Environmental Engineering Reference
In-Depth Information
suppliers and owners which, in the final analysis, must be paid by the general
public. An exhaustive analysis of fixed-price models is given by Mendoc¸ a
et al. (2010).
One of the first countries to introduce the fixed-price model was
Germany. Here, the Renewable Energies Act (EEG) went into effect in
the year 2000. It proved to be the starting point for growth in all renewable
energy sectors and the number of biogas plants increased considerably. The
EEG was revised in 2004, 2009 and 2012. The feed-in rates were changed
and certain plant constellations subsidized. Probably the most important
change as far as biogas is concerned was the adoption of a bonus for feeding
electricity from renewable sources. With this bonus, energy crops were
cultivated for the production of biogas and biogas crop production
established itself as a sector in its own right in agriculture. Along with
this development, many farm by-products that otherwise would have been
spread onto fields without utilization of the energy they contain provided
substrates for biogas production. In fact, about 10% of the liquid manure
produced in Germany already goes to biogas plants.
Other by-products such as feed waste, harvest residue and agricultural
products that cannot be marketed as food because of low quality are ideal
feedstock for biogas plants. According to calculations by the German
Biogas Association (GBA 2011), approximately 26.5 TWh of electricity per
year could be produced in Germany if all digestible agricultural by-products
and wastes were converted to biogas. This would be enough to supply
7.5 million three-person households with 3500KWh of electric power per
year.
The possibility of using very different substrates in biogas plants makes
biogas a particularly interesting source of renewable energy. However, this
also makes the design of a successful support framework much more
complicated than in the case of other renewable energy sources. There is not
only a wide variety of feedstocks, but there are also as many potential
utilizations of the product: transport fuel, heat only, or combined electricity
and heat. Furthermore, there is the question of whether the gas network
infrastructure should be used for biogas as well. If it should, the support
regulations must be defined accordingly. Before a decision on a support
instrument and its structure is taken, the direction in which the biogas sector
is to be heading must be clear. Looking at high energy efficiency, it seems
logical to place one focus of support on the production of electric power and
heat in cogeneration units. As biogas and also heat can be stored,
cogeneration systems that can supply both electricity and heat as and
when needed should receive particular support. Another focal support to
consider is biomethane as fuel because, among the biofuels, it has the
highest energy efficiency (Smyth et al. 2009). Basically possible, but not
advantageous for efficiency reasons, is the use of biogas or biomethane for
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