(324h) Experimental Investigations of a Salinity Gradient Solar Pond Under the Northern Cyprus Climate Conditions

Today, renewable energy sources gain importance day by day. It is crucial to develop devices and processes to supply energy from non-polluting and renewable energy sources for sustainable development of the world. Solar pond is an example of such devices that basically collects solar energy and stores it as thermal energy for a long period. Temperature in solar ponds can reach up to 100^oC indicating that thermal energy from solar ponds can be useful to various applications with low grade energy demand. It was reported that the solar ponds have the annual collection efficiency in the range of 15–25 %. The heat obtained from solar pond can be converted into electric power even at low temperatures. Solar pond plants depending on their size can generate rated power up to 5 MW itself or up to 80 MW as a hybrid solar electric generation system. One of the most important advantages of solar pond compared to the other energy sources is lower investment cost. Another important property is that solar pond is environmentally friendly in particular when it is used for electricity generation by driving a thermo-electric device or an organic Rankine cycle engine. The CO₂ emission for such processes is zero when a single solar system is used for electricity generation. Also, it was reported that the CO₂ emission can be reduced up to 65% when a hybrid system is operated for power generation. Solar ponds normally consist of three different salinity layers. The first layer, known as the upper convective zone (UCZ), is located at the top of the pond, and contains the least salinity level. The second layer, whose salinity level increases with depth, is called non-convective zone (NCZ). This layer is responsible to act as an insulator to prevent heat from escaping to the UCZ, maintaining higher temperature at deeper zones. The last layer made of a saturated salt solution, is responsible for energy storage, and is known as the lower convective zone (LCZ). The performance of the solar pond may decrease with the increasing evaporation rate, and decreasing the salinity gradient. Thus, it is critical to prevent these phenomena. Northen Cyprus is enriched in solar energy in particular during summer. The performance of a solar pond in this region has not been evaluated as yet. To take advantage of solar energy in Northern Cyprus, a salinity gradient solar pond is constructed and operated at Middle East Technical University Northern Cyprus Campus (METU NCC) located at Guzelyurt, Northern Cyprus. The pond is well insulated and made of stainless steel with 1m height, 0.64 m diameter and 1mm thickness. Several thermometers are installed in the pond at each salinity layer to monitor the temperature over time. Three sampling valves are installed to the pond to monitor the salt (NaCl) concentration at each layer over time. To adjust the salt concentration to its original level, two input ports were installed to wash the UCZ with fresh water or add salt solution to LCZ as required. The solar pond is planned for operating for a long term enabling a realistic comparative study with the existing energy storage system, flat-plate solar collectors, installed at the METU NCC.  Results concerning the operation of the experimental pond are presented and discussed.