Solar power providing electricity 24 hours a day in summer

Beyond Zero’s Matthew Wright and Scott Bilby talk to Santiago Arias, Chief Infrastructure Officer of Torresol about a first-of-its-kind commercial 'Power Tower' that supplies electricity 24 hours a day.

Santiago Arias podcast

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Scott Bilby: This morning on Beyond Zero we're talking to Santiago Arias, Chief Infrastructure's Officer for Torresol Energy ,which in English I think Torresol translates into ...

Mathew Wright: ...Sun Tower

Scott: OK. And Torresol are a company creating Concentrating Solar Power plants. Some of them are parabolic troughs. There's one using a sun tower technology...

Matthew: ...and that's the one we're talking about today. It's called the Solar Gem, which is GEMASOLAR.

Scott: Yes, excellent. So, both of these solutions at the moment employ storage solutions which significantly extend the operating range of the power plants, especially the sun tower ones. So, we really want to hear about that. So, hello Mr. Arius and thank you joining us in the studio.

Santiago Arias: Hello and good night from me.

Scott: It's good night from you and you're actually at the moment you're in Abu Dhabi.

Santiago: In Abu Dhabi, yes.

Matthew: At 2:30 in the morning. So, we really appreciate your time and certainly our listeners will too.

Scott: And well, we know that the Abu Dhabi connection with Torresol is that its part owned by the...

Santiago: MASDAR. The MASDAR Company.

Matthew: And they're organising a whole lot of investments in renewable energy infrastructure and zero carbon cities, I understand.

Santiago: Yes. Well, Torresol is a result of a joint venture in between SENER and MASDAR. SENER is a Spanish Engineering Company that was created in the fifties. The company has 2500 employees , mainly engineers, with offices in five countries and lately has been very active in the funding and erecting solar plants for all their companies. In particular, ANDASOL 1 and ANDASOL 2 and EXTRESOL1 and EXTRESOL2 in Spain for A.C.S.

And MASDAR is a company owned by the Abu Dhabi Government which is very interesting because really a country which is living in the oil producing [region] is not committed in renewable source of energy. So, both SENER and MASDAR have to created Torresol to promote, to operate and to exploit technical advanced Concentration Solar Plants.

As you were saying before, we are just now constructing 3 plants in Spain. Two of them are 50 Megawatt parabolic screw type and those are very similar to the existing one, ANDASOL and EXTRESOL. And the third one, which is maybe the most innovative, is a different animal, is a small 20 Megawatt centre plant, with tower, having 16 hours of storage capacity operating with molten salts.

Matthew: Now, that plant is very interesting. It's power tower technology, we'll talk about that in a minute. Given that the parabolic trough plants you have been involved in those and they're the tried and proven system, can you tell us why SENER or how it came about that you are moving to this new improved technology? Like, how did that happen?

Santiago: Yeah. Well, we believe that the tower system is, let's say from the engineering standpoint, is better than any other system. Obviously we need to exploit also the other plants; the ones that are let's say, now traditional because there are some existing facilities operating in the world.

So, in parallel, we are running a higher risk on the tower type, which is absolutely new in the world and, at the same time we are using the other ones, more conservative ones.

Matthew: So, if you can describe the power tower to our listeners. You know, explain what the heliostat mirror field is and things like that.

Santiago: Yes sure. Well I mean the first technology is very well known. There is some loops of oil that are receiving the concentration of the light from some mirrors located below, and then the mirrors are tracking the sun and concentrating the light on the tube which is heated up to 400 degrees and then from there the oil is delivered to a steam generation system, producing the steam and the steam usually moves the turbine that generates electricity. And in parallel to that, part of the oil, the heated oil, is used to heat some molten salts from, let's say, 300 degrees to 400 degrees [celcius], 750 Fahrenheit, I don't know if you're....

Matthew: We are Celsius.

Santiago: OK, then from 300 to 400 degrees and then during the night we reverse the system. We are cooling down the salts, heating the oil and the oil continues producing steam during the night meaning that we are able to produce, in our solar plant, also during the night.

The other system is, let's say, more complex. What we have is a tower and we have a huge number of heliostats, something like 2600 heliostats, for instance.

Matthew: They're the mirrors that are on the ground.

Santiago: Yeah, they are the mirrors on it. All of them are reflecting the light from the sun and concentrating the light in a single spot in a high tower. Then the process is very similar. I mean we are delivering molten salts from the ground level to the tower, heating up to 565 degrees [Celcius] and then we deliver them back to a hot storage tank. From there again, we pump them and we produce steam and electricity.

