Horizon, Host: Ted Simons

March 12, 2014


Host: Ted Simons

Arizona Technology and Innovation: Solar Thermal Energy


  • An Arizona State University research team is looking into ways to make solar thermal energy more efficient by adding solar photovoltaic cells to the process. Solar thermal power uses mirrors to heat a fluid to create power. One of the ASU research team leaders, Zachary Holman, will discuss the ideas being examined.
Guests:
  • Zachary Holman - Assistant Professor, ASU School of Electrical, Computer & Energy Engineering
Category: Technology   |   Keywords: technology, innovation, solar, energy, research, asu, project, thermal,

View Transcript
Ted Simons: Innovation looks at an ASU research team studying ways to make solar thermal energy more efficient. Assistance professor Zachary Holman joins us now. It's good to have you here. Before we get kind of fine tuning here the energy department's focus program. What are we talking about here?

Zachary Holman: The Department of Energy has a wing called the advanced research project agency or ARPE. They are funding a program to try to increase the efficiency of solar power on a utility scale. There's two main goals. One to use all colors or wavelengths of sunlight, the other to have some storage capability so that sunlight during the day can generate power during the night.

Ted Simons: I know there are two kind of twin research projects going on here. The $3.9 million one is for high heat photovoltaic device converting sunlight into electricity. That's a parallel tract to yours, right?

Zachary Holman: We're fortunate to win two 2 of 12 awards, completely different approaches. One was to have a photovoltaic cell that light is concentrated on. That cell gets hot, generates electricity and waste heat goes to generating electricity from the heat and project I'm working on has a different approach where we don't have hot PV cells but rather we try to combine the best of two existing mature technologies, one of which we call concentrating solar power, those are the big mirrors like the Solana plant in Gila bend. The other is photovoltaics.

Ted Simons: I want to make sure I get this right. You're putting these cells into large reflectors, we're looking at here, and these reflectors generate the heat and power but they also capture? Is that what you're working on?

Zachary Holman: Exactly. The picture that you have up now, these are the large mirrors like down at Gila bend. You can think of this as basically a more advanced version of the lens that a kid would use to burn a piece of paper. Focuses sunlight on to the tube running horizontally in the middle. You generate a bunch of heat that then powers a steam turbine. This is a conventional concentrating solar power plant. Our idea is to integrate photovoltaics, which are the blue colored things that you see on people's roofs, on ASU's roofs, for example, into the mirrors. Instead of having Silver covering the back side of the mirrors you have photovoltaic cells. The cells absorb some of the sunlight and convert it to electricity directly, and the rest of the sunlight is focused to that tube at the line focus, the concentrator, where it generates heat. That heat can be stored and converted to electricity at a later point in time.

Ted Simons: How do you store that heat? I understand sounds like a nifty concept. How do you do it?

Zachary Holman: Sure. Heat is a lot easier to store than electricity. Electricity we store in batteries. Batteries are expensive. Heat, most common way is or a way being investigated and will be used at the Solana plant is with molten salt. You have very hot liquid salts or molten salts and think of them being in a big vat. Think of it being a big thermos, if you will. You can put heat in there during the day, put the molten salt in, and if it's -- it basically acts as a big thermos then at night it will still be hot. You can take the heat out, run a steam turbine and generate electricity from it.

Ted Simons: So it can be either converted or stored.

Zachary Holman: Stored for the purpose of conversion at a later time. The advantage is a big problem with solar power at least when you go to lots of it, which we're nowhere close to in the U.S., but in Germany they produce all of the power at noon on a sunny day from photovoltaics, from solar power. The big problem is if they want to add more they have to have storage capacity. This system has integrated storage.

Ted Simons: As far as the mirrors again, this replaces those Silver mirrors. These mirrors are, what, half mirror, half photovoltaic? Hybrid kind of a thing?

Zachary Holman: It's a photovoltaic acting as a mirror to some colors of light. To our eyes it would just look like a black photovoltaic cell, but with wavelengths of colors of light we can't see, for example U.V. or infrared, it reflects light. I think some animals can see infrared, for example, we would look at it and it would look like a mirror rather than black to our eyes, black or blue.

Ted Simons: Interesting. How expensive would it be to retrofit some of these mirrors?

Zachary Holman: So the design we have come up with, these new mirrors which we call P.V. mirrors are supposed drop in place of the existing Silvered mirrors on plants like Solana. We expect a cost increase of something like 30%. However, the power output increase is supposed to be 50%. So cost increase 30%, power gain 50%. That means you and I would see cheaper electricity at our homes.

Ted Simons: I forgot to ask this. How long when you say it's stored, how long can that heat be stored?

Zachary Holman: The Solana plant in Gila Bend is designed for six hours of storage. Our new system, hybrid system, is design for ten hours of storage. So ten hours after the sun goes down you could still be generating electricity from that stored sunlight.

Ted Simons: Basic I will if you got a full week of rain in the wintertime, which we all seem to remember at one time we got here, start getting concerned toward the sixth, seventh day of no sun?

Zachary Holman: Sure. That will be true of all solar power. But our system has an advantage over the traditional concentrating solar power plants like Gila Bend. You might remember when you were a kid if you were trying to focus sunlight with a lens you always point it toward the sun. The direct component of light coming from the sun you can focus. If you were to point it at some other blue part of the sky you can't focus enough light to burn a piece of paper. Same is true for mirrored lenses but since our system has photovoltaic cells on them and they can accept sunlight from any angle they can accept what we call the diffuse component, sunlight being scattered from the ground or the clouds or molecules in the atmosphere. Basically they can generate electricity even on cloudy days although we won't get a lot of heat in the pipe. We do still have some benefit.

Ted Simons: How far along this is development?

Zachary Holman: We're actually just at the beginning. Things are still very exciting. ARPE announced the awardees for their focus program in February. We're scheduled for a May 1st start date of our three-year project.

Ted Simons: Three-year project a pilot to see how well it goes?

Zachary Holman: Absolutely. ARPE doesn't fund fundamental research rather they fund things they expect to transition to commercial products. By the end of three years we should have made three prototypes increasing in size until at the end of three years we have a prototype that's large enough to attract the attention of big companies like AVENGOA, who installed the Solana plant.

Ted Simons: Sounds fascinating and encouraging. Good information, good to have you here. Thanks for joining us.

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