NREL Explores Benefits of Solar-Powered Charging For Plug-in HEVs

Jan 24, 2008 2:51 PM
by David Morrison, Editor-in-Chief, Power Electronics Technology

Markel’s group is currently installing the hardware needed to permit controlled charge and discharge of the Prius PHEV’s battery. Markel expects that in the next couple of months, the vehicle will start generating data on the charge and discharge capabilities of the vehicle.

One of the issues that this research will address is how can utilities and auto consumers get the greatest value out of the battery. One aspect of this issue is the amount of wear and tear on the battery that will result from the utility using it for storage of the solar-generated energy.

Markel hopes that the experiments on the recharge station will highlight how PHEVs could potentially expand the market for renewable energy by powering both vehicles and the grid. He notes that the recharge station will also serve as an example of what NREL would like to do on a larger scale within its own facilities. NREL is currently planning an expansion that will provide the lab with additional parking lots. Experiments on this first recharge station could pave the way for NREL to install charging stations in the new lots.

NREL’s Prius was originally a standard model that was converted to a plug-in hybrid by Energy CS, an engineering firm that provides consulting and design services. Among the changes made in the conversion was the replacement of the Prius’s original battery pack with a unit supplied by Hymotion, a green technology company This battery pack uses Li-ion phosphate technology (a less volatile version of the Li-ion chemistry used in consumer electronics) supplied by battery developer Valence Technology.

According to Markel, the Li-ion phosphate battery pack has an available battery capacity of 9 kWhr. However, Markel notes that actual capacity in the Prius is about 6 kWhr because the Prius’s power train was not originally designed for the PHEV application. The 6-kWhr capacity equates to 50 miles of “blended” driving range where the vehicle is taking power from both the batteries and the gas engine.

For NREL’s Prius PHEV, the mode of operation depends on both vehicle speed and acceleration. Below 35 mph and with only light accelerations, the PHEV runs purely off battery power. Above those thresholds, the vehicle transitions into the blended driving mode. For more information, email Tony_Markel@nrel.gov.

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