5. Solving for Legacy CO2: Bioenergy + CO2 Capture — Full Spectrum Climate Solutions for the Anthropocene

Seaweed Farms in South Korea Visible from Space. Credit: Colossal

What if we could combine the efficiency of natural CO2 sequestration with the permanence and security of geological methods?

One of the most promising drawdown concepts that has emerged in recent years explores this: Bioenergy Carbon Capture and Storage (BECCS). BECCS combines biological carbon sequestration with geological storage methods, while also generating clean electricity or fuel.

Unique advantages are gained in this approach: efficient natural processes do the work of sequestering carbon, and then humans leverage our technology to lock away captured carbon for thousands of years. Furthermore, BECCS can displace fossil fuels by generating stable power to complement wind and solar energy.

Carbon Capture Power Plant in Germany. Credit: Climate Central — **Carbon Capture Power Plant in Germany. Credit:** **Climate Central**

Here’s how BECCS works:

Plants suitable to bioenergy generation are cultivated
These crops capture CO2 as they grow, via photosynthesis
After harvest, they are burned in a bioenergy power plant
Carbon scrubbers or other equipment capture CO2 before it escapes into the air
Captured CO2 is taken off site and deposited for safe storage

While BECCS is a favored choice by many for negative emissions technology, it faces two big challenges: land use conflicts and the high cost of BECCS power plants.

Land Use Conflicts

To realize the drawdown and clean energy generation benefits at an effective scale, BECCS would require large-scale cultivation of plant biomass. However, this would lead to conflict with food production. Already today 1 billion people go hungry, and as our world grows to 9+ billion, land to farm will become ever more critical.

Crop waste could be utilized to an extent in agricultural areas, yet is limited by seasonality, thresholds to aggregate enough material and the type of crop.

High Cost of Power Generation

Bioenergy generation is currently more expensive than other energy sources like natural gas, wind or solar. With the added equipment and carbon storage processes, BECCS power plants will cost even more.

I’ll address each of these two challenges in turn, beginning with land use conflicts.

Open Ocean Biomass Farming

If BECCS must displace food crops on land to be feasible, then we shouldn’t do it. Meeting people’s basic needs should take priority over carbon sequestration every time, especially when there are a multitude of ways to achieve drawdown.

However, what if we were to use water, not land to grow biomass for BECCS?

The ocean covers 71% of Earth’s surface and has vast stretches where people never go and the only plant life is microscopic algae. Here, there is no competition for space, and rather than doing harm, seaweed farms would likely support sea life, by reducing ocean acidification, cooling the waters and providing shelter habitat.

Even following ambitious goals for CO2 capture and bioenergy generation, we would only need to utilize a small percentage of the open ocean’s surface: extrapolating from a 2012 study of seaweed farming and BECCS, if we were to grow enough seaweed to cover 0.9% of the world’s oceans, we would sequester 5 billion tons of CO2, equivalent to 12.5% of humanity’s total emissions in 2020.

For growing great quantities of biomass on the high seas, giant kelp is one of the most promising, as it:

Grows up to 2 feet per day, one of the fastest-growing plants on Earth
Sequesters CO2 from the air at 20x the rate of terrestrial forests
Doubles its weight every 6 months and grows up to 175 feet long
Lives for several years and requires low resource inputs

Giant Kelp forest. Credit: Oceana — **Giant Kelp forest. Credit:** **Oceana**

For these reasons, Giant Kelp makes a prime candidate to supply BECCS power plants. Here’s how it would work:

After the kelp reached its maximum growth, it would be harvested, brought to shore and used to generate biomethane - basically the same natural gas that powers much of the U.S. already, minus the environmental and climate impacts. Its CO2 emissions would be captured and stored safely underground.

Kelp does have a few requirements for growth:

Hard, grooved surface to attach onto
Water temperatures 42°-72° F
Nutrient-rich waters

Since the open ocean lacks both sufficient nutrients and anything for kelp to attach, marine farms would need to provide these. Kelp farms can either be attached to a fixed growing platform, or allowed to freely float along ocean currents for hundreds of miles.

