Indian researchers and a Bengaluru startup are trying to turn fast-growing seaweed into biofuel, creating a potential new source of energy that doesn’t need farmland to grow.
India imports most of the crude oil it uses, and replacing even a fraction of that giant fossil-fuel appetite is not going to be easy. Solar panels and electric vehicles get most of the attention, but Bengaluru-based Sea6 Energy is looking in a much stranger place: the ocean. The company is developing a way to grow enormous quantities of seaweed at sea, harvest it using machines and then turn the wet biomass into something that looks remarkably like crude oil.
The idea is not to grow fuel crops across valuable farmland. Seaweed needs neither agricultural land nor freshwater, and it can grow while floating in the ocean. India’s seaweed industry is still tiny compared with its oil industry, but Sea6 has spent more than a decade trying to solve the biggest problem with seaweed biofuel: how do you grow enough of it cheaply enough to matter?
Farming the ocean
Sea6 Energy was founded in 2010 by IIT Madras alumni Nelson Vadassery, Shrikumar Suryanarayan, Sri Sailaja Nori and Sowmya Balendiran, with an unusually ambitious target: make seaweed cultivation large enough to become an industrial feedstock rather than a small coastal farming operation. Traditional seaweed farming is surprisingly labour-intensive.
Farmers attach pieces of algae to ropes, place them in the water and later return to harvest them by hand. Sea6’s answer is a machine called the SeaCombine, a catamaran-like system that mechanises seeding and harvesting and can operate in deeper water. The company has taken the technology well beyond the laboratory, including a large mechanised tropical seaweed farm in Lombok, Indonesia. In 2024, Sea6 announced what it called the world’s first large-scale mechanised tropical seaweed farm, covering one square kilometre. That matters because making fuel from biomass is fundamentally a volume game.
Once the seaweed has been harvested, Sea6 uses a process called hydrothermal liquefaction, or HTL, to turn the wet biomass into bio-crude. Instead of first drying the seaweed and then trying to extract sugars from it, HTL throws the wet biomass into a high-temperature, high-pressure environment. The process operates at around 350°C and pressures of up to 200 bars, dramatically accelerating the kind of transformation that takes nature millions of years when fossil fuels form underground. The result is a dark, viscous liquid that looks much more like petroleum than the green seaweed that went into the machine.
Sea6’s work has found that roughly 4–5 kilograms of biomass can produce about one litre of bio-crude. The process also produces other streams, including a clear liquid and biochar. The company has experimented with catalysts to increase the bio-crude yield and is also investigating hydrothermal gasification as another way of getting more value from the biomass.
The problem with the numbers
This is where the crude-oil comparison stops being just a catchy headline and becomes a rather intimidating engineering problem. IIT Madras’s Shaastra has reported Sea6’s estimate that replacing India’s current crude requirement would require enormous quantities of biomass. One earlier estimate put India’s crude-oil imports at roughly 200 million tonnes a year, with four to five times that amount of biomass potentially needed to produce an equivalent quantity of biofuel.
Sea6 has argued that land-based agriculture simply cannot provide that amount without competing with food production. Its answer is to move the farm offshore. The company has estimated that somewhere between 120,000 and 285,000 square kilometres of open ocean could be required to cultivate enough seaweed to replace 200 million tonnes of crude. Those numbers are enormous, which is precisely why the mechanisation matters.
Sea6 is not trying to persuade millions of people to harvest seaweed by hand. It is trying to build something closer to an industrial agricultural system, except the fields are floating in the sea.
Additionally, Sea6 is no longer working on the idea in isolation. In December 2024, the company signed a memorandum of understanding with Hindustan Petroleum Corporation Limited to jointly research technologies for converting tropical seaweed biomass into sustainable fuels and chemicals. HPCL’s Green R&D Centre in Bengaluru and Sea6 are working on the downstream side of the process, while Sea6 supplies biomass from its ocean farms.
The two companies are looking at scalable processes that could turn seaweed-derived bio-crude into useful fuels and chemicals, with applications including sustainable aviation fuel.
So while there is still a huge gap between demonstrating seaweed-derived bio-crude and replacing a meaningful chunk of India’s crude consumption, Sea6 itself has previously acknowledged that cost and scale are the central obstacles. Seaweed biomass has to become dramatically cheaper before biofuel made from it can compete with conventional petroleum, and producing enough of it would require ocean farms on a staggering scale.
India’s hybrid-fuel future
While the country is already experimenting with ethanol variations that have put a significant strain on the sugarcane and sugar industry, seaweed grows using sunlight and nutrients in the ocean. Additionally, large-scale cultivation does not require the farmland or irrigation demanded by terrestrial crops.
Sea6 is already selling other seaweed-derived products, including agricultural products and biomaterials, while continuing to develop the fuel side of the business. Its partnership with HPCL suggests the bio-crude is now being taken seriously enough to move into a more industrial phase. But crude oil is an enormous, deeply entrenched business, and seaweed has a lot of catching up to do.
If Sea6 can bring down the cost of ocean farming and scale its conversion technology, however, India could eventually have a very unusual new source of fuel.
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