Solar chemical

With the aid of solar energy, chemical reactions can be initiated. This can be photochemical or solar thermal reactions.

Photochemical detoxification

As the sunlight does not have enough UV rays for the disinfection of sewage or waste gases, a suitable catalyst must be used in addition. The European Union supports research projects that aim to develop such photocatalysts. One strives to thereby produce singlet oxygen, which is a short-lived, high-energy state of the O2 molecule. Oxygen is an effective oxidizing agent in this state.

Solar thermal hydrogen production

In the solar thermal hydrogen production trying to make hydrogen for a possible future hydrogen economy solar. Not only does the use of hydrogen but also the processing to methanol is getting more into focus. In principle, the process can take place with or without the addition of fossil fuels. There are different ways of doing, all of which are not yet ready for the market and compared for hydrogen production, for example, are much more expensive from natural gas by steam reforming.

Solar thermolysis

Pilot plants have succeeded in water ( H2O) directly into hydrogen (H2 ) and oxygen ( O2) split. Since it is not easy for a direct water splitting, the so-called solar thermolysis temperatures are necessary, which can not yet be generated with solar thermal systems or difficult to control their handling due to the material stress and the separation of the two product gases are used often thermochemical cycles.

Thermochemical cycles

In this method, heating a metal oxide in a reactor which is heated directly by means of concentrated light, thereby splitting off oxygen. The reaction is:

On passing from the reduced metal and leads to water vapor, it oxidizes and breaks out of the water vapor and oxygen to the desired hydrogen can be trapped. For this process, the couple Zn / ZnO and Fe3O4/FeO favors. With this procedure are theoretically process efficiencies of up to 40 percent are possible.

Fuel upgrading

The third important application is the fuel upgrading dar. This traditional fossil fuels such as coal, methane and by-products of petroleum refining as well as biomass is processed into higher-grade hydrogen. To this end, provides the thermal cracking:

These reactions are highly endothermic. The remaining carbon is not dispensed in the form of carbon dioxide into the environment. Applied to methane response results but a smaller electricity output than if the methane would be burned directly in a combined cycle power plant.

The second method represents the solar steam reforming

If coal is chosen as the starting material, it is called solar gasification. These reactions are highly endothermic. The necessary heat is not, as usual, produced by the combustion of part of the fuel, but by solar heat. For example, 48% of the hydrogen from methane is produced today. Here, about 30 % of the methane must be burned to drive the endothermic reaction. Due to the solar steam reforming no CO2 - neutral hydrogen is produced, but the CO2 emissions are significantly reduced.