CO2 Capture and Storage CCS

  

 

Everything you wanted to know about
CO2 Capture and Storage (CCS), but had no one to ask .

 

 

1. What is CCS?

CO2 Capture and Storage (CCS) describes a technological process by which the carbon dioxide (CO2) generated by large stationary sources - such as coal- fired power plants, steel plants and oil refineries - is prevented from entering the atmosphere.

That’s because it enables at least 90% of these CO2 emissions to be captured, then stored in geological formations – safely and permanently – deep underground (at least 800m). In fact, it uses the same natural trapping mechanisms which have already kept huge volumes of oil, gas and CO2 underground for millions of years.

Currently, all of the CO2 produced by these large stationary sources is released into the atmosphere – directly contributing to global warming.

2. Why is it a critical technology for combating climate change?

CCS is the single biggest lever to combat climate change (compared to, for example, energy efficiency which requires many different actions). In fact, CCS has the potential to address almost half of the world’s current CO2 emissions.

Experts estimate that by 2050, CCS could reduce annual CO2 emissions by 0.6 to 1.7 billion tonnes in the EU and by 9 to 16 billion tonnes worldwide. The upper end of this range would require its application to all fossil fuel power plants and to almost all other large industrial emitters – with the large volumes of hydrogen produced used for transport fuel.

3. What other benefits will CCS provide?

In addition to its potential to reduce CO2 emissions on a massive scale, CCS will also provide greater energy security – by making the burning of Europe’s abundant coal reserves more environmentally acceptable and reducing its dependency on imported natural gas. CCS could also facilitate the transition to a hydrogen economy through the production of large volumes of clean hydrogen which that could be used for electricity or transport fuel.

EU demonstration efforts on CCS will not only demonstrate the EU’s commitment to delivering on its own CO2 reduction targets, but spur other countries to do the same – especially large CO2 emitters, such as China, India and the US. As a global solution to combating climate change, CCS could therefore also give a major boost to the European economy – promoting technology leadership, European competitiveness and creating jobs.

4. How does CCS work?

CCS consists of three stages:
i. Capture: CO2 is captured and compressed at the emissions site.
ii. Transport: The CO2 is then transported to a storage location.
iii. Storage: The CO2 is permanently stored in geological formations, deep underground.

Each of these stages – capture, transport and storage – can be accomplished in different ways.

i. Capture processes:

    Post-combustion: CO2 is removed from the exhaust gas through absorption by selective solvents.
    Pre-combustion: The fuel is pre- treated and converted into a mix of CO2 and hydrogen, from which the CO2 is separated. The hydrogen is then used as fuel, or burnt to produce electricity.
    Oxy-fuel combustion: The fuel is burned with oxygen instead of air, producing a flue stream of CO2 and water vapour without nitrogen; the CO2 is relatively easily removed from this stream.

ii. Transport options:
Pipelines are the main option for large-scale CO2 transportation, but shipping and road transport are also possibilities.

iii. Storage options:

    Deep saline aquifers (saltwater-bearing rocks unsuitable for human consumption)
    Depleted oil and gas fields (with the potential for Enhanced Oil Recovery)

5. How long has CCS been in existence?

Although there are currently no fully integrated, commercial-scale CCS projects for power plants in operation, many of the technologies that make up CCS have been around for decades:

    CO2 capture is already practised on a small scale, based on technology that has been used in the chemical and refining industries for decades.
    Transportation is also well understood: it has been shipped regionally for over 17 years, while a 5,000km network has been operating in the USA for over 30 years for Enhanced Oil Recovery.
    Small-scale CO2 storage projects have been operating successfully for over a decade, e.g. at Sleipner (Norway), Weyburn (Canada) and In Salah (Algeria). The industry can also build on knowledge obtained through the geological storage of natural gas, which has also been practised for decades.

6. What’s the next step?

CCS technology now needs to be scaled up – including full process integration and optimisation – with demonstration projects of a size large enough to allow subsequent projects to be at commercial scale. This will also build public confidence in CCS as more and more people see that CO2 storage is safe and reliable.

