Bill Gould from Solar Reserve

Beyond Zero's Matthew Wright speaks to Bill Gould, a veteran of the solar industry, about solar reserve and the wider solar industry in the USA.

Bill Gould interview

download

Transcript

Matthew: On today’s program we are going to be talking about Solar Reserve and, in particular, we are going to be talking to Bill Gould who is a veteran of the solar industry. Bill Gould’s technical experience spans a pretty long time. I’m not sure exactly where he started out but he certainly worked at Bechtel and today he works for Solar Reserve. In fact he even worked at General Atomics, so it will be interesting to know what he was doing there.

In particular, he was the project manager of the Solar Two project, which was a very successful program run by the US Department of Energy in conjunction with some industrial partners, including Boeing and Bechtel. Bill has Bachelor of Science and Master of Science degrees in Mechanical Engineering at Brigham Young University and he’s a professional engineer in several States of the US. He has participated in numerous post-graduate courses and seminars and has authored a number of technical papers on solar energy. He’s a real solar energy expert, so we’re glad to have him on the line. Let’s see if we’ve got Bill there now. Hello.

Bill: Good morning. It’s good to be with you.

Matthew: It’s great to have you too. We’re going to just find out a bit about how you got involved in renewable energy and then we’d be very keen to find out about what’s happening in the United States, what’s happening with Solar Reserve’s power tower technology. So, just to kick it off, I was wondering could you tell us how you ended up in a role that involves solar energy, in such an early stage of the development of the solar industry globally.

Bill: Sure. After doing my Engineering degrees, I first was employed ‘on the dark side’, doing nuclear power plants and coal and oil-fired power plants, way back in the early seventies. But then in 1994 I was given the opportunity to manage a solar project for the very first time. It was the Solar Two project that you mentioned. And ever since then I have been excited to do clean energy and have been in the power business with solar energy since 1994.

Matthew: Did someone come to you or were you particularly drawn to the role to run the Solar Two project?

Bill: Bechtel had the contract to build Solar Two for the US Department of Energy and, as Bechtel was looking around for a project manager, it was given to me as an opportunity and I jumped on it, to have the opportunity to do something clean. Up to that time it seemed like the Sierra Club and a lot of other environmental groups were opposed to the projects that I was doing, and nuclear power, and burning coal. Now, with solar power, the Sierra Club and others ended up working on our behalf to help encourage the local authorities to permit our projects. That was a refreshing change.

Matthew: Can you tell us a bit about the history of the Solar Two project. I understand you received, obviously to commence that, you received the old Solar One site. What was that and how did you change that into Solar Two?

Bill: Yes. First let me tell you just a little bit about it. You start out with a large circular field of mirrors. We call them heliostats. These mirrors are very large, about the size of a billboard that you’d see on the highway, about 60 to a 100 square metres in surface area. Each of these heliostats, or mirror assemblies, is steerable in two axes so that it can follow the sun across the sky and the heliostats’ job is to bounce the sunlight to a heat exchanger on the top of a very tall tower. Then we capture that heat and use that heat to drive a normal steam turbine connected to an electrical generator to produce utility-scale power.

Now Solar One had that same configuration and we used water as the heat transfer fluid. We would pump the water up to the top of the tower and, after all the sunlight hit it, it would turn to steam. Then it would flow directly into the turbine. But there was a problem. That problem is that, if you had a shadow from even a small cloud cross this field of mirrors, the heat would suddenly plummet and you’d have a mixture of water and steam entering into the turbine. That was very bad. Water droplets would erode the turbine blades. The plant operators quickly learned that if you saw clouds in the sky you had to shut down the plant.

The US Department of Energy knew that that was not going to be a successful approach. So it commissioned Solar Two and in Solar Two we changed that working fluid water/steam to a liquid salt. It’s not table salt. It’s not sodium chloride. It’s a mixture of sodium nitrate and potassium nitrate like fertiliser that you put in the garden. We melt it and then we use that fluid to capture all the heat at the top of the tower. Then when it’s time to generate electricity we run that hot salt through a heat exchanger and then we boil water to steam and drive a normal steam turbine generator at the back end. Solar Two was about converting the facility from basically a water-based system to a two-cycle system where you had salt for collection and water/steam for electrical generation.

Matthew: So when a cloud came over, or when early night fell, you could continue operating the plant without any hiccups?

Bill: Well, that’s the key difference. If you’d have a cloud come across the field in Solar Two you would reduce the flow of the salt to match what energy was coming in or you could even stop the salt flowing entirely, and shut down the collection of energy, but the generation of electricity never stopped. It was never interrupted because we had already collected a lot of heat and stored it in the form of very hot salt in a very very large tank and, as long as we had heated salt in the hot tank, the electrical generation continued whether you had a cloud or even after dark.

In fact, just to prove that you could, we ran the plant, Solar Two, all through the night for an entire week – just to prove that you didn’t have to have sunlight as long as you had efficient energy storage.

