The rational management of natural resources and the utilization of waste products or sub-products is a matter under intensive discussion nowadays. Greece possesses a rich and unexploited reservoir of waste materials that can contribute immensely to her energy autonomy.

Due to the current legal framework the licensing procedure of biogas power plants has been significantly accelerated. Eligible substrates for biogas production through anaerobic digestion are animal manure, harvest residues, energy crops, and wastewater from agriculture-related industries. Animal manure is usually fermented together with other types of substrates because it has a relatively low biogas output by itself.

Biogas production is achieved via the anaerobic digestion of the available substrates in an anaerobic digestion tank. Depending on the state and origin of the available substrates and on the applied anaerobic digestion technology, pre-processing of the input material may be necessary. The biogas produced is used in an internal combustion engine CHP unit which produces electrical and thermal energy. The digestate which remains from the anaerobic digestion process is a valuable fertilizer with considerably less odor compared to the manure which was initially fed to the digester.

Except for the generation of electrical energy there are many other possibilities for the utilization of the biogas produced. The most important are:

• Direct Combustion in a boiler for thermal energy production

• Upgrading of the biogas in order to be used as vehicle fuel

• Upgrading of the biogas in order to be injected into the natural gas grid

The long-term availability of the substrates and the possibility of utilizing or selling the products (electrical energy, thermal energy, compost) of a biogas power plant play a determining role in the economic efficiency of the project. The renewable energy feed-in-tariffs by themselves make the investment economically feasible. However, the utilization of the thermal energy and the compost are in accordance with the principles of sustainable development and can secure the profitability of the investment to an even greater extent.

According to the current legal framework, the generation of electrical energy from biogas power plants is supported with the following feed-in-tariffs: