Combined thermosolar-biomass power plant in Spain

A combined thermosolar and biomass power plant has started commercial operation in Les Borges Blanques in Spain for the first time. At the heart of the arrangement lies a MAN Diesel & Turbo SE (MDT) turbo generator train, in which the latest MARC-R steam turbine from the Hamburg site celebrates its premiere. This has been possible with the collaboration of Spanish partner companies, Abantia and Comsa Emte.

Built on an area equivalent to 100 soccer pitches (70 hectares), the power plant, capable of producing an electricity output of 25 MW, feeds 22.5 MW into the national grid, not including the electricity it needs for its own use. This is enough to supply more than 27,000 Spanish households with environment-friendly, renewable energy. MDT has designed and supplied the turbo generator as well as the steam bypass and condensing systems.

The special feature of the hybrid power plant is the arrangement's ability to operate continuously, whatever the weather. This dispenses with the need to use complex, expensive solar-energy storage techniques.

Installed on two fields, parabolic troughs track the sun's position during the day, bundling the sun's rays in their focal lines through which absorber tubes run. Circulating around the absorber tubes is a thermal fluid that is thereby heated to a temperature of 400 °C, and then conveyed to the power plant block. Whenever there is not enough direct sunlight or at night when there is none at all, the biomass block is used instead, where a boiler fueled by timber, agricultural waste, and energy-producing plants generates the steam. These natural fuels only emit as much carbon dioxide (CO2) into the atmosphere as they extracted previously when growing.

The heat recovered is then used in a steam generator in order to provide steam at a high pressure and temperature. It is the steam that drives the MARC-R high-pressure steam turbine. Once the steam pressure and temperature have dropped due to expansion, the steam is reheated, before being conveyed to the low-pressure steam turbine. This extracts almost all the usable energy from the steam before it is once more condensed into water in the condenser.

The MARC-R is an interim heating turbine with two casings, constructed out of two repeatedly tried-and-tested machines, a MARC 2 backpressure turbine and a MARC 6 condenser turbine. The MARC-R forms part of the MARC, short for Modular Arrangement Concept. Says sales engineer Simon Radermacher, "The construction increases thermodynamic efficiency, thereby enabling us to enhance the overall efficiency of the power plant considerably."

As a result, the arrangement achieves an annual saving of around 24,500 tons of the greenhouse gas CO2, which would have been released if fossil fuels had been used for generation. According to Radermacher, any thermosolar power plant can be combined in this way, theoretically. Hence the hybrid technology achieves its aim of ensuring operational stability by means of renewable energy sources. These are available permanently and do not fluctuate.