One of the many tasks of running an electric utility is maintaining operating reserves and spinning reserves to handle seasonal peaks, and occasional generation failures.
Between peak demand that only occurs a few times a year, and the occasional shutdown for routine maintenance and response maintenance, utilities have to keep operating reserves — backup equipment that is only run a few hours or at most a few days per year. This is not only a capital cost, but a maintenance cost and an administrative cost. Such capability may not be run often, but when it is needed, it is really needed. This means regular inspection and even occasional cold starts to make sure such backup will work when needed. Further this means administration and management to make sure such tests are actually done, since they are the sort of thing that can slip through the cracks.
Utilities also need spinning reserves: either power that is generated in excess of that consumed, or special types of storage and generation that can be brought online within milliseconds or nanoseconds. Some spinning reserves compensate for routine variations in demand. But, like operating reserves, a significant amount of spinning reserve exists as backup for equipment failure and for unexpected extreme demand spikes.
If you were a utility, wouldn’t you love to buy power as needed for many operating reserve purposes thus needing to own, maintain, and administrate less of this seldom used equipment? Also, wouldn’t you love to greatly reduce your need for spinning reserves?
Well if electric vehicles ever come into widespread use, electric utilities will get their chance to do this. Both battery electric vehicles (BEV) which run entirely on batteries charged from the grid, and plug-in hybrid electric vehicles (PHEV) which run some of the time on batteries charged from the grid, and some of the time on liquid fuel could provide storage to substitute for most operating reserves and a significant portion of spinning reserves. On average, automobiles are on the road only an hour or two a day. (Yes some cars are driven much more than this, but others much less.) That means that a high percent of this battery capacity will be plugged into the grid 24 hours, even during peak automobile usage. For occasional use, such as seasonal peaks, demand spikes, and equipment failure, it would be quite possible to pull a little power from all or most cars plugged into the grid without taking too much from any single car. Car owners who let utilities do this would set their equipment so as not let their batteries be drained enough to cause them problems. As operating reserves were brought on line over the course of two to four hours, the power that had been taken would be restored. (The ability to rent battery use reduces but does not eliminate the need for operating reserves.)
Now there is an important point. Batteries today are expensive, BEV and PHEV battery packs even more so. In addition to cell costs, automobile battery packs need battery management, cooling, and shock protection – among other requirements. So at today’s prices you would not use precious battery cycles for daily use. It makes no sense to meet daily peaking and routine spinning reserve needs with today’s technology at today’s cost. This is not a knock on two way connections between electric cars and the grid – often called V2G. Handling seasonal peaks, out of parameter demand spikes, and occasional equipment failures is amazing enough. There are other kinds of technology that can handle daily needs at a lower cost than V2G – utility scale batteries of various types. The profit in using car batteries to replace other forms of storage, or to replace generation, comes from displacing capital that can’t be fully amortized in a reasonable period of time. It makes no sense to use it as a replacement for equipment that is run daily.
What about the improvements in electric car battery technology? I would indeed expect this. But I would also expect improvements in utility scale storage. Right now utility scale batteries are less expensive than electric car batteries for several reasons. They are bigger than car batteries, and thus provide economies of scale. Some utility scale batteries are much heavier per kWh than car batteries – a minor inconvenience for utility storage, a deal killer as the power source for an automobile. Utility scale batteries will continue maintain the first advantage of economies of scale, and depending on technology may maintain the second as well – a greater tolerance for high battery mass per unit of power than car makers can afford.
I would not emphasize this point, except that many in the renewable community confuse the potential of V2G to replace occasionally used capital with the ability to handle daily peaking, and to replace spinning reserves that protect against routine daily demand variations.
I recently ran into this statement from a staff member at the Institute for Local Self Reliance:
More electric vehicles means more electricity demand, but it also means storage. In Driving Our Way to Energy Independence, ILSR author David Morris notes that the Sacramento Municipal Utility District studied the impact of plug-in hybrid vehicles and found that the storage in a local PHEV fleet could fill in for 250 MW of wind power for 8 hours. If we electrify transportation nationally, we put millions—billions—of kilo-watt hours into car batteries.
This makes it sound as though V2G could pretty much let the SMUD become mostly renewable based. Not quite. First of all a high percentage of SMUD power is hydroelectric. Hydroelectric power is highly dispatchable, good for base load, load following and peaking. So SMUD is already in good shape to add a lot of variable renewable energy. So what about 250 MW of wind? Well SMUD has about 2,500+ MW of power. 250 MW is a bit less than 10% of total of SMUD capacity.
Nameplate capacity is not a great way to compare power sources anyway. Wind generators (like other sources) don’t run all the time, and mostly run at a lower rate than nameplate output. New large wind farms produce on average 35% to 40% of theoretical nameplate capacity (which is a big improvement over even a few years ago). SMUD sales in 2008 were slightly less than 13.4 million megawatt hours. 250 MW of wind farms at 40% utilization would supply about 876,000 megawatt hours, less than 7% of total consumption. This concrete example shows that V2G is extremely valuable, but does not fill the same functions as really large scale storage or long distance transmission. V2G, if electric car use was widespread enough to make it practical, would replace some extremely expensive functions. But, if we expect renewable electricity to replace most fossil fuels, we still need either larger scale storage than V2G can provide or long distance transmission, probably both.
Again, the misconception I’m correcting has never been spread by the V2G community. V2G advocates, quite correctly, are excited about what car batteries could legitimately do to add grid stability and lower grid costs for either conventional or renewable sources. It seems to be renewable advocates who are not V2G experts, and don’t read work by V2G experts carefully enough who expect V2G to substitute for other technologies it is not suited to replace, who get over-excited and attribute magic powers the V2G community has never claimed.
