Solar air conditioning technology
Solar air conditioning can be done through passive solar, solar thermal energy conversion and photovoltaic conversion.
In practice, the following processes are applied:
- Solar collectors convert solar radiation to heat that is then fed into a thermally driven cooling process or into a direct air-conditioning process
- Particularly in special applications, for example for cooling medication in remote areas that are not connected to the grid, a photovoltaic generator transforms solar radiation to solar power that then drives a refrigeration process – usually in the form of a compression chiller.
In most countries the electricity consumption for air-conditioning is increasing dramatically and it is expected to increase by a factor of 4 in 2020. With the higher demand comes several problems: the extensive use of electrically driven cooling is leading to capacity straining power demand peaks in the summer and increasing of green house gas emissions – either through leakage of cooling fluids or use of non-sustainable energy.
How is it solved?
Improved building concepts, targeting on reduction of cooling loads by passive and innovative measures, and the use of alternatives in reducing the remaining cooling and heating demands of buildings, are of interest. Solar air conditioning will play an increasing role in zero energy and energy-plus buildings design.
Solar cooling is an eminently smart technology because demand and supply of energy coincide: solar radiation is abundantly available especially in the summer time, where the need for air-conditioning is the highest. So it is sensible to resort to solar cooling and thus to cover a considerable portion of the load with low emissions.
Cooling and air conditioning of commercial and increasingly more of residential builidings is a growing market all over the world due to the increasing needs for thermal comfort, higher working and living standards and as a result of increased internal loads (i.e. from office equipment) and adverse outdoor air conditions that limit natural ventilation in urban environments. Solar energy can at least in principle cover a vast amount of the energy needs for cooling.
Solar cooling finds applications in office buildings, residential segments, laboratories and education centers, factories, hotels etc.
- Small sized SAC ( < 20KW)
- Medium sized SAC ( 20 KW – 150 KW)
It is true that SAC installations have proven their effectiveness in recent years but small and medium size plants are not still widespread into the market.
Market size and growth:
Worldwide, the market in air cooling and conditioning technologies is growing fast. Most of this demand is still being met using conventional electrical appliances, and the result, especially during summer, is an overloading of power grids.
However, the current energy situation is helping speed up the introduction of more efficient systems, and in recent years cooling apparatus have come on the market that can operate with small-scale solar thermal power (20-50 kW). The next generation of models running at 2-5 kW is currently being tested.
Research in this technology, focusses on new materials, cost reduction and the development of practical guidelines and planning tools. Combi+ solar systems, which provide hot water, heating in winter and cooling in summer, are expected to take a major market share between 2020 and 2030.
Solar cooling technology, solar thermal power in industrial processes and solar desalination and other processes are all gradually but successfully making their way onto the market and are expected to play a significant role in future energy supply.
How far from commercialization
Solar air conditioning has progressed considerably over the past years as a result of efforts toward environmental protection and new developments in components and systems.
The growth potential of solar thermal technology is possible due to solar radiation, which can be made most of it profitably around the world. Solar cooling is at the edge of wide market introduction and as a consequence considerable cost reduction is expected in short-medium term.
Investment and economics:
Investment cost for the total system comprises collector, collector support, storages, chilled water system, heat rejection, installation and monitoring.
There are enough arguments to refute the high investment costs of solar cooling installations. The increasing energy prices, for example, will reduce pay-back times in the future. Besides, if externalities of conventional cooling systems are considered, solar energy will be even moreconvenient. In the other hand, the prices of thermal cooling equipment are decreasing and will keep decreasing in the next years: specific investment costs of solar cooling kits were about 5.000 - 8.000 €/kW in 2007 and are expected to decrease down to 3.000 €/kW in 2010.
By incorporating the solar thermal system into the heating system, an annual amount of 500 MWh of primary energy will be saved.
Current challenges to implementing solar air conditioning include limited awareness on know-how, lack of reliable design instruments and technology information.
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