Biogas · Glossary

Biogas is a combustible gas mixture. It is formed when microorganisms break down organic matter in a moist environment in the absence of air. This process is called anaerobic digestion or fermentation. The gas consists mainly of methane and carbon dioxide. In addition, there are smaller amounts of water vapour, hydrogen sulphide, oxygen, nitrogen, ammonia, hydrogen and other trace gases. In energy terms, the methane share is what matters most, because methane is the main combustible component. Technical sources generally give raw biogas as containing roughly 50 to 75 percent methane by volume and roughly 25 to 45 (in some cases up to 50) percent carbon dioxide. The exact value depends on the substrate, process engineering and process management. Agricultural plants are often in the lower to middle part of this range.

In the power system, biogas is usually used in a combined heat and power unit (CHP). A gas engine drives a generator and produces electricity. The waste heat from the engine and exhaust gas can be used as useful heat. This coupled generation of electricity and heat is called combined heat and power. Alternatively, biogas can be upgraded to biomethane. In this process, carbon dioxide, water and hydrogen sulphide are largely removed. For injection into the gas grid, a methane content of about 98 percent is achieved. The gas can then be transported, stored and used in technically similar ways to natural gas.

The energy quantity of biogas cannot be described by gas volume alone. One standard cubic metre of pure methane contains about 10 kilowatt hours. One cubic metre of raw biogas with about 60 percent methane therefore yields only about 6 kilowatt hours. Figures in kilowatt hours, standard cubic metres or methane share are therefore only meaningful when taken together. For the electricity market, what also matters is not just how much energy a plant delivers per year. It is also important what electrical power it can provide at a given point in time. With biogas this distinction is particularly important: digestion runs relatively steadily, but power generation can be shifted in time using gas storage and additional engine capacity.

Distinction from biomass, biomethane and natural gas

Biogas is a form of biomass used for energy. However, not all biomass becomes biogas. Wood, straw or solid residues can be burned, gasified or used in other ways. Biogas is produced specifically by the digestion of moist organic substrates. These include, for example, liquid manure, solid manure, biowaste, sewage sludge, food waste and energy crops such as maize and grass. What remains after digestion is called digestate. It contains nutrients and is usually applied to agricultural land as fertiliser.

Biomethane is not a different feedstock but upgraded biogas. Chemically, its methane is identical to the methane in natural gas. Biomethane can therefore replace natural gas in many applications. This technical similarity easily leads to imprecise wording. Biomethane is renewable insofar as the substrates regrow or arise as biogenic residues. Natural gas, by contrast, is a fossil energy carrier. Both consist predominantly of methane, but differ fundamentally in origin, climate balance and supply.

Equating biogas with "green gas" is also too crude. Biogas can have a very good climate balance if residues are used, methane losses are avoided and the heat is put to sensible use. It becomes problematic when substrates compete for land, nitrous oxide arises during cultivation, digestate is stored poorly or methane escapes. Per tonne, methane is many times more potent as a greenhouse gas than carbon dioxide. Even small leaks or unburned methane in the exhaust gas, known as methane slip, can significantly worsen the climate impact.

Technical function in the power system

Biogas differs from wind energy and photovoltaics in that it provides chemically stored energy. Wind and solar power depend directly on the weather. Biogas is produced continuously in the digester, but it can be stored temporarily to a limited extent and converted into electricity later. A biogas plant can thus deliver electricity specifically when the residual load is high, that is, when wind and photovoltaics do not cover electricity demand.

This controllability has limits. A biogas plant is not a battery and not a storage power plant that can be called upon arbitrarily quickly. The biological process needs stable temperatures, suitable substrates and even feeding. If more gas is produced than can be stored or consumed, technical and economic problems arise. In an emergency, gas has to be flared. Gas storage at agricultural plants is typically sufficient for hours to a few days, but not for seasonal shifts over weeks or months. For flexible operation, engine capacity, gas storage, heat storage and heat use, grid connection and remuneration must fit together.

