Storing the sun: The magic of concentrated solar thermal
Barely a day goes by in Australia without the toxic renewable energy debate rearing its ugly head. Depending on who you ask, renewables are either the cause of, or the answer to our so-called “energy crisis”.
Now I don’t want to delve too deep into this polarising debate for fear of irreversibly damaging my brain, but to me, it seems rather obvious that a rapid transition to clean energy should be a priority for this country. Not only will this provide the jobs and investment we continually bang on about, it will also help us meet our measly targets set in the Paris Climate Agreement.
But to achieve this transition, renewables need to overcome the energy storage hurdle. While using batteries to store renewable energy is getting a lot of press right now, another storage option arguably shows even more potential to solve this conundrum – concentrated solar thermal.
What is concentrated solar thermal power?
Concentrated solar thermal (CST) is different to photovoltaic solar (solar PV) which is the technology you might find on your eco-friendly neighbour’s roof. Solar PV technology uses sunlight to directly produce electricity through the transfer of electrons. Check out this short video for a simple explainer of this process.
No, a CST array will not fit on your roof. Image credit: J R, via Flickr
While CST also uses the suns energy to generate power, it does so indirectly. This is the thermal aspect of CST. It uses the heat from the sun to warm a fluid like water, oil or molten salts to a few hundred degrees Celsius. This fluid is then used to create steam which spins a turbine and generates electricity.
But “a few hundred degrees Celsius” is really hot. The sun doesn’t produce temperatures that high anywhere on earth, even though I swear my insulation-less share-house bedroom must go close in summer.
To reach these extreme temperatures sunlight must be concentrated.
Concentrating the sun
Remember when you were a kid and aimed the light reflected from your watch into the eye of an unsuspecting mate? Don’t deny it, it was such a classic gag.
We all did this… via GIPHY
Now imagine doing the same but on a massive scale, with thousands of your buddies joining in. The sunlight would become concentrated to such a degree that your poor (and probably ex) friend’s eyeball would be incinerated.
A concentrated solar thermal plant works on these same principles, except instead of watches and eyeballs, sunlight is directed at a central tower from reflecting panels covering an area of few square kilometres.
That’s one hot tower. Image credit: National Renewable Energy Lab, via Flickr
How is energy stored?
Using heat and not light to generate electricity is the key to CST’s ability to store energy. If the fluid used to absorb heat is properly insulated, it will lose heat very slowly – much like your thermos full of tea. This means that even after the sun has gone down, stored heat can be deployed to generate steam to produce electricity.
The future of CST
CST technology is continually developing new techniques to increase its energy storage capabilities. An exciting example of this innovation is using sand rather than salt or water to absorb heat. This technique is explained in depth in Tim Flannery’s new book Sunlight and Seaweed.
I am optimistic about the future of CST technology. With further innovation and investment, concentrating sunlight has the potential to become a major asset as this sunny country of ours transitions to a clean energy future.