Gas supply by local mircro grids
The economy of biogas plants producing mainly electricity is strongly endangered or not given due to high raw material prices.
New, economically more attractive forms of biogas utilisation are necessary. A possible, alternative utilisation would be direct marketing of fermentation gas to the consumers by a local "biogas micro grid". In the biogas micro grid the cleaned and conditioned biogas is led directly to the consumers at a low pressure level. This offers a chance to gain considerable higher profit at relatively lower costs than by selling the generated power to national fixed feed-in tariffs, which are often not cost-covering.
The aim of this project was to investigate the economical and technical feasibility of biogas micro grids. The study showed that the technical implementation of biogas micro grids on basis of the (current) state of the art is feasible. However, certain basic conditions have to be considered.
It is advantageous to maintain the micro grid at a constant gas quality of approx. 90 % CH4, as the end consumer equipment (gas burners) and the measurement technique (consumption measurement) are not suitable for strong fluctuating gas qualities.
However, methane-enrichment of the biogas up to the natural gas quality in accordance to ÖVGW G31 is not necessary, but gives a considerable advantage regarding the seasonal gas storage, the feed into the natural gas grid or the use as fuel.
The load management is certainly a challenge, especially in completely self-sufficient biogas micro grids. In order to obtain a day-time and seasonal balance between production and consumption, storage of relatively large quantities of biogas is necessary. There still exists a substantial R&D need of economically effective storage technologies.
The accomplished calculations of biogas costs in different prototypical micro grid structures and a pilot location, demonstrate the competitiveness of biogas micro grids compared to fossil fuels. The calculations showed that the costs are considerably affected by investment and operating costs for biogas storage and the backup-system of the biogas micro grid.
In an industrial area or a rural local area the methane-enriched biogas (bio-methane) with a lower heating value approximately 10.7 kWh/m3 (corresponds to the lower heating value of natural gas) can be supplied to the end consumers for respectively 0.61 and 0.65 €/m3. However, these costs are only valid for a biogas micro grid, whose load peaks are covered by natural gas. The costs of biogas in a self-sufficient micro grids with a seasonal storage rise up to 0.75 €/m3. Nevertheless, regarding the expected increase of prices for oil and natural gas biogas supplying is economically attractive.
In comparison: the price of natural gas for private customers is presently at about 0.58 €/m3 (Wienenergie 2008), that of light heating oil is between 0.89 and 1.02 €/litre (the lower heating value of oil is 10.08 kWh/litre).
Therefore the use of biogas (bio methane) is economically effective and offers a cost advantage of up to 40 % compared with heating oil. Thus, biogas micro grids are an attractive option for a sustainable regional power supply.
DI Dr. Dieter Hornbachner,
HEI | Hornbachner Energie Innovation
- DI Josef Bärnthaler, Energieagentur Obersteiermark
- DI (FH) Harald Bergmann, Energieagentur Obersteiermark
- DI Georg Konrad, HEI | Hornbachner Energie Innovation
- DI (FH) Christian Pinter, Fachhochschulstudiengänge Burgenland GmbH
- Dr. Ing. Ludwig Targyik-Kumer, Ingenieurkonsulent für technische Physik
- DI Dr. Christian Wartha, Fachhochschulstudiengänge Burgenland GmbH
- Diana Köbrunner, HEI | Hornbachner Energie Innovation
- Rusbeh Rezania, HEI | Hornbachner Energie Innovation