7. Why should we use CCS, given its link to fossil fuels?

Scientists have confirmed that unless we stabilise CO2- equivalent concentrations at their current level of 450 parts per million (ppm), average global temperature is likely to rise by 2.4ºC to 6.4ºC by 2100. If we fail to keep below 2ºC, devastating – and irreversible – climate changes will occur.

This means reducing CO2-equivalent emissions by 50% by 2030. But with world energy demand expected to double by 2030 and renewable energies to make up ~30% of the energy mix by this date, only a portfolio of solutions will achieve this goal. This includes energy efficiency, a vast increase in renewable energy – and CCS.

Around 750 new coal power plants are already planned for the period 2005–2018, totaling more than 350 Gigawatt (GW), of which 50 will be in Europe, almost 300 in China, 200 in India and 50 in the US.

8. Why is it so important to deploy CCS as soon as possible?

Time is of the essence. Any delay in the roll-out of CCS could not only lead to unnecessary CO2 emissions but additional costs, as instead of being able to apply it to the current pipeline of coal plants, a retrofit would be required, increasing the cost of achieving the same emissions reduction. With decisions on the building of new power plants being made now in Europe, it is vital that we are not locked into an infrastructure that is not optimised for CCS.

Indeed, every year that CCS is delayed is a missed opportunity to reduce CO2 emissions. Today, we have ~450 parts per million (ppm) CO2 equivalent in the atmosphere, with concentration rising at over 2 ppm per annum. The Intergovernmental Panel on Climate Change states that if we are to avoid major climate change effects, we must not exceed this 450 ppm. Delaying the implementation of CCS by just 6 years would mean CO2 concentrations increasing by around 10 ppm by 2020.

9. If we are at such a critical phase, why isn’t it already being deployed?

The incremental costs of the first large-scale CCS demonstration projects will be exceptionally high – too high to be fully justifiable to company shareholders.

That’s because all ‘First Movers’ will incur:

    Unrecoverable costs from making accelerated investments in scaling up the technology.
    Market risk due to uncertainty over:
    a) which CCS technologies will prove the most successful
    b) the future CO2 price and
    c) construction and operational costs.

Based on an independent study recently undertaken by McKinsey and Company, it is estimated that the total incremental costs of 10-12 CCS demonstration projects would be €7 billion - €12 billion.

Industry has already declared its willingness to cover both the base costs of the power plant (without CCS) and a major portion of the risks of implementing these CCS demonstration activities. Given that it will bring incalculable benefits to both the public and European industry and that these projects are inherently loss-making, public funding has therefore been provided to support 12 industrial-scale CCS projects. Without this, commercialisation will be severely delayed – until at least 2030 in Europe.

10. Why are public funds needed for CCS demonstration projects?

Currently, a CCS demonstration project would be a loss-making enterprise for industry, given the current price of implementing and using the technology; the current price of carbon; and uncertainty surrounding long-term viability and profitability. No shareholder can therefore be expected to fund it fully at this stage.

The typical cost of a demonstration project is likely to be in the range €60-90 per tonne of CO2 abated. Recent analyst estimates for Phase II of the European Union Emissions Trading Scheme (EU ETS) range from €30 to €48 per tonne of CO2 and, at this stage, similar levels are assumed beyond Phase II (up to 2030). In this range, the carbon price is insufficient for demonstration projects to be “stand-alone”, commercially viable.

Assuming that CCS demonstration projects would cost between €60 and €90 per tonne of CO2, and projecting a median carbon price of €35 per tonne of CO2, there is an “economic gap” of €25-€55 per tonne of CO2 per project. This corresponds to around €500 million - €1.1 billion, expressed as a Net Present Value (NPV) over the lifespan of a 300MW size power plant. The range depends on variations in specific project variables, such as capture technology and capex, transport distance and storage solutions.

11. The UK and the Netherlands are well on their way to implementing CCS demonstration projects – won’t these be enough to make the technology commercially viable?

As it is not yet known which CCS technologies will prove the most successful, it is vital that the full range is tested – including higher-risk technologies – optimised across projects and locations. As each region has its own challenges, local demonstration is also important in order to maximise public and political support.

