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In an innovative step forward, RayGen of Australia has combined concentrated solar with utilization of waste heat (through the Rankine cycle) to create cost-effective long-duration energy storage (LDES). I’ll do my best to explain, but if you prefer moving pictures, you can watch the video here.
RayGen is touting its technology as better for long-term storage than pumped hydro or lithium-ion storage batteries. What I was fascinated by was the ability to use what was essentially a nuisance byproduct — hot water — to store energy.
The Rankine cycle is similar to how a steam engine operates and has applications in geothermal energy work. The information in this article is gleaned from RayGen’s manufacturing, commercialisation, solar power plant demonstration and technology reports. All are linked in the article for those who want more precise information. RayGen has produced a wealth of reports, and I am not a technology person, but hopefully I can synthesise the relevant information and not make too many mistakes.
From RayGen’s manufacturing report: “The backbone of RayGen’s PV Ultra technology is the PV Ultra (satellite-grade solar- thermal) module which captures 90% of the energy of the sun.” The video makes it clear that this is a combined efficiency rating, using the solar photovoltaic energy and heat of the sun.
“A field of automated mirrors focuses light and directs it onto a collection of modules mounted on a receiver with a beam nearly 1000x more powerful than unconcentrated sunlight. Water is used to actively cool the solar modules during operation, resulting in the generation of a secondary energy stream in the receiver: heated water. This water forms the basis of RayGen’s long-duration energy storage system, ‘Thermal Hydro’. The hot water is stored in a thermally insulated, excavated pit. A second pit is used to store water at 0°C, produced via industrial chillers powered either behind-the-meter from RayGen’s on-site PV Ultra or from the grid.
“If electricity is needed during sun hours, it can be directly exported when produced by the PV Ultra modules. If electricity is needed outside of sun hours, RayGen’s system utilises the stored 90°C water to heat a working fluid in the Organic Rankine Cycle (ORC) system, generating synchronous power on demand. The chilled 0°C water improves the thermal efficiency of the ORC cycle, yielding an overall round-trip efficiency of 70-80% (made possible by the integrated byproduct heat captured from PV Ultra operation).”
Like a steam engine, the steam runs a turbine to produce electricity.
Pumped hydro is limited by geographical constraints, lithium-ion batteries are best for short-duration power storage. RayGen believes that its Solar Power Plant System combines the economics of pumped hydro with the siting flexibility of batteries for a grid-scale energy storage solution. RayGen claims that its system is compatible with mixed land use. “RayGen can provide incremental storage hours at very low cost. This is achieved by simply extending the pit volume and adding more water, comfortably delivering 12–24 hours of storage whilst providing essential inertia to strengthen and stabilise the grid.”
RayGen is being partially funded by the Australian Renewable Energy Agency. But also has some significant industry partners that are looking to RayGen to supply synchronous, dispatchable power. RayGen’s solar-plus-storage technology can store power from both RayGen solar generation and the grid. “It provides a solution to grid congestion by storing excess electricity generation from intermittent renewables and increases the value of renewable energy by acting as a dispatchable generator that can respond to market factors.” This adds another income stream for RayGen — stabilising the grid through FCAS. “RayGen’s ORC engine is naturally synchronous and, through the introduction of a clutch, can operate as a synchronous condenser even when the ORC is not generating,” the company adds.
“RayGen’s Solar Power Plant (SPP1) system was developed to demonstrate the technical and commercial capabilities of RayGen’s Solar Hydro technology. This Solar Hydro technology combines both PV Ultra generation and Thermal Hydro storage to deliver long-term energy storage and generation. The plant comprised of 4MW of PV Ultra and 3MW/50MWh Thermal Hydro storage in Carwarp, Victoria. It completed construction and initial commissioning in August 2023.”
The plant is now fully operational and able to dispatch power over periods up to 11 hours. The Organic Rankine Cycle (ORC – look out Bilbo) system achieved net thermal efficiency of 11%. The chiller system demonstrated a Coefficient of Performance (COP) of approximately 80% and an Overall Equipment Effectiveness (OEE) of almost 100%. These terms are usually used to describe the heating and cooling efficiency of air conditioners.
RayGen is manufacturing its PV Ultra module in Melbourne, Victoria, Australia. It is described as only 10cm x 10cm yet has the power capacity of 7,500W (2.5kW electricity, 5kW heat). It is the use of this “waste” heat which makes the system more cost effective. “Like solar PV, RayGen generates electricity using the photoelectric effect; like concentrated solar power (CSP), RayGen focuses sunlight using tracking mirrors; but unlike any other technology, RayGen utilises a field of mirrors to focus sunlight onto a central receiver of photovoltaic modules.”
RayGen is aiming for scalability both with its systems installations and manufacturing capacity. Its next production plant is expected to produce 1 GW per annum and at a fraction of the cost of solar panels due to the energy density, resulting in reductions in factory foot print.
RayGen’s commercialisation report has further explanation. See especially figure 1. “RayGen’s modules are almost 2,000x more powerful than traditional solar panels – withstanding almost 1,000x solar concentration, and using cells almost 2x efficiency. One third of the sunlight is converted into electricity, and two-thirds into heat (hot water at 90°C). RayGen’s Thermal Hydro system utilises the waste heat captured during the active water cooling of the modules, as the thermal energy source for an Organic Rankine Cycle. RayGen’s modules contain no silicon.” Thus, they produce less e-waste.
RayGen’s demonstration plant in Carwarp, Victoria — a 4 MW PV Ultra and 2.8 MW Thermal Hydro facility — can deliver up to 17 continuous hours of stored energy to the local electricity network. AGL, the second largest energy provider in Australia, is a strategic investor in RayGen and has a commercial offtake agreement. The demonstration plant produces sufficient clean, renewable energy every year to power nearly 2,000 local homes.
RayGen’s hi-tech solar matches traditional solar PV on cost, land area, and output, and it enables heat capture and agrivoltaics, transforming the solar supply chain.
Australia is installing more and more “Big Batteries.” RayGen is seeking to fill the niche of medium to long-range energy storage to aid Australians in their quest for net zero. It is another part of the solution to remove gas from the grid. RayGen sees itself as within the category of advanced thermal storage systems, like those that use molten salt, storing energy in the form of heat. RayGen has a strong pipeline of projects across all Australian mainland states for both grid-connected and standalone industrial and mining facilities.
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