Solar plant keeps working, even after sundown

A concentrated solar power plant in Spain has just supplied its first uninterrupted day of electricity to the network, providing energy to the grid even after sundown thanks to molten-salt storage.

Located in Fuentes de Andalucía (Seville), the Gemasolar plant is property of Torresol Energy, a joint venture between Masdar — Abu Dhabi’s clean-energy initiative — and SENER, a Spanish engineering and construction company.

The plant, barely one month into commercial operation, can store solar energy in molten salt using a thermal-transfer technology developed by SENER. The system enables the facility to deliver 15 hours of electricity production without solar radiation, helping to overcome fluctuations in the energy supply.

“Gemasolar achieved optimal performance in its systems in the last week of June,” said Diego Ramírez, director of production at Torresol Energy. “The high performance of the installations coincided with several days of excellent solar radiation, which made it possible for the hot-salt storage tank to reach full capacity. We’re hoping that in the next few days our supply to the network will reach an average of 20 hours a day.”

The salt storage system allows the plant to stretch its electrical production hours to beyond sunset, regardless of the cloud cover. With a 19.9-megawatt steam turbine, Gemasolar is able to supply electricity to some 25,000 households.

Eventually, the plant is expected to be able to supply 24 hours of uninterrupted production per day on most summer days, providing a higher annual capacity factor than most baseload plants such as nuclear power plants.

“The prove-out of both this technology and the commercial approach we have taken to funding and operating the facility are of huge significance to the solar industry,” said Frank Wouters, director of Masdar Power.

SENER has applied its solar technology with thermal-storage capacity in plants throughout Spain, some of which are already in commercial operation. This system significantly improves performance compared to plants with no storage capacity. In addition, it makes it possible to manage the supply of electricity sent to the network and respond to spikes in demand. In this way, the reliability of solar energy becomes comparable to that of conventional fossil-fuel power plants, which is decisive as the demand for renewable energy increases.

Gemasolar is the first plant to apply the thermal-storage system in a configuration with a central tower and an array of heliostats. The main difference between it and plants with parabolic-trough technology is its ability to reach a much higher operating temperature (over 500 degrees C) by dispensing with oil and directly using salts as a transfer fluid. The molten salts make it possible to generate hotter steam at higher pressures, which significantly boosts the plant’s efficiency.