Energy is the double-edged sword at the root of the climate crisis. Cheap energy has improved lives and supported tremendous economic growth.
But because most of it comes from the combustion of hydrocarbon fuels, we now have a legacy of high atmospheric carbon dioxide (CO2) and an emissions-intensive economy.
But what if we could turn the relationship between energy and emissions on its head? We would need a technology that both generates electricity and removes CO2 from the atmosphere.
The good news is that this technology already exists. In addition, New Zealand is perfectly positioned to do this “decarbonization” more cheaply than anywhere else in the world.
And the timing couldn’t be better, with the government’s scoop Emission reduction plan (released this week) calling for bold projects and innovative solutions.
We are investigating how we can burn forest waste for electricity while capturing and locking the emissions in geothermal fields. Because forests CO. remove2 from the atmosphere as they grow, this process is emission negative.
This also means that a carbon tax can be converted into revenue. With the New Zealand CO2 price at a record high of NZ$80 per tonneand foreign companies announcing: billion dollar funds to buy offsets, now is the time for cross-sectoral collaboration to make New Zealand a global leader in decarbonisation.
Bioenergy with carbon capture and storage
Artificial carbon sinks are engineered systems that contain CO. delete permanently2 from the atmosphere.
Bioenergy with carbon capture and storage (BECCS) achieves this through the CO. to catch2 from burnt organic matter – trees, bio-waste – deep underground. An added bonus is that the energy released during combustion can be used as a substitute for hydrocarbon-based energy.
The Intergovernmental Panel on Climate Change (IPCC) said Climate mitigation pathways must contain significant amounts of BECCS to limit global warming to 1.5 . However, the technology is still new, with only a few plants around the world currently operating on a large scale.
Cost is a major barrier. New projects require expensive pipelines to remove the CO . to be moved2and deep injection wells to store it underground. Because CO2 has more buoyancy than water, there are also concerns that any gas stored underground may leak out over time.
This is where geothermal fields can help.
Geothermal systems for BECCS
Geothermal energy is a reliable source of energy in New Zealand, providing nearly 20% of our electricity. We use deep wells to tap underground hot water reservoirs, which then travel through a network of pipes to a steam turbine that generates electricity.
After that, the water is pumped underground again, so that the reservoir does not “dry out”. New Zealand companies are world leaders in geothermal resource management, and some are even experiment with reinjection the small amounts of CO2 that come with the geothermal water.
Herein lies the opportunity. Geothermal systems already have the infrastructure needed for a successful BECCS project: pipelines, injection wells and turbines. We just need to figure out how to combine these two renewable technologies.
We propose that by burning forest waste we can raise geothermal water to higher temperatures, producing even more renewable energy. then, CO2 from the biomass combustion can be dissolved in the geothermal water – such as a soda stream – before being injected underground again.
Projects in Iceland and France have shown that dissolving CO2 in geothermal water is better than injecting it directly. It lowers the cost of new infrastructure (liquid CO2 compression is expensive) and means that reinjection wells built for normal geothermal operation can continue to be used.
Unlike pure CO2 which is less dense than water and tends to rise, the re-injected carbonated water is about 2% heavier and will sink. As long as equal amounts of geothermal energy are produced and reinjected, the CO2 will remain safely dissolved, where it can slowly turn into rocks and be locked up permanently.
How do the numbers stack up?
Us first modeling shows that geothermal BECCS can have negative emissions on the order of -200 to -700 grams of CO2 per kilowatt hour of electricity (gCO2/kWh). Compared to approximately 400 gCO₂/kWh positive emissions from a natural gas plant, this is a dramatic reversal of the energy emissions trade-off.
Applied to a geothermal system the size of Wairakei (160 megawatts), a single BECCS geothermal system could trap a million tons of CO2 every year. This is equivalent to taking 200,000 cars off the road and, at today’s prices, would yield tens of millions of dollars in carbon offsetting.
These could be traded through the emissions trading system to buy valuable time for slow decarbonisation industries, such as agriculture or cement, to get to net zero.
In fact, most of New Zealand’s geothermal fields are located near large forests with extensive forestry activities. Estimates estimate our production of forest waste at about three million cubic meters every year. Instead of letting it rot, this can be turned into a valuable resource for geothermal BECCS and a decarbonising New Zealand.
We can do this now
Teething problems need to be solved as costs are reduced and production is scaled up. New Zealand now has a chance to get on that curve. And the whole world will benefit if we do.
The success of BECCS geothermal will lead to new partnerships between New Zealand’s geothermal generators, manufacturers and the forestry industry. Forest owners can help turn wood waste into a valuable resource and reduce port costs.
Most importantly, geothermal operators can leverage their vast reserves of injection wells and detailed understanding of the subsurface to permanently lock in atmospheric carbon.