Electricity Generation from Biogas: How It Works, at Every Scale

Electricity generation from biogas is not new. Millions of biogas plants operate around the world, and many of them make electricity. The biogas generators needed to produce electricity from biogas are available at every scale of output, and the technology to clean the raw gas before it is burned is tried, tested and ready to use wherever it is needed.

Electricity generation from biogas has significant potential in the field of alternative energy, helping governments meet their Paris Agreement targets for cutting carbon emissions under global climate agreements.

Electricity generation by internal combustion engines

An internal combustion engine converts biogas into mechanical energy. That mechanical energy turns an electric generator, which produces electricity.

Biogas generation systems that supply on-site renewable energy are used to power and heat farms and facilities, to generate electricity for sale to the grid, and to support power utilities. On-site biogas power plants can be configured to deliver electricity, heat and/or cooling, and can serve a wide range of farm and business applications.

Biogas engines

Internal combustion engines are commonly called biogas engines when they run on biogas. The gas is carefully mixed with the right amount of air, then drawn into the engine as the pistons move down and create a vacuum.

The charge is compressed and ignited, and the resulting rotational force drives a shaft inside an attached generator. Alternating-current electricity is produced as that movement induces a current in the generator’s wire coils.

Alternators and dynamos

Because most generators produce alternating-current electricity, they are also known as alternators (or, historically, dynamos). Suitable generators are available in almost every country and in every size.

Alternatives to internal combustion engines

Internal combustion engines are not the only option. Stirling engines and gas turbines are alternatives. Steam turbines are almost never used with biogas; that equipment is more typical of large industrial applications generating steam, such as power plants or waste-recovery sites using incineration.

Fuel cells

Biogas can, in principle, be converted directly into electricity using a fuel cell. In practice this needs very clean gas and expensive cells. It remains largely a matter for research and specialist demonstration, and is not usually a practical option for everyday biogas plant operators.

Generator sets for electricity generation from biogas

The most common method of generating electricity from biogas is to convert the gas to power using a generator set (genset). In many cases, even standard three-phase electric motors can be converted to work as generators.

Reciprocating engines are popular for small to medium outputs because they are more efficient and cheaper than small gas turbines. Gas turbines, however, can be more efficient in a cogeneration cycle that produces both heat and electricity.

Cogeneration – combined heat and power (CHP)

Cogeneration, or combined heat and power (CHP), is the simultaneous generation of electricity and useful heat. Heat engines never convert all of their thermal energy into electricity, so capturing the waste heat — for digester heating, buildings or processes — greatly improves overall efficiency.

The technology is well understood and maintenance is straightforward. Using a mix of technologies, farms and businesses can produce their own electricity, heating and cooling from biogas.

The economic viability — and the aims — of those using electricity generation from biogas vary with the size of the plant and whether the site has a mains supply or is off-grid.

In the sections that follow, we look at electricity generation from biogas from the small scale up to the large:

Electricity generation from small-scale biogas plants (home biogas)

Generator sets can be bought off the shelf for smaller outputs, from single-home to community-digester sizes. It is not normally viable to buy one and pay back the cost through reduced electricity bills for a small digester if a mains supply is already available.

Off-grid, it is a different matter. Biogas electricity can transform quality of life off-grid, giving families good lighting in winter and powering a television, phone charging and even broadband. This use of biogas is set to keep expanding for small-scale plants — but it is only one example of the technology’s potential.

The other biogas sources used for electricity, which we discuss below, are:

• commercial on-farm biogas;
• landfill-site biogas;
• wastewater sludge biogas from municipal sewage treatment works.

Large biogas plant and commercial on-farm electricity generation

For larger installations, electricity generation is often used to power the farm itself, and may also supply neighbouring homes and businesses — especially where the locality is off-grid. Where farms are on-grid, as most AD facilities in developed nations are, the plant commonly feeds surplus power into the local and national grids.

The decision to install a plant in these circumstances often turns on whether supplying power to the grid is economically viable. Historically that rested on Feed-in Tariffs. Those schemes have since been wound down or replaced in many markets — the UK’s Feed-in Tariff, for example, closed to new applicants on 31 March 2019 and was succeeded by the Smart Export Guarantee. As a result, the economics increasingly depend on self-supply (avoiding bought-in power), export arrangements, biomethane certificates and whatever renewable-support scheme applies locally, rather than on a single generous tariff.

