Our studio guest is Prof. Bernhard Schink, of the University of Konstanz. He is the co-author of a study carried out for the German National Academy of Sciences, Leopoldina. It evaluates the chances and limitations of bioenergy.
What are the limits of bioenergy?
We have to realize that the efficiency of energy transformation by green plants is very limited. Of the sun radiation that reaches the plant, only 1 percent is converted into biomass, and the transformation of the biomass into energy carriers leads to further losses. Photovoltaics, for instance, has efficiencies in the range of 15 percent. Compared to that, the biomass production is off by at least one order of magnitude. Even if we could slightly increase the productivity of plants, it would still be far away from other techniques.
OK, energy from biomass might not compare well with photovoltaics, for example, but it has some advantages.
For sure. Bioenergy has the advantage that it can be stored and it can definitively contribute to our energy needs. Waste materials left over from agriculture are being used for bioreactors. We are somewhere in the range of 5 percent of our energy needs that we can be covered that way. Everything beyond that is not really bearable for the environment in the long-term perspective since whenever we carry out intensive agriculture we also use fertilizers and so on which contribute to greenhouse gas production.
Now, your own report actually made recommendations to policy-makers. What was the most important piece of advice that you could give them?
Our main message was not to increase biomass production any further for energy needs, but rather to concentrate on waste and leftover materials. And of course to save energy, and cut down on our energy needs. That is a very important area.
But despite that, biomass still looks set to stay. What in your opinion is the most efficient way to use it?
The most efficient way to use biomass is in the formation of biogas rather than biodiesel or bioethanol, because biogas production already covers the entire plant material rather than only the starchy parts of the plants that can be used for ethanol production, for instance. So there the efficiency is substantially higher. And the technology is there, it's easy.
(Interview: Anne O'Donnell)