A new solar technology is twice as efficient, cutting the cost of Concentrated Solar Power (CSP), by doubling operating temperature to 1,000°C.
For most innovative research in clean energy, the dreaded “Valley of Death” after lab scale success is the sad place where great innovations go to die for lack of commercial trials.
But that will not be the case for particle receiver technology which is cutting edge technology for tower CSP, the thermal form of solar that uses the heat from sunlight reflected from mirrors and can store its solar energy. (see how CSP works.)
Commercial experience is key to developing innovative technologies, and there is an unobstructed path from lab to commercialization for researchers investigating a red sand abundantly available near Riyadh in Saudi Arabia for particle receiver CSP.
Saudi Arabia will be first to commercialize particle receiver technology, a super high temperature, high efficiency, low cost form of CSP.
The Saudi Electricity Company is funding and assisting Hany Al-Ansary, Associate Professor in Mechanical Engineering at King Saud University, and international collaborators with research into using red sand for heat transfer in particle receivers.
Al-Ansary, who holds 9 patents in this field, presented the Paper on the results of the red sand tests before an audience of the world’s top CSP research scientists at the 23rd SolarPACES Conference in Chile.
The utility plans the first ever commercial trial of particle receiver tower CSP in 2018.
Why particle receiver research matters
Particle receivers can attain temperatures almost twice as high as molten salts, yet hold stored heat just as as well.
“Molten salt is limited to around 565°C,” Al-Ansary said. “but depending on which type of particles, you can get much higher temperatures, up to 1,000°C. Our group worked on different containment structure designs, and with simple masonry materials and a well insulated tank, we reduced heat loss to under 1% per day, similar to molten salt.”
High temperatures increase efficiency, making particle receivers a good fit with high efficiency supercritical CO2 air Brayton power cycles.
High temperatures enable CSP to replace fossil fuels in thermochemical processes like splitting water (H2O) to extract hydrogen (H2) at 800°C or make carbon-neutral solar fuels like the fuel airplanes use at 1,300°C.
Tower CSP with thermal energy storage is key to a carbon-constrained future because thermally stored solar can cut the use of natural gas plants for flexible on-demand electricity generation. Particle receiver technology can help this happen.
Researchers have investigated many materials able to achieve these targets. The advantage of sand is cost. Each particle receiver plant would cycle thousands of tons of sand through its system.
“We’re excited about sand because it doesn’t matter how much you need, the cost is almost nothing,” he pointed out. At scale, some materials, particularly engineered particles, could become a considerable fraction of initial costs. “When you are talking about thousands of tons of an engineered material, at some point, that becomes prohibitive.”
How a particle receiver works
Falling particle receiver technology makes it possible to nearly double today’s power tower temperatures to 1,000°C.
At a 20 MW scale, the receiver aperture in the tower would be about 10 meters wide by 10 meters tall and sand would be fed from the hopper to fall in a 3 cm thick curtain through a 10 meter wide slot, exposing the sand particles to the heat of hundreds of “suns” of intensely focused sunlight from a solar field of mirrors focused on the receiver.
Unlike storage tanks in molten salt CSP, hot and cold storage tanks would be stacked right inside the receiver tower along with the heat exchanger, so there is much less pumping of storage material, reducing parasitic costs.
The 100 meter tall tower would be about 30 meters in diameter with the storage tanks stacked vertically inside. The cold tank would be half way up the tower, “so we only need to lift the particles from the middle to the top to heat them.”
Obstacles stop the particles from falling too fast
To prevent the sand falling too fast, chevron-shaped obstacles slow their descent, an earlier innovation previously tested at Sandia in the US by the international research group. Without the obstacles, sand fell at 5 or 6 meters per second, even in just a 1 meter drop height,
If the particles are allowed to fall too fast there are gaps and some of the heat will hit the back wall of the cavity instead of being absorbed “so this is a valuable energy that you spent millions to concentrate but you will end up not using it.”
With particles slowed by the chevrons, Al-Ansary’s group got results of almost 1,100°C in the lab without the sand agglomerating, and even out in the field, attained temperatures above 700°C.”
The world’s first commercial particle receiver will be in 2018
Particle receiver research is very fortunate to have backing ready to go in a visionary research field with less visionary commercial support.
The Saudi Electricity Company is banking on building the world’s first commercial particle receiver in the middle of 2018, following final testing in January and February.
“They said they are actually preparing for the next phase which is maybe around 5 MW. They would like it to be generating and they would like to sell that electricity,” he said.
“Once we complete testing on this smaller scale, as soon the results from the current facility are confirmed, they are ready to go. They already have the contractor lined up.”
Saudi Electricity Company engineers have even been involved in helping with the research, and there will be an opportunity to tweak the engineering at scale.
“We’ve actually had some engineers from the utility working with us on a daily basis on this project so it is really a joint effort, just making sure that we have a mature design such that when we go to the third phase it will be fully commercial.”
Sandia has a much larger solar field but the Riyadh test system enables commercialization as a fully integrated power system with a heat exchanger and turbine – and a first buyer. Only the receivers were tested at Sandia, not the entire power system.
Remote Arabian settlements need 1 GW worth of small projects
Away from Riyadh, parts of Saudi Arabia have an ideal solar resource for CSP (annual DNI of 2,600) the form of solar which needs clear skies. And many remote regions lack power.
“Our national utility is excited about this idea because they have many remote areas that are not served by the grid, where 5 or 10 MW is more than enough,” said Al-Ansary. “They told me that roughly the potential, just inside Saudi Arabia, for those areas Is about a thousand megawatts (1,000 MW). So they can build about 200 of these.”
A 5 MW turbine that could operate on the heated air from a particle receiver, not based on combusted fuel, or on steam (like a molten salt CSP plant), is available commercially.
’There is a company that is basically friendly to switching from one fuel source to another one. The combustion process happens outside the turbine which means it is very easy to bypass, whereas in the case of the large GE and Siemens gas turbines, the combustion chamber is embedded inside and to bypass it would take some really heavy engineering,” he said.
The calm confidence with which Al-Ansary described each step from research to the impending commercialization was really striking.
Even though clean technology innovation is absolutely crucial to a livable planet, such access to easy transition is rare. Al-Ansary confirmed it.“Indeed, we are lucky to have this support,” he agreed.
Presentation: Hany Al-Ansary On-Sun Experiments on a Particle Heating Receiver with Red Sand as the Working Medium
Paper: Hany Al-Ansary – On-Sun Experiments on a Particle Heating Receiver with Red Sand as the Working Medium
Patents: H. Al-Ansary Patents through 2017
Previous published work:
H. Al-Ansary Prospects for Use of Solar Thermal Energy in High-Temperature Process Heat ApplicationsApplied Mechanics and Materials, Vol. 819, pp. 16-20, 2016