DryRSP

The DryRSP project (for Dry Rankine Solar Power) focuses on the Rankine cycle driven thermodynamic solar power processes. This concerns the industrial concentrated solar power (CSP) plants using steam as working fluid and large scale concentrating solar fields which are operated for more than 30 years and experience for about ten years an extensive worldwide development. At lower working temperature levels and in the range of domestic or tertiary applications, it concerns the organic cycle based systems (ORC) under strong R&D development in Europe and France. Three years ago, the cooling technology currently used on the CSP condenser has been highlighted by SolarPaces-IEA as a major bottleneck of those processes. To every MW of produced electricity, 2 thermal MW at 55°C have to be dissipated within the surrounding environment. Up to date, this waste heat is efficiently extracted by means of an evaporative cooling technology responsible for a too important water consumption (3.7 m3/MWh) or by air cooling heat exchangers inducing simultaneously a reduction in the whole cycle efficiency and a parasitic electricity consumption, or an hybrid combination of both. Those power plants being mainly to be implemented in desert and arid areas, the wet cooling approach leads to major water conflict of use and major corresponding over costs. Moreover, the predicted global warming should enhance both the water needs and the air-cooling penalty. In the case of ORC systems, the highest temperature level of the cycle being significantly lower than for CSP, the effect of the cooling efficiency is much more pronounced. Using a conventional dry air cooler, the extraction of the condenser heat would consume 60% of the ORC power ! For those ORC, out of the water consumption, the wet tower induces large over costs and additional maintenance operations due to the salmonella hazard. Therefore, innovative efficient dry cooling technologies are highly needed to allow a competitive development of thermodynamic solar processes. The main objective of the DryRSP project is to design and assess such a dry cooling technology able to dissipate the waste heat without water consumption, allowing sub-cooling of the thermodynamic cycle below the dry-bulb temperature and eventually to produce water during night by condensation of the surrounding air humidity. The approach is based on the use of the already existing solar field of the plant as macro heat exchanger. This offers a huge heat transfer surface area available 24h a day for heat transfer with the surrounding air (mix convection for cooling) and with the extra atmospheric space at 3 K (radiative transfer for sub-cooling). This approach offers a new functionality to the solar field which represents currently 50% of the investment cost of a solar power plant. During night, when the solar field is not under power operation, the cooling effect can be stored to be used daily or (under favorable climate conditions) to be used to produce fresh water by condensation of the surrounding air humidity. The DryRSP project takes advantage of the complementary skills of the 4 national partners: the PROMES laboratory (Processes, Materials and Solar Energy Laboratory, UPR CNRS 8521 Perpignan/Odeillo) specialist in concentrated solar materials and processes, the SPE laboratory (Sciences For Environment, UMR 6134, Vignola/Corte) acknowledged in physical systems for the environment and specially in radiative cooling, the EXOSUN company involved in CSP solar power plants and the EXOES company involved in ORC solar power. This consortium is advantageously completed by the LESEE laboratory (Solar Energy and Energy Saving Laboratory) of the International Institute for Water and Environment Engineering of Burkina Faso giving to the project the opportunity to adapt the technology to sub-Sahelian conditions.