Dillinger heavy plate for the first solar power tower plant in South Africa

In November 2012 the construction works for the solar power tower nearby the South African town Upington in the Northern Cape region have begun. The power station with a scheduled output of 50 MW and a yearly electricity generation of 180 GWh was developed by a Spanish company, which is worldwide leader in the field of solar power tower technology. The project is a technological advancement of the two existing solar power tower plants PS10 and PS20 located in Spain.

After projected completion in 2015 the powerhouse will provide clean and sustainable power for approximately 65,000 homes and will avoid 183,000 tonnes of CO₂-emission a year in context of renewable energy. For this reason the tower aids South Africa’s Department of Energy in its goal to bring 17,800 MW online from renewable sources by 2030.

Covering an area of 300 hectares 4,200 dual-axis solar mirrors (heliostats), totaling up to 576,800 m² of mirror surface, focusing solar radiation on three receivers located on top of a centralized 205 m high tower. By the use of this concentrated solar radiation superheated steam with a maximum operating temperature of 530 °C is generated. Using this high temperature the steam cycle reaches an increase in efficiency by 30 % compared to its forerunner Planta Solar 20 (PS20). To produce electricity from the superheated steam conventional steam turbines are used. To make them work efficiently the saturated steam has to be cooled down after the outlet of the turbine. For this process a unique natural draft dry cooling system was developed, which reduces the water consumption of the heliostation by 80 % compared to common wet cooling systems. Centerpiece of the plant is an integrated energy storage consisting of 19 steam accumulators each with a weight of 260 tonnes. With the aid of these, enough superheated steam at a temperature of 530 °C is stored to maintain power generation for duration of two hours during absence of solar radiation.

For the construction of the here used steam accumulators Dillinger supplied 2,600 t of low alloyed, quenched and tempered pressure vessel steel SA 533 Type B Class 2 in thickness of 12 – 107 mm, width of 2,450 mm and length of 12,350 mm to its customer placed in Oman. The specified requirements by the customer with reference to limitation of chemical analysis, improved toughness values, reduced hardness values, limitation of the yield strength and severe parameters for the post weld heat treatment turned this delivery to a highly sophisticated project also on the part of the steel producer.