As importantly, EU CCS demonstration efforts will ensure that cross-border projects – where CO2 is stored in a different country or region to where it is captured – are not excluded. As capture and storage locations are unevenly distributed throughout Europe, cross-border pipelines will play a crucial role in the wide-scale deployment of CCS and the development of clusters in major industrial areas as the next key step.

12. How much will it cost to retrofit CCS technology to existing power plants?

In general, retrofitting an existing power plant would lead to a higher cost for CCS, but these are highly dependent on specific site characteristics, including plant specifications, remaining economic life and overall site layout. For this reason, no generalisation or “reference case” would be meaningful.

There are four main factors likely to drive the cost increase for retrofits:

    The higher capex (capital costs) of the capture facility: the existing plant configuration and space constraints could make adaption to CCS more difficult than for a new build.
    The installation’s shorter lifespan: the power plant is already operating so where (for example) a new plant with CCS may run for 40 years, the capture facility of a 20 year-old plant is likely to have only a 20 year life, reducing the “efficiency” of the initial capex.
    There is a higher efficiency penalty, leading to a higher fuel cost when compared to a fully integrated, newly-built CCS plant.
    There is the “opportunity cost” of lost generating time, because the plant would be taken out of operation for a period to install the capture facility.

13. How can we accelerate the building of CCS projects?

Building a CCS project is a lengthy process: a fully integrated project can take 6.5-10 years before it becomes operational. However, Final Investment Decision can only be made once permits have been awarded across the entire value chain. In the case of CO2 storage, this can take as long as 6.5 years. In such a scenario, even a commercial project started as early as 2016 would not itself become operational until 2024.

Ideally, 10-12 CCS demonstration projects should be operational by 2015. The first early commercial projects should be operational by 2020, with the remaining demonstration projects sufficiently advanced for early commercial projects to be ordered from 2020 onwards. Some 80-120 large- scale CCS projects could therefore be operational in Europe by 2030.

There are several ways we can fast-track the building of CCS projects:

    Starting a commercial project as early as possible during the building of the demonstration project so that – for example – build can start after just one year of the demo being in operation.
    Accelerating feasibility studies etc.
    Making faster investment decisions
    Shortening the tender process
    Introducing special measures to shorten the permitting process.

Some projects, by their very nature, will of course be quicker to build than others, e.g. retrofitting existing power plants with CCS; using well-known oil and gas fields with infrastructure and seismic data already available; those with only a short distance from the power plant to the storage site, etc.

14. How much CO2 can be captured using CCS?

One 900 MW CCS coal-fired power plant can abate around 5 million tonnes of CO2 a year. If, as projected, 80-120 commercial CCS projects are operating in Europe by 2030, they would abate some 400 million tonnes of CO2 per year.

By 2050, CCS could reduce annual CO2 emissions by 0.6 to 1.7 billion tonnes in the EU and by 9 to 16 billion tonnes worldwide. The upper end of this range would require its application to all fossil fuel power plants and to almost all other large industrial emitters – with the large volumes of hydrogen produced used for transport fuel.

15. Isn’t more energy utilised where CCS is implemented?

The absolute efficiency penalty, estimated at around 10% for the reference case (meaning plant efficiency drops from 50% to around 40%), drives an increase in fuel consumption and does require an over- sizing of the plant to ensure the same net electricity output.

However, next-generation technology - such as ultra-supercritical 700°C technology for boilers, coupled with drying in the case of lignite - will achieve a 50% level of overall plant efficiency. While this technology is not currently available, it is expected to be when early commercial CCS projects are built around 2020.

16. Where will CO2 be stored?

The regional distribution and cost of storage in Europe will play an important role in any roll-out of CCS. Most experts agree that depleted oil and gas fields and deep saline aquifers have the largest storage potential.

Depleted oil and gas fields
Depleted oil and gas fields are well understood and around a third of total oil and gas field capacity in Europe is estimated to be economically useable for CO2 storage. With an estimated capacity for 10 to 15 billion tonnes of CO2, this is sufficient for the lifetime of around 50 to 60 CCS projects. However, most of these fields are located offshore in northern Europe and the transportation to and storage of CO2 in these fields (excluding capture) is around twice as costly as onshore fields.

