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We manage forests of seaweed to produce renewable natural gas, food, and biodiversity, plus sequester carbon to reverse global warming.



The E7 and many other developing countries have access to oceans and need more than just energy.  They need an interrelated mix of food, jobs, water, land, terrestrial fertilizer, and energy.  While Fiji is not an E7 country, it is a good place to start ocean afforestation because:

·       Fiji imports diesel to make electricity.  Diesel fueled electricity is expensive at about US$0.15/kWh (fuel only) for a Caterpillar 3516 2 MW engine-generator.  Biogas can directly replace diesel for electricity generation with minor engine modifications.  (Biogas and biomethane also directly replace coal, oil, and natural gas.)

·       Fiji has 40,000 ha of sheltered water bays.  About 20,000 ha of sheltered water can grow sufficient seaweed to completely displace Fiji’s diesel-fueled electricity (500 GWh/yr).

·       Fijians need the other products of Ocean Afforestation to support sea level rise refugees from other small islands with jobs and food.

In an ocean forest (see diagram), sunlight powers the growth of seaweed that absorbs CO2.  Some of the managed seaweed forest is harvested every day into large microbial anaerobic digesters.  The bacteria separate the seaweed into biogas and plant nutrients.  The plant nutrients are dispersed back to the forest to grow more seaweed.  Biogas is 60% bio-CH4 (identical to natural gas) and 40% bio-CO2.  Methane is easier to transport and store than hydrogen, making a biomethane economy more practical but with all the benefits of a hydrogen economy.

Ocean forests can produce 12 billion tons per year of bio-CH4 (600 quads or 176 million GWh) while storing 19 billion tons of bio-CO2 per year directly from biogas production when covering 9% of the world’s ocean surface.  That is 100% of U.S. Energy Information Agency projected world fossil fuel use in 2030.  See details in peer-reviewed paper by N'Yeurt, et al., 2012.

Category of the action

Decarbonizing energy supply

What actions do you propose?

1.     Start the shallow water biogas and terrestrial fertilizer production business in Fiji.  Dr. N’Yeurt monitors adaptation programs for the twelve member countries of the University of the South Pacific.  He is investigating the best ways to mesh Fiji’s issues: excess terrestrial plant nutrients and seaweed in bays; expensive imported fuels; future climate refugees; etc. with Ocean Macroalgal Afforestation ecosystems.  PODenergy, Inc. and the Ocean Foresters are developing a business plan with multiple income sources, in concert with Dr. N’Yeurt’s research proposal and plans.

The site in Fiji could be ready soon for an investment of $7 million to install facilities on 2,500-ha site, which would generate 7 MW continuously, yielding $3 million annual profit or $30 million profit every ten years.  The Fiji Electricity Authority is currently offering US$ 0.115/kWh in contracts with independent renewable power producers for up to 500 gigawatt-hours per year.  After the initial $7 million investment, it is expected that bank financing would be available to generate $40 million in annual profits by replacing all imported diesel fuel.

One of Ocean Foresters' concepts for the Paul G. Allen Ocean Challenge is an example of our confidence in positive side effects from managing seaweed.  That concept title is “Managed seaweed raises ocean pH while remediating ocean dead zones”.  This concept is led by Dr. Charles Yarish who has several nutrient remediation projects operating off the U.S. New England coast.  Our process will employ whatever seaweed grows locally in ways that work with the local ecology.  If there is a reef, the seaweed farms and forests might be arranged to raise local pH or intercept sediment runoff without shading the reef.

The Ocean Foresters team also includes researchers at Scuola Superiore Sant'Ann, Italy.  They are also investigating ways to convert the excess plant nutrients and seaweed in Orbetello Lagoon into energy and terrestrial fertilizer.


2.   Develop open-ocean seaweed forests to replace natural gas with bio-CH4 while storing the bio-CO2.  We expect that developing open-ocean seaweed forests to reliably produce bio-CH4 for less than US$4 per thousand cubic feet will cost about $100 million spread over ten years.  Expect several more decades to expand the forests to completely replace natural gas, oil, and coal, which could generate profits of $100 trillion per year.

For example, the Sargasso Sea is a natural seaweed forest ecosystem full of life and biodiversity.  We can imitate the Sargasso Sea first in Fiji’s sheltered water and then migrate the managed forest ecosystem to the coastal dead zones and open ocean “nutrient deserts” near other developing countries.

