Moving from internal combustion engines to electric vehicles presents several engineering challenges: building a charging infrastructure, improving storage technologies, and updating an aging electric grid. But rather than looking at EVs as strictly consumers of electricity, some visionaries are treating them as a resource, using EV batteries to smooth out minor differences between supply and demand. The US Air Force has been experimenting with the Vehicle to Grid (V2G) concept on the the Los Angeles Air Force Base (LAAFB) microgrid. What they learn will help engineers design an interactive grid that makes room for renewable energy and turns every consumer into a potential producer of energy.
Image courtesy of the USAF
It’s All About the Money
The military has been charged with the task of electrifying as much of its non-tactical fleet (up to 200,000 vehicles) as is economically feasible. Reducing CO2 emissions and making the grid more reliable are side goals, but the primary impetus that drives this project is money: EVs cost less to operate in the long run. Moreover, smart charging capabilities will save even more money by allowing the vehicles to charge their batteries when electricity is cheap and sell power to the grid when prices are high. Buy low, sell high; can’t argue with that!
Microgrids
A microgrid is a semiautonomous power grid, usually connected to the main grid, that includes power generation as well as energy users. The generation can come from renewable sources or fossil fuels. There are two reasons to build a microgrid: to save money by generating your own electricity (while still having the main grid as a backup source), and to improve reliability by being able to generate some or all of your own power when the grid goes down. Microgrids are often found on college campuses, hospitals, and military bases.
Any time you connect to the grid, whether it’s a grid-tied rooftop photovoltaic (PV) array or a large microgrid, agreements must be made with the local utility. Each utility has its own regulations, so part of this project is to see how utility regulations affect the design and implementation of a microgrid.
Electric Fleet Vehicles
Forty-two vehicles, both hybrid and fully EV, were included in the study. A variety of makes and models are included, helping to create demand and competition in the EV industry. Each vehicle has its own charging station, specially equipped with Vehicle-to-Grid (V2G) technology.
Image courtesy of the USAF
Overseeing the fleet is the Bosch PEV management software (eMobility), which manages charging, discharging, and resource allocation. For example, the software knows when every vehicle is in service, scheduled to be in service, or parked. It also monitors each vehicle’s state of charge. These parameters help to determine when the vehicle should be charging and when it could serve as a resource.
Image courtesy of Bosch
The financial component is governed by Distributed Energy Resources Customer Adoption Model (DER-CAM), which monitors energy prices from various sources in real time, and selects the most cost effective source for that time period. For example, the college where I teach has a natural gas cogeneration plant. The college’s software continually monitors electricity prices and natural gas prices and determines whether we should buy electricity or generate our own. The combination of eMobility and DER-CAM will determine when the EVs will consume electricity and when they’ll provide it.
Demand Response
Charge during low-demand times, sell during high-demand times - it sounds good on paper, but most fleet vehicles like delivery trucks and buses are operating during the day, which is also when electricity demand is at its highest. But if we expand the possibility to all vehicles eventually being electrified, the demand response aspect becomes more feasible. Small-scale grid storage can provide short bursts of power, exactly what EV batteries are designed to deliver. Baseload plants (coal, nuclear) can’t be turned on and off easily, so they operate near full capacity all the time. Renewables like solar and wind are intermittent; they might produce energy when it’s not needed. Since the grid has to perfectly balance supply and demand, it sometimes tells wind farms to turn off a few turbines. Instead of shutting down a valuable source of clean energy, the excess can be diverted to storage devices (including EV batteries).
The military isn’t the only group exploring the use of fleet vehicles as grid-level energy storage. Here’s a school district that has a similar idea:
Billion-Dollar Potential Of The American School Bus
That’s great if you’re an organization with a large fleet, but what about the individual with an EV parked in her garage? A variety of similar tools are becoming available, such as this joint venture between Duke Energy and Siemens, an EV charging station that can be monitored and controlled via a smartphone or tablet app.
Peer-to-Peer Energy Network
EVs, smart grid, and storage technologies are still relatively young. As they grow and mature together, the grid will gradually change from a client-server model (centralized power generation) to a peer-to-peer model (distributed generation). For utility companies, this is both a threat and an opportunity. I hope they’ll see it as more of the latter.