No one can predict what future vehicle technology will dominate the new
car market, but it appears that electric drive will be a key feature. The use of an electric-drive component in a
hybrid vehicle configuration dramatically improves a vehicle's fuel economy. Hybrid electric vehicle technology has emerged as an option for consumers seeking less polluting,
energy efficient vehicles, with most auto makers offering a hybrid model or announcing plans to do so in the next several years. In the future, many believe that fuel
cell powered vehicles using electric drive and some battery storage will prove to be commercially viable.
of hybrid electric vehicles means solar-fueled transportation may
be at hand along with
a new solar market.
Given this shift in the new vehicle market to models with at least partial electric drive incorporating a
battery storage component (larger than those used with conventional
internal combustion engines), the opportunity now arises for electricity generated from solar photovoltaics (PV) to serve a portion of the energy needs for transportation. The potential for solar energy to meet transportation needs largely will depend on future vehicle designs and the amount of PV manufactured for use in vehicle charging, whether in stationary or
vehicle integrated PV (VIPV) applications.
We believe that VIPV may offer advantages over the use of a stationary PV system for charging hybrid electric vehicles. Imagine that one-third of the 16 million new vehicles sold in the United States in 2004 were integrated with 200 watts of photovoltaic capacity each. That would represent more than 1,000 megawatts of
PV, comparable to the capacity output of a large electric power plant. The potentially modest up-front cost of integrating PV into the vehicle's body panels may be offset by the consumer appeal of a solar hybrid or the economic value associated with the efficiency improvements derived from VIPV. Could VIPV be the route to
large scale solar transportation and the next hot market for solar photovoltaics?
Past Efforts Were Narrow in Scope
Solar advocates have made a number of attempts to develop PV as an energy source for transportation, but with limited success. One set of experimental projects involved the integration of PV in a parking/shade structure equipped with charging stations for
battery equipped, electric-drive vehicles (EVs). Several parking spaces beneath the solar parking structure would be reserved for EV parking, enabling solar-powered vehicle charging. For instance, the Los Angeles Department of Water and Power (LADWP) built a system that delivers
700 kilowatt-hours (kWh) of solar electricity per day directly to the electric utility grid. The LADWP carport is also equipped with an EV-charging station. As a second example, three PV systems were installed in the parking areas of three North Carolina schools for EV-charging purposes. An analysis of one of the installations found that a 1.87-kW PV array could provide roughly 17,000 miles worth of driving range for an EV.
In the 1990s many were optimistic that EVs would gain commercial success, spurred in large part by the California zero Emission Vehicle (lEV) Mandate. Over the years, the California Air Resources Board has revised its lEV mandate to allow other low polluting vehicles to gain credits. Although several large automobile manufacturers had offered EV models, most, if not all, EV programs have been scrapped in favor of hybrid electric and fuel cell technologies. Thus, it seems unlikely that EVs will emerge as a consumer choice in the near future.
Another attempt to facilitate the use of PV for transportation involves national and international solar car races, which have spawned design team competitions to produce prototype PV integrated vehicles. Every other year, for example, the American Solar Challenge invites teams from around the globe to compete in a grueling 2,000 mile race using vehicles powered only by energy from the sun. In another race, the World Solar Challenge, solar powered cars race across Australia.
Many university based teams have formed over the years to build solar powered vehicles to compete in these races. The students on these technical teams have made significant advances in vehicle design and performance over the years. However, these vehicles were never intended for mass markets. Their impractical design and futuristic appearance is unlikely to appeal to the car buying public.
Hybrids Present New Promise
The emergence of hybrid electric drive vehicles creates a new opportunity for solar to provide some portion of the energy used for transportation. Several major automobile manufacturers offer hybrids, including Honda (with the Civic, Accord and
Insight), Ford (Escape) and Toyota (Prius and Highlander). In addition, most every major automaker has announced plans to begin selling hybrids or expand their hybrid vehicle offerings during the next several years.
What's Ahead in Sustainable Transportation? Solar Vehicles
This Toyota Prius was retrofitted with 270 watts of photovoltaic capacity and additional battery storage. The conversion has increased the fuel economy of the vehicle by 10 percent. Even the big automobile manufacturers are eyeing the vehicle-integrated photovoltaics (VIPV) opportunity. Ford Motor Co. unveiled the Reflex, a diesel-electric concept vehicle with VIPV at the 2006 North American International Auto Show.
Hybrid vehicles use both an internal combustion (IC) engine and electric motor to power the vehicle. The use of the IC engine and electric motor is optimized electronically to deliver the desired performance and achieve superior gas mileage relative to conventional vehicles.
However, there are several approaches to building hybrid electric vehicles. These vehicles sometimes are categorized as mild, full or plug-in hybrids. Though all hybrids offer fuel economy advantages over
IC engine vehicles, full and plug-in hybrid designs offer the best fuel economy. The improved fuel economy is achieved through the use of a large electric motor (with a smaller IC engine) and greater battery storage capacity.
In recent months, excitement has been building concerning plug-in hybrid vehicles, which have the potential to dramatically reduce U.S. dependence on foreign oil. Though no commercially available models exist today in the U.S., researchers have built prototype hybrid electric vehicles that include more battery storage than currently available hybrids and feature plug-in capabilities. Engineers with the California Cars Initiative have converted several Toyota hybrids in this fashion. They claim to improve the vehicle's fuel economy from its Environmental Protection Agency rating of 60 miles per gallon (highway) to more than 100 mpg. The for-profit company
E-V Concepts plans to offer upgrades to Toyota Prius hybrids for 2004 and new model years. The
E-V Concepts upgrades increase the vehicle's battery storage capability and provide plug-in capabilities, and are expected to cost $10,000 to $12,000.
Many advocates of plug-in hybrids believe that getting the major automobile manufacturers to embrace the concept is critical. Plug-In Partners, an effort spearheaded by Austin Energy in Texas, hopes to generate enough nationwide support for plug-in hybrids to convince the major auto manufacturers that a profitable market exists for these vehicles.
Plug-in vehicles create an especially attractive case for solar powered transportation. Similar to the examples cited above, hybrids could obtain a portion of their energy from solar resources using either a stationary PV system or vehicle-integrated PV approach.
A stationary PV system would allow solar to serve as a fuel option only for plug-in hybrid vehicles. In this case, a stationary PV system could feed electricity directly into the vehicle's battery pack.
Alternatively, like vehicles developed for solar car challenges, PV cells could be embedded onto a hybrid electric vehicle's body panels that are exposed to sunlight the hood, roof and possibly the trunk. Ultimately, the degree to which solar displaces gasoline for transportation depends on the amount of energy produced from a PV array whether stationary or vehicle integrated and the efficiency of the vehicle's drive train.
VIPV offers advantages over, or at least complements, the use of PV in stationary applications to provide electricity to a hybrid electric vehicle. Unlike PV deployed in stationary vehicle charging applications, any commercially available hybrid vehicle could benefit from having PV integrated onto the vehicle. Further more, regardless of where the vehicle was parked, provided it was exposed to the sun, solar would be topping off the battery pack or providing ventilation. In future hybrid vehicle designs with greater battery storage, VIPV could offer some mobility even if traditional fuel supplies were disrupted.