Our ecosystem differs from earlier attempts to produce energy from seaweed in several key ways.  Most important is our use of large but inexpensive containers for the energy-nutrients separation process.  Large engineered geotextiles (plastic fabrics and films) can be formed into ocean-based process facilities whose capital cost ($/volume of process vessel) is 1% of their land-based counterparts. The inexpensive containers allow more time for the bacteria to digest, less pre-digestion processing (little or no dewatering or chopping needed), and mixtures of feedstock species.  The economics for this situation appear to favor “loose” seaweed ecosystem management (a diverse forest ecosystem, instead of a mono-crop farm).

The key process, anaerobic digestion, is routine and extremely robust, in both nature and wastewater treatment throughout the world.  Dr. Migliore’s team has demonstrated substantial biomethane production from natural seaweed collected in Orbetello Lagoon, Italy, where an excess of nutrients causes an excess of seaweed growing on the lagoon floor.  They are examining ways to export the nutrients as a terrestrial fertilizer after first anaerobically digesting the seaweed to produce energy. 

What makes the entire concept sustainable and profitable is recycling the nutrients left after digestion back into the forest to keep it expanding in a controlled way that benefits the entire ecosystem. There are no negative side effects.  For example, there is no problem with controlling any excess or invasive growth of seaweed.  We just harvest and digest it.

Our ecosystem also differs from earlier attempts by starting the design to be sustainable at the scale of the current fossil fuel industry while producing multiple products.  For example, our Life Cycle Assessment includes conceptual design of materials and energy for three ways to recycle nutrients back to the forest, a container where bacteria convert ammonia to nitrate and dissolved CH4 to CO2.  Products include: biodiversity, energy, food (plants, shellfish, fish), fertilizers, chemicals, pharmaceuticals, and stored CO2.  But the cost analysis does not subsidize the energy operation with income from the food and other operations; they are additional profit centers.

In earlier energy production operations, CO2 was a waste.  The stored CO2 from seaweed forests is so inexpensive, a reasonable carbon dividend (see Action 6), would allow countries with ocean forests to price the storage operations slightly below the dividend rate but above costs to store CO2, initially.  They could subsidize the bio-CH4 cost to benefit their economies and increase market share. 

Later (perhaps by 2060) fossil fuels may be sufficiently expensive and the quality of life in E7 countries high so that E7 countries can flip to subsidizing legacy CO2 removal and storage with profits from their bio-CH4 sales.


3.     Spread the shallow water ecosystems from Fiji to E7 and other countries.  Fiji is the largest (population) member country of the twelve-country University of the South Pacific (USP).  A project started on USP’s Fiji campus can be expanded nearly simultaneously to the USP member islands and quickly to most of the 52 Small Island Developing States.  Perhaps 100 of the 140 developing countries could enjoy significant energy, food, fertilizer, and other product production from sheltered water seaweed farms and forests. The system is expected to generate profits wherever the wholesale price of renewable electricity is above 10¢/kWh $US.

Dr. Lisa Colosi’s (2012) life cycle assessment (LCA) at the University of Virginia of our system indicates an energy output:input ratio of 6 for sustainably growing seaweed, which is converted to bio-methane and the bio-methane is converted to electricity.  Larger scale operations could be more efficient.  The ratio will vary somewhat for local conditions: stronger waves or currents causing a lower ratio; in tropical locations the steady solar energy may generate a higher ratio.  The LCA is based on an offshore 300 MW power plant connected to shore with 100 miles of high voltage DC cable.  The power plant converts bio-methane from 100,000 hectares of seaweed forest to electricity at 50% efficiency.


4.     Deploy open-ocean ecosystems.  For example, 80 million hectares of seaweed forests in the Indian Ocean (1% of that ocean) could supply all of India’s energy up to about 3,000 kWh per capita per year.  Additional discussion of open-ocean systems is provided in the Ocean Forester’s entry under “Agriculture and Forestry.”

The digestion container shown in the figure can be on the surface of the ocean in a sheltered bay (or large freshwater lake), or in the open ocean at least 50 meters below the surface to protect it from storms.


5.     Replace coal and oil with natural gas as quickly and completely as natural gas supply allows during the decade or two needed to ramp up bio-CH4 production.  Japanese methane hydrate recovery techniques and U.S. hydraulic fracturing (fracking) technology promises a global glut of natural gas.  In addition, global warming is destabilizing methane hydrates.  We need to extract and burn destabilized methane hydrates before they disassociate (melt).  (The Ocean Forester’s entry under “Hydraulic fracturing” explains a concept for preventing methane leaks and detecting methane hydrate dissociation.)

Already, natural gas can be converted into any of the products essential to the world economy: jet fuel; diesel; gasoline; plastics; chemicals; hydrogen; etc.  Scientists are rapidly developing new ways to store and transport methane.