Deep saline aquifers
While much less work has been done to map and define deep saline aquifers, most sources indicate that their capacity should be sufficient for European needs overall. Preliminary conservative estimates by EU GeoCapacity indicate that Europe can store some 136 billion tonnes of CO2 - equivalent to around 70 years of current CO2 emissions from the EU’s power plants and heavy industry. At the higher end of these estimations, EU GeoCapacity estimates some 380 billion tonnes of CO2 could be stored in Europe alone.

17. Storing enormous quantities of CO2 underground must present some risk?

The geological formations that would be used to store CO2 diffuse it, making massive releases extremely unlikely. Indeed, because the CO2 becomes trapped in the tiny pores of rocks, any leakage through the geological layers would be extremely slow, allowing plenty of time for it to be detected and dealt with. In fact, it would not raise local CO2 concentrations much above normal atmospheric levels.

Higher concentration leaks could come from man-made wells, but the oil and gas industry already has decades of experience in monitoring wells and keeping them secure. Storage sites will not, of course, be located in volcanic areas.

18. But won’t CO2 storage increase the likelihood of seismic activity?

A detailed survey takes place to identify any potential leakage pathways before a CO2 storage site is selected. If these are discovered, then the site will not be selected. In areas where some natural seismic activity is already taking place, we can ensure that the pressure on the CO2 does not exceed the strength of the rock by making the volume of CO2 stored relative to that of the storage site. CO2 storage has even proved to be robust in volcanic areas: in 2004, a storage site in Japan endured a 6.8 magnitude earthquake with no damage to its boreholes and no CO2 leakage. But then CO2 has remained undisturbed underground for millions of years – despite thousands of earthquakes.

19. How will we know if the CO2 is leaking?

Before a CO2 storage site is chosen, a detailed survey takes place to identify any potential leakage pathways. If these are found to exist then the site will not be selected. In Europe, underground gas storage (natural gas and hydrogen) has an excellent safety record, with sophisticated monitoring techniques that are easily adaptable to CCS. On the surface, air and soil sampling can be used to detect potential CO2 leakage, whilst changes underground can be monitored by detecting sound (seismic), electromagnetic, gravity or density changes within the geological formations.

The risk of leakage through man-made wells is expected to be minimal because they can easily be monitored and fixed, while CO2 leaking through faults or fractures would be localised and simply withdrawn; and, if necessary, the well closed.

20. Who will be liable for CO2 storage sites over the long-term?

As the CO2 will remain stored underground indefinitely, long-term liability will follow the example set by the petroleum industry, whereby the state assumes liability after a regulated abandonment process. Indeed, EU law governing the safe and permanent storage of CO2 has already been approved and is currently being implemented at national level.

21. Large stationary emitters of CO2 also include refineries, steel and cement plants - how are they linked into what the EC is doing?

The EC encourages the deployment of CCS in other sectors, as 25% of all European CO2 emissions addressable by CCS come from refineries and the cement, iron and steel industries.

 

The European CCS Demonstration Project Network

The EC has established a Network of CCS demonstration projects to generate early benefits from a coordinated European action.
CCS demonstration projects fulfilling minimum qualification criteria are invited to join the Network and benefit from its operations.
The Network allows early-movers to exchange information and experience from large-size industrial demonstration of the use of CCS technologies, to maximise their impact on further R&D and policy making, and optimise costs through shared collective actions.
It is envisaged that, as the Network evolves, its EU-wide, integrating and binding role may be reinforced and complemented by other measures in support of further development of CCS technologies, building towards the establishment of a European Industrial Initiative.

To help fulfil the potential of CO2 Capture and Storage (CCS), the European Commission is sponsoring and coordinating the world’s first network of demonstration projects, all of which are aiming to be operational by 2015. The goal is to create a prominent community of projects united in the goal of achieving commercially viable CCS by 2020.
The CCS Project Network fosters knowledge sharing amongst the demonstration projects and leverage this new body of knowledge to raise public understanding of the potential of CCS. This accelerates learning and ensures that we can assist CCS to safely fulfil its potential, both in the EU and in cooperation with global partners.

