The recent spike in gasoline prices (the subsequent crash in prices is temporary) amplified the interest in alternative energy sources for transportation. Many of the proposed solutions involve “electric cars”, that is, cars that store and use electrical energy as their primary source of energy for conversion into mechanical drive. This contrasts with “hybrid” drives like the Prius, which primarily use energy stored in gasoline with electrical augmentation to improve efficiency.
There have been millions of words written about these cars and why they are the “future”, but there is one aspect that I have never seen concretely addressed: how to supply power for use in the western United States, where typical transportation distances are much greater than in the Eastern United States and Europe where population density is much higher.
In the western United States a trip of 100 miles each way is not infrequent. It might not be a daily occurrence, but it happens often enough that a car with only a 100 mile range would be very inconvenient if it couldn’t be recharged rapidly. Rapid recharging means single digit minutes, not hours. What does this sort of recharging capability imply for the electrical generation system?
The EPA limits gasoline pumps to 10 gallons per minute, but most average between 5 and 10 gpm. So let’s say we refuel at 5 gallons per minute. Gasoline has an energy content of approximately 131MJ/gal (mega joules per gallon, please forgive the mixing of unit systems). At 5 gallons per minute, the typical fuel pump is moving 655MJ/minute, or 10.9MW!
So if a thousand cars are trying to recharge at the same time, that is a 109GW load. The largest nuclear generating station in the United States, currently the Palo Verde Nuclear Generating Station, is rated at 3.2GW. (Why nuclear? Because all of the other significant power generation methods use fossil fuels which essentially just move the problem, not solve it. Solar is not yet ready for prime time.) A thousand cars refueling at the same time in a major city would not be unusual.
Let’s look at it another way, current US gasoline consumption is 390 million gallons per day. Assume that the vast majority of that gasoline is used for transportation. The energy content of gasoline, again is 131MJ/gal., which equates to 51,090,000 GJ/day, or 591 GW of continuous power usage. That is 184 Palo Verde sized nuclear power plants.
This naïve analysis doesn’t take into account any efficiency gains from using electric cars, so let’s do that. Assume that the average car is on 20% efficient, so 80% of the energy content in the gasoline is wasted. And for the sake of argument let’s say electric cars are 100% efficient. That means we only need one fifth as much electrical power to replace the gasoline. So we only have to build 36 new Palo Verde size plants.
So is there an alternative? No.
Another popular alternative fuel proposed for transportation is hydrogen. Many breathless articles have been written about hydrogen fuel celled cars like Honda’s FCX Clarity. They completely ignore the question “where does the hydrogen come from?”
Let’s ignore the considerable question of hydrogen distribution, getting the gas to the end user, and stick with actually obtaining the hydrogen in usable form. Hydrogen is most easily obtained by electrolyzing water, splitting the H2O into it’s component parts. That requires electricity, a good estimate of how much generating capacity would need to be dedicated to producing hydrogen gas can be found above. But that again ignores the inefficiencies in the electrolysis process itself.
If we want to move away from petroleum fuels (regardless of which country straddles the oil deposit) we need to start building generating capacity right now. By the time the generating capacity is in place, maybe we will have cracked the energy storage problem (hydrogen or electrochemical storage) problems that are at the forefront of most research now.