It’s All Done With Mirrors
/We recently took a few days off to go camping in the eastern Sierras. We had a great time, which Marcie will talk more about in a future blog. Our less-than-direct route to get back home took us through the small town of Tonopah, NV, once known as “The Queen of the Silver Camps”.
As we approached Tonopah, we couldn’t help but notice what appeared to be a huge spotlight sitting atop a tall tower. It was bright enough to create retinal afterimages if you looked at it for more than a few seconds. Rather odd, we thought. We weren’t too far from the infamous Area 51 – if we were more conspiracy minded, we might have assumed it was some secret, extraterrestrial related project.
In actuality, what we were actually seeing was the Crescent Dunes solar power project, a 110-megawatt concentrated solar power (CSP) plant. More than 10,000 mirrors, known as heliostats, are adjusted by computer-controlled motors to focus the sun’s rays onto the top of the matte black tower, creating heat. This heat is used to superheat water, which can be used to run a steam turbine generator. But unlike most solar power plants that only produce electricity when the sun is shining, the Crescent Dunes plant uses a novel approach to store the heat, so that the plant can continue producing electricity long after the sun goes down.
View from an airliner. Courtesy of Murray Foubister
Rather than heating water directly, the sun’s rays are used to melt salt in a reservoir at the top of the tower. The molten salt, at a temperature of 1,050 degrees F (566 degrees C), flows down into a 3.6 million-gallon insulated tank and is used as needed to boil water via a heat exchanger. The cooled but still-liquid salt is then pumped back up and into the reservoir for reheating. The molten salt tank is so large that it can continue to boil enough water to operate the steam turbine at full power for 10 hours.
How it all works
Construction of the plant was completed in 2015, but like many new technologies, it suffered a number of operational difficulties and setbacks – the biggest being a catastrophic failure of the tanks used to hold the molten salt. Nevada Energy canceled its contract with the plant for non-performance in 2019, forcing the owners into bankruptcy. In 2021, new owners took over, restarting the plant and entering into a new contract with NV Energy, but, as of August 2023, the plant’s performance still wasn’t up to full capacity.
Still, even if the plant ever reaches its full design capacity of 110 megawatts, the cost of producing electricity from a more common photovoltaic (PV) array is significantly less than the cost per kWh for the Crescent Dunes plant. If, however, the added cost for a battery bank sufficiently large enough to provide 10 hours of power from a PV array once the sun goes down is factored in, the Crescent Dunes plant will be competitive. It’s a short term advantage, though. The National Renewable Energy Lab (NREL) in Colorado estimates that by 2030, the cost of battery technology will have dropped enough to make it a cheaper alternative.
BTW, Archimedes is purported to have invented the first large scale solar furnace, which he described as a heat ray, and which was supposedly used to burn attacking Roman ships during the siege of Syracuse in 213 BC. Whether or not there is any truth to the legend is debatable, however. Several attempts to replicate his heat ray have met with mixed success, and most historians think it was of limited use, if it was implemented at all. Flaming arrows and catapults were probably more effective. Flinging molten salt at those pesky Romans probably would have also worked.
Archimedes Heat Ray - Courtesy of Wikipedia
See you next time...