Sometimes it is sun, sometimes it is rain, and sometimes it is clouds. And then night comes anyway. And how to use the sun in such changing conditions? It is very possible that concentrated solar energy is a solution.
Concentrated Solar Energy, What Is It?
This question is valid at the beginning. In our previous post on solar energy, you could find out how huge amounts of energy our star produces and explore the issues related to the operation of photovoltaics and solar collectors. We also mentioned that you can harness solar energy with focusing mirrors.
How it’s working?
At the outset, we must disappoint you – you will not put up 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 the most of it?
Generally, the greatest amount of direct sunlight is around the tropics of Cancer and Capricorn ( here’s a good map ). The leader in terms of the installed capacity of the CSP (short for Concentrated Solar Power) installation is Spain, which has 2.3 GW at its disposal. The United States is in second place, with installations with a total capacity of 1.8 GW. And globally, at the end of 2016, all installations of this type had a total capacity of 4.87 GW. While this is only a fraction of the total global green energy capacity (here are the latest RES statistics ), this technology has potential. First, let’s check …
How Does Concentrated Solar Energy Work?
You must have played with a magnifying glass once as children, right? But we are not talking about enlarging the letters, but focusing the sun’s rays on various objects (preferably flammable). Even with your own skin, you could see that the temperature at the point of concentration was high enough to burn yourself. In fact, in this video you can see what this temperature can do with various items.
The technology of focusing the sun’s rays was known already in antiquity. Apparently, Archimedes himself constructed a “death ray” from mirrors aimed at enemy ships. Though 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 being 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 are parabolic mirrors, focusing a beam of sunlight on a special tube. Such tubes (there are usually a staggering number of them) are placed at an appropriate 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 close to 400 ° C.
Then this hot liquid, giving off heat in the exchanger, heats the water enough to turn into steam, which in turn sets the turbine in motion, which generates electricity. Almost the same as in a traditional coal-fired power plant, except we have no greenhouse gas emissions or air pollutants .
Solar towers like from sci-fi movies
The second most 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 from such mirrors (they are movable and align themselves with the sun) and are directed directly at the tall tower. For what?
At the top of the tower there is a tank with molten salts (60% sodium nitrate, 40% potassium nitrate), which, thanks to a focused beam of sunlight, heat up to over 560 ° C (and sometimes up to 1000 ° C). This hot mixture is then used to produce steam and electricity, just like an installation with parabolic mirrors.
Fresnel solar plates and mirrors
There are still two less widespread technologies available. The first is a system of plates focusing solar energy on a receiver mounted on an extension arm that acts as a motor. Inside there are thin tubes filled with hydrogen or helium and cylinders. The concentrated solar energy heats up 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?
The last, but slightly simpler option of using the sun’s rays are the so-called Fresnel mirrors . It is a system similar to parabolic mirrors, with the difference that the sun’s rays reflected from the mirrors heat the working medium (in this case it is usually water) in one larger and longitudinal receiver. Further, the principle of operation is similar. Pictures say more than a thousand words, so take a look.
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 most need energy? It turns out, however, that the first two technologies can work around the clock. How it’s possible?
Concentrated solar energy around the clock
The key to solving this puzzle is storing energy in a hot salt mixture. And not for half an hour, but even for several hours. This means that energy from 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 to build a CSP power plant using two 200 MW solar towers has just started. One of the requirements is to be able to store and generate energy for 15 hours after sunset. The power plant is to be put into operation in 2021, and the electricity it produces is expected to cost around PLN 3.6 ($ 0.95) per kilowatt hour.
Surprisingly, it can be even cheaper. Three CSP power plants built in Chile (to be launched in a few years) will sell electricity for PLN 2.4 per kWh ($ 0.63) without any subsidies. They too will use solar tower technology (two or three) with a 14-hour energy storage time. Their maximum thermal power is over 1 gigawatt, thanks to which they will be able to provide Chileans 7,100 GWh of clean energy straight from the Sun every year. This is enough to power a total of over 2 million homes around the clock! The best part is …
More and more CSP power plants are built
Israel is building one too. And that’s right with the record-breaking 240-meter-high solar tower . Around it, there will be 50,000 mirrors covering over 3 km2 of surface. In 2018, it is to start producing electricity, which will provide 1% of the entire country’s demand.
Apparently not much, but it is always 1% of pure energy more. And this is what the world needs to replace fossil fuels and reduce the emissions of greenhouse gases that heat our planet. And there will be more clean energy, because more installations of this type are already under construction or will be built in Morocco, South Africa, China and Australia. Whatever it is, it is happening and more and more countries are energetically enlightened.
The International Energy Agency (IEA) has estimated that by 2050 more than 11% of electricity will be produced thanks to 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 power can be provided by CSP power plants even when the sun is not shining. Great, but …
Why write about it, if it will not work in Poland?
Ok, you can think like that, because we are not a solar power (annual radiation in Poland is only 1000 kWh / m2 – in Chile it is over 3 times more), so theoretically, such technologies will not work for us. How about the fact that in the nearby town of Brønderslev, exposed to the sun’s rays, a solar power plant has been operating since last year, using parabolic mirror technology? Can you? You can!
Its thermal power is 16.6 MW, and the mirrors are arranged in 40 rows, 125 meters each. The working medium is a special oil that heats up to 330 ° C. It is successfully enough to produce electricity. But this installation can also be used to generate heat for heating houses. And this option is used by the Danes, which would also be useful here to replace at least a little coal burnt in combined heat and power plants.
Additionally, the entire installation will be supplemented with a biomass power plant to generate even more electricity from renewable energy. If our government wanted to, it could carry out such projects also in Poland. Because it is green energy that we will have to rely more and more and no “clean coal” technologies will help here. And the more and cheaper renewable sources you choose, the better. How not, how yes!