In the near future, we may see a transition to an electric-based transportation system, specifically with electric vehicle drive trains and vehicles which drive on battery power, with or without an additional internal combustion engine to provide for extended range operation. This is already starting to happen with hybrid vehicles being produced by most manufactures and models like the Chevy Volt coming out, which are equipped with a fully electric drive-train and the ability to travel short distances without burning any fuel.
This is where the idea of “vehicle to grid” power comes in. The idea is that since we don’t drive our cars all the time there will be a large number of batteries and motor-generators connected to the power grid. So why not use them for something? The basic idea is that the vehicles would charge during times of relatively low power demand and that during times when demand is high, these vehicles would instead discharge to provide power to the grid. Owners who back-feed the grid with power from their cars would be paid a premium for the power to make it worth their while. Power would be priced based on grid demand, thus allowing vehicle owners to make money by charging when demand is low and discharging when demand is high.
Apparently those who are behind this concept believe that in the years to come our power grid will be pushed so close to the brink of complete collapse that it will be necessary to resort to vehicles for energy storage and generation in order to avoid regional blackouts becoming a common occurrence.
There are three basic vehicle-to-grid systems proposed, based on the vehicle type:
- Battery Electric Vehicles – The vehicle’s battery charges when plugged in during times when there is power available on the electric grid, but if there is a time of high demand when power is in short supply, the process is reversed and the battery discharges electricity back on to the grid
- Plug in hybrids/Extended Range Electric Vehicles – These vehicles have batteries which allow them to travel short and medium distances on only battery power. They also have a gasoline or diesel engine connected to a generator to provide power when driving beyond the range of batteries. Since the batteries on these types of vehicles are of limited capacity, they would be exhausted after only a relatively short period of time and most of the electricity back-fed to the grid would come from the internal combustion engine powering the generators.
- Fuel Cell Vehicles – These vehicles would never charge from the electric grid and would get all their power from fuel, such as hydrogen, which would be purchased at filling stations just as gasoline is. Today most hydrogen comes from the steam reforming of natural gas, but since the entire point of using hydrogen is to allow for an “renewable” form of energy that is not fossil fuel based, presumably this hydrogen would be produced from water by means of electrolysis or thermochemical reactions. (using hydrogen as a fuel presents other issues that go beyond the scope of this post)
So this sounds like a great idea, right? Actually it’s a horrible idea.
Unfortunately, all of these proposals suffer from some rather extreme problems, which makes it unlikely that they’ll ever actually be used on any large scale. If they are ever used it will be only because of mandates and subsidies, not because they actually are desirable or benefit utilities or their customers.
Some of the big, fundamental problems of the whole concept include the following:
It complicates control and management of the power grid – Even when using only a few power plants, keeping the electric grid up and running smoothly is a twenty four hour a day job. Reserve must be maintained, transmission lines must be utilized efficiently and without overloading and loads must be balanced. At any time, a grid operator needs to know how much power is being drawn, where that power is being consumed and the status of all their power plants, including which ones have additional capacity that can be called up.
The “vehicle to grid” concept would mean that grid operators would need to know the status and availability of thousands or millions of tiny generators. They’d need to know where they are located and whether the local transmission lines had the capacity to transmit electricity to the areas where it is needed. They would need to be able to communicate to each of these vehicles and throttle them up and down, calculating, in real time, which ones were suitable for use. Power would be flowing every which way. Residential areas would be generating some of their own power while transmitting some extra to commercial areas, which would be simultaneously getting some of their power from centralized power plants. Some residential areas would be drawing power and then five minutes later, they would have surplus power. Industrial customers would be drawing power from numerous sources at once.
If this is not complicated enough, power grid management is more complex than just keeping demand and production in balance. Frequency and phase must be maintained across the grid and where non-synchronized transmission lines meet, phase compensation must be used to keep them from experiencing a phase miss-match. Loads must be balanced across the three legs of a three phase system, so that no one leg ever has significantly higher or lower voltage, which could cause severe damage to equipment. Factors like inductive reactance and standing waves need to be taken into consideration.
It is not simply an issue of the current grid not being designed for this. Even if a new grid were built from the ground up, the control and communication issues would be daunting and require numerous complex management systems.
It’s unreliable - One of the biggest issues is the fact that it places a great deal of importance on something that can’t necessarily be counted on. By making vehicles a major contributor to power generation, the habits of vehicle owners becomes a major factor in whether power can be reliably provided. If demand is high on a given day and there are many vehicles connected to the grid, then there will be sufficient capacity. However, if a large percentage of the public is not home or has chosen not to have their vehicle back-feed the grid on a given day or night, then a spike in demand could cause a major power shortage.
