SHFCA Energy Conversion and Storage 2013

Event Report: SHFCA Energy Conversion and Storage

Date publishedFormat
04 Apr 2013PDF (431 kb)

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SHFCA Wind Turbine


The Scottish Government intends for half of all electricity generated in Scotland to come from renewable sources by 2020. It also intends for Scotland to generate twice as much electricity as it needs and to export half (allowing it to claim that 100% of the electricity it uses is renewable). The rapid increase in approved planning applications for wind farms in Scotland seems to indicate that it is on track to meet these targets, but the integration of a variable, unpredictable energy source like wind into the electricity supply is problematic; many would argue that at 50% penetration it becomes impractical without some form of large-scale energy conversion and long-term storage.

At times of peak output, wind energy cannot be fed directly into the grid if it exceeds demand; this would lead to an unbalanced and unstable grid. Without storage, this excess goes to waste – and may also incur a cost penalty. In the UK in 2011 a total of £15.8 million was spent paying operators of Scottish wind farms to constrain their supply so as to not overload the grid. The total energy lost was 75,000 MWh. On the other side, the unreliability of wind power means it needs to be backed up with dispatchable power, usually fossil-fuel based, and the grid may actually receive much less renewable energy than would be expected on the basis of installed capacity.

The use of water electrolysis, powered by excess wind energy, to generate hydrogen for storage has thus been proposed for serious consideration in Scotland, as it has elsewhere.

On the 8th of March at Strathclyde University in Glasgow, the Scottish Hydrogen and Fuel Cell Partnership (SHFCA) held a members’ meeting to examine the subject of ‘Energy Conversion and Storage’ in this context. The meeting, which featured several excellent speakers and stimulating debate, was held in conjunction with the Energy Technology Partnership and was supported by Scottish Development International. Fuel Cell Today was invited to attend as a guest and this event report will highlight some of the key points of discussion.

Store electricity, use energy

Professor Ian Arbon of the UK’s Institute of Mechanical Engineers (IMechE) began by commenting that ‘energy’ is not equivalent to ‘electricity’ and legislative efforts to introduce renewable energy often have too narrow a focus on electricity. Yet electricity accounts for only about a fifth of final energy consumption, while heat is close to half of the total (see our recent Analyst View on this subject here). Meeting the demand for heat is complicated by the fact that it is seasonal, peaking in winter and falling away in summer. The consumption of energy for transportation also exceeds consumption of electricity and the volumes of fuel needed to meet this demand are vast. Consequently, electricity that has been converted to another form for storage could be used most efficiently to service energy demand elsewhere, rather than being converted back to electricity. But provision for energy storage in the current system is meagre: while the UK consumes around 1,000 GWh of electricity every day, currently available storage capacity covers around 3% of this.

Is hydrogen storage feasible?

As Marc Crowther from GasTec pointed out, the need for storage has been masked by the fact that fossil fuels are already in stored form and to meet intermittent demand suppliers need only close and open the ‘tap’. In moving away from fossil fuel reservoirs, society will have to start carrying energy storage charges. But building renewable or nuclear power plants to only meet peak demand (and thus run intermittently) would price them out of the market; to make the best use of the capital investment these plants should run continuously. Storage allows for separation of energy production and use, thus increasing the efficiency of both and potentially making storage itself cost-effective.

So what are the options? When it comes to storing large quantities of energy over a period of months in a readily available form there are very few choices available. Both Crowther and Nigel Holmes of SHFCA emphasised that, among these, the use of hydrogen is not as speculative as one might think. Hydrogen is already a well-established commodity in global industry (although most of it is captive, i.e. produced at the point of use and therefore not ‘visible’ to the outside world). Currently 95% of this hydrogen is produced from fossil fuels but the proportion of industrial electrolytic hydrogen is at 4% and growing.

Compressed underground hydrogen storage in salt caverns is proven, taking place under Teesside in the UK and in Texas for example. Even bulk distribution of hydrogen in large pipelines over extended distances is common industrial practice around the world.

From an economic point of view, energy storage can be viewed as just another form of energy resource (i.e. a source of kilowatt-hours) and can be compared on that basis. Crowther‘s indicative calculations show that hydrogen storage can be competitive, with the cost per kWh coming in under the cost of grid electricity. But what do you do with the hydrogen once you’ve made it?

