From roll-up solar cells to spray-on technologies, researchers at South Dakota State University are in the midst of a 10-year project meant to provide alternative energy to military operations. I spoke recently with Dennis Helder, the university's associate dean of engineering research and professor of electrical engineering, about what the project entails.
Why is the military focused on alternative power sources?
One of the most costly parts of the modern military scenario is fuel. The modern soldier carries a lot of equipment that's powered electrically. From the individual soldier on up to the units, companies, battalions and brigades, they have very large power requirements. One of the most critical aspects of supplying our military forces is getting power to them. In most places today, that means getting petroleum or diesel fuel to them to run generators. It's high time we develop a more efficient way of using that energy, as well as alternative ways of generating energy.
What are some of the solar technologies you're working on for the military?
There are several types of opportunities that can be considered, [including] classical types of solar cells that we see on top of buildings. For operations where the military's going to be in one place for a period of time long enough to make it cost efficient, they can deploy solar energies similar to the solar we have now. At other levels, the technology we're developing now in terms of flexible solar cells, as well as even spray-on solar cells, are very attractive to the military because they often find themselves in situations where they have to do something quickly, but still try to generate a useful amount of power. Having something you can roll up when you're moving and roll it out when you're in a fixed location is very attractive. [Another example is] some of the spray-on technologies. You set up a large tent or you have a large vehicle [and] you can spray the surface with a solar cell and generate electric power. These are short-term solutions and they may not generate a lot of power, but they can make a difference.
How do spray-on solar cells work?
In principle, it's about the same as taking a paint can and spraying it on. Let's say you have a metal vehicle, for example, that forms one end of the conductor. Think of it as a battery. A battery has a positive end and a negative end. You use the vehicle as either the cathode or the anode. You spray on the solar cell and you lay a transparent conductor over the top. That forms your other electrode and you've got a solar cell. The sun generates the energy between those two electrodes.
What are some of the primary challenges you face as you work on solar technologies for the military?
In this area there are some fundamental challenges that affect you, no matter what the application.
- One is efficiency. How much energy can I get out of my device? Or, conversely, how big does it have to be for me to get something useful? That's one of the fundamental things for these spray-on technologies.
- Secondly is reliability or robustness. In the military environment, things have to be pretty tough. If they're going to break, they're going to be a liability rather than an asset.
- The third is cost. We still have to make these so they're cost effective and worth doing, as opposed to using conventional methods. The organic and flexible and spray-on cells should be really cheap. A can of spray-paint is very cheap. But making them work well and reliably and last for an extended period of time -- that's where the challenge is.
How far along are you is this process?
A lot of these technologies are fairly long-term. Some of these devices are out there, but to get the efficiency and reliability up is not a short-term process. We're on a five to 10 year horizon for these technologies -- to really get them into the marketplace. Conversely, if we think more about some of the conventional solar cells we have now, those are silicon-based technologies. The ability to perhaps make those significantly cheaper and still as efficient as they are is a little bit shorter term. We're hoping for a one to five year time frame for those.
That's one of the nice things about solar. There are quite a few different technologies being pursued by a lot of different companies. Part of the reason for that is there are a lot of different applications where these various technologies can excel. It also gives us an interesting future. There might be a breakthrough this year in one technology and another the following year. I think we can look forward to a lot of advances over the next decade.
You're designing these technologies for the military, but could they also have use for the general public?
I think that's very true. In general, I believe military technology will transition eventually into the commercial world. One area I've had some experience in is airborne imaging systems. The military uses a lot of these unmanned vehicles with surveillance equipment. Those are making their way into the civilian world. I think that's going to be the case with a lot of these applications, as well as some of the microgrid applications. There's almost a parallel effort going on in some cases. There are so many different opportunities and saving energy is such a high priority these days.
Do you have anything else to add?
I'd like to wave the flag a little bit. On a personal note, my son was in Iraq in 2004. He was guarding fuel convoys. He was the guy in the Humvee carrying a machine gun. These were the guys that were dying with these IEDs. I think whatever we can do to help decrease the number of these convoys and decrease that weakness on the battlefield ultimately is going to save lives.
Photo: Dennis Helder / Courtesy of South Dakota State University