Biogas an all-rounder

Biogas: The Energy Revolution’s All-rounder

Biogas is created during the fermentation of biomass. It is a gas containing methane which, thanks to its manifold uses as a supplier of renewable power, heat and fuel, makes a major contribution to secure, environmentally-sound energy supply. Biogas can either be stored or injected into the natural gas grid, which makes it particularly versatile. As an all-rounder in the energy supply market, targets from the German federal government intend biogas to cover around 6% of the demand for natural gas by 2020, creating thousands of new jobs in the process.

Biogas, like natural gas, is a gas mixture consisting chiefly of methane. It is produced by microorganisms as they decompose plants and liquid or solid manure. Biogas is also generated in sewage plants and at landfill sites. The most common method of using biogas for energy production is through converting it into heat and electricity in combined heat and power plants (CHP). The thermal energy can be used for instance to heat buildings, meaning that the energy is used twice over – and thus particularly efficiently. During the biogas manufacturing process, roughly an equivalent amount of carbon dioxide is generated as is absorbed by the energy crops during their growth cycle, or as would be released naturally in the rotting of waste. This makes power and heat from biogas plants particularly climate-friendly.

Heat and power from one energy source

In 2009, biogas plant operators in Germany generated around 11.5 billion kilowatt hours of biogas power, and sold this to their respective energy suppliers at rates laid down in the EEG. This was equivalent to over twelve percent of the total electricity generated from renewable sources – or approximately 2.5 percent of German power consumption. This enabled carbon dioxide emissions reductions of over eleven million metric tons per year. But biogas production itself also has an indirect impact on climate protection. The controlled fermentation of liquid manure and compostable waste prevents the release of harmful gases such as methane, which has a much more potent influence on the greenhouse effect than carbon dioxide.

A biogas plant with an installed electrical capacity of around 500 kilowatts (kW) generates around four million kilowatt hours of electricity and 4.4 million kilowatt hours of heat each year from approximately two million cubic metres of biogas. This replaces the equivalent of 440,000 litres of fuel oil. This means that a farmer can generate enough power to supply over 1,000 four-person households each year from one power plant. At the same time, the CHP plant will produce sufficient heat to supply 150 households.

Transporting heat: from biogas plant to the public district heating network

Whilst the purchase of electricity by utility companies is governed by legislation, biogas producers are required to market the heat they generate under their own steam. Only in a few rare cases are the heating requirements at the farmer’s own site such that heat produced by the biogas plant can be fully exploited there throughout the year. Instead, the heat can be fed, for example, into a district heating network. In addition to residential housing, facilities which require heat over the entire year are particularly appealing to plant operators – these could be swimming pools, greenhouses or fish farms.

Micro gas grids: from biogas plant to combined heat and power plant

If purchasers of heat are located at too great a distance from the biogas plant, transporting the heat is extremely complex and costly. In these cases, the CHP plant can be constructed where the heat is needed. The biogas is simply transported there via a separate pipe, as demonstrated in Hollich, North Rhine Westphalia. There, the gas travels down a three-kilometre micro gas pipe to the CHP plant in the town where it is converted into power and heat. Among the buildings supplied by the waste heat are several municipal administrative buildings, schools and a home for the elderly.

Biomethane in the natural gas grid

After processing, biogas can also be injected directly into the existing natural gas grid. In this scenario it exploits the infrastructure available and finds application as a natural gas equivalent (called biomethane). By the end of 2010, around 70 plants in Germany will be generating and injecting into the grid almost four billion kilowatt hours of biomethane. This corresponds to the quantity of energy required to cover the heating and hot water requirements of 200,000 four-person households. If this quantity of biomethane were to be used as fuel, it could power 235,000 natural gas vehicles travelling 20,000 kilometres per year.

Energy that can be stored and used at the drop of a hat

Biogas can be stored without difficulty which means that it can be used at any time in any location – irrespective of where it is produced. Hybrid power plants, for example, are able to take advantage of these qualities. They combine different renewable energy sources to complement one another, such that the amount of energy required is always at hand. Owing to its aptitude for storage, biogas is particularly valuable here, as it is able to compensate for fluctuations in other renewable sources such as wind or solar energy.

Biogas as a fuel

A further possibility for exploiting biogas is its use as a fuel. Fuel from one hectare of maize would allow a vehicle to travel around 70,000 kilometres – which is one and a half times around the world! A car can travel around 22,000 kilometres on biodiesel from one hectare of rape, and with bioethanol from one hectare of grain it would travel over 40,000 kilometres. Germany’s first filling station devoted purely to biogas was opened in 2006 in the town of Jameln in Lower Saxony (district of Lüchow-Dannenberg), and a second is under construction in Dannenberg. In addition, many natural gas filling stations also offer their fuel with ten or 20 percent biomethane content.

Biogas to cover six percent of natural gas requirements

In line with plans from the German federal government, it is intended that six billion cubic metres of biomethane be injected into the natural gas grid each year by 2020. This equates to six percent of current German gas consumption. In order to achieve the quantities targeted by the government, the German Biogas Association is calling for new legislation on the grid injection of renewable gas. Comparable to the EEG in the electricity sector, this should regulate connection and purchasing obligations for gas injection and establish realistic feed-in tariffs. The German Biogas Association anticipates that the law could generate investment totalling ten billion euros by 2020, and predicts that an additional 10,000 jobs could be created to add to the industry’s current total of 16,000.