CCS Project Network Advisory Forum

To guarantee that the Network is valuable to the wider energy community in Europe, an annual Advisory Forum has been established to review progress and specify the knowledge that can most usefully be generated by the CCS Project Network.

• The first Advisory Forum meeting was held in Brussels on 17 September 2010.
  Read more..
• The second Advisory Forum Meeting was held on 16 June 2011 in Brussels. Read more..

CCS World News

• 2012-07-18 - Carbon capture would create substantial challenges, witnesses say at energy ...
• 2012-07-18 - Opinions Divided on Climate Change and CCS in Saskatchewan
• 2012-07-18 - Planned Tees CCS project could be in line for EU cash
• 2012-07-13 - Yorkshire leads race for €1.5bn EU carbon capture funding
• 2012-07-16 - Codexis releases enzyme CO2 capture results
• 2012-07-16 - U.S. DOE advancing Hydrogen Energy plant in California
• 2012-07-16 - Yorkshire leads race for €1.5bn EU carbon capture funding ...
• 2012-07-15 - UK Don Valley project leads EU funding bid
• 2012-07-15 - Alberta projects get funding boost
• 2012-07-13 - Don Valley leads UK CCS charge for €1.5bn EU funds
• 2012-07-13 - EU says up to 1.5 billion euros ready for low-carbon investment
• 2012-07-12 - Anglo mines to become carbon neutral, CCS-aware by 2030
• 2012-07-12 - Clean coal tech is ready, but theres a catch

Membership of the CCS Project Network is open to all European projects that are at a sufficient scale and level of maturity that will generate valuable output and knowledge about industrial-scale CCS demonstration.
The application process for membership of the Network is designed to be as simple and transparent as practicable, but sufficiently robust to ensure that all members are large-scale demonstration projects at a similar level of maturity.
Project developers may submit applications at any time to demonstrate that they fulfil the eligibility criteria, can provide evidence of the maturity of the project, commit to knowledge sharing and agree to the Network organisation and procedures. The qualification criteria and application process are described in the Qualification Criteria document. The Network is open to all qualifying projects and will not distinguish between EU-funded and non-EU funded projects.

Eligibility Criteria

Projects in the Network shall have sound plans to demonstrate the full CCS value chain by 2015 and shall fulfil the following technical criteria:

• The CCS project shall for a fossil fuel-fired power plant have a minimum gross production of 250MWe before CO2 capture and compression
• The CCS project shall for an industrial plant realise a minimum of 500kt per year of stored CO2
• The CO2 capture rate shall not be less than 85% of the treated flue gas stream
• The project, i.e. the plant to which CCS is applied, shall be located within the European Economic Area (EEA)

Knowledge Sharing

Projects in the Network are committed to knowledge sharing with similar projects and other stakeholders in order to help accelerate CCS deployment and raise public engagement, as described in the Knowledge Sharing Protocol document.

Key documents

European CCS Demonstration Project Network Qualification Criteria
European CCS Demonstration Project Network Knowledge Sharing Protocol

Learn more about CCS

To learn more about CCS, please have a look at the following videos, kindly provided by ZEP:

http://www.ccsnetwork.eu/index.php?p=videos

CROATIAN CENTER of RENEWABLE ENERGY SOURCES (CCRES)
special tanks to

Daniel Rennie
Global CCS Institute
Actualis, Level 2
21 & 23 Boulevard Haussmann
PARIS 75009 France

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Jose Manuel Hernandez
Programme Manager - EU Policies
European Commission

CROATIAN CENTER of RENEWABLE ENERGY SOURCES (CCRES)

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Tiny Green Factories

New ways to turn photosynthetic green algae into tiny “green factories” for producing raw materials for alternative fuels.

Overturning two long-held misconceptions about oil production in algae, scientists at the U.S. Department of Energy’s Brookhaven National Laboratory show that ramping up the microbes’ overall metabolism by feeding them more carbon increases oil production as the organisms continue to grow. The findings — published online in the journal Plant and Cell Physiology on May 28, 2012 — may point to new ways to turn photosynthetic green algae into tiny “green factories” for producing raw materials for alternative fuels.