An illustrative example: a plant produces as much gas as a 500-kilowatt engine consumes in continuous operation. If the engine capacity is tripled to 1,500 kilowatts (so-called oversizing), the plant needs to run only about one third of the time on an annual average. The rest of the time the gas storage fills up. The annual electricity quantity thus remains the same, but it flows concentrated into hours with scarce supply and high prices.

Historically, many biogas plants were designed for electricity production that was as steady as possible. For a long time, remuneration under the Renewable Energy Sources Act (EEG) mainly rewarded the kilowatt hours fed in. With growing shares of wind and photovoltaics, the value of biogas has shifted. Electricity from biogas is then particularly useful when it does not flow as a constant baseload but in hours of scarce supply. The flexibility premium (for older existing plants) and the flexibility surcharge were therefore intended to incentivise larger generators, additional storage and operation oriented to the electricity market. This flexibility only arises, however, once the plant has been modified and is operated accordingly.

Legal framework in Germany: Biomass Package 2025

In Germany, the Act amending the EEG to make biogas plants more flexible and secure follow-on support, in short the Biomass Package, has reorganised support. It is dated 21 February 2025 and was promulgated in the Federal Law Gazette on 24 February 2025. Because the EU Commission's state aid approval was still missing, the new rules initially did not take effect. According to the Agency for Renewable Resources (FNR), the approval has been in place since September 2025. The key points for biogas plants in the EEG:

Higher tender volumes for biomass: 1,300 megawatts in 2025 instead of the previous 400 megawatts, and 1,126 megawatts in 2026 instead of 300 megawatts, in each case plus unawarded quantities from the biomethane tender. For existing plants after the end of their original remuneration, follow-on support is extended from 10 to 12 years.
The flexibility surcharge rises from 65 to 100 euros per kilowatt of installed capacity per year.
Stricter flexibility requirements: plants above 350 kilowatts must be oversized at least threefold in order to receive further support. They receive remuneration only for a limited number of operating quarter-hours per year. If electricity prices are only slightly positive, below 2 cents per kilowatt hour, support is not paid.
In the tenders, preference is given to existing plants that already operate a heat supply, such as a heat network.
The so-called maize cap is being lowered. It limits the permissible share of maize and cereal grain in the substrate to 30 percent by mass for 2025 and to 25 percent by mass from 2026.

These rules apply to plants supported under the EEG. Which version applies in an individual case depends on the year of commissioning and the support regime. According to the FNR, the state aid approval of the EEG expires at the end of 2026. Further adjustments are therefore to be expected.

Economic and institutional context

Biogas sits at the interface of agriculture, waste management, the electricity market, heat supply and climate policy. A plant procures substrates and operates a biological process. It produces gas, generates electricity and heat, utilises digestate and must comply with emissions and safety requirements. Its profitability therefore depends not only on the electricity price. Substrate costs, lease prices, transport distances, heat customers, grid connection, permits, EEG remuneration and the requirements for digestate storage also play a role.

At agricultural plants, energy crops and farm manures are particularly important. Energy crops deliver plannable gas yields, but take up arable land and can encourage tight crop rotations. The falling maize cap sets a legal limit here. Liquid manure and solid manure yield less gas per tonne. From a climate policy perspective they can nevertheless be valuable, because digesting them can reduce methane emissions from open storage. Biowaste and food waste are also interesting, but require proper collection, hygienisation and suitable waste logistics.

A large part of the system effect is decided by heat use. If the waste heat of the CHP is only partly used, the overall efficiency falls. If it is used in a heat network, for livestock buildings, drying, commerce or municipal buildings, the energy balance improves significantly. According to FNR figures, around 10 percent of renewable heat in 2024 came from biogas plants, and in many places they form the basis for heat networks. A plant without sensible heat use does deliver renewable electricity, but wastes a considerable part of the energy contained in the gas.

Typical misunderstandings

First misunderstanding: biogas is automatically climate-neutral because it is renewable. This simplification ignores the process chain. What matters are the substrates, emissions during cultivation and the treatment of digestate. Added to this are methane losses at the digester, storage, engine and upgrading, as well as the question of which fossil energy carriers are actually replaced. Climate protection does not come from the label "biogenic", but from a controlled material and energy chain with low losses.