Landfill-site biogas electricity generation

In Europe and many other developed nations, environmental laws have for years required landfill owners and operators to extract landfill gas (LFG), in order to prevent methane escaping — methane being a powerful greenhouse gas.

Electricity generation is far more viable where the operator is already legally obliged to install an LFG extraction system. In that situation, the cost of extraction is effectively carried by the waste-tipping gate fee, so it is much easier to show a profit on the power sold once the extraction overhead is attributed elsewhere.

That collecting and burning landfill gas should be a cost borne by all responsible communities is now incontestable, given what we understand about the greenhouse effect and climate change.

How damaging is it not to collect and flare or use landfill gas?

Releasing methane straight to the atmosphere is far more damaging than the carbon dioxide produced once that same gas has been burned in a flare or an engine. According to the IPCC Sixth Assessment Report, as summarised by the US EPA, methane’s global warming potential is about 27–30 times that of CO2 over 100 years, and roughly 80 times over a 20-year horizon. The short-term figure is the one that should alarm us, because it captures the intense near-term warming that uncontrolled methane causes — which is exactly why preventing leaks and flaring or using the gas matters so much.

(An earlier version of this article cited a single “60–80 times” figure; the clarification above reflects the correct IPCC 20-year and 100-year values.)

Given global pledges under the Paris Agreement, and at subsequent COP events, to cut greenhouse-gas emissions sharply, laws requiring landfill gas to be extracted and either flared or used should be a straightforward decision. Not doing so is a huge missed opportunity, because requiring all LFG to be captured is usually one of the cheapest carbon-reduction measures available.

Preventing the leakage of landfill gas (biogas) to the atmosphere is, in fact, “low-hanging fruit” for governments beginning to reduce their carbon emissions — and this holds for all nations where energy costs are not heavily depressed by cheap local renewable or fossil sources.

In New Zealand, for instance, national conditions are often unfavourable for feeding electricity into the grid, because hydro-power makes generation so cheap. The same is true for parts of the US with local oil wells and fracking — although, under the US EPA’s Landfill Methane Outreach Program (LMOP), there have been moves to raise landfill-gas capture and its use or flaring to cut emissions.

In such places, limited economic viability means biogas electricity may stay confined to a few pilot schemes, at least until governments give carbon reduction a higher priority. Even there, however, cost analysis shows that electricity generation from biogas can be environmentally sound and sensible for an integrated farm unit.

Large US dairy farms are a good example of an “integrated farm unit” where generation remains viable even when local energy prices are low. Anaerobic digestion has been taken up gradually at such farms for well over a decade, and these schemes generally succeed once the wider benefits of AD — better waste management and savings on bought-in fertiliser — are factored in.

Wastewater sludge biogas from municipal sewage treatment works

Around the world, many municipal sewage operators have recognised the huge potential of anaerobic digestion for electricity generation. Installing AD plants for biogas production also solves an old headache: how to deal with the enormous tonnages of sewage sludge removed daily from every treatment works as it cleans the wastewater before discharge to local watercourses.

The problem in the past was that sewage-sludge digestion was slow — generally slower than farm biogas plants — and much of the organic content simply washed out in the digestate, even though the sludge had been successfully treated for disposal. That is now changing.

Recently there have been important developments in pre-treating sewage sludge before it enters the digester, so that the hard-to-digest cell structure is “lysed” first. By lysed, we mean the tough cell walls are broken open so the methane-producing microbes can access far more of the cell contents. This is done through a process called hydrolysis, and better, lower-energy hydrolysis methods are now emerging that break the cells down far more effectively than before.

The result is that many treatment works can now power the entire site most of the time from the electricity made from their own biogas — and sell the surplus to the local grid. A great deal of work is under way to extract still more energy per tonne of sludge, and today’s best lysing technology will almost certainly be bettered in the years ahead. Best of all, every unit of this energy from sewage sludge is renewable energy.

A possible challenge for electricity generation from biogas

Electricity generation from biogas has one big competitive weakness, and it may divert a growing share of biogas to another use: as a transport fuel, after purification and compression.

