A central tower structure with a receptor area in its top segment, a liquid circulation cycle including storage tanks and heat exchanger facilities for power generation via an adjacent turbine, and an array of mirror units that focus the rays of the sun onto the receiver make up the Gemasolar plant. The Gemasolar site extends over an area of 185 hectares to accommodate the vast field of heliostats.
The mirrors are designed to turn and tilt to ensure that maximum sunlight is reflected onto the designated area on the tower as long as the sun remains in the line of sight throughout the day. NORD Drivesystems has supplied 5,300 NORDBLOC.1 design geared motors for the Gemasolar heliostats. Two geared motors in each of the 2,650 flat mirror units enable highly accurate movements for two axes to track the path of the sun.
Operated by Torresol, a joint venture between Spanish engineering giant SENER Ingeniería y Sistemas and Masdar, Abu Dhabi’s state-owned future energy enterprise, Gemasolar is a commercial-scale CSP (concentrated solar power) plant with central tower technology that implements a heat storage system based on molten salts.
Liquefied nitrate salts are pumped up from a storage tank and run through the receiver section, absorbing the heat impact of the highly concentrated solar radiation in that tower segment. The temperature of the liquid that passes through it usually exceeds 500ºC. Once they leave the receptor, the molten salts flow through a heat exchanger where they cool down again, with the resulting water vapour driving a steam turbine that feeds a generator. The generated energy is supplied into the electrical grid.
A unique feature of the Gemasolar plant is the innovative storage option. Whenever there is more heat energy available than the turbine is able to convert, the extra energy is stored by diverting some of the flow of molten salts before the liquid reaches the heat exchanger. Kept in a special tank, the hot medium can be used at a later time when insufficient solar radiation is available for standard operation of the plant.
This solution enables the system to generate power from stored heat for up to 15 hours throughout long periods of cloudy skies or even darkness. The resulting total of 6,500 hours of productive operation per year makes this plant much more efficient than more conventional renewable energy facilities that are totally dependent on changing conditions.
The sunlight concentration is achieved by 2,650 flat mirrors all continually pointing at the same receiver region on the installation’s one central tower with each of them depending on a powerful, sturdy and robust drive solution to ensure reliable tracking of the sun. The application exposes all equipment to very high environmental temperatures, requiring the components to be manufactured to withstand such conditions.
Torresol’s heliostats are equipped with size 5 NORDBLOC.1 series geared motors, which play an instrumental part in ensuring that the equipment withstands the harsh environment.
Key features of NORDBLOC.1 series geared motors:
Designed to withstand greater forces than previous models of the same size
User-friendly mounting options allow for cost-efficient, direct motor mounting, or attachment of very short, space-saving lightweight IEC adapters
Ventilation is ensured in all mounting positions
Aluminium gear housings provide robust, natural corrosion protection out of the box
FEM-optimised design increases robustness in a lightweight construction
UNICASE design enables mounting of larger bearings for gears up to size 6
ATEX versions can be supplied for even more demanding conditions than high temperatures and adverse environmental conditions