Anaerobic digesters that function like an animal's rumen could be used for the production of biogas at greater scale in New Zealand, one expert believes. Photo: RNZ / Alison Ballance
Farmers could help drive the biogas industry as demand grows for greener alternatives to LPG and fossil fuels.
It comes as the country currently faces a gas supply crisis with reserves falling faster than expected and use dropping sharply.
Rising costs of electricity and unstable supplies have seen commercial users scrambling to find alternative sources of energy for operations like horticultural greenhouses.
New Zealand's supply of gas was down nearly 21 percent in 2024 compared to 2023 due to natural field decline, according to the Ministry of Business, Innovation and Employment.
And in that time, natural gas consumption fell to its lowest level since 2011.
Crops grown for biogas are broken down by microbes in tanks, releasing gas that can be purified into renewable energy for heat, fuel, or electricity.
Biogas plants could be found scattered across countrysides worldwide, notably in countries like China, Germany, France and across Scandinavia.
Crop physiologist Dr Rocky Renquist was involved in gaseous biofuels research from a New Zealand agricultural point of view.
Renquist said the anaerobic digester infrastructure existed in New Zealand, and ideally farmers could be contracted by gas plants and their investors to grow high-yielding crops on marginal land for biofuel production.
"The North Island has an advantage with that big pipeline network because as long as you grow these crops somewhere that's not too far from the pipeline, you can purify that biogas and the biomethane and then inject it into the pipeline.
"So basically, little by little you can be replacing the fossil gas that is in there.
"It's actually a climate change problem, and biogas is going to avoid that whole problem with taking fossil carbon and putting it into the air."
Renquist said using crops or even manure in the tanks could create a closed-loop nitrogen cycle with on-farm environmental benefits too.
"The environmental advantage is it can improve the farm management at the same time as giving [farmers] another option for land use, and then it's reducing the carbon emissions.
"And it is producing the fuel that can be used in stationary locations for heat but also for generating electricity, it can also be used for transport fuel with trucks that are used in a region... So it has got diverse uses."
Artichoke has been identified as one high yielding crop that could be grown at scale in northern regions for biogas production. Photo: RNZ/Cosmo Kentish-Barnes
The anaerobic digestion used in the process to create biofuel was the same used to turn Auckland's food and/organic waste into biofuel and fertiliser at the Ecogas Reporoa site.
Ecogas was granted resource consent in Christchurch this month to build a similar facility.
Renquist said artichoke in the more temperate Hawke's Bay would be a top yielder versus lucerne in the South Island, based on his earlier studies from a decade ago.
The research team created a scenario where 230 hectares of crops provided by 12 farmers could provide enough energy to supply the area's agricultural needs, equating 1 million cubic metres of methane covering more than 900,000 litres of diesel, he said.
"So things that can be switched over, you could make a very big switch from just that one operation, a medium-sized digestive tank and the facilities that go with it and to purify it. And then the biomethane would be able to supply all that energy.
"We were really well convinced and we had the science from doing the research to back it up, so we were just surprised that it still hadn't caught on at that time.
"And of course, economics and the natural gas or fossil gas supply differences from 10 years ago with now probably have a lot to do with the renewed interest."
He said planting crops for biogas production could also be a more sustainable land use for farmers.
Renquist, a life member of the Bioenergy Association, recently presented a webinar with fellow researcher Stephan Heubeck on crop feedstocks for high biogas yields
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