Second misunderstanding: biogas can be expanded without limit. It is more controllable than wind and photovoltaics, but the quantity of sustainable substrates is limited. More energy crops mean more competition with food production, nature conservation, soil fertility and other uses of biomass. In the future energy system, biogas is therefore more of a valuable, limited resource for times of high demand for firm capacity than a supplier of electricity that dominates in terms of volume.

Third misunderstanding: annual balances say enough. The quantity of electricity generated per year says little about the contribution to security of supply. What is decisive is whether power is available in the hours in which it is needed. A plant feeding in evenly supplies renewable electricity statistically, but relieves critical hours less than a flexible plant with the same annual output. The assessment thus shifts from the mere kilowatt hour to the timing of supply. This logic also underlies the new EEG requirements.

Fourth misunderstanding: biogas is a storage facility. Biogas contains storable energy, but the storage function depends on the plant as a whole. A digester is not an electricity store; it produces gas from substrates. Only gas holders, engine capacity and mode of operation turn it into electricity generation that can be shifted in time. For seasonal storage tasks, biomethane in the gas grid is more suitable than raw biogas at an individual plant. But even there, the available biomass limits the possible energy quantity.

Role in a renewable power system

With the growing electrification of heat, transport and industry, electricity demand also rises in hours in which wind and sun do not deliver enough. Biogas can then play a special role, because it converts renewable chemical energy into dispatchable electrical power. This role does not resemble that of a baseload power plant, but rather that of a controllable resource with limited availability. Its value rises when it is deployed specifically in hours of high residual load. Industry-related studies see great potential here. A study from the University of Erlangen-Nuremberg cited by the FNR concludes that biogas plants could cover around half of the residual load by 2040. Such values, however, depend strongly on the assumptions.

New requirements for plant operation and regulation follow from this. Remuneration systems should reward not only quantities but also temporal availability, flexibility and, where appropriate, firm capacity. Grid operators pay attention to feed-in capacity and connection conditions. Municipalities consider heat networks and land use. Farms organise substrate cycles and nutrient balances. The term biogas therefore touches not only a generation technology but also the responsibilities of energy, agricultural, waste and climate policy.

For the distinction from other renewable energies, the scarcity of the resource is central. Photovoltaics and wind energy are limited above all by land, acceptance, grids and material chains. Biogas additionally depends on organic material flows that are also important for soils, livestock farming, waste treatment and industry. A sensible use therefore treats biogas not as a mass substitute for fossil gas, but as a controllable form of energy with its own use value.

Biogas thus means more than a gas from organic digestion. It stands for a limited, technically controllable and institutionally demanding energy source. Its benefit in the power system arises where sustainable substrates, low methane losses, utilised heat and flexible power generation come together. If these conditions are missing, biogas remains renewable. However, its contribution to climate protection, security of supply and system costs is then easily overestimated.

Sources

Biogas — Fachagentur Nachwachsende Rohstoffe e. V. (FNR); unbekannt. Abschnitt zur Entstehung und Zusammensetzung von Biogas
Themenportal Bioenergie: Biogas — Fachagentur Nachwachsende Rohstoffe e. V. (FNR); unbekannt. Abschnitt Gasverwertung
Gesetz zur Änderung des Erneuerbare-Energien-Gesetzes zur Flexibilisierung von Biogasanlagen und Sicherung der Anschlussförderung (BGBl. 2025 I Nr. 52) — Bundesgesetzblatt (bereitgestellt von der Clearingstelle EEG|KWKG); 2025-02-21 (ausgegeben 2025-02-24). Gesetzestitel und Änderungen zu den Biomasseausschreibungen; nur im Suchergebnis-Auszug eingesehen
Biomassepaket zieht scharf: Chance für den Biogassektor, zum Systemdienstleister der Energiewende zu werden — Fachagentur Nachwachsende Rohstoffe e. V. (FNR); 2025-09-18. Pressemitteilung, Haupttext und Abschnitt Hintergrund

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Edited by eCMS on 11.11.2026 15:53