The future is now: Grid-tied electric vehicles

At Southern New Hampshire University, as a complement to our work on renewable energy hedges, we are working to transform energy use on campus. One project under way is a system of grid-tied electric vehicles (Vehicle to Grid, or V2G) combined with a solar photovoltaic charging system and smart computer control.

The V2G plug-in hybrids and electric vehicles will replace traditional fossil fuel cars on campus and become an economic source of power for the electric grid during peak times. V2G cars can help balance the system load, reduce storage requirements, and reduce the need for fossil fuel baseload plants.

Hybrids and electric vehicles can now use lithium ion batteries to become V2G plug-ins, either as original equipment or as supplementary aftermarket power modules. Lightweight lithium ion batteries have greater power density and are capable of thousands of charge cycles, making them suited to the grid’s fluctuating need for power.

On campus, we are designing a small, experimental, grid-tied parking lot that charges vehicles via an overhead photovoltaic (PV) array. The system will monitor vehicle battery charge, solar output and New Hampshire electric system demand.

With a real-time controller (designed, built and tested by my associate Pentti Aalto), we can respond to price signals from the five-minute electric grid spot market (ISO New England). A rise in demand on the electric grid is reflected in spot prices for power. When the grid calls for more power, we would feed in the available surplus from the car batteries and the PV charging system, thus helping to reduce spot prices and satisfy the system’s need for power.

We plan to start simply with electric campus service vehicles, adding batteries to extend their range and improve V2G charging capacity. We’ll then focus on converting hybrids owned by volunteer staff, faculty or students, modifying them to be V2G plug-ins.

The parking lot PV system will feed the grid directly or charge the vehicle batteries. The vehicles will make money selling power into the grid during high-load conditions by responding to five-minute spot market price signals above, for example, 25 cents per kilowatt-hour. In the future, our V2G cars will act as power sources, making money for us and keeping the grid in balance.

A V2G car with fully charged batteries (4 kilowatt-hour capacity) could provide the grid with 10 kW of power for 12 minutes (50 percent maximum discharge). Five million parked cars could provide 1,000 megawatts of power for an hour during peak times with a 2 kW total discharge. 1,000 MW is the size of a very large baseload coal or nuclear plant.

Overall, vehicles optimized for V2G power could provide even more energy into the grid. In 2001, there were 230 million cars, trucks and buses in the United States.

Parking lot solar can be easily integrated into plug-in electric charging stations. It also provides shade for cars, and can thus reduce the energy needed to cool a hot car when starting it up during the summer. The system also can markedly increase the value of the parking area without requiring the use of any new land.

There is plenty of parking area in the United States — an estimated 19 billion square meters — a reasonable fraction of which is suitable for PV.

In 2007, Kyocera installed a 25-panel, 235 kW system above a 186-vehicle parking lot. Google switched on a 1.6-megawatt rooftop and parking lot installation at its California headquarters last year.

Companies such as A123Systems of Watertown, Mass., are bringing to market nanotech-based lithium ion devices to convert hybrids to plug-ins. Their product is designed to increase the efficiency of a Toyota Prius from 46 mpg to 100 mpg or more by extending vehicle electric range. Initially, it will not feed power back into the grid. Conversion kits will be commercially available in 2008.

Smart grid control

A key aspect of achieving the promise of V2G systems and a renewable electric grid is the ability to implement smart control between the electric grid, user devices, power sources such as V2G batteries, distributed generation such as PV, cogeneration and heat pumps.

Our control algorithm, a major feature of our work, must be able to:

• Choose grid and/or PV power to charge vehicle batteries to required levels

• Balance the need to feed PV power into the grid or charge car batteries based on the price of power and the levels of battery depletion

• Use available V2G car battery power to provide short-term power into the grid, based on price signals reflecting system needs and peak load

• Keep accurate track of the monetary value of grid power consumed and of PV and car battery power sold to the grid

Using our prototype real-time controller, we scrape the five-minute price signal from the ISO New England Web site and send it via the Internet to a satellite pager network. The programmable controller, using our algorithm, will efficiently and economically operate and monitor the vehicles, the PV charging system, and the grid interface.

In the future, we should be able to use two-second ISO New England price and load signals to automatically control electric loads at SNHU and distributed power sources, such as V2G car batteries and cogeneration units. This real-time smart grid will reduce pollution, be more stable and efficient, minimize and optimize electric use, and integrate centralized and distributed renewable power and energy storage.