Governments everywhere are under pressure to cut urban air pollution, and many want options available now rather than waiting for the full roll-out of electric and fuel-cell vehicles. Using biogas as a transport fuel, thanks to its clean-burning properties, is both an efficient use of the resource and available today.

Vehicle manufacturers are already modifying engines for HGV and bus fleets to run on compressed, upgraded biogas (bio-CNG / rCNG), with bio-LNG emerging for long-haul lorries. This use increasingly competes with on-site electricity generation for the output of farm and commercial biogas plants. Even so, we would expect electricity generation from biogas to keep rising overall, as new biogas plants come on stream, despite competition from biomethane for transport.

Conclusion

Making electricity from home biogas can be hugely valuable for people in developing nations, greatly improving quality of life off-grid. At larger scales, electricity generation from biogas makes sense for the health of our planet too.

For large AD plants and landfill-gas sources, the trend is increasingly towards upgrading biogas to biomethane — for grid injection or for transport fuel — rather than burning it on site for power. Yet, taken as a whole, large-scale electricity generation from biogas is likely to continue rising globally, because the number of plants keeps growing. The sensible conclusion is not that one use wins outright, but that biogas should be directed to whichever use delivers the most value and the greatest emissions saving at each particular site.

In reality, professionals can do only so much, and change is not coming fast enough. Yet all hope of holding climate change to tolerable levels is not lost. The pressure is increasingly coming from the financial system itself, rather than from governments — many of which have become more reluctant to subsidise the renewable-energy and waste-to-resource industries (biogas among them) that can help.

A lead on cutting carbon has come from outside the civil engineering profession

Institutional investors are acting to understand and address the risks that climate change poses to their investments. Companies that fail to advise clients on those risks expose themselves to the threat of litigation.

This scrutiny followed an early, high-profile warning from Bank of England governor Mark Carney, in his role as chair of the Financial Stability Board, delivered at Lloyd’s of London in 2015. It spelled out the potential scale and severity of climate-related risks to global financial markets and led to the creation of voluntary, consistent climate-related financial disclosures for companies to use when informing investors, lenders and insurers (via New Civil Engineer).

Looking back from today, that direction of travel has only strengthened. Climate-related financial disclosure has moved from voluntary to mandatory in many jurisdictions, and the civil engineering profession has formalised its own response — the Institution of Civil Engineers now frames reaching net zero as a core duty for the sector it serves. The 2018 call for “a revolution in the structure of engineering” has, in part, been answered.

This is where professionals have a duty to inform their clients about the anaerobic digestion process, and about how the biogas benefits help cut carbon emissions and therefore the effects of climate change. Some of the main benefits are summarised below.

Benefits of anaerobic digestion as an energy producer

Businesses of every kind — agricultural or industrial — can diversify their income by installing anaerobic digestion facilities for their organic waste, or by sending that waste to AD plants. Because the AD process yields an energy source, it is ideally suited to broadening and strengthening a business’s income. Society benefits too, through the reduced carbon emissions that well-implemented projects deliver.

Benefits of anaerobic digestion as a waste-management technique

Running a business more holistically — and avoiding the waste of a resource, namely its organic waste — is one of the important benefits of anaerobic digestion. This matters increasingly to businesses seeking shareholder investment, precisely because of the climate-related risks to those investments described above.

Why the biogas benefits grow more important with each passing year

The biogas benefits of recycling waste material have added a new dimension to waste management. In response, the supportive legal framework being put in place across Europe to harness waste better is a vital boost to the wider biogas industry. Within that circular-economy framework, the large-scale development of anaerobic digestion (AD) and its biogas benefits is an essential component.

AD is not only a renewable energy source. It is also an environmentally friendly, cost-effective way of dealing with much of what we think of as waste.