Matthew: Now, there's a number of advantages I understand to that. So first, can you tell us about the fact that you use salt as a working fluid. So, instead of having the oil you're only running the salt up the tower and what the advantages are there?

Santiago: Yes, well the salt has some advantages compared to the oil, mainly the temperature. I mean, the oil degrades at 400 degrees [Celcius] then you have to be very careful not to overheat the oil. The salts have no vacuum pressure, meaning that they don't produce any pressure when temperature is high. And you can reach highest temperatures, in fact you are not limited by the fluid any more, we are limited by the materials, by the piping materials and things like that. So, we are limiting the temperature to 565 degrees [Celcius] to generate the best possible steam, the steam having the maximum pressure. So, it is the most effective for the turbine to operate.

Matthew: So, for listeners who don't understand. To actually be able to run at higher temperatures means that overall you can actually extract more energy out of a mirror field. Is that right?

Santiago: Yes. Operating at higher temperatures, what happens is that the generation of the electricity, using a turbine, is having a maximum efficiency. So yes basically, as higher the temperature is, as higher the efficiency of the system is in converting the solar energy into electricity.

Matthew: Now, I also understand that because you are sticking to salt going from the hot tank to the cold tank and back again and not having the extra stage of the oil and the steam you're actually losing less ...

Santiago: ...less energy, that's true. Yes I mean, in the process of passing the oil to salts and then back from salts to oil you have the transfer of heat and obviously you need heat exchangers that are reducing the temperature and also obviously you have some heat losses as well.

Matthew: plant? Have you broken ground? Have you actually started any construction or are the drawings finished?

Santiago: We already started in December, what I am speaking about, GEMASOLAR, we have started in December last year. The tower is growing something like a few centimetres per day; it's a very interesting construction process. And we're expecting the plant to be completed at the end of the next year [2010]. Then there will be something like six months startup period and well, I'm crossing my fingers, we're expecting in one year's time to reach the maximum power, the maximum capacity or maximum efficiency.

Scott: And whereabouts is this plant going to be?

Santiago: Excuse me?

Scott: Where will the power plant be?

Santiago: That plant is going to be installed in the south of Spain close to Cordoba, in one of the hottest spots of Spain. The other two are going to be located more on the south [ 10.51 unintelligible], close to Arcos de la Frontera.

Matthew: And how many hours of sun does the location where the GEMASOLAR plant is going to be located? How many hours of sun a year do you get?

Santiago: That's the biggest difference against, let's say, the traditional solar plants. I mean by having a capacity of 16 hours of storage, in GEMASOLAR, we will be able to run more than 6000 hours per year. So, compared to a normal plant which normally operates 2000 or 2500 hours per year you can imagine that we produce much more power. We deliver more power to the network, to the grid, than any other plant.

Matthew: So, basically your power plant with the molten salt storage, will be able to deliver in summer, say, power all night long. Is that right?

Santiago: Yes. In fact, we are planning, again, we have to prove it yet, but our idea is to run practically in summer time 24 hours over 24 hours. Then in winter time, maybe we have to stop sometime during the night because the number of hours of insolation obviously is lower and depending on the conditions there will be some nights that we have to stop and start the turbine again, but that's something which is not desirable.

Something which is also interesting is that, since we have this huge storage capacity, really the operation is going to be simpler than most of the other plants because I have something like teams and systems and computers and equipment focus only on tracking the sun and getting the highest energy into the tanks. And I have another team which is independent of the first one, and on other systems, pumps, etcetera that are just emptying the hot tank, transferring into the cold tank at the rate that we need. I mean, the rate that we consider appropriate to fulfil the requirements of the grid at the time that we prefer.

We need that, for instance, in most of the European countries the peak of electricity consumption is about 8 or 9 in the night and obviously at that time the PV, the photovoltaic plants are not operative. Wind also tends to decrease and we are the only, lets say, alternative energy that we are able to provide energy at that time. So this, from the, let's say, social standpoint is a major difference compared to the rest of the plants.

Matthew: This morning on Beyond Zero we're talking to Santiago Arias, Chief Infrastructure Officer for Torresol Energy, a company creating Concentrating Solar Power plants, some using parabolic troughs and some using tower technology, both employing storage solutions. And significantly the operating range of the power plants in this case are 15 hours after dark.

And Santiago, a bit more about the solar salt system. Can you tell us the difference between how much salt you need when you're operating at, how many tonnes of salt you need when you're operating at higher temps versus how many tonnes of salt you need if running a parabolic trough plant at lower 400 degree temps?

