I have read many blog posts and articles where the authors confuse energy sources with energy transports. Failing to make this distinction makes it impossible to discuss energy policy coherently, so I wanted to write a post about this topic.
An energy source is something occurring in nature from which humans have found a way to harness energy. Waterfalls, sunlight, petroleum, and plants all fall into this category. Frequently, though, energy sources are not in the same physical or temporal location where the energy is needed and cannot be easily transported, so an energy transport is required to move the energy. Examples of energy transports include electricity and hydrogen.
The easiest way to distinguish between an energy source and an energy transport is to compare energy in versus energy out. Petroleum products release more energy when used then it took to refine the petroleum, so it is an energy source. On the other hand, it takes more energy to produce hydrogen then what is released when it is used, so hydrogen is an energy transport.
It’s not always clear whether something is an energy source or merely a transport. Ethanol has been touted as a “green” energy source, but by some peoples’ calculations it takes more energy to produce corn ethanol than what you get using it, making it an energy transport. You still need an energy source to produce the power required to make the corn ethanol.
It’s important to note that energy transports are not equally efficient. For example, high-voltage electrical lines lose a much smaller percentage of the power being transported compared to low-voltage lines, which is why high-voltage lines are used for long-distance energy transport. The less energy lost by an energy transport, the more efficient it is.
When looking at the energy efficiency of a device, measuring how efficiently it uses the energy in an energy transport is not helpful; instead, you need to look at how much energy is required to make the energy transport to begin with. For example, hydrogen-fuel cars do not actually run on hydrogen energy. The energy in the hydrogen used by the car was generated using an energy source like oil, coal, or solar. Therefore, to determine the true efficiency of a hydrogen car, you need to look at how much energy (oil, coal, solar) was required to produce the hydrogen. Sometimes there are multiple intermediary energy transports — coal generates electricity which is used to create hydrogen to run the car — so the question becomes, how many miles per poud of coal does your hydrogen car get?
When talking about alternative energy, it’s important to be clear whether you’re talking about better energy sources or better energy transports. While it’s important to use efficient and eco-friendly energy transports, if the energy being transported was generated by inefficient or dirty energy sources we’re not that much better off. For example, too many people claim that electric cars are more eco-friendly than gas-burning cars without stopping to consider how we will generate that electricity. Since a lot of our electricity is generated by burning coal, is switching cars from a petroleum-based energy source to a coal-based energy source really a good idea? Likewise, hydrogen is a relatively clean energy transport and may eventually be practical for powering cars, but what energy sources will we use to generate that hydrogen?
One of the reasons people focus on energy transports is that our options for energy sources are limited, and all of them have significant drawbacks:
- Petroleum is considered “dirty”, and there’s a relatively limited supply pumped mainly by countries hostile to us.
- Coal is considered even more “dirty” than petroleum, and there’s a limited supply too.
- Most solar power plants require solar cells with all sorts of toxic chemicals that leach out into the ground. Solar is also very expensive and because of the inefficiency of today’s solar cells is limited to relatively small parts of the world.
- Hydroelectric requires dams that cause ecological damage to fish and streams.
- Natural gas has a very limited supply.
- Nuclear generates toxic waste and requires a lot of overhead to safely run a generation plant.
- Wind is limited to very few areas of the world and causes ecological damage to birds. Some recent studies have suggested it also modifies the surrounding climate by altering wind patterns.
- Geothermal is also limited to very few areas of the world.
However, if we are serious about becoming more eco-friendly, we must start seriously discussing where we should be getting our energy from, instead of only discussing the best ways to get that energy into our cars, homes, and offices.
