Can “solar hydro" replace coal and gas-fired power stations?

Organic Rankine Cycle (Source: Applied Sciences, 9 (1) 49, 2019)

RayGen, with the support of AREA (Australian Renewable Energy Agency) and in collaboration with other companies, is on-track to test a 50MWh “solar hydro” project in NW Victoria. The plan is to eventually develop a 200MW solar power plant with around 100MW/1000MWh storage. This is enough to help replace retiring coal and gas fired power stations.

The plant will consist of mechanical mirrors on the ground concentrating sunlight and heat to RayGen’s efficient collector on a raised tower. The collector consists of mirrors and super-efficient PV modules which can collect both light and heat. The specialist panels convert about 30 per cent of the sunlight to electricity and capture around 60 percent of the excess heat. 

The heat is stored as hot (92^°C) water in one reservoir while the electricity is used to chill water to 2^°C, which is stored in a cold reservoir. Between the two tanks is the Organic Rankine Cycle system (see above diagram), which has a special organic fluid circling within it. At the evaporator, the fluid is heated to a gas by the stored hot water which then drives a turbine to generate electricity. The organic gas then passes to the condenser where it is cooled back to a liquid by the stored cold water. 

With the organic fluid coming to boil at a lower temperature than water, it means that the system has a high efficiency. Since the water temperature differences are stored like a battery in the reservoirs, the system can generate electricity when required. “The temperature difference of about 90^°C has a similar energy storage capacity as pumped hydro with a height of 1000 metres – so really, really big pumped hydro.” says RayGen’s Will Mosley. “RayGen is able to deliver the economics of pumped hydro and the flexibility of batteries.” (RenewEconomy) 

Read more: 
- RayGen edges closer to “solar hydro” success with new strategic partnerships. RenewEconomy, April 16, 2020. 
- World-leading solar technology born in Melbourne, that’s ultra-cool. ARENAWire, September 28, 2017. 
- Solar power plant phase 1. ARENA, January 2020. 
- Renewable energy storage, solar power technology. RayGen