the field of renewable energy. He
has published widely on the topic of solar energy and advanced vehicle concepts.
Dr. Letendre has served as a consultant on a range of projects for a variety of
organizations including the National Renewable Energy Laboratory, California Air
Resources Board, Union of Concerned Scientists, Northeast Sustainable Energy
Association, and SUNY Albany's Atmospheric Sciences Research Center. Prior to
joining the Prometheus Institute, Dr. Letendre was an Associate Professor of
Business and Environmental Studies at Green Mountain College in Poultney, VT. In
1997, he received a Ph.D. from the University of Delaware in Urban Affairs and
Public Policy with a concentration in energy policy and economics. In addition,
he holds a masters degree in economics from Binghamton University, formerly
State University of New York at Binghamton. Prior to pursuing his doctoral
studies, Letendre was employed as an energy economist with the Research Triangle
Institute in North Carolina.
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