Concentrated solar energy: Technology to generate electricity
In this article we will talk about concentrated solar energy, everything you need to know about this technology. Sometimes the sun, sometimes the rain and sometimes the clouds. And then night comes anyway. And how to use the sun in such changing conditions? It is quite possible that concentrated solar energy is a solution.
Concentrated solar energy : what is it?
At first, that question is valid. In our previous post on solar energy, you were able to discover how many amounts of energy our star produces and explore the problems related to the operation of photovoltaics and solar collectors. We also mentioned that you can harness solar power with focusing mirrors. How is it working?
At first, we must disappoint you: you will not install such an installation on the roof or in the garden. In fact, concentrated solar energy is only used in a few countries. Why? Because it takes a lot of sun to generate heat or electricity. Where is most of it?
Concentrated solar energy is known mainly in Spain and the United States / Source: REN21
Generally, the greatest amount of direct sunlight is found around the Tropics of Cancer and Capricorn ( here’s a good map ). The leader in installed capacity of the CSP installation (short for Concentrated Solar Power) is Spain, which has 2.3 GW. The United States ranks second, with facilities with a total capacity of 1.8 GW. And globally, at the end of 2016, all such facilities had a total capacity of 4.87 GW. While this is only a fraction of the world’s total green energy capacity (here are the latest statistics from RES ), this technology has potential. First, let’s see …
How does concentrated solar energy work?
You must have played with a magnifying glass once when you were a kid, right? But we do not mean to enlarge the letters, but to focus the sun’s rays on various objects (preferably flammable). Even with your own skin, you could see that the temperature at the hotspot was high enough to burn you. Well, in this video you can see what this temperature can do with various items.
The technology of focusing the sun’s rays was already known in ancient times. Archimedes himself apparently constructed a “death ray” from mirrors aimed at enemy ships. Although the Mythbusters proved that this would not be a practical weapon, in theory it should still work. Theory is theory, but concentrated solar energy is currently used to produce clean energy. How?
Mirror, after all, what is the best reflection of the sun in the world?
The most widespread CSP technology in the world is parabolic mirrors, which focus a beam of sunlight on a special tube. Such tubes (there are usually a staggering number of them) are placed at a suitable distance from the mirror (at the focal point) so that the working medium contained in them (e.g. thermal oil, molten salts) can absorb as much solar energy as possible. So, in other words, heat up to about 400 ° C.
Parabolic mirrors, or solar concentrators, in all their glory / Source: DLR
Then this hot liquid, which emits heat in the exchanger, heats the water enough to turn into steam, which in turn sets the turbine in motion, which generates electricity. Much the same as a traditional coal-fired power plant, except that we have no greenhouse gas emissions or air pollutants .
Solar towers like the ones in science fiction movies
The second most widely used CSP technology is solar towers . It sounds a bit like a concept from futuristic movies and it looks a bit like that. And it works by placing mirrors, called heliostats, over a large area. The sun’s rays are reflected off these mirrors (they are mobile and align with the sun) and are directed directly at the tall tower. So that?
Concentrated solar energy in the form of a solar tower is impressive / Source: Torresol Energy Investments, SA
At the top of the tower is a tank with molten salts (60% sodium nitrate, 40% potassium nitrate) which, thanks to a focused beam of sunlight, is heated to more than 560 ° C (and in sometimes up to 1000 ° C). ). This hot mixture is then used to produce steam and electricity, just like a parabolic mirror installation.
Solar Fresnel Plates and Mirrors
There are still two less widespread technologies available. The first is a plate system that concentrates solar energy into a receiver mounted on the arm, which acts as a motor. Inside are thin tubes filled with hydrogen or helium and cylinders. Concentrated solar energy heats the entire system enough to expand the hot gases. These, in turn, set the pistons in motion and then, through the shaft, the generator produces electricity. Hmm, it’s a bit complicated isn’t it?
On the left a solar panel (source: energy.gov), on the right a Fresnel mirror (source: seia.org)
The last option, but a little easier, to use the sun’s rays are called Fresnel Mirrors . It is a system similar to parabolic mirrors, with the difference that the sun’s rays reflected by the mirrors heat the working medium (in this case it is usually water) in a larger and longitudinal receiver. In addition, the principle of operation is similar. Pictures say a thousand words, so take a look.
Concentrated solar energy can be converted in 4 ways / Source: Peter Heller – The performance of concentrated solar energy (CSP) systems
Great, but what if we have such wonderful solar technologies, if they don’t work when the sun disappears below the horizon, which is when we would need energy the most? However, it turns out that the first two technologies can work around the clock. How is it possible?
24 hour concentrated solar energy
The key to solving this puzzle is to store energy in a hot salt mixture. And not for half an hour, but even for several hours. This means that the energy for a CSP power plant can be produced around the clock. Fantastic!
Bathed in sunlight, Dubai likes to use solar energy. They already have quite a few solar panels installed there, but a project has just started to build a CSP power plant using two 200 MW solar towers. One of the requirements is to be able to store and generate energy for 15 hours after sunset. The power plant will come online in 2021, and the electricity it produces is expected to cost around PLN 3.6 ($ 0.95) per kilowatt hour.
Gemasolar Power Plant in Spain from a bird’s eye view / Source: Torresol Energy Investments, SA
Surprisingly, it can be even cheaper. Three solar thermal power plants built in Chile (to be launched in a few years) will sell electricity at PLN 2.4 per kWh ($ 0.63) without any subsidy. They will also use solar tower technology (two or three) with an energy storage time of 14 hours. Their maximum thermal power is greater than 1 gigawatt, thanks to which they will be able to provide Chileans with 7,100 GWh of clean energy directly from the Sun each year. That is enough to power a total of more than 2 million homes throughout the day! The best part is …
More and more solar thermal power plants are being built
Israel is also building one. And that’s true with the record-breaking 240-meter-tall solar tower . Around it, there will be 50,000 mirrors covering more than 3 km2 of surface. In 2018, it will start producing electricity, which will provide 1% of the demand for the entire country.
This is what a solar power plant in Israel should look like when completed / Source: HELIOSCSP
Apparently not much, but it is always 1% more pure energy. And this is what the world needs to replace fossil fuels and reduce greenhouse gas emissions that warm our planet. And there will be more clean energy, because more such facilities are already being or will be built in Morocco, South Africa, China and Australia. Whatever it is, it is happening and more and more countries are lighting up energetically.
The International Energy Agency (IEA) has estimated that by 2050 more than 11% of electricity will be produced by installations using solar concentrators, which could reduce CO2 emissions worldwide by up to 8%. In turn, the IRENA agency reports that in Europe alone in 2030 more than 4% of energy can be provided by CSP power plants even when the sun is not shining. Great, but …