Not only must there be enough vehicles connected and ready to generate, but they must be in the right locations and connected to sufficiently high capacity power lines to transmit electricity to the areas of demand. If a major traffic jam stops many people in critical areas from getting home when anticipated, or if an event like a holiday causes many to travel, the generating capacity may suddenly not be there.
It’s undesirable to have vehicles discharge – Imagine coming home from work and plugging your vehicle in to charge. The next morning, when you get in your car, you expect the batteries will be fully charged, or at least nearly fully charged. Likewise if you have a charger at the parking lot where you work, you expect that by day’s end you’ll have batteries that are full for the drive home. If your vehicle has been discharging, however, then you’re going to have a big problem. It has been proposed that vehicles could be designed to only allow discharging a portion of their battery capacity or only when high rates are offered. However, electric vehicles already have issues with range and starting off with less than full batteries is not going to help. Since the capacity of vehicle batteries is pretty low to begin with (in grid terms) if you only allow the vehicle to discharge a relatively small portion of the batteries, it won’t make much difference to begin with.
Of course, if your vehicle is not purely electric, such as a plug-in hybrid, then you’ll be a little better off, because you’ll probably still have some gasoline left to drive on. Of course, once the vehicles batteries are depleted, you’ve defeated the entire purpose of a plug-in hybrid and those big batteries become nothing but dead weight you may as well not even have in the vehicle. If power demand is high enough, your engine will have come on to generate power, resulting in not only your batteries being dead, but a significant amount of your expensive gasoline having been burned. Of course, if you park your car in a garage, this may not even be an issue, because you’ll already be dead from carbon monoxide poisoning before you even realize the predicament you’re in.
A hydrogen vehicle would be no better off, as hydrogen fuel also costs money and the power company would have to pay out astronomically high rates to make burning through your own hydrogen worthwhile.
It’s horribly inefficient - A consequence of thermodynamics is that any time energy is stored, converted from one form to another or transmitted, some of it will be lost. This loss may be very large, as in a thermal engine, or it may be very small, as in an electric transformer. However, the loss always compounds, so if power goes through a series of transformers, inverters, charge controllers, voltage regulators and other such devices, each will contribute some loss that compounds.
There are, of course, ways of keeping this loss to a minimum. One important consideration is the efficiency of systems being used. As a general rule, bigger is better. Huge steam turbines at power plants are far more efficient than small engines. Big centralized equipment can be maintained at higher tolerances than would be economical for millions of tiny engines and it is cost effective to invest more in efficiency when its only one unit. The engine in a car may have a total thermal efficiency of 30%, but a combined cycle power plant can easily be greater than 50%
An example of this would be inverters. If batteries are to be connected to the grid, the current will need to be inverted to produce alternating current. Utility scale inverters are very effecient, some of them achieving close to 99% of total power effeciency. The smaller units that would be used in combination with an automobile are nowhere near this effecient. Considering the compounded loss from transmission, charging, discharging, inversion and retransmission, this loss becomes a big consideration.
The fact that energy would need to be repeatedly transmitted to and from centralized regional lines only makes the situation worse. Electricity companies try to avoid using energy storage when possible, but occasionally methods like pumped storage hydroelectric are used for load balancing. When this is the case, these facilities are located near power generators and connected directly to regional lines to reduce the loss of repeated conversion and retransmission.
It trades cheap fuel for one of the most expensive – Cars run on gasoline because it is easy to transport, tanks can be refilled easily, it’s reasonably stable and has numerous other desirable qualities. They do not run on it because it’s the cheapest fuel around and that is becoming more and more of a consideration. Generating power by burning coal is filthy, but at least its economical. Uranium may be even more economical and natural gas, though more expensive, is still a lot better than burning gasoline.
With the exception of some areas of the Middle East, only a tiny portion of the world’s electricity is generated from burning petroleum and the power plants that do burn petroleum usually burn relatively inexpensive bunker oil or other heavy fuel oils, not highly refined gasoline. Gasoline does burn more cleanly than heavier petroleum-based fuels, but using it for power generation would borders on insanity.
Hydrogen could, in some ways, be even worse. If hydrogen is generated from water (the only way of doing it in a truly “clean” and fossil fuel free manner) then a great deal of energy is lost in the conversion of heat and/or electricity to hydrogen and then back to electricity by a fuel cell. The price of hydrogen would therefore always be higher than the price of an equivalent amount of electrical energy. This may be considered worthwhile if it allows portability of energy, but the idea of paying for hydrogen at a filling station only to convert it back to grid electricity is absurd.
