First results from a Linear Mirror II system with a solar air heat exchanger
In many countries already a relevant fraction of electric energy is provided by renewable energy sources, mostly photovoltaic, wind energy and hydro energy [1][2] In comparison, the contribution of renewable energy sources to thermal energy consumption is much lower, in spite of the fact, that industry as well as private homes consume more thermal energy than electric energy [3] As a consequence, new and improved systems for providing renewable heat energy become a necessary condition for further reducing the level of CO2 production. These new technologies must provide thermal energy at elevated temperatures also in winter, also at northern latitudes and in a simple and economic way. The Linear Mirror technology was developed to meet these requirements [4] in its standard version, the Linear Mirror provides hot water at temperatures up to 100degC also in winter, and at a rather high efficiency, due to the low specific heat of its absorber [5] The limit of 100degC is applied by the control software in order to ease the integration of the Linear Mirror into existing heating systems. The Linear Mirror can also be used to provide higher temperatures as well for example, during an experiment for producing biochar from simple biomasses using only solar energy "solar carbon" a temperature of up to 500 degC was reached [6] In order to use water as a heat carrier at temperatures above 100 degC, high pressure installations are necessary, which tend to be complex and expensive and may create security problems. In addition, transferring the heat from the pressurized water to the application process may be difficult and inefficient. For instance, it would be difficult to torrefy or pyrolyze cheap biomasses by means of hot water rotating drums or similar devices would be needed, or additional water air heat exchangers [7] It would be simpler, if one had a flow of hot air available. Then one could roast cheap biomasses in the same way as coffee is roasted, which is a cheap and simple procedure. Unfortunately, for roasting coffee, the hot air is provided by a gas flame, which is not CO2 neutral. It would be of great advantage to have a solar air heat exchanger available, which can produce hot air from concentrated sun light.