11-09-14 Hydrogen in Centralised Power Generation

Hydrogen in Centralised Power Generation

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14 Sep 2011PDF (581 kb)

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11-09-14 Hydrogen in Centralised Power Generation

Power grids operate at two broad levels: transmission and distribution. Transmission networks carry centrally-generated power to areas of demand, where grid supply points distribute it locally through distribution networks. On the distribution level localised microgeneration is becoming a popular avenue for stationary fuel cells. The EneFarm project in Japan has led the way, and the technology is gaining pace in other regions; Ceramic Fuel Cells recently announced that its BlueGen domestic fuel cell is the first to be accredited for use in the UK Feed-in Tariff scheme. A lot of excitement surrounds the potential for distributed generation and the rise of smart grids, but what of the ageing backbone, the transmission networks of the world’s grids?

For the foreseeable future widespread energy supply will still rely on the use of a centralised transmission network. The use of fuel cells here is a possibility, as demonstrated by South Korean MCFC supplier POSCO Power, who is in the process of building a 60 MW fuel cell power plant in Hwaseong to help meet the stringent demands of the country’s Renewable Portfolio Strategy (RPS). Such large-scale fuel cell deployments come at great cost over other centralised renewable energy generators, and will continue to do so for some time. However, there are avenues of great potential for hydrogen within centralised generation.

A national grid must always be able to meet the needs of its users. This requires it to be: stable, maintaining a required electrical frequency (50 Hz in the UK); balanced, continuously matching supply to demand, often through CO2-intensive spinning reserve plants; and adequate, ensuring total generation capacity is never outstripped by demand.

National electrical supply can be split into three tiers: base, intermediate, and peak load. Base load is a permanent minimum amount of electricity that is required at all times and is met by cheap predictable long-running power sources, primarily coal-fired plants. Intermediate power plants are more flexible and can scale output to suit the needs of the grid, but at a cost to the system operator. These can include nuclear, hydroelectric and gas/diesel combined cycle turbine plants. Finally, peak power generators are called upon to meet short term spikes of requirement and as such must be able to output instantaneously.

Governments are increasingly pushing for the inclusion of renewables in the energy mix in the interests of carbon abatement and increased energy security. The South Korean RPS calls for 2% of total energy generation to be renewable in 2012, and 10% by 2022. However, many renewables suffer from problems of variable load. Wind and solar PV are susceptible to sudden troughs and peaks in output at the whim of atmospheric conditions. Troughs in output may seem most worrisome, however peaks can be just as troublesome. In the past year eight Scottish wind farms have received over £4.3 million in curtailment payments to stop producing electricity in fear of the grid being overloaded. The cost was ultimately passed to consumers and such behaviour can seriously undermine grid stability. Simply increasing renewables would require an increase in inefficient spinning reserves to backup potential shortfalls in energy supply.

Evidently if national energy mixes are to become more dependent on renewables then an effective way of stabilising their variable output must be implemented. Systems are already in place to deal with grid fluctuations in most areas, usually through CO2-intensive pumped hydroelectricity plants. However, increased renewables would demand the construction of more of these plants, raising issues of climatic, local environmental and financial costs.

Hydrogen is a versatile energy carrier, no different in principle than electricity – a way to store and move energy generated from another source. Hydrogen offers exceptional energy density and long term storage potential, and can rival existing grid storage methods in a way that electrical storage methods such as batteries cannot, but it is its versatility that makes it such an appealing option for grid integration. Hydrogen could be piped directly to refuelling stations or distribution level fuel cells with little electrical loss, or in times of peak demand, converted centrally. The diagram below (Source: FCHEA) highlights just some of the ways hydrogen storage and fuel cells can tie into existing grid architectures.

FCHEA scheme

The solution is by no means perfect; energy is lost every time hydrogen is converted to and from electricity. However, hydrogen and fuel cells can offer a solution to allow national targets for variable renewables to be met in a way which does not require fossil-fuelled backup. Stored hydrogen from zero-emission wind and solar can provide the dual benefit of a cleaner national energy mix, and contributing to the future of decarbonised transport.

Jonathan Wing   Market Analyst



Image: Silhouetted power lines (Source: Flickr - blhphotography)


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