Matthew: And that particular design, Solar Two, how many hours of full output was it designed to capture, to run into the night?

Bill: Well, this was a demonstration plant, a pilot plant. It was not designed for commercial activity. So the Department of Energy gave us enough money to be able to have three hours of full power storage in our salt tanks, or we could run at a reduced output all night long. It proved a concept, of course, for commercial plants. You get much larger salt inventories, much larger tanks, and currently we run some of our plants almost 24 hours a day at full power because we have millions of pounds of salt in inventory.

Matthew: Now, talking about your current plants, can you tell us about the evolution from the completion of that project – I understand it completed in something like 1999 – and what happened from the learnings from that, and what scale-up has occurred? Where have you come from Solar Two, with three hours of storage and 10 megawatts’ turbine reading, to what you have now? How did that evolution happen over the years?

Bill: Well, that’s an interesting story. The plant was shut down in 1999 after we finished all of the tests that the Department of Energy and our utility partners had asked us to perform. We measured everything and then we took the plant apart and did metallurgic analysis on the steel and things like that.

We wanted to go ahead and start building big commercial-scale plants but in 1999 the cost of natural gas and coal was really low. Twelve years ago we didn’t have as much of an environmental movement as we do today. Today we have governments in several places wanting to reduce greenhouse gases so they’ve mandated that utilities have cleaner forms of generation than in the past. That wasn’t true in 1999.

So, after we shut the plant down, we did a few studies but nothing much happened until about 2008. At that time a few of us got back together and decided that the economics now would favour picking up the technology and going again. So we formed Solar Reserve and we have skilled up the technology from that prototype. So now we are offering plants the size of 100 megawatts, maybe 200 megawatts, whereas Solar Two was only a 10-megawatt plant. Now it’s fully utility scale and ready for commercial development.

Matthew: In terms of the different components of that technology, a really important part is the receiver. Can you tell us a bit about the receiver and the company involved. I understand that the kind of metals they use are similar to what’s in jet engines. Can you talk a bit about that?

Bill: The receiver was designed by Rocketdyne, a US company that designed and built the space shuttle engines. In fact, Rocketdyne has built all of the liquid-fuelled engines that the United States has used to launch satellites and the space shuttle. It has a similar construction in that the nozzle of the space shuttle is made up of hundreds of little tubes that carry exotic fluids. In the case of a rocket, they carry liquid hydrogen and you feed it through these little tubes and then interact it with oxygen to produce that fantastic flame.

The design for our receiver is similar but it’s child’s play in comparison. The receiver is nominally a cylinder composed of many hundreds of tubes. We flow this liquid salt that I mentioned through these tubes. The sunlight shines on those tubes and the heat is transferred into the salt. It’s similar conceptually but the challenge is much easier than when you build a rocket engine. We only raise the temperature a few hundred degrees whereas, of course, with a rocket engine you’re talking about thousands of degrees.

Matthew: That’s obviously at the top of the tower and that’s where all the light from the thousands of mirrors is being received. These mirrors, these heliostat mirrors, can you tell us a bit about them. I understand there’s 17,500 in the current design. Can you tell us how big they are, how they work and a bit about the field size?

Bill: Sure. The field is about 2.7 kilometres in diameter. It’s a big field. We have 17,000 of these heliostats. Each heliostat is about 60 or70 square metres, or about like a highway billboard. It’s steerable. We’ve got a motor, got two motors, and a computer in each heliostat. So that means we have 17,000 small computers in the field. They track the position of the sun in order to be able to reflect the sunlight to hit that receiver at the top of the tower. The heliostats move in rotation and also, they angle up and down, so that you can accurately follow the sun and know exactly where that beam is going. They are slightly concave so that they can keep the sunlight focused as tightly as possible and have as much of the sunlight as possible hit the receiver. It’s a big part of the overall plant.

Matthew: Can you tell us a bit about the future possibility of these plants. How big could they get?

Bill: There are some natural thresholds, natural constraints. Our furthest heliostat is one and a half kilometres away from the tower. That’s a good challenge to be able to bounce the sunlight and hit a relatively small target a kilometre and a half away! We do all sorts of comparisons to see how far you could actually put a heliostat and make it economical.

Of course, you couldn’t put it 10 miles away because you would have difficulty with precise aiming and the sunlight is going to diffuse a little bit. You won’t keep a small spotlight. It’s not like a laser. Also you’d have some attenuation of the light that passed through dust or slight amounts of moisture or fog.

We think that probably the threshold is somewhere between one and a half kilometres and one and three-quarter kilometres. That’s where the marginal cost of the next heliostat probably is greater than the marginal contribution. We’ve done studies for large international utilities that want more power than 100 or 200 megawatts. They want 1,000 megawatts. The way to accomplish that is by using a modular approach, where maybe you have ten towers on one station, controlled by a single controller.

There’s a lot of economy to be achieved if you have a modular approach. Of course it’s a very big land area but, you know, in the places where we put these plants, people don’t want to live. These plants are typically located way out in the desert where there’s just very little living and land is dirt cheap. So that works out OK for us.