Santiago: Yes, that's exactly the, major difference. The oil has that limitation of 400 degrees maximum and increasing the temperature provides higher efficiencies. Also the storage tanks could be smaller because the, lets say, the enthalpy of the accumulative there is higher than operating at 400 degrees. So, it's a major difference and really helps us to be more efficient.

Our idea is to try to reach the parity cost as soon as possible. 'Parity cost' meaning that the solar energy being, let's say, equivalent in producing cost compared to the traditional ways of producing electricity. By doing that, by using the molten salt system and the bigger storage system, we are thinking that we will be reducing, in middle term, will be reducing the cost of the solar energy.

Matthew: And how much less salt do you use in a tower versus a trough?

Santiago: How much, I'm sorry?

Matthew: How much less salt do you need for the same amount of energy in a tower versus a trough?

Santiago: Sure. Well, it's something like half of the amount that you need on a trough system.

Matthew: So, big savings there because you're obviously spending half as much on buying that salt.

Santiago: Yes.

Matthew: Now, another question about the tower. It's quite interesting because you're actually pumping the salt up and the salt's obviously at 500 degrees as it comes down. What do you do at night? Do you drain the salt out of the tower or do you have to keep it warm, or do you just slowly pump it through or...?

Santiago: Well, the salt has pretty high thermal inertia, so the possibility of having freezing in the piping system are very reduced. However, during the night we are planning to drain the system. Since we are operating in a tower, all the systems are located above the tanks and the tanks have a huge amount of molten salts. Just for instance, if not operative they will decrease the temperature at less than one degree per day. You need something like 20 or 25 days with no operation before starting the heating system.

We have also some electrical system to provide energy in case that we need to, for instance for maintenance or something like that, we need to stay a long time without operating the plant.

Scott: So, Mr Arius, how many days would that be that the plant, even if the plant completely shut down and it wasn't working, how many days would it be before the molten salt froze?

Santiago: Something like 15 days.

Matthew: So, you've got a lot of time.

Santiago: Well, yes on top of that we have gas heaters and also we have electrical heaters, so there's plenty, I mean the possibility of having the frozen salts inside the tank should be a disaster, so usually we need to be preventing that. But, I mean, the risk is like we need to be operating very poorly the plant to reach that situation.

Matthew: So, it's very unlikely that could ever happen.

Santiago: Yes.

Matthew: Now we don't get lot of, obviously with the language difference between Spanish and English, we don't get a lot of news in depth about the situation in Spain. But we do know there's a lot of solar plants under planning and in fact we read in a Bloomberg article, and we haven't been able to confirm this, that there's actually 14000 megawatts of plants that have been announced or are in planning across Spain. Is that something you're aware of?

Santiago: Yes. Well, the political situation in Spain is helping us a lot. I mean, the government is sponsoring the electrical (electricity) we produce by paying a certain fee over the cost of the electricity we produce meaning that something which today is not yet, let's say profitable, it makes it very profitable.

Then there are plenty of companies right now making the same kind of projects we are doing. Something like 12 plants are going to be constructed or are in construction right now. So yes, the situation is that by doing that, Spain has become, let's say, the reference for all countries right now.

Matthew: Solar hot spot!

Santiago: Yes. In fact today in Abu Dhabi , it was funny [laughs] because everybody, all the speakers in the summit were speaking about Spain, the situation in Spain and referring to the Spanish plans they are doing and things like that. It's like everything is concentrated in Spain right now. I hope that in the future there will be some other countries where some speculation in the United States, for instance, where once the legislation is clear, we will be there and many other Spanish companies will be there doing the same we are doing in Spain.

Matthew: Now before I ask you about that feed in tariff, you're at a conference. Can you tell us a bit about the conference?

Santiago: Well, it was in Abu Dhabi in a conference for solar energies and water in the Middle East.

Matthew: Yes. Ok, now the feed in tariffs. So, this support mechanism which is enabling the earlier adoption of the technology to get to a point where it can reach that parity. Can you tell us about the feed in tariff, about what limits are on it and what sort of rates you get relative to regular rate of electricity?

Santiago: Well, first of all, the price of electricity, it is perceived that in the future it will go up again, I mean, we are enjoying now very low prices but this is, in the long term, obviously the prices of electricity from gas or from coal or whatever is going to increase. This is the first factor to reaching the parity.

But on top of all that really I think the Spanish government is doing something very clever, because they are promoting these kind of energies, just the first ones, allowing some companies to operate, some companies to do their own experience and obviously by doing that, by installing these kinds of plants we are getting some cost reductions due the industrialisation of the parts to be manufactured. And we are expecting that obviously the price of the solar energy, by doing plants, will go down. That happened already with the photovoltaic energy and we are expecting something similar on the thermal solar energy.

