Background
Global climate change and fuel poverty are the two most pressing issues in energy production today. Globally 17% of the population, that’s 1.2 billion people, are currently without electricity. It is obvious that we need to massively increase our global energy output. However, as climate change is an ever present and pressing issue also, we cannot just increase our reliance on fossil fuels in order to solve this problem. In the UK alone, the last fourteen months have consecutively broken temperature records, the highest global temperature has also been recorded over the first six months of 2016. The ten warmest years on record all follow after the year of 2000 (on track to become eleven as this is written in the month of July 2016) (See Figure 1). Whilst global energy output increase is essential, this must be done in a clean and efficient manner, and more importantly it must not add further greenhouse gas emissions to our planet’s atmosphere.
Data source: NASA/GISS
Credit: NASA Scientific Visualization Studio
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2015
Despite the importance of maintaining climate stability, globally in 2013 67% of electricity was still generated by burning fossil fuels (see Figure 2). The IEA predicts that globally renewable sources such as wind and solar power will rise from 22% to 26% by 2020. In the UK the power from renewable energy has increased six fold since the year 2000. However, in the same period electricity consumption increased globally by over 55%. It is vital that renewable sources of energy proliferate even more that they have over the past decade and replace fossil fuels as the lion’s share of energy production, while also keeping up with increasing demands for electricity.
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Figure 2. Pie chart showing the percent of global electricity produced by each source in 2013. Data from the IEA 'Key World Statistics' Report, 2015.
A significant cost of renewable energy proliferation stems from its intermittency. In a coal fired power plant or a nuclear fission reactor it is possible to control energy output in line with fluctuating demands. However, with some renewable sources, electricity is only generated when the wind is blowing or the sun is shining. If this energy is not utilised, then it is wasted, and if it is not enough then power must be generated from other sources such as polluting fossil fuels or expensive nuclear options.
As wind and solar power production becomes more widespread the problem of intermittency becomes and increasingly significant (and expensive) issue. A 2003 report by Carbon Trust predicted that when 10% of electricity in the UK is produced by renewable sources it could cost up to £2.6 billion to build the infrastructure to mitigate this intermittency, and cost £40 million a year to maintain. As the UK approaches a state where 20% of our electricity is renewable, the cost of building infrastructure rises to £4.5 billion, and at 40% the yearly cost could reach up to £1 billion, potentially adding £390 on average to yearly household energy bills. Currently the best plan is to avoid the problem and simply to triple the number of wind turbines and solar farms built. The theory is that if a large number of them are spread over a wide enough area approximate reliability could be achieved. This is not only three times more expensive than is strictly necessary but it means a large proportion of the energy being produced will be wasted.
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Figure 3. Graph showing every production in Giga Watts (GW) over a 24 hour period in Germany, 2013. Dark blue indicates energy produced by solar power, light blue indicated energy produced by wind turbines & grey indicated electricity produced from conventional sources such as coal, nuclear or natural gas.
<img src="media/images/shewimage.jpg" class="project_fig_three showFullSizeImage" /> In Germany for example, solar power capabilities have increased by 400% since 2008. With no effective storage methods however, they ran into problems with electricity production skyrocketing during the day and rapidly falling at night, known as ‘peaking’ (see Figure 3). This causes major disruption, not only from of the risk of overloading circuits but also because other methods of power generation must be wound down during the day and cranked up again at night; an expensive process. If the energy produced from renewable technologies could be stockpiled as a sustainable fuel it could be released when it is needed, thus making if far cheaper to manage.
Our team BioWire is exploring a new way of mitigating this expensive problem. The key to this is the unique physiology of the gram negative bacteria Shewanella oneidensis MR-1. These ‘rock-breathing’ microbes possess the MtrCAB protein complex, termed a molecular nanowire (see Figure 4). This porin cytochrome complex can channel electrons across the cytoplasmic membrane using iron heme cofactors. This protein can then be used to channel electrons into the cell’s periplasmic space and to hydrogenase enzymes. These enzymes can use electrons to reduce two protons (2H+) to one diatomic hydrogen molecule (H2). We can use this pathway in Shewanella oniedensis MR-1 (see Figure 5) to convert energy from renewable sources to a clean fuel, hydrogen. Theoretically this can be done on a large scale using the microbial fuel cells at wind and solar famers, so all of the energy produced is captured and stored as Hydrogen. This Hydrogen can then be stockpiled and burnt in centralised facilities to generate electricity in line with demand. Our project aims to demonstrate the possibility of this concept
<img src="media/images/periplasm.png" style="width:800px; margin-top:20px;"/>
Figure 5. Diagram of the Periplasmic space of Shewanella oneidensis, demonstrating the molecular system we are working on. Thin black arrows indicate protein-protein interaction & blue arrows indicate protein flow. Part A demonstrated the natural molecular physiology & part B shows a hypothetical ‘thermodynamically optimised’ system.
Other methods of hydrogen production do exist, however few have been scaled as economically and successfully as natural gas reformation. Natural gas reformation uses fossil fuels as an energy source, and produces carbon dioxide or carbon monoxide as a bi-product. A vital goal of our project is to enhance the capabilities of carbon neutral energy, hence our focus on enhancing renewables and storage of this energy. Other current methods to store electricity include lithium ion batteries. The main problem with this method is that if renewables proliferate as much as is necessary to fuel global energy demands, the scale at which lithium ion batteries would be needed would make them prohibitively expensive. Another method is pumped-storage hydroelectricity; however, this faces its own limitations. Namely this would require a lake up a mountain to store energy as gravitational potential energy. This imposes an upper limit on the amount of power you can realistically store.
The most prolific extant method for carbon neutral hydrogen production is the electrolysis of water. By running a current through water, H2O is split into O2 and 2H+ ions, which is then reduced to H2. This approach however has its issues, and in 2012 it only produced 0.25% of global hydrogen. In 2016 new approaches allowed for an increase in hydrogen production via electrolysis three-fold, but this still pales in comparison to hydrogen from steam reformation of natural gas. Currently electrolysis is not economically scalable due to the high cost of electricity. As renewables become more abundant, electrolysis will become cheaper but this is not enough to outcompete fossil fuels today. This is compounded by increasing prices of noble metal catalysts such as iridium which have been increasing rapidly in 2016.
Fundamentally there is no cheap, large scale (terawatt hour scale) method of storing electricity. It is difficult to draw comparisons between our approach and other emerging methods as the data does not yet exist because all of these technologies are in their early stages and none of them are economically scalable yet. Our project aims to perform some proof of concept experiments where our objective is to explore the potential of using bacterial systems to store energy as hydrogen. We are attempting to increase the yields of hydrogen produced from Shewanella oneidensis MR-1, in comparison to the wild type strains. In this way we hope to demonstrate the potential microbial fuel cells have as an energy storage system (see Figure 6).
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