When most of us think of solar power being used to generate energy, we likely picture solar cells. Concentrated solar power plants use lenses or mirrors to heat fluid which is used to generate high-pressure steam to drive a conventional turbine.
A new experimental steam generation solar power plant that opened last week in southern Spain is aiming to improve on the efficiency of existing steam solar power systems by using water as the direct working fluid and incorporating novel methods for energy storage.
The pilot steam solar power plant is located in the municipality of Carboneras, and is the result of collaboration between the German Aerospace and Spanish utility company Endesa and officially put into use on March 31st.
The water in the receiver tubes is kept at a pressure of up to 120 bar, which results in the creation of superheated 500C (932F) steam. That higher temperature allows the whole process to work more efficiently, bringing down the cost of thermal solar power generation and making it a more viable option. Heat gathered by the plant can be stored in both sensible and latent forms, for use in creating energy when the sun isn’t brightly shining. In the sensible heat system, heat from the steam is absorbed by a concrete energy storage system, so it can later be released to create more steam and drive the turbine. The steam is used to heat salt for energy storage when it reaches a temperature of 305C (581F) and changes from a solid to a liquid state. When the salt cools back down below 305 degrees and reverts to its solid form, that energy is released.
The Carboneras steam generation solar power plant now boasts the world’s largest high-temperature latent heat storage facility. “The advantage of such a system is its capacity to store large amounts of energy in a small volume and with a minimal temperature change,” said Doerte Laing, Thermal Energy Storage Research Area Manager at the DLR Institute of Technical Thermodynamics. “The energy in the system can be transferred and absorbed very efficiently by phase transition at a constant temperature.”
Researchers plan to keep the plant in use until the end of the year to validate the direct steam generation solar power process itself, the storage methods, and the flexible pipe connections that are necessary for the mirror and receiver tube assembly to pivot as it tracks the Sun.