circular economy energy

Six examples of good bioenergy

Britain’s electricity supply is undergoing an impressive transformation from fossil fuels to clean energy. Wind is the cheapest and biggest contributor, with rising amounts of solar on the grid. You’ve also got a growing bioenergy sector. Here’s how capacity currently breaks down, from the government’s latest quarterly update:

The bioenergy category covers several different ways of generating energy from organic matter. The graph here shows electricity generation, which could be through burning biomass or anaerobic digestion. The broader bioenergy category would include biofuels and biogas.

Some forms of bioenergy are problematic, such as burning trees for fuel, or first generation biofuels. But it’s important to recognise and distinguish between good and bad bioenergy. Here are six of the good kind:

Sewage gas – In 2010, the first sewage gas facility in Britain was switched on in Didcot, Oxfordshire. It captures the gases that are naturally emitted from sewage waste, purifies the resulting biomethane and injects it into the gas grid. It takes about 20 days in-between flushing a toilet and being able to burn the gas in your boiler. This particular facility is pretty small, providing enough gas for around 200 homes. We could be doing this in many other places.

Agricultural waste – there are lots of waste products from agriculture that can be used for energy, from manure or slurry from animal farms, to straw or post-harvest residues. I’ve written before about burning sugar cane waste called bagasse, and maize production also leaves abundant waste biomass. In the Philippines, coconut husks and shells are burned either for energy or for heat in food drying. Returning organic material to the soil is important for sustainable agriculture, and some can be fed to animals too, but uses don’t necessarily need to be mutually exclusive. If the energy is generated by anaerobic digestion rather than burning, the digestate can still be used as a fertiliser.

Grass – energy crops should be avoided where they compete with food crops, but grass can be grown on marginal land. Nottinghamshire county council, for example, grew elephant grass on a former landfill site and then used it for biofuels. When the right species are grown on contaminated or brownfield land, this could serve as a form of bioremediation that restores the soil. Ecotricity are currently expanding into using grass for biogas. Bamboo, a form of grass, is sometimes grown for energy.

Food and commercial waste – obviously the first priority with food waste is to reduce it, but there is always going to be a certain amount of it, especially at the commercial level. This can be used for energy. The food waste could come from homes through council waste bins, and there are also wastes from manufacturing that can be incorporated. The Adnams brewery has a biogas plant that generates energy and fertiliser from the grain left over from making beer. Waste from forestry can also be useful here, including sawdust or thinned-out trees – this is particularly useful in combined heat and power plants, so that the heat from combustion isn’t wasted.

Cactus – my favourite bioenergy project is cactus used in anaerobic digesters. Cacti don’t need irrigation or fertiliser, farming them brings jobs and income to arid regions, and the biogas process produces clean water and soil improver as by-products. Cacti for energy is a restorative technology that can build soil and create better conditions for farming, while producing gas or electricity at the same time. It’s being developed in the south of Madagascar, where it will displace cooking with charcoal or wood and help to slow the deforestation of the island.

Algae – There has been a lot of talk about algae biofuels, and in the last five years or so the first large scale commercial plants have opened, mainly selling biofuels that can be blended with crude oil for transport. Algal biofuels have also been used in bioremediation. A decade ago a Seattle based company called Blue Marble harvested algal blooms from Puget Sound and fed them into its anaerobic digester. It was a one-off project, but one worth noting. The world has a growing number of ‘dead zones’, where fertilizer run-off has led to algae proliferating and squeezing out all other life. Using the algae for energy could pay for the clean-up, with the digester moving on to seaweed as the ocean recovers.

In short, there’s a lot going on within the category of bioenergy. I regularly see biomass written off or excluded from discussion of renewable energy. This is presumably due to its association with throwing trees into former coal power stations. That does happen far too frequently, but we should be specific about what we oppose or we risk ruling out a host of useful technologies.

Bioenergy isn’t subject to the vagaries of wind or cloudy days, and can help to produce more balanced renewable energy without the need for storage. It can help to deal with wastes as part of a circular economy. It can be done at small scale and in low tech ways that make it appropriate for many developing country contexts. It can even be restorative, helping to heal and reverse previous exploitation of land and sea.

The next time you hear someone exclude biomass, tell them about the cacti.

1 comment

  1. That’s interesting that the gas that comes off of sewage could be burned to produce energy. I like that idea since that would be a pretty limitless source of energy over time. I’ll have to consider settings something up that could make use of that biogas if I decide to use green sources of energy for my home.

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