Today, let us take you back to a discovery that was made more than 2200 years ago. Legend has it that Archimedes defended the city of Syracuse (Sicily) from the fleet of the Roman general Marcus Claudius Marcellus using rays of solar energy generated by hundreds of soldiers equipped with polished bronze shields. Deployed along the coast, they are said to have directed the rays of the Sun onto the Roman ships that besieged the city, concentrating them to such an extent that the ships eventually caught fire. A couple of millennia later, somebody had the bright idea of using the same trick to generate thermal energy.
We don’t know if the legend is true or not. What is certainly true is that Archimedes invented numerous weapons that the Syracusan army used to resist the Roman attacks for some two years. Now, though, students at MIT have shown that it really is possible to set fire to a reconstruction of a Roman ship by concentrating the light reflected by 300 polished bronze shields onto it. Since scientists never discard an idea simply because it is a bit eccentric, a couple of millennia later somebody thought that it might be possible to use the same trick to generate thermal energy. To cut a long story short, of all the projects developed using this technology we will focus on the thermodynamic solar power plant that bears the name of Archimedes himself. Designed by Italian Nobel laureate Carlo Rubbia and located in Priolo Gargallo, Sicily, the Archimede Power Plant is made up of 30,000 square metres of parabolic mirrors that concentrate the rays of the Sun into their geometric focus.
The sunlight is concentrated into over 5,000 metres of tubes or receivers that contain a heat-transfer fluid that is heated to a high temperature by the concentrated rays. The fluid reaches 550 °C, so it is not possible to use water as it would immediately become steam. Instead, special mixtures of molten salt that turn liquid at high temperatures are used. These, in turn, are used to heat industrial buildings or homes or are pumped to a heat exchange where they boil water to produce steam to run turbines for electricity generation.
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