Our objective is to stop global warming. However, direct solar energy collecting can only supply up to 60% of the energy need of the society. Only chemical fuel can fill the remaining part. And it is important that this part do not rely on fossil fuel.
Now with cheap direct solar power, it is possible to produce renewable chemical fuel with sufficiently low cost. There are two basic methods. A rough cost analysis of the methods can be found here.
Chemical method.
On the one hand, solar electricity can be used to electrolyze water and produce hydrogen. Hydrogen can be used directly as a renewable fuel, but it is hard to store and to transport.
Hydrogen can also be combined with nitrogen to form ammonia in a Haber Process. As ammonia is the base of most fertilizers, the reliance on fossil fuel of the fertilizer industry can be removed.
On the other hand, one can capture atmospheric CO2 with reasonable cost (see this for example).
Now hydrogen and CO2 can be combined to form methanol, which is not only a very good fuel by itself, but can also serve as a base material for the plastics industry.
For those who don't like the toxicity of methanol, note that it can be further transformed to ethanol through a chemical reaction with CO2.
Biological method.
This means biomass, which already has an important success. However, current production mode of biomass either disputes land use with food supply or other vital crops, or results in accelerated deforestation. This is not sustainable.
A sustainable biomass production must use land that has previously no or few vegetation on it, and must not strain the availability of fresh water and other resources. This can now be done with solar-powered desalination of sea water.
There are several places in the world simultaneously satisfying the following three conditions: close to an ocean, very high insolation, plenty of arid land nearby.
Such places include the whole north coast of Africa, Somalia, Middle East, north-west Australia, West USA, south Africa. In any of these places, large scale solar power plants can be installed. Electricity generated by these power plants will be fed to water desalination plants to produce large quantities of fresh water. The fresh water is then lead to irrigate the nearby arid land. With plenty of sun, enough irrigation and enough synthetic fertilizer produced by solar power, all sorts of plants can be grown. In particular plants for biomass production.
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