Giant Kelp Farm. Credit: Fisheries Research and Development Corporation (Australia) — **Giant Kelp Farm. Credit:** **Fisheries Research and Development Corporation** **(Australia)**

A fixed platform is easy to harvest, and to artificially provide nutrients and cold water that kelp needs to grow, but is more expensive and susceptible to damage from storms.

Wave-powered pumps could siphon cold, nutrient rich water up from the ocean depths to fertilize the kelp beds. Remotely controlled sea robots, such as those created by Marauder Robotics, could reduce predation from pests like invasive purple urchins, which have devastated Northern Pacific kelp forests recently.

The free floating approach is cheaper and can move with storms, rather than resisting heavy waves and possibly becoming unmoored. However, it would be difficult to control the growing environment in case predators eat the kelp or naturally-available nutrients are lacking.

Floating platforms would be deposited off shore, and set adrift into nutrient-rich currents that could carry these platforms hundreds of miles. Given that these currents are relatively predictable, harvesting boats could be waiting for these platforms once they have completed their journey and are fully grown.

Kelp growing underwater. Credit: UCSB — **Kelp growing underwater. Credit:** **UCSB**

Enabling a 100% Clean Energy Grid with Kelp-based Natural Gas

Energy generation from BECCS will not be cost competitive on a one-one basis: the whole process of growing and harvesting kelp, extracting biomethane, burning it for power and capturing the resulting CO2 emissions, will certainly be more expensive than solar, wind, gas, coal or nuclear energy.

However, BECCS power generation ought to be worth paying a premium price, for three reasons:

It provides clean base load power, which is crucial to balancing solar and wind as part of a 100% clean energy electricity grid, and would be much cheaper than relying solely on solar, wind and battery storage to hit 100%.
Biomethane extracted from kelp is for all intents and purposes, natural gas. This means it can plug into existing gas infrastructure, such as pipelines and power plants, without having to build entirely new facilities. That alone would save huge sums of money.
BECCS has massive potential to capture CO2 from the atmosphere for long term storage, since it is carbon negative power.

Many U.S. states and nations around the world have set ambitious targets for 100% clean energy, yet they are still figuring out how to achieve this.

It is possible to simply use solar, wind and battery storage. Yet it is very inefficient and costly: solar and wind must be overbuilt to account for their intermittency and to ensure adequate power generation during periods of peak use. A consequence of this is that solar and wind will produce far too much energy for the grid to handle at certain times, requiring lots of electricity to be discharged before it can be used.

Lastly, massive amounts of batteries would be needed to store power and manage fluctuations, which would be very expensive.

Within a balanced grid, solar and wind are very cost competitive - it just doesn’t make sense for them to do all of the work.

That’s why a power grid that is supplied by 60-80% solar, wind and batteries is much more efficient and affordable than one that is 100%. The key question is how to supply the last 20-40% of clean base load power.

Hydroelectric, geothermal and nuclear power can provide some of this, but all are limited by either geographic availability, climate disruption and public concerns about safety or other environmental impacts.

The best option to support lots of solar and wind is actually natural gas, since it can be cycled up quickly to fill gaps in supply from intermittency. Or would be, if it had no greenhouse gas emissions and didn’t require fracking.

This is where kelp power comes in.

Biomethane can be extracted from kelp and combined with hydrogen to become natural gas (for zero CO2 emissions, the hydrogen would need to be made using clean energy via an electrolyzer). The final product would be pipeline-ready natural gas, and could be used in existing gas power plants. These would need to be fitted with carbon capture equipment.

Undoubtedly, these facilities would need financial support from the government. Their high cost would need to be weighed against alternative options for clean base load power, along with the benefits of utilizing existing gas infrastructure and the ability to sequester carbon using efficient biological processes.

In many near shore marine ecosystems, kelp is the “anchor” for ocean life, according to the Ocean Conservancy. Where natural kelp forests have been devastated, like along the U.S. west coast, large scale kelp farms could provide habitat, shelter, food and buffer local waters against rising oceanic acidity levels. These factors, along with potential economic benefits to local fisheries, ought to be considered as well.

All in all, kelp for bioenergy carbon capture offers us a powerful tool to tackle climate change on multiple fronts - if we are willing to invest in it.