Hydrogen for heat, electricity and transportation

Obviously, one option is to use the hydrogen directly – preferably in fuel cells. But, according to Alastair Rennie of AMEC, hydrogen and fuel cell support mechanisms are “impressive by their absence”. This is despite the fact that hydrogen can function as a common energy vector and fuel to link the electricity, heating and transportation sectors. Rennie said that the value of hydrogen should primarily be assessed in terms of its use in fuel cells for efficient generation with storage being ‘added value’ as the means of delivery. For this, demand for hydrogen as a fuel must be stimulated and, to this end, AMEC has worked on a proposed feed-in tariff (FiT) for all sectors on a common baseline. The UK Hydrogen and Fuel Cell Association (UKHFCA) is submitting this proposal to the Government for implementation from early 2014. The proposed mechanism is as follows:

Heat‘RHI [Renewable Heat Incentive] low-carbon hydrogen FiT’

The hydrogen component value is proposed as equivalent to the 2013 rate + the RPI value for biogas injected into the gas grid, which is 7.3 pence per kWH2.

Transport‘HFC fuel supply offset’

The offset reflects the need to bring green hydrogen at a per-mile cost lower than fossil fuels, at the right purity and pressure, and at sufficient locations. The value proposed is £2.8813/kg + VAT, which is net 17.3p/kWe

Electricity‘HFC power FiT’

The fuel cell efficiency is relative to non-fuel-cell technologies below 50 MWe which do not have duty efficiencies above 44%. The power consumer’s marginal cost benefit is 5.1p/kWe; net 17.3p/kWe

Lobbying for political support is needed to get this in place before next year, and the aim is to lock in at least ten years to create predictable conditions for investment.

Distribution to industry

Geoffroy Ville from McPhy Energy told us that the company is working to connect a variety of markets using hydrogen as a common energy vector, and this includes the industrial market. Currently, hydrogen production from natural gas for industrial applications accounts for around 2% of global man-made carbon dioxide emissions. Displacing some of this with renewable hydrogen generated by electrolysis is a worthwhile target and McPhy is working with gas distributors like Air Liquide to make this hydrogen available to their customers. The company is also participating in projects like the French ‘PUSHY’ project that is assessing the use of renewable hydrogen for industrial supply, via McPhy’s proprietary electrolyser and solid hydrogen storage solution. In this model, the renewable energy producer invests in the electrolyser and sells hydrogen to the gas distributor (at, say, €5/kg). The gas distributor invests in hydrogen storage and then sells the hydrogen to an industrial customer in accordance with demand and at a mark-up (~€10/kg).

Although the hydrogen is used as a commodity rather than a fuel the distinction is immaterial in terms of CO2 reduction and could lead to the production of ‘climate-friendly’ fertiliser, for instance.


McPhy is also targeting power-to-gas, a term which refers to the injection of electrolytic hydrogen into the gas distribution grid. If this hydrogen is generated using renewable electricity, then its injection into existing gas distribution displaces fossil fuel and increases renewable energy use.

This is a concept that Filip Smeets from Hydrogenics described as “spreading like wildfire” because decades of predictable supply have meant that grid-scale energy storage was not necessary, but this lack of storage is now leading to an overbuilt and underused electricity system as new energy sources are introduced. Power-to-gas offers a way to improve this situation and to shift the renewable capacity to heating and transportation where it is sorely needed; Smeets stated that it may be the only way to achieve a ‘green’ transportation sector at acceptable cost. He believes that, with appropriate legislative support, widespread adoption can be achieved within three years.

There are limits to how much hydrogen the gas grid can accept. Theoretically, a hydrogen concentration of up to 20% by volume should be manageable, but in practice there are other considerations to take into account and many countries currently restrict hydrogen concentration to much lower levels. This still allows plenty of capacity for energy storage but there is an alternative to using hydrogen in its pure form, as it can be used for production of synthetic hydrocarbon fuels.

Production of hydrocarbon fuels

A relatively easy conversion is the reaction of hydrogen with carbon dioxide to produce methane (and water). This is conventionally done using the Sabatier process at elevated temperatures and pressures over a nickel catalyst:

CO2 + 4H2 → CH4 + 2H2O

Iain Russell presented an alternative way to accomplish the same reaction biologically, employing methane-producing archaea. This process can take place at 1 barg pressure and at low temperatures of between 30°C to 75°C. Full production can be reached from standby in two minutes and the organisms are relatively robust, so that rigorous purification of the CO2 stream is not necessary.

Air Fuel Synthesis has a method for producing petrol, via methanol, using hydrogen, CO2 and electricity. The company’s CEO Peter Harrison said the ultimate intention is to harvest CO2 directly from the air, making it a fully renewable process, but initial implementation will use CO2 captured from point-source emitters like power stations. This is not renewable CO2, but some displacement of carbon emissions from transportation should be possible by ‘reusing’ the carbon atoms.


General consensus at this well-attended SHFCA event was that hydrogen generated by electrolysis as a means to store excess renewable energy can effectively increase usable renewable capacity to cut carbon dioxide emissions in a range of sectors. And this is not a distant prospect, as in many instances it can be implemented today.


Marge Ryan     Market Analyst


Industry Review

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