Matthew: Given that the cost of solar photovoltaic has come down so much, if a utility wanted a single module at a slightly bigger size, would it be feasible now to have photovoltaic on trackers ringing the plant, have the plant throttle down at, say, 10 am in the morning and then pre-emptively curtail some of the PV, and bring the plant back up at 4 pm or 5 pm in the evening? Is that some future prospect, so that you could actually operate the turbine even if you wanted a similar to baseload, 75% capacity factor plant? Would a hybrid like that ever be economic?

Bill: That’s a great question. In fact, that’s the state of the art. We’re proposing just such a plant like that right now. You know, utilities look at two components of pricing. Energy is the first component and that’s simply the cost per kilowatt-hour. The second parameter you look at is capacity and that means that you can guarantee, to the utility, that when they want electricity you can deliver it. Oftentimes the utility contracts in the Unites States have those two components and they are priced separately.

Now you’ve recognised that the PV prices are very low now. They’ve come down dramatically in the last five years and they do wonderfully well in lower energy costs. But there’s no dependability. You are dependent upon on clear skies, and if clouds come across, it’s beyond your control and you’re not going to produce any electricity. Now the molten salt power tower, on the other hand, can collect energy all day long and store it, and not use it until the utility wants capacity.

So we’re proposing a combination, a hybrid plant in many locations that would use a large photovoltaic field, coupled with a molten salt power tower. All day long on a clear day the photovoltaic panels collect energy and generate electricity. The molten salt power tower next door collects the energy and puts it into the hot tank and stores it. Then when the sun goes down, the PV drops off to zero and we fire up the molten salt power tower. The power tower can keep generating electricity all night long if you design it that way, because it has stored up the energy and not produced electricity during the daytime.

Matthew: That’s fantastic. That obviously allows you now to offer a slightly larger module. Is it now 30% larger because you don’t actually have to generate during the day?

Bill: Well you can size them to match what the utility needs. One of our customers is in the State of Nevada, which includes Las Vegas, and during the evening, say from 6 pm when the sun goes down till midnight, even into the early morning hours, all those lights on the Las Vegas strip are burning bright. People have their air-conditioning turned up full. So the load in Nevada, for example, has a peak from about 2 pm to maybe 2 am. So we can squeeze our CSP production, our molten salt power tower production, into the timeframe that the utility wants.

It’s kind of like this. You can decide the size of the output, whether it’s 80 megawatts, 100 megawatts, 200 megawatts, and given that amount of output, based on the inventory you have in the salt pan. For example, you might have a 200-megawatt plant that operates for only six or eight hours whereas a 100-megawatt plant, half the size, operates twice as long. You’ve got the same amount of energy but the customer gets to decide how to spend it.

Matthew: Back to Tonopah, can you just tell us a bit about that plant. I understand works have already started there and the official ground-breaking is happening in the next coming week or so.

Bill: Yes, we are pretty excited about that. It’s official name is Crescent Dunes but it’s right adjacent to the town of Tonopah in Nevada, which is about halfway between Las Vegas and Reno, out in the desert. There’s actually some small mining communities in the area but basically our plant is just out on the sand. We started construction in August and we expect to complete it by December 2013. We just received a loan guarantee from the US Department of Energy for $737 million. We were able to find equity partners to invest with us and now that plant is going up in the desert. That plant is going to be 110 megawatts of net output. It will operate over a long period of the day.

Matthew: And is the receiver design already finished? Is it in manufacture at the moment?

Bill: That’s right. The receiver is completely designed and manufacturing is going on now. They have started to weld the tubes into the receiver. It will be delivered in pieces in about six months and then it will start to be erected.

Matthew: And are the heliostats all ready for manufacture?

Bill: They’re ready for manufacture. They have not yet started installation of the heliostats. We are going to wait until after the winter weather. We’ll probably start in March of next year, drilling all the holes and planting all the heliostats in the field.

Matthew: So what sort of works are happening right now? I guess some earth moving and what else?

Bill: The longest activity in our schedule is the erection of the tower in the centre of the field. The tower is 560 feet tall. We put the receiver on top of that concrete tower. It’s a slip form concrete tower which means that once you’ve finished the basic foundation, and are starting to go up with a chimney-like tower, you have one continuous pour that operates 24 hours a day for about three months to get to the top. It’ll look just like a chimney on a coal-fired power plant and it’s about the same diameter and wall thickness, except it’s got a little bit more steel in it to support the receiver that goes up on top. So right now we’ve finished the foundations for the tower and we’re assembling the equipment to perform the slip form concrete work.

Matthew: Fantastic! We’re going to have to leave it there. We’d love to speak again at some point. What’s the web address of Solar Reserve so people can find out more?

Bill: It’s www.solarreserve.com. Pretty simple.

Matthew: Thanks very much, Bill, and hopefully we can speak to you again soon.

Bill: Nice talking to you.

transcript by Bronwyn L.