Solar thermal industrial applications

Solar energy is intermittent – it is available during sunny days only. It can be used to generate electricity through photovoltaic cells, but a more efficient use is to concentrate the heat by focusing the sunlight with parabolic mirrors. This is useful and efficient for heating water, but can also be used in manufacturing processes, and for chemical systems generating energy storage media, such as hydrogen and methanol.

Examples of manufacturing processes which can exploit solar high-temperature energy include cement and metals manufacturing and recycling heavy metal waste. These processes need heat of up to 2000°C. Concentrated solar heat can therefore potentially save huge amounts of fossil fuels.

Current global energy consumption could be supplied by solar energy systems, at 20% conversion efficiency, covering 0.1% of the land. Solar radiation on the Earth’s surface is about 1-3 kW/m2 on average. It makes sense to maximise the use of solar energy available in the range ± 30° from the equator, where solar intensity is over 3 kW/m2 for many more hours in a year. To do this, it is better to convert the energy into a chemical storage form, rather than electricity. Some of the infrastructure for such a system already exists in the petroleum industry – oil and gas, as well as coal, are after all chemical stores of solar energy from millennia ago. Oil tankers could just as easily transport fuel generated in desert regions through power-to-fuel solar thermogeneration.

Thermolysis of water

At high temperatures above 2500 K and depending on the pressure, water splits into hydrogen and oxygen.

H2O → H2 + ½O2

Um das Trennungsproblem, wobei ein Explosionsgefahr besteht mit der Trennung des Wasserstoffs vom Sauerstoff bei hohen Temperaturen, werden zweistufige Wasserspaltungs-Zyklen eingeführt, die auf sogenannten Metalloxid-Redox-Systemen basieren.

1. Solarthermal (endothermic) dissasociation of metal oxides at high temperatures (> 2300K):

MxOy → xM + (y/2)O2

2. Hydrolysis (exothermic) of metal products at moderate temperatures (< 900 K), through which molecular hydrogen and corresponding metal oxides are formed:

xM + yH2O → MxOy + yH2

With such reduction-oxidation systems, efficiencies of more than 30% can be achieved.