It puts wear and tear on vehicles unnecessarily – Batteries don’t have unlimited charge cycles and are expensive to replace. This is a major issue that is faced by battery electric vehicles. Maximizing battery lifetime is a critical concern when it comes to creating viable electric vehicles for the mass market. One thing that would NOT help the situation is using these valuable batteries for more than propelling the vehicle.
The same is true of fuel cells and internal combustion engines. All engines wear with use, and in addition to reducing their total lifetime, the more an engine is used the more it will need maintenance, such as oil changes and the replacement of everything from spark plugs to air filters.
It would necessarily be enormously expensive – In addition to the gargantuan expense of equipping every car with a static inverter, control interfaces and communication systems the price paid to end users to generate electricity would necessarily need to be very very high. After all, they’re burning your gasoline or hydrogen, putting wear and tear on your expensive batteries and potentially causing you some pretty extreme problems with mobility. It’s going to need to be pretty high a payback to justify that kind of sacrifice and to cover the costs incurred.
If the price paid for electricity is very high then so to must be the price it is sold at, and this creates a huge problem. If you own a car and are a net producer or produce nearly as much electricity as you consume, you might come out okay, but what about those who don’t own a car or who have a long commute and thus can’t afford to have their batteries constantly discharged? They’re going to have a very hard time paying for the exorbitantly high cost of electricity. Of course, the largest users of electricity are industry, so unless they generate their own power, industrial users will simply be wiped out.
There are better, cheaper, more efficient ways of storing electricity – At first it might seem like it’s using a resource free for the taking, but the fact that vehicle to grid requires such enormous upgrades to the system and such uneconomical pricing models, it costs more to use vehicles than it would just to build dedicated energy storage facilities. In circumstances where energy storage is needed for the grid, pumped hydroelectric has been proven to be economical and reasonably efficient. There are also utility scale battery systems which tend to be used for shorter duration and smaller application uses, but offer higher efficiency. If on-demand generation is required, there are modular gas turbine generators that work well for non-spinning reserve.
It’s worth noting that batteries, generators and engines are all optimized to their purpose. Designing something like an engine involves a lot of compromises and trade-offs. Ideally you’d want the engine to be as small as possible, as cheap as possible, as efficient as possible and as reliable as possible. Yet these ideals are often in opposition to each other, thus requiring that the designer choose which ones are most important and which can be compromised. For example, the engine inside a car should ideally be as efficient as possible, but if achieving higher efficiency means making the engine much heavier then it may not be worth the added weight, as the additional efficiency would be lost to the added energy required to move the heavy engine around. Yet in a static application, weight doesn’t really matter, so a heavy and efficient engine is desirable. Similarly, the batteries in a vehicle should have an efficient charge cycle, but it’s also important that they charge rapidly. It may be worthwhile to design batteries with lower charge cycle effeminacy if it means they can be charged rapidly.
Providing power to the grid and storing large amounts of energy in a static location is a much much different job than propelling a car around town. Thus the systems that do one are not going to be that good at doing the other. It’s possible that the same kind of system could do both, but it would not do both very well. One might compare it to the concept of a flying car. It is possible to make a car that can also function as an airplane and there have been many built over the years. However, due to the completely different nature of the requirements, they end up being capable of both driving and flying, but don’t do either very well.
Finally, it should be noted that there’s no environmental benefit to this at all – If anything, the increase in batteries that need to be manufactured and replaced and the huge losses involved make it a very bad environmental policy. There are many who like to talk about “distributed generation” being better for the environment, but don’t explain why burning fuel in a lot of little put-put engines is better than burning fuel in one place.
There actually have been some who claim that vehicle to grid systems would result in lower emissions of sulfur, carbon dioxide and other pollutants. However these claims are based on the presumption that gasoline engines are used to provide most of the power. Compared to coal, gasoline produces less CO2 and more water per unit of energy and while coal is filthy, gasoline burns reasonably cleanly. However, if you’re going to burn gasoline to make power, you could just as easily do it in a big centralized power plant and at least get a little bit better efficiency. Then again, if you are planning on burning gasoline to make electricity, you may as well consider just burning money instead.
This entry was posted on Friday, February 5th, 2010 at 11:38 pm and is filed under Bad Science, Enviornment, Obfuscation, Politics. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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