Waste is a massively underestimated cause of carbon emissions, as the former CIWM President, Professor David C. Wilson, has pointed out:

“One could make a case that better resource and waste management has the potential for reducing GHG emissions across the world economy by 15, 20 or 25 percent, or even more. Such numbers by their nature are ‘guesstimates’, and as such are anathema to climate scientists. However, whatever number we choose to use, the message is still the same. Our sector provides a useful entry point to make very significant contributions to climate mitigation targets. And some of those reductions could be seen as ‘low-hanging fruit’, and/or offer significant reductions over a short timeframe.” (via Don’t Waste Our Climate)

If waste materials are not recycled and are left to decay in landfill, the methane and carbon dioxide they release cannot all be collected, and the remainder escapes into the atmosphere. Worse still is the open burning of waste in backyards where no proper collection exists, as is common in many developing nations. Again quoting the CIWM President, on his own work to measure real emissions from waste:

“…early results suggest that the CO₂ equivalent of black-carbon emissions from uncontrolled burning in backyards in Mexico was 15 times larger than the methane released from the decomposition of equivalent amounts of combustible biodegradable waste disposed at a final disposal site. This suggests that urgent action is needed to reduce domestic open burning of waste, and that this would have a significant impact — both on improving local air quality and respiratory health, and on reducing climate change.” (via Don’t Waste Our Climate)

We would add that those very same backyards could reduce emissions far more effectively if they had the benefits of biogas plants installed in them.

Biogas production can play an important role in reducing emissions from rotting manure, farm wastes and slurries, and in replacing petrochemical-derived artificial fertilisers. In doing so, this proven technology abates significant carbon emissions, and by displacing fossil-fuel energy it greatly reduces climate-damaging greenhouse-gas emissions.

Help us publicise the benefits of anaerobic digestion and biogas production

Professionals need to inform their clients about anaerobic digestion. Yet the benefits of anaerobic digestion and biogas are still not appreciated by all professional opinion-formers as they need to be, before the technology can realise its potential.

We hope that, in a small way, reading this article has improved your understanding of the biogas benefits in reducing carbon emissions — and therefore the effects of climate change that AD technology can help reduce.

If so, please join us in helping to publicise the potential of anaerobic digestion and biogas-plant development worldwide, for its many climate and societal benefits.

Electricity generation from biogas: frequently asked questions

How is electricity generated from biogas?

Most electricity from biogas is produced by burning the gas in an internal combustion engine, known as a biogas engine. The engine converts the gas into mechanical energy, which turns a generator (alternator) to produce alternating-current electricity. Gas turbines, Stirling engines and, rarely, fuel cells are alternatives. A generator set is the most common arrangement, and combined heat and power (CHP) captures the engine’s waste heat to raise overall efficiency.

Is it better to burn biogas for electricity or upgrade it to biomethane?

It depends on the site, but since around 2017 the trend for large new plants has shifted towards upgrading biogas to near-pure biomethane for injection into the gas grid or for use as a transport fuel, rather than generating electricity on site. Upgrading is often seen as a more flexible and sustainable use of the gas, especially in Europe under the REPowerEU biomethane goal. Electricity generation still makes sense where heat can be used on site or where the plant is off-grid.

Why is capturing landfill gas so important for the climate?

Landfill gas is roughly half methane, and methane is a powerful greenhouse gas. According to the IPCC Sixth Assessment Report, as summarised by the US EPA, methane’s global warming potential is about 27 to 30 times that of carbon dioxide over 100 years, and roughly 80 times over a 20-year horizon. Burning the gas in a flare or engine converts the methane to far less damaging CO2, so capturing and using or flaring landfill gas is one of the cheapest and most effective ways to cut emissions.

Can a small home biogas plant produce useful electricity?

Yes. Generator sets are available for outputs from single-home to community-digester sizes. On a site that already has mains power, it is usually not economic to pay back the cost of a small generator through bill savings. Off-grid, however, biogas electricity can transform quality of life, powering lighting, a television, phone charging and even broadband.

Does using biogas as a transport fuel compete with making electricity?

Increasingly, yes. After purification and compression, biogas can be used as bio-CNG (rCNG) for HGVs and buses, with bio-LNG emerging for long-haul lorries. Because this is an efficient, available way to cut urban air pollution, it competes with on-site electricity generation for the output of farm and commercial plants. Even so, overall electricity generation from biogas is still expected to grow as more plants come on stream.

Archived article originally published on 15 August 2018. Updated with added information July 2022. Thoroughly updated and re-verified in November 2026.