Scott: Now, Torresol is part owned by MASDAR, as we said earlier a company from Abu Dhabi and I'll just say, for the audience, that's M-A-S-D-A-R, as opposed to the car company, M-A-Z-D-A. But MASDAR is a company in Abu Dhabi, and is owned by the Abu Dhabi government and obviously they're very keen to see power plants like Gemasolar built in Abu Dhabi. So, is it likely, as soon as the Gemasolar plant in southern Spain is built, in the next year after that they're going to see them built in Abu Dhabi as well?

Santiago: I mean, the Abu Dhabi government is willing to do that. I think that we're going to start with parabolic trough plants, but yes, as soon as Gemasolar is gaining confidence in the results and things like that, we are trying to do a bigger plant in Abu Dhabi. That's the next project we are going to do out of Spain.

Matthew: And when you say a bigger plant, is the actual, is it going to be more mirrors, like a bigger mirror field for the same tower or does a bigger plant mean multiple modules, multiple towers all next to each other?

Santiago: SENER is contemplating both possibilities. In fact, there are some of the combinations that are very interesting. Like having shared towers for the same fields so each mirror is going to be focusing on the tower depending on the hour of the day to improve the efficiency of the system. But so far the project we were aiming to do in Abu Dhabi was a big, single tower with plenty of heliostats. But yes, sure this is a possibility.

The other possibility is maybe a multiple tower system with sharing the heliostats. This is very interesting, the possibility of sharing the mirrors so they are used in the most profitable way by reflecting the light to the tower more convenient depending on the position of the sun.

Matthew: Now, the current plant that's being built in Spain is 17 megawatts and it can run obviously at like a 75 percent capacity factor. Those new plants that you're contemplating, how big could they go for one tower do you think? Could they be 50 megawatts or what sort of size?

Santiago: Yes, we're contemplating the possibility of constructing something in the range close to 50 megawatts; maybe we are not going to be reaching 50 megawatts, but close to that figure.

Matthew: And what about using smaller mirrors that are closer to the ground so that you can get more light off the ground?

Santiago: More mirrors means more complexity. I read that the manufacturing of the smaller mirrors could be cheaper and easier. However, the control and the operating maintenance cost, once they have been installed, maybe are going to be higher. Just imagine that it's a very complex control system. We need to be controlling 2600 mirrors bidirectional, in two directions, and at the same time each one has a different angle to be reflecting the light on a single spot.

So, imagine that the same control system not for 2600 but for 30 or 40 thousand units that you need in case that, for the same power, you are using a smaller heliostats. So, my impression is that maybe it is easier to manufacture smaller heliostats, but then the complexity of, and the operation cost will be higher than the case of really big heliostats.

Matthew: Fantastic. Now, I've just got an SMS from my girlfriend and she's a developer of a storage system called of ammonia thermo-chemical storage at the Australian National University and she says, 'Could she visit the tower on her way to the SolarPACES conference in September?' [laughs]

Santiago: OK. OK, that's really funny. In fact, we're going to have another summit in Bilbao, Bilbao is in the north of Spain, next week, so maybe they can also be interested in attending there.

Matthew: I'll let her know. Thanks. She's actually listening to the show.

Scott: I think were just running out of time now, Santiago but thank you very much for allowing us to interview you this morning at the horrendous time of 2:30am in the morning from Abu Dhabi!

Matthew: We really appreciate that.

Santiago: Thank you.

Matthew: And your commitment to solar technology which is something we respect.

Scott: And I'll just say, before you go Santiago, we're very impressed by the sun tower because it was hard to find information on this project, but what you've told us today is very impressive indeed. So, thank you very much.

Santiago: You're welcome.

Matthew: Great. So, we've been talking to Santiago Arias, the Chief Infrastructure Officer for Torresol Energy. That's a company doing Concentrating Solar Plants and, in particular, the most innovative GEMASOLAR, solar power tower technology. You can find out about them at w-w-w. T-o-r-r-e-s-o-l. com, that's www.torresol.com [correction http://www.torresolenergy.com]

And they've got a great video on their web site and you can find out how the tower works and see the salt move up from the hot tank through the tower receiving the sun and into the cold tank. So, I'd recommend you do that or you can find that video on YouTube if you search for Torresol, T-o-r-r-e-s-o-l. So, from us...

Scott: I'll see you later.

Matthew: and that's beyondzeroemissions.org

Transcript by Kevin