Wednesday, July 07, 2010

What are the prospects for solar cooling?

In partnership with Energie-Fakten.

The energy demand for air-conditioning and cooling is rising worldwide: on the one hand, this is driven by the increasing use of information-technology equipment in the work environment resulting in more need for cooling. In homes, with increasing prosperity, the demand for cooling is on the rise as well. In hot and sunny regions, air-conditioning is not a luxury, but a basic prerequisite for further development. Because of the rapid industrialization of today's emerging and developing countries worldwide, a significant expansion in the need for air-conditioning can be expected. And at the same time we can expect higher mean temperatures in summer in urban areas, both as a consequence of local and global climate change. In regions such as Southern Japan, Southern China, Southern India and California, the Near and Middle East, the power system works already close to its capacity limits in the summer months because of the high power consumption of conventional air-conditioning.

Spacious modern glass buildings often have to cope with increased heat loads from solar radiation in the summer and have significant cooling requirements. Internal heat loads - from persons and an increasing number of electrical appliances – further add to the cooling requirements. Builders, engineers and architects have high hopes for solar cooling - because the sun shines strongest when buildings need to be cooled most. At first glance, solar radiation and the demand for cooling in buildings go well together.

Over the past two decades, a number of different solar thermal technologies have been developed, which are generally operated in combination with other cooling techniques. For economic reasons, they have rarely developed into a true competitor of the traditional cooling techniques - although they have demonstrated their value in the market.

With solar cooling using thermal solar collectors (mainly flat plate or evacuated tube collectors) heat from the sun is used to power a cooling process on the basis of absorption or adsorption. These must be designed so they can use the low temperature heat from solar collectors - below 70 ° C. This limitation of thermal solar collectors excludes any use of the main cooling technology - the conventional compressor cooling process, because it needs mechanical energy for the compressor. Such mechanical energy requires electric motors or gas turbines.

Since solar cooling usually does not suffice for all loads, one needs cold storage and additional back-up systems which add further costs to an already expensive system.

To mitigate the high investment cost of solar cooling, one should search for other uses for the thermal solar collectors (eg for heating drinking water). To realize cost-saving benefits for smaller plants, they should be used in combination with passive cooling or free cooling. In the case of passive cooling, the building is ventilated at night with cooler outside air. Passive cooling of buildings, however, quickly reaches its limits when heat loads are high, or when night temperatures are not cool, e.g. in urban areas during the summer. For new buildings, one can reduce heat load through proper design. New buildings should therefore have a high quality envelope, which minimizes solar radiation entering into the building in summer - for example through appropriate windows, shading devices, external blinds, etc. From an economic perspective, not only technology matters, but also the temporal and quantitative profiles of the cooling demand as well as the cost of the energy that is used in the competing technology - the electric compression cooling machine.

If power generation in sunny regions with solar thermal power plants or photovoltaic systems can achieve significant cost reductions in the future, the economic possibilities of solar-electric air-conditioning will be interesting. This technology is compatible with both conventional, electrically powered air-conditioning units and with the power system. Meanwhile, solar-electric cooling plays only a minor role - for example, for cooling of the medication in less developed rural areas without connection to the grid.

1 comment:

solar energy said...

I believe solar cooling is a good idea. But we are still having problems with solar heating as it is. Yet, the idea of a solar-powered temperature regulator is nice.