Where’s all that “green” energy going to come from?
On the left is a breakdown of how energy is produced. On the right (pink boxes) is a breakdown of how energy is used.
On the far right, in grey, is a summary of the final outcome of the process. This is the first, and most, shocking aspect of this chart. “Energy Services” is basically energy that was used for some actual purpose like lighting your home, driving your car, building your widgets. “Rejected Energy” is waste. Energy that was not put to any productive end. More than half of all energy produced is wasted.
Now, there is “waste” and there is “waste”. A lot of this is due to the nature of the way that energy is produced, distributed, and used. When electricity is transported by wires from the power plant to your house, some is lost (roughly 7%), and there isn’t a simple way to change that under our current electrical system. Back at the power plant, only about 1/3 of the energy in fossil fuels is captured as electricity, a figure that hasn’t really changed since the 50’s. Some of this is due to thermodynamics that make it difficult to transform and transport electricity and some is due to old, inefficient technology, sloppy design, and outright waste. But the end result is that only about 30% of energy used to produce electricity is used for any purpose.
Even worse is petroleum used in transportation where less than 25% of inputs end up doing any actual work. Note that in this case, the figure actually hides a huge amount of waste depending on how you define “actual work”. If the purpose of burning gas in a car is to move around 1-2 tons of steel plus you and your stuff, this is your figure. If the purpose is to move you (provide mobility) the loss here is substantially higher.
Many see great promise in the switch to electric cars. The Nissan Leaf is rated to get a gasoline equivalent of 99 mpg, roughly a 300% improvement over an equivalent gas powered vehicle. But consider that even at that level of efficiency, more than 2/3 of the electricity has already been wasted by the time it gets to your car’s battery (and before you account for moving around 3,500 lbs. of steel, glass, etc.) While an impressive improvement compared to currently technology, I think this best serves to illustrate just how inefficient current technology is.
Another big picture question is about the relative efficiency of end use types. Residential, commercial, and industrial users all waste around 20% of their energy inputs. Transportation by contrast wastes about 75%. I suspect there are numerous reasons for this difference. One is that energy transformation by burning tends to be wasteful. With electricity, that transformational loss has already happened upstream. With gasoline, it is typically happening in your car’s engine, which is not well equipped to transform energy efficiently.
In overview, there’s two pretty obvious areas where it might make sense to focus our efforts. The two main areas of loss are at the generation of electricity and at the generation of movement with gasoline. These two areas have a feature in common, there are actually multiple transformations going on; fuel is burned to create heat, heat is used to create movement (kinetic energy), and for electricity the kinetic energy is used to generate watts. Each step loses a large portion of the input’s energy, typically as heat.
A big factor in most power plant designs (of all types) is water supply for cooling. These are factories designed specifically to generate heat, and yet they go to great pains to have a system to cool themselves down. Cogeneration plants are a more advanced design to directly address this waste. Instead of excess heat being a waste product, it is distributed to be used directly as heat in homes and/or businesses. This saves this lost energy and avoids yet another transformation where some fuel would be turned into heat at the final location. But the limitation is distance. It is hard to move heat over any significant distance and so this only works where power plants can be located in the vicinity of home and businesses.
Now one way to avoid heat based loss completely is to generate electricity in a way that has none, solar and wind. Follow the little yellow line from “Solar” on the left and notice how it goes directly to the end user, skipping the entire Electricity Generation step that loses so much energy. Of course, it’s a bit hard to follow that line because it is so little. For how much you hear about it, it is somewhat shocking to see how little energy Solar and other renewables currently supply. But its important to remember two things. First is that solar is really in its infancy and it is growing fast. The fact that it’s a negligible part of current production doesn’t mean that that can’t change quickly. Second, remember that a kilowatt of solar is not the same as a kilowatt of coal generated electricity. Bypassing the wasteful multistep conversion process means that every unit of electricity generated from the sun replaces roughly three times that much of equivalent energy in inputs. A little bit goes a long way.
Next, the chart reveals why a general movement away from centrally produced energy to distributed production may make sense. As efficient as solar is, it still loses that 7% transmission cost when it has to go over long distances. If that solar cell sits on your roof, you’re instantly 7% more efficient that a centralized power plant using the same solar cell technology. Similarly with cogeneration plants, it may make sense to start putting energy production closer to its end user. In the past, the efficiency of scale of producing power in a central location outweighed this factor. In the future, perhaps the efficiencies of scale will shift to producing small but advanced power generation systems so every home can have the latest technology in solar, fuel cell, or other power generation systems.
A final point that comes up for me from this chart is just how well it illustrates why reducing energy consumption is so important, and perhaps more important than using it more efficiently or generating it more sustainably. In terms of bang for your buck, it makes more sense to insulate your home, change your lightbulbs, and drive your car less than it does to buy a more efficient furnace, put a solar panel on your roof, or buy an electric car. This chart illustrates perfectly why. End use efficiency matters, but you’re still fighting all the loss that’s happened before that energy even gets to you. Every watt or gallon you don’t burn never has to make that journey at all.
Transforming our energy infrastructure to one that is moderately sustainable is a massive undertaking and we don’t have a lot of time. For now, the fastest and most cost effective way to reduce emissions is simply to use less energy. This not only buys us more time to switch over our generation to better forms, but also frees up funds to be invested in more productive uses than sending them them up a smokestack.
Update: Via Grist again, I’ve come across an article about waste heat recovery in Orion Magazine. It explores the slowly growing market for systems that use waste heat from power plants, manufacturing, and other larger scale operations to generate electricity. One manufacturer of this kind of equipment claims that a single installation at a US steel plant in 2004 “generated roughly the same amount of clean energy as was produced by all of the grid-connected solar collectors throughout the world.”
Since waste heat is typically the single biggest energy waster in fuel burning processes, it somewhat begs the question of why more isn’t already being done to tap this. The article blames regulatory issues surrounding electricity generation and general ignorance/inattention to the potential by industry. The government does not currently recognize waste heat recovery as “renewable” energy which would open up the industry to a number of incentives and advantages that could help it grow. The biggest technical hurdle seems to be that most of these heat sources run cooler than is needed for traditional electricity producing turbines. But it appears that progress is being made using lower boiling point materials than water for the turbines and in scaling down the units to suit medium scale operations.
Defining this process as “renewable” energy seems a bit of a logical stretch. On a engineering level, this is about improving the energy transformation efficiency of an industrial process. If I get an extra 10% of energy from burning coal, how is that 10% renewable? It may be that providing some incentives to spur development and growth in this industry is a good idea. But I think the fact that those would be needed simply points again to the fact that energy is in general, under priced. Fully rational pricing of energy that includes internalities and externalities would make this waste heat valuable enough that companies would be lining up to use it without prodding. Regardless, it does help to clarify the point that making fairly simple improvements to our current energy system may be the quickest and most cost effective way to bring down our usage and emissions in the short term.