Natural gas has nearly twice the energy per ton of CO2 emitted as coal.


6.     Implement a carbon dividend (tax, fee, credit, whatever).  With Ocean Afforestation, E7 countries could agree to a carbon fee because they could gain carbon storage income in excess of their carbon storage expenses from countries using fossil fuels.

A carbon fee in excess of about US$20 per ton of CO2 can be used to store the seaweed forest’s bio-CO2 and subsidize the production of bio-CH4.  For example, a carbon dividend of $50/ton of CO2 would allow E7 countries to drop the price of biomethane from US$4 per 1,000 cu ft to $2.8 per 1,000 cu ft.

When fossil fuel use stops, the carbon dividend drops to zero.  If E7 countries want to fund ongoing removal of legacy carbon, they sell the biomethane for $4.7 per 1,000 cu ft.

No Other Alternatives Can Meet the Scale Required

McLaren (2011 and 2012) has analyzed the cost, readiness and potential capacity of dozens of other carbon removal technologies.  He concludes that even if all the reasonably-priced alternatives  were implemented, the total would sequester less than half of the total current emissions of 32 Gt/yr, and less than 5% of the requirement to reverse global warming, which, as this chart shows, can only be done by Ocean Afforestation.

Who will take these actions?

Most of the continually increasing 20 scientists, engineers, and business people on the Ocean Foresters team are listed in Mark Capron’s profile.

Action 1 will be taken by a combination of Fijians, PODenergy, Inc., Ocean Foresters, Fiji government, individual philanthropists, and individual investors.

Action 2 will be taken by governments and non-profits funding universities, crowd investors, individual philanthropists, and individual and corporate investors.

Actions 3 and 4 will be taken by investors and corporations in the host countries.

Action 5 will be taken by free-market actors as they recognize sustainable, abundant, and relatively inexpensive biomethane availability.

Action 6 will be taken by governments as they recognize that Ocean Macroalgal Afforestation makes a carbon dividend (credit, fee, tax, whatever) much less painful than continued “free” CO2 emissions.

Where will these actions be taken?

Action 1 starts in Fiji and the University of the South Pacific member countries with support from developed countries.  It grows to the Small Island Developing States (SIDS) and larger countries.

Action 2 is likely to start in Hawaii, or California, or Mexico, but may also start in India, China, Chile, or Japan.  Hawaii has the advantage of proximity to both many small islands, the equator, and the center of  the North Pacific gyre.

Actions 3 is in lakes, lagoons, and bays (many lakes in Africa with excess or invasive water plants); any sheltered water, any country.

Action 4 is in the open ocean.

Action 5 plays out in many nations, starting with those lacking coal, oil, and wind resources, but having coal and oil consumption infrastructure.

Action 6 makes unilateral sense for any country developing their Ocean Afforestation economy.



What are other key benefits?

Food, negative carbon, biodiversity.  We can increase incidental but sustainable fish production to potentially provide 200 kg/yr/person for 10 billion people.

Ocean Macroalgal Afforestation (OMA or seaweed forests) is a holistic ecosystem sustainable at scale in every sense of the word:

1)     Environmental sustainability addresses issues beyond solar radiation or carbon capture such as: species biodiversity, food, and energy.

2)     Climate sustainability is a robust process unaffected by increasing CO2 nor a cause of droughts, floods, heat, cold, changing wind patterns, and ocean acidification.

3)     Political sustainability improves the quality of life and opportunities in all countries.

4)     Social sustainability counters the water, food, jobs, and natural disaster stresses of climate change.

5)     Energy sustainability stores more carbon permanently with less than 10% of the energy generated.

6)     Economic sustainability via multiple products from the seaweed forest ecosystem.


What are the proposal’s costs?

Dr. N’Yeurt’s paperestimates $4 per 1,000 cubic feet of bio-methane exported from the Ocean Macroalgal Afforestation Ecosystem.  The University of Virginia life cycle assessment found the most likely ratio of energy output:input to be 6 for bio-methane production or 4 for combined bio-methane production with storing CO2.  The cost of capturing and storing bio-CO2 is estimated at $16 per ton of CO2.

The University of the South Pacific needs US $1 million to design, build, debug, and operate two trial and training facilities for two years: a) a 2-ha sheltered saltwater biogas production facility in Laucala Bay; and b) a washed-up-on-beach freshwater biogas and terrestrial fertilizer production facility.

