Hydrogen at a biogas plant: local use scenarios and whether they make sense

A biogas plant can be a starting point for hydrogen production, but in most cases selling biomethane, bioCNG or electricity gives a better economic result than producing hydrogen on site, because every energy conversion carries losses and costs. Electrolysis powered by biogas electricity consumes 50–55 kWh/kg H₂, and the energy of 1 kg of hydrogen (33.3 kWh by calorific value) is therefore about 60–65% of the energy drawn as electricity. Converting gas into electricity in a CHP engine with 40% efficiency further lowers the efficiency of the chain. Hydrogen at a biogas plant makes sense in niches: where there is a steady local customer, when hydrogen is used to support a biological process, or when it is combined with surplus energy from other sources.

Scenario 1: electrolysis from biogas electricity

A CHP engine generates electricity that powers an electrolyser. Chain efficiency: biogas → electricity 40% → hydrogen (33.3/52 = 64%) = about 26% of the biogas energy in hydrogen (LHV). By comparison, biomethane from upgrading retains about 90–95% of the biogas energy. It is therefore the worst route in terms of efficiency. In addition, hydrogen from biogas electricity is not RFNBO (energy from biomass), and its status requires a separate assessment. Application: only if hydrogen is absolutely needed and the biogas electricity cannot be sold at a lower price.

Scenario 2: biomethane reforming

Biomethane is converted into hydrogen (see the entry on reforming). Consumption of about 3.4 kg CH₄ per kg H₂ means an efficiency of about 70% relative to the energy of the biomethane. It has value with local industrial demand and the availability of a reforming plant; on a small scale it is expensive.

Scenario 3: hydrogen to support methanogenesis

Adding hydrogen to the digester or a separate reactor makes it possible to convert the CO₂ in the biogas into additional methane (biological methanation in situ or ex situ). The advantage is the use of CO₂ and tolerance of impurities; the disadvantages are limits on gas-to-liquid transfer and small scale. The economics depend on the electricity price (see the entry on methanation).

Scenario 4: fuel for farm machinery

Hydrogen as a fuel for tractors and machinery is at an early stage of development. A tractor's energy requirement is several hundred kWh a day in season, so a plant of suitable capacity and a hydrogen refuelling station (compression to several hundred bar) are required. At present a more practical and cheaper solution for farm machinery is bioCNG/bioLNG or biodiesel, and in future electric solutions.

Scenario 5: supply to industry or transport

If a plant consuming hydrogen operates nearby (chemicals, refinery, glass), and the plant is looking for hydrogen with a low carbon footprint, the biogas plant can become a supplier. This requires large scale, certification and hydrogen transport infrastructure (pipeline, trailers). For a single agricultural plant the scale is usually too small.

Comparative example

Assumptions: 1000 MWh of chemical energy in biogas a year (at 55% CH₄).

The differences are enormous. Hydrogen makes sense only if its value to the customer per MWh is much higher than the value of biomethane or electricity.

Decision criteria

1. Is there a steady hydrogen customer with a contract?
2. What is the cost of the whole chain (production, purification, compression, storage, transport)?
3. Does the hydrogen qualify for support or a premium, and what regulatory requirements does it meet?
4. Does the alternative (biomethane, bioCNG) not give a better result?
5. Is technical competence available, and willingness to accept the risk (ATEX, hydrogen)?

Safety and formalities

Hydrogen has a wide flammability range (about 4–75% by volume in air) and very low ignition energy, so hydrogen installations require a separate hazard assessment, Ex zones, detection and procedures. A biogas plant that already manages ATEX zones for biogas has a certain competence advantage, but adding hydrogen means new requirements for equipment, high-pressure storage and operation. Permits, insurance and training should be added to the costs, and their scope depends on scale.

Summary

For most biogas plants hydrogen is not a natural product. Sensible niches exist, but every project should start with an energy balance and a contract with a customer, not with the technology.