Researchers at the University of Arizona are looking at how to use compressed air to store solar and wind power. Professor Pierre Deymier, director of the School of Sustainable Engineered Systems at the University of Arizona, and graduate student Krishna Muralidharan discuss the project.
Ted Simons: Renewable energy is the focus of tonight's edition of the ongoing series "Arizona Technology and Innovation." How do you store solar and wind energy when the sun doesn't shine or the wind doesn't blow? Tonight we hear from researchers looking at compressed air as a possible solution. I talked to Professor Pierre Deymier, the director of the school of sustainable engineering systems at the University of Arizona, and graduate researcher Krishna Muralidharan, from the U. of A.'s department of material science and engineering about using compressed air to store sunshine and wind.
Ted Simons: Gentlemen, thank you so much for joining us tonight on "Horizon." The goal of this is to store energy, wind energy and solar energy, when there's no wind and no sun, huh?
Pierre Deymier: Yes, indeed. What we know is, if you have solar power, it just works during the day. The idea is to store some of the extra energy produced by the solar panels into some form, in our cases compressed air energy storage, so you can recover that energy at night.
Ted Simons: How do you recover compressed air? How does that work? Compressed air turns into energy. How does that happen?
Krishna Muralidharan: Well, compressed air is the foremost energy, for storing potential energy in the form of compression. When you expand it, the energy that's being stored can then be turned into useful energy as the air is being expanded. It could run a turbine or run the motor of an electrical appliance.
Ted Simons: Can it be also used -- released directly?
Krishna Muralidharan : Yes, it can be released directly. There are some problems, what we call efficiency problems if you just try to expand directly. The means of compressing into expansion.
Ted simons: So compressed air is heated, correct? Driving the turbines from there and thus you've got electricity. Have you got that right?
Pierre Deymier: You don't really need to have electricity. The solar panel produced electricity and it goes to run a pump, like a bicycle pump. It's a mechanical pump that is pulling air in the tank under high pressure. Think about the tank as being your own bicycle tire. You have energy there. It's like balloon, if you release the balloon and you know it's going fly in the air, so it has energy. It's the same thing. When you want to recall the energy, you could run these compressed air from this tank into a turbine for instance, and you can get mechanical work. This work or mechanical energy can be transformed into electricity with a generator or not. It doesn't make sense to us at some point to use a generator to convert this compressed energy, back to electricity to run an appliance. Let's say have you an air-conditioning unit. It is nothing but an electric motor running a compressor. We can use the compressor as a way of running an air-conditioning unit without using electricity.
Ted Simons: And that's an example of a small scale appliance that can be used.
Krishna Muralidharan: Exactly. What we call high efficiency small scale storage system can work, run an appliance on its own without using the power from the electrical grid. The idea is to compress it in such a way that it works in conjunction with the power production of a solar panel. Take a single solar panel, it's unpredictable with the sun. What we have done is to build an appliance that works in conjunction with the power production, and stores it in a very efficient manner. If you put the hand there, you can feel the air getting hotter and hotter. We have developed a prototype where energy is not wasted into heat. It's rather used efficiently just to compress the air completely, not to waste energy in terms of heat. And then doing the same thing during the energy recovery phase.
Ted Simons: So on the small-scale deals, the small-scale storage, is it like a propane tank?
Krishna Muralidharan: Exactly. We use propane tanks or scuba tanks as storage systems. The idea is to completely build the prototype off the shelf equipment. You can get a propane tank and use an appliance to store the air in the tanks.
Ted Simons: These small scale storage projects could have military applications as well, correct?
Pierre Deymier: Whenever you need energy in a place where there is no grid, these types of applications would be useful. One project that we have developed was a telemedicine unit for an Indian reservation. You may not have electrical power but you still need to run the TV to do telemedicine diagnostics of patients. We experimented with the Tohono O'Odham Nation of Tucson. You form the energy not in the propane tank, but store it in the frame of that structure. That's where you have energy ready to be used when you need to use it. You could store your energy into this inflatable telemedicine unit and release the energy when you need it.
Ted Simons: Would that be considered large scale applications or is it a whole different ballgame?
Pierre Deymier: This would be small-scale, still medium scale. We can scale up that type of technology to an entire building. It doesn't have to be just a small unit. We are thinking about a thousand square feet. But for an entire building you could store the energy not in tanks but into the frame of those buildings.
Ted Simons: And I understand as well as another focus here -- and I find this fascinating -- underground storage reservoirs where you can store the energy underground?
Krishna Muralidharan: Yes. There have been successful implementations of such underground storage. The most famous example is the one in Germany where they use this to augment the functioning of a power plant. Another example right in the U.S. in Alabama, where they use underground caverns to store the energy and then use it for augmentation of the working of the power plant. Another one is in Briscoe, Iowa.
Ted Simons: You don't need a huge area, anything that's porous would work, for the most part?
Krishna Muralidharan: Yes. But it's much more than that. You have to ensure there's no leaks and there's been a lot of effort in trying to do what's happening to locate the caverns.
Ted Simons: We're basically talking about squeezing energy out of thin air here with this compressed air. This is fascinating stuff. How are these projects funded? What's going on here?
Pierre Deymier: The projects are funded from the foundation Arizona, and also from the Department of Energy. They are also in cooperation with the research institute for solar energy. A team is supported of researchers and students involving geoscientists and geoscientist and geoengineers for large scale research, material sciences like Krishna, and also civil engineers and mechanical engineers. It is trying to pool the resources and know-how of a large group of members, researches, and students.
Ted Simons: Last question, very quickly. Is this close to being a viable alternative to energy forms we have right now? And if it's close, how close?
Pierre Deymier: So in terms of the last cave storage I mentioned, indeed, it's already in place. The difficulty here is finding appropriate geosites where you can store the compressed air without loss and without leaks. That's one of the difficulties. This technology is already in place. In terms of locating the smallest caves, technology in buildings is not yet tested. For the small scale, it's very close to being operational.
Ted simons: Close enough, do you think? How long do you think we have to wait?
Krishna Muralidharan: I think within a year. The appliances can be integrated that can run just off compressed air. What we are working on is high efficiency operation, so without any loss of energy. The idea of using these compressed air units that can last the entire duration or lifetime of the solar panel itself, unlike chemical batteries where you have to keep changing it. You buy it, it's mechanically robust and the panel could last up to 20 years.
Ted Simons: Again, it sounds very promising. Gentlemen, thanks for joining us, we appreciate it.
Pierre Deymier:director, School of Sustainable Engineered Systems at the University of Arizona;Krishna Muralidharan:graduate student;