13-04-24 Size Matters Fuel Cells and Electrolysers on the Power Grid

Size Matters: Fuel Cells and Electrolysers on the Power Grid

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24 Apr 2013PDF (296 kb)

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13-04-24 Size Matters

When it comes to centralised energy production, specifically electricity generation, size matters. Both fuel cells and electrolysers are vying for the opportunities available in this market, with fuel cells offering clean power generation and electrolysers providing renewable energy storage and grid stabilisation services, but what are the challenges in terms of scale, and how are they being tackled? Electrolysers and fuel cells provide different benefits, so we should consider the question for each technology in turn.

The largest nuclear and coal-fired power stations around the world have capacities in excess of 6,000 MW; the largest fuel cells manufactured commercially range from 400 kW up to 2.8 MW in size. Clearly there is a gap in terms of scale, but fuel cells do have a benefit which falls in their favour: modularity. In the Republic of Korea, POSCO Energy is building a 58.8 MW fuel cell installation, which is essentially a large number of fuel cells connected in a modular fashion. The country is interested in fuel cell technology due to incentives as part of its Renewable Portfolio Standard (RPS). The standard began in 2012, mandating that companies with generation capacity in excess of 500 MW must supply 2% from New and Renewable Energy (NRE) and the percentage increases year-on-year up to 10% NRE by 2022. Different NRE are afforded weightings under the RPS which in turn relate to financial payments as indicated in the table below.


New and Renewable Energies




Onshore wind, refuse-derived fuel and tidal


Offshore wind and fuel cells

NRE weightings under the Korean RPS (Source: POSCO Energy)

Penalties can be imposed on any shortfalls, calculated on the difference between mandated generation and actual generation. Of the seven companies who fell under the auspices of the RPS in 2012, only one (Korea Hydro & Nuclear Power Co., Ltd) met the requirements; the Government is considering if infringement was due to lack of will, or simply a result of infrastructure issues, and fines will be issued as appropriate. In 2013, the requirement has increased to 2.5%, so fines for lack of compliance will only increase from now on.

As the RPS progresses, larger and larger fuel cell installations can be expected, but the units themselves will not necessarily grow in size; what is more likely is that the number of units in a single installation will increase. The benefits of this are clear: servicing and maintenance can be performed on individual units without taking the entire ‘power plant’ offline, effectively increasing its overall capacity factor.

Outside Korea, other companies are also interested in developing large fuel cell installations and one company with ambitious targets is Mitsubishi Heavy Industries (MHI). It is developing what it calls a triple combined cycle power generation system which integrates solid oxide fuel cells (SOFC) and gas turbine combined cycle (GTCC) generators and which boasts a 10% efficiency gain on conventional systems. MHI currently has a system on test at a Tokyo Gas facility which includes a 250 kW SOFC. In the future, MHI plans to scale up its technology in a modular fashion, producing systems for prime power applications – the biggest of these power plant concepts is a planned 800 MW.

On the other side of the power grid, we are witnessing growing interest in large electrolysers as tools to stabilise the ever-growing contribution of variable renewables, to provide energy storage services and also to generate fuel in support of the future hydrogen economy. The largest onshore wind farm (Alta Wind Energy Center in California) has a capacity of 1,000 MW, and offshore installations (such as Greater Gabbard in the UK) can reach 500 MW. Sizing an electrolyser to provide energy storage can therefore be difficult, because obviously one size will not suit every wind farm. Currently a number of companies are developing megawatt-scale PEM and alkaline electrolysers and the belief is this will facilitate the first steps toward proving electrolyser technology in this relatively new application. Again, as in the case with fuel cells, modularity is most likely to be the solution. Currently the world’s largest single stack PEM electrolyser is Hydrogenics’ 1 MW system it recently announced will be installed at an E.ON power-to-gas facility in Hamburg, Germany. Obviously in the future much larger systems will be made, but they are likely to contain multiple stacks, or be connected to form a multi-megawatt system.

Even accounting for the low capacity factors of wind farms (less than 40%), the electrolyser capacity needed for energy storage in these large renewable facilities is up around the hundreds of megawatt level. Modularisation is nothing new to the electrolyser industry however, with the largest installations, such as the alkaline electrolysis plant at Sable Chemicals in Zimbabwe, reaching well over 100 MW by employing large numbers of individual units connected to provide the necessary scale. While the demands of the power grid in terms of cost and rapid response times are dictating changes and improvements in electrolyser technology, it is likely that modularity will be employed – as it will be for fuel cells – to address the challenges of meeting the required capacities.

That is not to say individual fuel cells and electrolysers will not get larger, but economies of scale are required in order to meet cost targets for these systems and the versatility provided by modularisation makes these volumes easier to achieve. Cost savings can be achieved by increasing the size of the units themselves, but at the moment, systems around 1 MW in size are large enough and manufacturers must wait until the opportunity for larger systems becomes clearer. For fuel cells, incentives such as the Korean RPS are providing a degree of clarity as to the requirements over the coming decade, and system sizes will most likely increase in stages to suit. For electrolysers the future will most likely be defined in countries like Germany where power-to-gas projects are being deployed, storing energy as hydrogen to connect wind power plants to the natural gas grid.

Size does matter, but cost is king, so taking advantage of the inherent modularity of both fuel cells and electrolysers allows them to compete on cost and grow in line with future developments.

Dan Carter     Manager




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