How we can make solar power at night

We all know about photovoltaic solar panels. But there’s another, almost forgotten type of solar energy: concentrated solar power. Its big advantage is that it can store the sun’s heat for a long time and turn it into electricity when needed – for example at night, when normal solar panels lie idle. Is it set for a comeback? 

#planeta #solarenergy #concentratedsolarpower

We’re destroying our environment at an alarming rate. But it doesn’t need to be this way. Our new channel Planet A explores the shift towards an eco-friendly world — and challenges our ideas about what dealing with climate change means. We look at the big and the small: What we can do and how the system needs to change. Every Friday we’ll take a truly global look at how to get us out of this mess.

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Credits:
Reporter: Malte Rohwer-Kahlmann
Video Editor: Frederik Willmann
Supervising Editor: Kiyo Dörrer
Factcheck: Alexander Paquet
Thumbnail: Em Chabridon

Read more:

CSP project databases:
https://solarpaces.nrel.gov/?utm_medium=domain-switch&utm_source=csp&utm_campaign=solarpaces

https://cspdata.com/

NREL best practices study:
https://www.nrel.gov/docs/fy20osti/75763.pdf

Status of CSP plants installed worldwide:
https://www.mdpi.com/2571-8797/6/1/18

Chapters:
00:00 Intro
01:18 How CSP works
02:49 Technology race
05:07 Crescent Dunes
07:03 Comeback?
10:51 Conclusion

