Storing electrical energy is a huge problem. A lot of gear we use every day use some form of battery and despite a few false starts at fuel cells, that isn’t likely to change any time soon. However, batteries or other forms of storage are important in many alternate energy schemes. Solar cells don’t produce when it is dark. Windmills only produce when the wind blows. So you need a way to store excess energy to use for the periods when you aren’t creating electricity. [Kris De Decker] has an interesting proposal: store energy using compressed air.
Compressed air storage is not a new idea. On a large scale, there have been examples of air compressed in underground caverns and then released to run a turbine at a future date. However, the efficiency of this is poor — around 40 to 50 percent — mainly because the air heats up during compression and often needs to be prewarmed (using energy from another source) prior to decompression to prevent freezing. By comparison, batteries can be 70 to 90 percent efficient, although they have their own problems, too.
The idea explored in this paper is not to try to store a power plant’s worth of energy in a giant underground cavern, but rather use smaller compressed air setups like you would use batteries to store power at the point of consumption. The technology is called micro-CAES (an acronym for compressed air energy storage).
Although the article compares them to batteries, they seem more akin to fuel cells, to us, even though the technology is quite different, of course. Batteries usually have a fairly limited lifespan and often produce just a few times the amount of energy required to manufacture them. CAES and fuel cells typically have very long lifespans, so they produce a lot more energy over that lifespan than was used in their construction. There’s nothing very exotic or toxic either. An air storage tank, a compressor and a generator is all you need.
Keep in mind “micro” here is in context of giant underground storage caverns. The article estimates that a system for a typical residence would cost about $10,000. More than batteries, but with a lower total cost over time because batteries wear out. No one is suggesting your laptop or cell phone will run on compressed air.
This sounds great, but there are two major problems. First, the amount of air you have to store to be practical is an issue. The other problem is the system efficiency is low. Worse, these parameters are interrelated. So storing at a higher air pressure to get more air in a particular volume will also reduce efficiency.
The main extra proposal to help make micro-CAES practical is to take advantage of the heat produced on compression to heat water and living space. On decompression, the heat absorbed can be used for air conditioning and refrigeration. This reduces the electric demand for those tasks, making the overall system more efficient. In other words, if you could reduce electric usage by half because of the cooling and heating properties of the micro-CAES, that will offset the low efficiency of the unit.
The other way to possibly make micro-CAES practical is by using low pressure so that there isn’t much heat produced or consumed. You can read all the pros and cons of this approach in the original post.
This is an area of active research around the world. It struck us that this would be an area where a citizen scientist could make a real impact. There’s nothing super exotic about it. Air compressors and tanks are easy to obtain. Generating with a turbine is easily accomplished, too. We have a feeling a little hacker ingenuity could go a long way in making real advances in this area. Your tough choice? Do you publish in a journal or do you submit your work to the Hackaday tip line? We vote for the tip line.