If you could steal the heat from the sun-rich summer and give it to the sun-poor winter, you could be the Robinhood of the world’s energy needs. Hey sunbeams, Trace here for DNews. Solar recently grabbed headlines when the Department of Energy found solar power generation employs more people than generating electricity from oil, coal, and gas combined. In part it’s because of construction, but also because solar workers do way more than just building solar panels… they also work on thermal energy projects. The sun provides enough energy in about one hour to power the entire planet for a whole year, and a lot of that is heat! We’re actually pretty bad at leveraging this free energy the universe gives us, but scientists are working to capture more of it! For example, researchers from Switzerland developed a new way to capture summer heat and store it all the way until wintertime by taking advantage of the chemical properties of Sodium Hydroxide, or NaOH.
NaOH is a white crystalline odorless solid that reacts with water. When you pour water on a mixture containing concentrated NaOH, it releases heat in what’s called an exothermic reaction. To control the exothermic reaction, the researchers exposed the NaOH steam… allowing it to release small amounts of heat at a time, just enough heat to heat up a metal pipe. A solar collector can help reverse this reaction by evaporating the water leaving NaOH behind. If water is added to the mixture again – heat will again be released, and this back and forth can be reversed again and again! Right now, the NaOH system is still a prototype, so we haven’t solved the world’s energy needs just yet. But the researchers are looking for industrial partners to help commercialize their technology, which they think could be used to heat homes in the winter. All thanks to chemistry and the sun.
As you know, solar energy isn’t constant. In the summer, we get more heat than we need, so we use energy to cool down. Come wintertime, we don’t have enough heat, so we use more energy to warm up again. The most challenging and most important part of solar energy isn’t just how to create it: it’s how do you store it? Not just because of a cloudy day, but a cloudy season. If we repeated this simple chemical reaction all summer, using the sun to add energy, the generated heat could be stored until needed in the winter — weaning ourselves off of dirty fossil fuels… but how? Batteries suck. We’ve talked about this a lot. They’re actually one of the worst options for solar energy storage – mostly because current batteries are limited in the number of times you can charge them, they’re fairly expensive, and the types of batteries you would need for this application would be huge.
With a bit more chemistry and physics, you can store the power of the sun in salt! Most power generation facilities use heat to generate steam and turn a system of turbines. Seriously. Nuclear, coal, gas, solar. All of them. Wind and hydro just turn the turbines with something else. The Abengoa Solar's Solana plant in the Arizona desert uses over 3,000 parabolic mirrors to heat water and turn their turbines, but they also can focus the sunlight to heat large insulated tanks of salt causing it to melt. The molten salt stores the energy gathered during the day, which can later be used to turn turbines at night! Unfortunately, this strategy can only store energy for 6 hours. To store energy throughout the year we’ll have to get more creative — like by putting it underground, which is actually what the Swiss researchers suggested for their NaOH system — a geothermal probe. Today, one of the most common strategies for seasonal solar thermal storage is known as borehole heat storage.
This essentially uses the heat capacity of soil to store large amounts of heat underground for months! It works by drilling an array of boreholes from about 30 to 200 meters deep into the Earth. During hot summer months, the heat is transferred to water which is then stored deep in the soil and rock inside the borehole! That stored heat can later be extracted when needed and used for all sorts of things. Italy, Germany, Sweden, and the Netherlands all use these systems, sometimes seemingly keeping nest eggs of heat under their houses like a neighborhood of giant chickens. The challenge with the borehole strategy, though, is that you need access to drillable land, and for most people, like those who live in urban areas, that’s simply not an option. Hopefully, someday, with a combination of solar thermal plants, geothermal and borehole facilities, as well as concentrated sodium hydroxide, we might get close to weaning ourselves off of fossil fuels forever. If solar energy is so great, why aren't we using more of it? You can find out by watching this video. And let us know down in the comments what your favorite type of energy generation is.
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