Check out this documentary from the late 70s. "…the light is converted directly into electricity. No moving parts. It’s the perfect solar machine." People were fascinated by photovoltaic solar cells. It’s just… they were OUTRAGEOUSLY expensive. "This is the biggest collection of photocells ever assembled. It cost a quarter of a million dollars, yet it only produces enough electricity for three or four families." And that’s where a rival technology came into play: Large mirrors that can also turn sunbeams into electricity. By focusing the light from the sun and using its heat. "What you’re seeing is the world’s first commercial solar electric power plant. It’s called Solar One." Concentrated solar power seemed like the most promising solar technology back then. But skip to today and it’s been almost completely forgotten. The story behind it is one of great expectations… "…pure, clean, consistent and reliable energy…" …equally big disappointment… "…the Crescent Dunes project failed." …and, maybe, one of revival. Because concentrated solar can do one very crucial thing that solar cells can’t. You might have seen a concentrated solar power – or CSP – plant that looks like this before. Especially if you’re into your Hollywood sci-fi. CSP plants can also look a bit less futuristic, like this. But fundamentally, they work the same way: They use mirrors to reflect and concentrate sunlight. "It’s simply grabbing the heat that is coming from the sun. And I really love that." This is Xavier Lara, who calls himself a "CSP evangelist". He’s a mechanical engineer who’s worked on many concentrated solar projects around the world. "So you are concentrating roughly about 1000 times the sun in a particular point." In this type of CSP plant, that particular point would be the top of the tower. Inside it, there’s a fluid – usually molten salt, so salt in its liquid form – that gets heated up by the sun’s energy. The hot molten salt is then pumped down to a generator that boils water to produce steam. Which in turn can be used to spin a turbine that generates electricity. "The same kind that you can have in a normal, let’s say, fossil power plant. But without burning any fossil fuels." After that, the salt has cooled down, so it gets pumped up the tower and the cycle starts again. For this process to work properly, you need a lot of direct sunlight. Which is why you find some plants in countries like Chile, Morocco, the United Arab Emirates or India. But most of them are in the hot parts of Spain and the US. So why is it that when we hear "solar energy", most of us immediately think of photovoltaic solar cells – and not mirrors that concentrate sunlight? "I’m old enough to remember in 2010 or so, we were super optimistic about solar thermal electricity generation." Jenny Chase is a solar analyst at the energy research firm BloombergNEF. Back then, there were, for example, big dreams to set up huge concentrated solar plants in the Sahara and send the electricity to Europe via cable. "For a long time, solar thermal was the main utility-scale solar technology. However, what happened then was that semiconductor technology got really cheap and photovoltaics got super cheap." In a little over a decade, the price for electricity from solar photovoltaics dropped by almost 90%. There were a bunch of reasons for this – mainly policy support in Germany which kickstarted a growing solar industry in China. We covered them in this video, you should check out after this. Concentrated solar power also became cheaper. But in 2011 it started costing more than photovoltaics. Today, it’s more than twice as expensive. This meant people began to turn away from it and put up ever cheaper solar panels instead. "It wasn’t so much that solar thermal lost – it was more that photovoltaics won." That is also because with solar thermal or concentrated solar, every single mirror needs to individually track the sun’s movement, so they always direct the rays to exactly the right point. And depending on the size of the plant, this could be thousands of mirrors. And then you have to account for clouds, which may block one part of the mirror field, but not all of it. That makes it hard to control the temperature at the top of the tower which needs to stay within a fixed range. Compared to all this, solar panels are just pretty easy to handle. "When you then put it on your roof or when you put it on a field or when you put it on a lake or wherever you put it, it’s just very simple." This is Richard Thonig, who’s been researching concentrated solar power technology and policy for the last decade. "It’s just sitting there and you have to clean it maybe from time to time. But it’s not operationally complex as CSP where you have mirrors that you need to adjust under real environmental conditions." CSP plants are generally also custom-built, which makes them expensive. So in order to make them worth it, they need to be BIG, which means more challenging to engineer and handle. A case in point… …this megaproject. "Welcome to the future of power generation!" Crescent Dunes, in the US state of Nevada, was supposed to revolutionize clean electricity. It cost a whopping 1 billion dollars to build and when it started to run in 2015, expectations were high. And then the problems began. It never reached its expected average output, which was supposed to power 75,000 homes. Also because there were lots and lots of outages due to technical problems, often to do with the molten salt the plant used. "Molten salt is a pain to work with because if something does go wrong and it drops below its melting point, then you don’t have molten salt anymore, you have solid salt. And then your pipes are full of solid salt and this is a big pain to sort out." One time, the plant had to shut down for eight months on end. Another time, a molten-salt tank leaked and the ground got contaminated, so the entire tower had to be taken down. The plant eventually closed and SolarReserve, the company behind it, ceased to operate. "They were really rock and roll and Silicon Valley type of guys that were, okay, we’re going to revolutionize the world and we need to build lots of these towers. And they were, you know, move fast and break things. And, and it turns out for CSP, that wasn’t the right approach, right? Because you need to figure stuff out, do operations and maintenance, then build the next plant. It takes some time." Crescent Dunes generates small amounts of electricity again but it tarnished the image of CSP, particularly in the US, which hasn’t built another big plant since. Other megaprojects, like the idea to build big plants in the Sahara to power Europe, also fell flat. Today, ALL of the world’s plants taken together have a generating capacity of 7 gigawatts. For comparison: There are 1,700 gigawatts of photovoltaic solar panels out there. So CSP’s never made it big, and it’s seen its fair share of setbacks. But there is one reason why we shouldn’t give up on the idea yet. And that’s the same reason why China has been building many of these in the past years. Because there’s one thing that photovoltaics can’t do. "The thing about photovoltaics is it really does not generate at night." But concentrated solar can. Newer plants don’t just heat up molten salt to use straight away. They also have big tanks to store it once it’s hot. It only cools by 1 degree Celsius per day in there and can be used to run the turbine at a later point. Like after the sun has gone down. Or when lots of people are using lots of electricity all at once. It’s important to have these clean sources of energy we can dispatch around the clock, as we plug more renewables into our grids. Because they only work when the sun shines or the wind blows. Having this flexible supply might also justify paying a little more. "The future of CSP moved to a different niche, right? So it used to be a power technology like wind and PV, and now it’s really very much a storage technology." There are of course other ways to store electricity, like lithium-ion batteries that now often get built right next to solar farms. But they’re typically used to shift up to four hours’ worth of energy. You can build bigger batteries, to cover the night, for example. But that would be very expensive. Since molten salt is quite cheap, it’s more economical to use this for longer periods. It’s also possible to use electricity from solar panels to heat up the molten salt. But that’s less efficient than directly using CSP to capture the sun’s heat – at least in places with lots of sunshine. "CSP has been in the doldrums for about 15 years because we lost the daytime energy battle. But the reality is for the provision of nighttime dispatchable energy in the deserts, there’s nothing that’s this cheap." This is Craig Wood, the CEO of Vast, a company that’s working on new designs to fix the problems concentrated solar power had in the past. "Without our system, you know, without solar thermal in those hot sunny places, you end up needing to burn fossil fuels for the nighttime energy." They already built this small demonstration plant in eastern Australia to prove their technology works. Their next step is to build a bigger one with eight hours of storage. This report by the US National Renewable Energy Laboratory served as their manual. It was compiled after the failure of Crescent Dunes and analyzes all the problems it and other CSP plants encountered. "And that’s really critical because, you know, if you can’t learn from the mistakes of the past, then there’s not really a future for the technology." As you can see, they built several small towers instead of one big one. They say this makes it easier to build and to vary the size of plants without having to come up with custom designs each time. Which saves money. Also, it’s liquid sodium – so a metal, and not molten-salt – that’s circulating through their system. If this becomes solid in case of a shutdown, it’s easier to melt again than salt. But Vast are not the only ones who took an interest in the CSP report. "That book becomes the Chinese CSP engineer handbook, like their Bible." "What has now changed everything for CSP at the moment is that China is getting into it big." China is rediscovering concentrated solar power. There are around 30 plants in development, way more than anywhere else. That’s because every renewable park with 1 GW capacity now MUST include 10% of storage. And the government issued this notice, saying it will support the "large-scale and industrialized development of solar thermal power". The idea is simple. During the day you use solar PV to produce cheap electricity and concentrated solar to heat up your storage tanks. Then at night, when the solar panels lie idle, you use the stored heat to run your turbine. So what does this mean for concentrated solar? Can the technology really stage a comeback? Well, a lot depends on whether China’s solar towers become a success. "Those solar towers then have a real possibility of developing economies of scale to really figure out how everything works. And then we’ll hopefully see the same thing that we saw with PV or with wind, that those supply chain gains from China really enable very cheap or better products that will be available also in other countries in Africa, potentially in Europe, potentially in the US." But this would also mean those other countries have to see the potential and put policies in place to support the technology. Without support, it will be hard for CSP to get off the ground again. Either way, it will likely never get as big as people once thought it would. Solar cells have won the technology race and captured the mass market. But CSP might have found a new niche. And it will be exciting to see whether it can fill it. "Had you ever heard about this crazy-looking solar technology? And what do you think about it? Let us know in the comments and don’t forget to hit subscribe because we have more videos like this for you every Friday."