German scientists have come up with a procedure for storing surplus wind and solar electricity as biomethane. The upgrading of biogas to natural-gas quality is making particular headway in Germany, Sweden and Switzerland. Yet the basic parameters still need to be set for the international transport and trade of biomethane. 04/2010


Könnern gross

 


Jürgen Schmid can well imagine that renewable energy sources will by mid-century be able to meet global electricity requirements entirely. “A full supply is conceivable, and in the long run even economically advantageous,” he says. The head of the Fraunhofer Institute for Wind Energy and Energy System Technology (IWES) thinks that by that point in time electricity from renewable energy sources will be producable at lower costs than coal, gas and oil. Schmid is well aware that the considerable fluctuations in wind energy need to be balanced out. On windy days there is a surplus of electricity in the network, on calm days too little so that other power plants are needed to supply enough energy. According to him, these fluctuations could be partly offset by a “trans-European supernetwork,” by load management in intelligent distribution systems, and by power storage in electric vehicles.


He also presents a previously little-known method for converting surplus wind and solar electricity into natural gas. The method starts by using the familiar process of electrolysis to manufacture the high-quality energy carrier hydrogen from electricity and water. The hydrogen then reacts with carbon dioxide in a methanation facility forming methane – synthetic natural gas (SNG). This SNG can be fed into existing gas networks, stored in tanks and, when needed, reconverted to electricity in gas power plants.

The carbon dioxide required for SNG production would be obtained, says Schmid, from biogas plants, where it is separated during the gas refining process. Another possibility is to use the hydrogen directly in biogas refining. The raw biogas, still replete with carbon dioxide, would react with hydrogen in the methanation facility to create methane. “This way we’ve not only used the surpluses in the electricity grid, but we also have a new procedure for processing biogas,” he adds. Together with the Center for Solar Energy and Hydrogen Research (ZSW) in Stuttgart and industrial partners, IWES has already developed an initial application.

Ideas of this sort fall on fertile ground in Germany. The country already produces 16 percent of its electricity from renewable energy sources such as wind and hydropower, biomass and solar radiation. And in recent months, the production of highly refined biomethane has picked up considerably, being fed into the natural-gas distribution system and sold as “bio-natural gas” at gas stations, on the heat market or for the production of green electricity. According to the German Biomass Research Center (DBFZ), there are 32 biogass processing facilities nationwide producing a total of 100 million cubic meters of biomethane in natural-gas quality annually. The German federal government has set as its goal an annual supply of six billion cubic meters of biomethane by the year 2020. By 2030, its target is ten billion cubic meters – about a tenth of German natural gas consumption. 

Whereas most German biomethane plants were built in the last two to three years, Sweden began as early as the late 1990s. The Scandinavian country meanwhile has 39 plants capable of producing about 50 million cubic meters annually. Switzerland also has well-developed biogas processing facilities, with 17 plants upgrading around eight million cubic meters to natural-gas quality. Austria, the Netherlands, France, Norway and Spain each have a number of biogas processing facilities as well.

Seventeen plants are currently in operation in the United States, producing biomethane from landfill gas and feeding it into gas networks. The U.S. plants are large-scale units. The landfill gas recovery facility on Staten Island, for instance, which went into operation back in 1981, produces about 40 million cubic meters of biomethane annually. Things are quite different in India. Countless small-scale low-tech biogas facilities are scattered throughout the country, mostly producing gas for cooking. Industrial companies also make gas from waste products and use it to produce electricity at power plants. Producing biomethane in natural-gas quality, however, is still in its infancy. For example, there is a research project at the TERI University in New Delhi in which upgraded biomethane is used for generating electricity or as fuel.

Unlike India, Europe has a well-developed natural-gas grid. Frank Scholwin, division director at the DBFZ, sees that as a solid foundation for the Europe-wide transport and trade of biomethane. Both of these could gain momentum with a new technology currently being tested at pilot facilities: the thermochemical gasification of biomass. The facilities are considerably larger than the standard biochemical plants now in use, which produce gas from agricultural base materials such as liquid manure, corn and grain. Such materials can only be transported relatively short distances due to cost factors. Thermochemical gas plants, on the other hand, work with solid biomass like wood, which can be transported economically to production facilities even from far away. This taps into a sizable catchment area for Europe-wide biomethane production: “Thermochemical supply makes it possible to feed into gas networks almost anywhere in Central Europe,” Schwolwin says. “From there the gas can be shipped to almost every corner of Europe.”

The DBFZ has also determined how much biomethane can ideally be produced with existing supplies of biomass in Europe and with available plant technology. The “technical potential” was 300 billion cubic meters in 2005 and is expected to rise to 484 billion cubic meters by the year 2020. This almost equals the current natural-gas consumption of the European Union. And yet this “technical potential” can only be developed to a limited degree, for several reasons. Scholwin admits that the framework conditions for a European-wide feed-in of biomethane still need to be created. Biomethane producers have to have access to gas grids, and international trade has to develop in this area. What’s more, biomethane, still rather costly, would have to become more competitive with natural gas. Schwolwin can see this happening with the help of credit vouchers from emissions trading.  


Interview with Prof. Frank Scholwin, head of the Biogas Technology Department at the German Biomass Research Center.

You estimate the amount of biomethane potentially exploitable using available technologies to be 300 billion cubic meters in 2005 and 484 billion cubic meters in 2020. Why does the amount increase so drastically by the year 2020?

Scholwin: We assume that the yields of biomass plantations will increase due to three factors. These are, first of all, the success in cultivating bioenergy crops, where we expect a two-percent increase per year. Second, we reckon with considerably higher efficiency in the crop yields of Eastern Europe, with more than double the production expected in some countries. Third, we expect better results in conventional agricultural products, leading in turn to more efficient use of soils and freeing up more acreage for the cultivation of renewable resources.


What are the key factors determining how extensively this biomethane potential is exploited?

The key factor is the willingness of political actors, as well as how the countries of Eastern Europe implement their own objectives in producing and harnessing sources of renewable energy. There are also economic issues involved in the production and transport of biomethane, issues we are currently working on together with institutions in these countries. The technical regulations regarding access to the natural-gas grid in these countries is a surmountable obstacle. Current regulations do not provide for biogenic gases being fed into the system – the same situation we had in Germany just a few years ago.


In many Central and Western European countries as well, there has been little or no biomethane processing and network supplying to date. What do you think are the reasons for this?

The main reason is still the lack of competitiveness economically. Without politically motivated incentive systems or subsidies, the production and use of biomethane will not be competitive with natural gas. Incentive systems only exist in a handful of countries. Furthermore, many European countries have little or no experience in biogas production. That’s why the tendency is to build local biogas facilities with combined heat and power or heat generation. Finally, there is the question of whether a gas grid is available or whether there is experience with natural-gas applications – for example, in motor vehicles.

     
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