“We are interested in algae because they grow very quickly and can efficiently convert carbon dioxide into carbon-chain molecules like starch and oils,” said Brookhaven biologist Changcheng Xu, the paper’s lead author. With eight times the energy density of starch, algal oil in particular could be an ideal raw material for making biodiesel and other renewable fuels.

But there have been some problems turning microscopic algae into oil producing factories.

For one thing, when the tiny microbes take in carbon dioxide for photosynthesis, they preferentially convert the carbon into starch rather than oils. “Normally, algae produce very little oil,” Xu said.

Before the current research, the only way scientists knew to tip the balance in favor of oil production was to starve the algae of certain key nutrients, like nitrogen. Oil output would increase, but the algae would stop growing — not ideal conditions for continuous production.

Another issue was that scientists didn’t know much about the details of oil biochemistry in algae. “Much of what we thought we knew was inferred from studies performed on higher plants,” said Brookhaven biochemist John Shanklin, a co-author who’s conducted extensive research on plant oil production. Recent studies have hinted at big differences between the microbial algae and their more complex photosynthetic relatives.

“Our goal was to learn all we could about the factors that contribute to oil production in algae, including those that control metabolic switching between starch and oil, to see if we could shift the balance to oil production without stopping algae growth,” Xu said.

The scientists grew cultures of Chlamydomonas reinhardtii — the “fruit fly” of algae — under a variety of nutrient conditions, with and without inhibitors that would limit specific biochemical pathways. They also studied a mutant Chlamydomonas that lacks the capacity to make starch. By comparing how much oil accumulated over time in the two strains across the various conditions, they were able to learn why carbon preferentially partitions into starch rather than oil, and how to affect the process.

The main finding was that feeding the algae more carbon (in the form of acetate) quickly maxed out the production of starch to the point that any additional carbon was channeled into high-gear oil production. And, most significantly, under the excess carbon condition and without nutrient deprivation, the microbes kept growing while producing oil.

“This overturns the previously held dogma that algae growth and increased oil production are mutually exclusive,” Xu said.

The detailed studies, conducted mainly by Brookhaven research associates Jilian Fan and Chengshi Yan, showed that the amount of carbon was the key factor determining how much oil was produced: more carbon resulted in more oil; less carbon limited production. This was another surprise because a lot of approaches for increasing oil production have focused on the role of enzymes involved in producing fatty acids and oils. In this study, inhibiting enzyme production had little effect on oil output.

“This is an example of a substantial difference between algae and higher plants,” said Shanklin.

In plants, the enzymes directly involved in the oil biosynthetic pathway are the limiting factors in oil production. In algae, the limiting step is not in the oil biosynthesis itself, but further back in central metabolism.

This is not all that different from what we see in human metabolism, Xu points out: Eating more carbon-rich carbohydrates pushes our metabolism to increase oil (fat) production and storage.

“It’s kind of surprising that, in some ways, we’re more like algae than higher plants are,” Xu said, noting that scientists in other fields may be interested in the details of metabolic switching uncovered by this research.

But the next step for the Brookhaven team will be to look more closely at the differences in carbon partitioning in algae and plants. This part of the work will be led by co-author Jorg Schwender, an expert in metabolic flux studies. The team will also work to translate what they’ve learned in a model algal species into information that can help increase the yield of commercial algal strains for the production of raw materials for biofuels.

This research was funded by the DOE Office of Science and the DOE Office of Energy Efficiency and Renewable Energy.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time.

CCRES 

special thanks to  

Brookhaven National Laboratory

Croatian Center of Renewable Energy Sources (CCRES)

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Capture the Carbon Dioxide

 Capture the Carbon Dioxide

In nature, photosynthesis uses the energy in sunlight to split water into carbon dioxide and hydrogen. A typical plant cell relies on a series of electron carriers, which create a photosynthetic circuit that allows plants to capture the carbon dioxide they need, and then convert it into the biomass that fuels cell growth. At the same time, plants produce hydrogen, a molecule that can be used in a variety of renewable and sustainable fuel technologies, but that is also expensive to produce in large quantities and currently involves non-renewable natural gas reformation.

