Surprisingly renewable energy

KIC InnoEnergy’s Dr Roland Doll outlines the efforts being made by Marin Biogas to harvest the potential of a surprising renewable energy source from the sea

The Holy Grail for biomass-based energy production is arguably a sustainable feedstock – one that doesn’t require any land use changes and has no impact on the environment, and a team of Swedish entrepreneurs might have not only found one that does just that – but may actually go further by improving the environment it comes from. KIC InnoEnergy, the innovation engine for sustainable energy, was introduced to Marin Biogas in 2014 when they took part in that year’s call for innovation proposals. The driver behind KIC InnoEnergy investing in Innovation Projects, is to connect innovators with industry and academics to form consortia that could turn sustainable energy concepts into marketable products and services. Marin Biogas is exactly the kind of project that we look to support through our various programmes and the story of how they came to develop their offering is as interesting as the technology that they are preparing to take to market.

Ten years ago, a number of Swedish municipalities joined forces to build a biomass power station to serve their region. However, they recognised that the volume of biofuel required would be difficult to collect without taking land away from vital foodstuff production – a widely recognised problem.

So, eager to get the project off the ground, they explored other natural resources and contacted marine entrepreneur and scientist, Fredrik Norén and his company Marin Biogas, to source a material that could be ‘grown’ and harvested with the minimum possible environmental impact.

Cultivation of marine wildlife

Norén and his team initially started exploring traditional marine wildlife for cultivation – blue mussels. However, the tough protective shells could not be ground down to the necessary consistency for the biomass boilers and weren’t considered a suitable feedstock. So, the team went back to the drawing board and came up with ascidians, or ‘sea squirts’ (so-called as they use their sack-like bodies to ingest water and nutrients and then ‘squirt’ out waste water) as an alternative. These invertebrate tunicates have traditionally been cultured for food in the Far East, but large-scale farming for other uses had never been considered. Norén’s team believed that because of their fast growth rate the ascidians might have the potential to be used to create quantities of biomass for energy production.

The theory was relatively straightforward. The ascidians could be cultivated and harvested in the same way that mussels are farmed. Once taken out of the water, they could be processed to produce a product which could then be used to create biogas in an anaerobic digestion plant.


However, the team quickly realised that mass cultivation of these little ascidians brought even more benefits to the table. Every year, large stretches of the Swedish seas, particularly off the Baltic coast, see an increase in phytoplankton over the spring and summer months. These ‘blooms’ of algae are widely documented phenomena and occur naturally. In recent times, their size and duration have been increasing as a result of inorganic fertilisers used in farming (which are particularly nitrogen dense) leaching into local waterways and ultimately out to sea.

Ascidians feed on phytoplankton, and so while higher levels of nitrogen in the water create larger phytoplankton blooms, cultivating vast quantities of ascidians in a relatively small area meant that large amounts of the excess nitrogen could be removed from the water. This creates an additional and widely unforeseen upside to the process.

Furthermore, once the ascidians had been harvested, and waste products removed, the team discovered a further ‘leftover’ by-product. The resulting digestate was rich in nutrients that could be used as a commercial fertiliser – recycling the harvested nitrogen from the sea and returning it to the land. This effectively creates a circular process for the removal of harmful nitrogen and recycling it into a more useful form.


Marin Biogas had developed a concept with three key benefits at each stage of its production and use, all deriving from the original goal of creating an economic feedstock for biogas producers; and all with the potential to solve multiple environmental challenges.

Currently, the concept is in demonstration mode – with a hectare of ascidians being cultivated just inside an island on the Swedish west coast, producing 1,200 tonnes of product which could generate 0.6 GWh of energy. The ascidian product is being used as biomass by a range of energy producers, including E.ON, and the team that developed this unique renewable energy source are now looking at how to scale up production.

Success of failure?

Interestingly, the success or failure of the concept could hinge on the circular nature of its benefits. The three different value chains produced by the cultivation, harvesting and processing of the ascidian are the reason that this method of energy generation is so unique. However, this also means that enabling a large-scale deployment of this model would be dependent on multiple variables. While the biomass benefit has been recognised, it is probably the value that comes from nitrogen removal that could turn out to be its biggest enabling factor.

So, provided large-scale deployment can be realised, just how big could this get?

Norén and his team believe that the ascidians could produce up to 9 GWh of biogas per annum, which would double the total Swedish production of biogas today.

Looking further offshore, Europe has enormously productive seas which could be used for this type of cultivation. One option that the project is looking at is the possibility of farming ascidians around offshore wind farm sites. Not only are these sites accessible (as the turbines require maintenance), but they also benefit from being protected from both shipping traffic and fishing, so could provide ideal environments for larger-scale commercial cultivation.

Marin Biogas could see the technology being licensed to areas across the globe that also suffer with algae bloom caused by intensive farming and other nitrogen-rich industries. With the added benefits of producing both biomass and an organic fertiliser, if the product can be up-scaled commercially, the circularity of the process has the potential to make it the most renewable energy source available.


Dr Roland Doll

Thematic Field Leader for Energy from Chemical Fuels

KIC InnoEnergy

This article first appeared in issue 12 of Horizon 2020 Projects: Portal, available here.