Solar Cooling

Unlike solar thermal heating systems, the highest need for cooling (during the hottest months of the year or the hottest hours of the day) coincides with the greatest availability of solar power. For the purposes of air conditioning in the hot months, solar thermal installations are of interest even in locations that do not get intense sunlight throughout the year.
While this field of renewable energy is growing slowly, several successful installations can be pointed to as examples, generally supplying whole buildings with sustainable air conditioning. For example, the 2008 Olympic sailing center in Qingdao was fitted with a solar-based air conditioning system that provided cooling and heating as needed by way of a 638 m² collector area, with a connection to a local heating system to care for peak times. The University Clinic of Freiburg im Breisgau, Germany, has an entire lab building serviced by a solar-based air conditioning system.
More importantly perhaps than providing pleasant indoor working conditions in offices and public buildings is the role solar cooling can play economically and for people's health. Agriculture and food industry in hot countries with uncertain to spotty access to electricity can benefit from systems that work either completely independently or that at least put a greatly reduced strain on the grid by getting the energy needed for cooling of food processing and storage refrigeration locally from renewable resources.
Both air conditioning systems and food processing cooling systems are based on the principle of sorption. In adsorption chillers, a cooling aid such as ammonia or a water-lithium bromide solution boils at low temperatures, its evaporation withdrawing warmth (or adding cold) to a cooling system. The solar energy is needed to turn the cooling aid back into a liquid form and then repeat the process of evaporation, thereby creating more cold.
An adsorption chiller uses a solid substance for sorption, frequently environmentally harmless silicate gel, with water as the cooling aid. Fewer manufacturers produce these systems, but the models that have been developed are of a smaller scale and more variable in use than the usually larger scale absorption systems which only make sense for very large buildings and require resources accordingly.

Solar thermal cooling systems in Africa
Due to the scale of the systems that have been installed and tested in Europe and the cost involved, solar cooling systems do not yet play a great role in Africa despite the good conditions in terms of solar energy.
Co-funded by the European Union within the framework of the Mediterranean Renewable Energy Program, the MEDISCO project aimed to develop and carry out pilot projects of solar thermally driven cooling concepts for the food and agro industry in the Mediterranean region. Between 2006 and 2010 it supported setting up a cooling system for a winery in Tunisia and one to cool the milk processing at a Moroccan dairy farm. In these pilot projects, researchers from the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, Germany, showed that it is in principle possible to supply food and agricultural businesses with reliable refrigeration based solely on solar energy. The technology as such is not yet deemed ready for open market, but the eventual potential for a variety of businesses is huge.
More immediately promising are refrigeration units which provide cooling at a household or perhaps village level to end users in remote areas where electricity-based refrigeration is not even an option, never mind the environmental factors.Fresh and unspoiled food, but also medication require access to refrigeration and cooling. Refrigeration units of different types have been developed for the use of unelectrified rural communities, while paying heed to scarcity of resources and the need of the communities that the units are easy to build and maintain. One example is a solar thermally powered ice maker that avoids expensive diesel fuel or photovoltaics and can produce enough ice for a small business or to provide low cost refrigeration for families (5 kg per square meter of collector per sunny day). Another is a solar-powered fridge which uses a solar collector and the mineral zeolith as a sorbant; the zeolith cartridges have to be replaced after a few days. The system can work with recycled 'normal' fridges and requires no outside electricity at all.