After debugging techniques and training operators at the 2-ha and beach trial sizes, expanding the saltwater biogas and 7 MW capacity electricity production to a commercially viable 2,700-ha forest involves an investment of US $3 million.  Income from the electricity generation is expected to exceed expenses by US $2 million per year.  Income from the Carbon Development Mechanism, food, and other products has not been quantified.  We are still researching the minimum commercially viable washed-up-on-beach biogas and terrestrial fertilizer facility.  Once the sheltered water version of OMA is proven in Fiji, we export the ecosystem to the sheltered water of other countries.

Open-ocean operations are substantially different from sheltered water operations.  A more expensive but quicker approach is to develop open-water techniques in parallel with the sheltered water development.  We estimate needing US $100 million to design, build, debug, and operate the first commercially viable cluster of 10,000-ha open-ocean forests, then it will be profitable, with potential profits totaling $100 trillion.


Time line

Year 1 –   Design, procure, and install equipment for the Fiji trial and training facilities.

Year 2 –   Debug operation of the 2-ha ecosystem, start engineering and permitting for 2,500-ha sheltered water forest.  Commence conceptual design and location selection for open-ocean trial facility.

Year 3 –   Engineer, permit, and procure equipment for 2,500-ha sheltered water ecosystem.  Design and build open-ocean trial facility.

Year 4 –   Install and commence operation of 2,500-ha sheltered water ecosystem.  Operate and debug open-ocean trial facility.

Years 5-8 – Ramp-up sheltered water installations to 1,000,000-ha per year (3,000 MW electrical capacities per year) for about ten years.  Design, build, operate, and debug commercial open ocean ecosystem.

Years 8-15 – Ramp-up open ocean installations to 100 million ha per year (20 quads per year) for about thirty years.


Related proposals

Finalist – Agriculture and forestry:Ocean Afforestation” explains using seaweed forests for food, energy, and CO2 storage.

Finalist – Replacing Diesel …: “Replace the diesel, reuse the engines, waste & seaweed biogas” aids transition from diesel to biogas fuel. 

Finalist – Hydraulic fracturing ….: “Methane-sniffing drones with distributed mobile sensors!” enables a low leakage methane economy.

Electric power sector: “Replace coal and oil with renewable natural gas (biomethane)” – Ocean afforestation provides sustainable biomethane.

Geoengineering: Withdrew to avoid Negative carbon via Ocean Afforestation being branded with adverse perceptions of geoengineering.

Shifting Cultures ….: “Rapid Planet Change” needs ocean afforestation holistic global ecosystem.

Electric power sector and Fossil fuel sector: “Save the methane!” suggests a carbon fee slows oil drilling while ocean afforestation builds the biomethane economy.


N’Yeurt, A., Chynoweth, D., Capron, M.E., Stewart, J., Hasan, M. 2012. Negative carbon via Ocean Afforestation. Process Safety and Environmental Protection 90, 467-474

The above paper lists 32 references for the calculations involving the Ocean Macroalgal Afforestation ecosystem.  There are seven supplemental information documents, some with more references:

OMA-Macroalgae Production & Density Calcs 2012 – 42 references

OMA-Process Concepts 2012 – 2 references

OMA-Global Calculations 2012 for Table 2 – 2 references

OMA-Algal Yields Calcs & Refs 2012 – 45 references

OMA-N2O-Emissions Calcs 2012 – 2 references

OMA-Artificial Geologic Seafloor Storage Of CO2, 2012 – 38 references

OMA-Ammonia Concentrating To Fertilizer 2012

Colosi, L. 2012. Private communication.

Migliore, G., Alisi, C., Sprocati, A.R., Massi, E., Ciccoli, R., Lenzi, M., Wang, A., Cremisini, C., 2012 Anaerobic digestion of macroalgal biomass and sediments sourced from the Orbetello lagoon, Italy, Biomass and BioEnergy 42, 69-77

Japan taps gas from methane hydrate, BBC News, March 12, 2013

Fracking: America’s Alternative Energy Revolution, John Graves, ChFC, CLU, Safe Harbor International Publishing, 2012

Latimer, J.S., M. Tedesco, R.L. Swanson, C. Yarish, P. Stacey and C. Garza. 2013.  Long Island Sound: Prospects for the Urban Sea. Springer Publishers, NY

Yarish, C., A.E. Sperr, R. Wilkes, X.G. Fei, A.C. Mathieson, and I. Levine. "Developing a Commercially Viable Seaweed Industry in New England." for Nori Research Project (1996-1998)

Yarish, C. 2010. Macroalgae for CO2 Capture and Renewable Energy--A Pilot Project. Gas Technology Institute Project Number 20960, Department of Energy Netl Program

Long Island Sound Cash Crop Makes Its Way To Manhattan Tables, CBS news, June 20, 2013.