In order to keep zero-emission vehicles in cold climates both warm and truly zero-emission, alternative heating systems must be devised which are not powered by fossil fuels. Heating of electric vehicles presents a considerable challenge if batteries are not to be used as a source of energy in order to keep the vehicle range up. It appears that kerosene heaters are presently used in many electric vehicles in cold climates.

Solar electric systems can provide energy to charge the batteries of electric vehicles so that the vehicles are truly zero-emission. However, using electricity for space heating is not the most efficient strategy from a thermodynamic point of view. In this study a solar thermal system was designed in detail to provide space heat for an electric bus. The system could be scaled appropriately for an electric car or for fleets of vehicles.

The system was sized to provide heat to keep the driver's area at 27 C in an existing "winterized" electric bus in Lowell, MA during the equivalent of five hours each day down to –18 C ambient. Other analysis (Duffy, Reinhardt, and Chien, 1996) has shown that the total heating season load during ten hours a day each school day with Boston TMY, taking into account passive solar gains, is equivalent to the above (1300 kWh/year).

Based on the specifications and on system's analysis, a systematic search was used to determine the best of several alternative design approaches, with the help of a morphological matrix. A detailed finite-difference model was developed with MATLAB to simulate the thermal performance.

A solar collector with an area of 31 m2 on the garage roof and an underground water storage tank of 6 m3 were designed to provide 90% of the needed energy. A heat pump system was designed to transfer heat from the tank to the heat storage in the bus. The electricity for the heat pump provided the other 10%. The heat storage system in the bus (designed and built by Chien, Duffy, and Reinhardt) is based on phase-change material CaCl6. The PCM is charged to 45 C. Excess heat can be used for garage space heat and warm water for washing vehicles.

With an estimated 20-year electricity savings (7 cents/ kWh at a 3% inflation rate and a 5% discount rate) of roughly $2300 for bus heating and another $5300 for other uses, it would be hard to justify the cost of such a system at today's energy prices. However, it shows, at least in the design phase, that an essentially-true-zero-emission system is possible and that electric vehicle infrastructure must not be neglected.

For more information contact John_Duffy@uml.edu