A photosynthetic organism such as green algae tends to use solar energy to generate either fixed carbon or hydrogen—while this is fine for growth, it is not particularly efficient for making greater quantities of hydrogen. Facing this challenge, NREL researchers wondered if they could find ways to boost the hydrogen-making capacity of photosynthesis. They posed a key question: What controls the partitioning of electrons between these two competing metabolic pathways?

A team from NREL, along with colleagues from the Massachusetts Institute of Technology and Tel Aviv University, set out to answer this question. They hypothesized that they could engineer the process by "rewiring" algaes catalytic circuits, or pathways. To do so, they would replace the normal hydrogen-producing enzyme, hydrogenase (H2ase), with a ferredoxin and hydrogenase fusion protein. They speculated that inserting this kind of a fusion protein into this reaction path could divert more electrons into hydrogen production and push the algae into making more hydrogen and fixing less carbon dioxide. If successful, this engineered photosynthetic circuit could potentially increase efficiencies and thus bring down the price of hydrogen. In its more than 30-year history of innovation, NREL has been a leader in working with green algae for hydrogen and biofuel production, as well as with finding ways to speed renewable fuels to market to help meet the nations clean energy goals. It is this expertise that encouraged MITs Iftach Yacoby to partner with NREL, which enabled the researchers to collaborate on technical innovations such as the CdTe-H2ase.

During NRELs work with green algae, the labs own Senior Scientist Paul King and other researchers worked with hydrogenase enzymes as a key component of the photosynthetic hydrogen production equation. These biological catalysts can convert electrons and protons into hydrogen gas, or convert hydrogen into electrons and protons. For this work, the team chose to use in vitro tests under anaerobic conditions. They were able to demonstrate how the hydrogenase and other enzymes compete to regulate whether algae uses the solar energy it captures through photosynthesis to produce carbon compounds or hydrogen. As they studied these interactions, they were able to devise a procedure to engineer the proteins that compose electron transfer circuits. 

The first element of their strategy was based on their hypothesis that they could have more of the electrons go to hydrogen if they altered the composition to replace hydrogenase with a ferredoxin-hydrogenase fusion. In the anaerobic test tubes, the team confirmed that the photosynthetic circuit can switch from capturing carbon dioxide to producing hydrogen by substituting the fusion. The hydrogen production was carried out in the presence of the CO₂ fixation enzyme ferredoxin:NADP-oxidoreductase (FNR). This process is a biological model for using solar power to convert water into hydrogen. The basis for this switch was modeled as two new Fd-hydrogenase circuits (boxes 1 and 2, Figure 2), and a reduced level of FNR activity modeled as a third circuit (box 3, Figure 2). 

King considered these results promising, because they suggest that fusion is an engineering strategy to improve hydrogen production efficiencies, and might be useful in resolving the biochemical mechanisms that control photosynthetic electron transport circuits and product levels from competing pathways. The next phase, already underway, is to introduce the fusion protein into green algae Chlamydomonas and determine if rewiring can take place to improve hydrogen-production efficiencies. Even though this is only one of a number of variables to consider, this strategy has already signaled an avenue to pursue in the drive to reduce the cost of hydrogen fuel and make it cost-competitive for industry.

Enlarge image

Photosynthetic electron transport pathways that support carbon dioxide fixation and hydrogen production. Light-activated PSII extracts electrons from water and transfers them, while parallel circuits couple Fd to either FNR for carbon dioxide fixation or hydrogenase production.
Credit: Paul King, NREL

Enlarge image

Engineering of the hydrogen-producing enzyme to create an Fd-H2ase fusion changes the composition of the hydrogen production circuit to include both direct (box 1) and indirect (box 2) H2 production modes. The CO₂ fixation circuit (box 3) remains open, but operates at a reduced level.
Credit: Paul King, NREL

CCRES special thanks to NREL

NREL is a national laboratory of the U.S. Department of Energy, Office Energy Efficiency and Renewable Energy operated by the Alliance for Substainable Energy, LLC.

CROATIAN CENTER of RENEWABLE ENERGY SOURCES ( CCRES)

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