Small is powerful

The growing trend towards deregulation of the world’s power marks a shift from centrally generated electricity towards local distribution.

The electricity crisis that caused shortages and soaring prices in California 18 months ago is threatening to return, leading to fresh fears of blackouts and power chaos.

Falling electricity prices and financial difficulties have led power companies to postpone or cancel more than half the new plants planned during the 2000-2001 ‘crisis’, prompting warnings of fresh chaos by 2005. The disruption of California’s power supplies, which cost businesses millions of dollars, has intensified the debate over the future of electricity distribution.

In the UK, where the national grid is well established and generally reliable, the deregulation of power markets is being accompanied by a move from centrally generated electricity towards local, or distributed generation.

This trend, also being seen across other parts of the world, is expected to reduce costs to consumers, as it is cheaper to pipe gas to local sites than to take electricity out to pylons, as well as improving power quality and making energy supply more secure, particularly in developing countries.

Generating power locally also increases efficiency, because a great deal of electricity is turned into heat during transmission via the grid, and could mean the end of massive pylons and ugly overhead lines. Not only are transmission losses reduced, though: with power generated so close to individual homes, or even within buildings such as hospitals, it is possible to go a stage further and use the excess heat produced in the process to provide heating, again increasing the overall efficiency of the plant.

As a result of these efficiency improvements, combined heat and power (CHP) stations produce much less carbon dioxide for a given amount of power than other methods of generating electricity.

The UK government wants to see 10,000MW of electricity produced by CHP plant by 2010, putting the country one third of the way towards meeting its international commitments to reducing carbon dioxide emissions.

Many existing CHP stations are run on gas-powered engines drivingelectrical generators, while some companies are developing mini gas turbines, capable of converting gas into electricity and small enough for use in local plants.

But it is fuel cells that are seen as the most attractive proposition for use in these local power stations in the future, as they are simpler, cleaner and much more efficient than other technologies. To introduce them across the country on a wide scale, however, many issues, both technical and economic, remain to be tackled.

Fuel cells convert chemical energy directly into electricity, accounting for their increased efficiency, and they can be made small enough to fit into individual homes and small buildings. They produce low levels of noise, and do not need smokestacks or cooling towers, making them unobtrusive and suitable for city centres and sensitive rural areas.

Fuel cells will play a significant role in decentralised power, but it will be some time before they are commercially available, says John Young, Hopkinson and ICI professor of thermodynamics at Cambridge University.

There are still technical issues to be resolved if they are to be used to provide electricity and heat for hospitals or local housing estates, not least that of producing devices capable of generating sufficient power. Individual cells are very small (a few square centimetres) and a large number will have to be fitted into a device if it is to produce up to 1MW of power, says Young.

‘Everyone seems to think that a 1MW device would sell quite well, but that will take longer to develop than smaller systems.’ Smaller units should be available in around five years, but 1MW systems are unlikely to be on the market until 2010, he says.

There are various types of fuel cell, but the front-runner for power generation is solid oxide, which is more efficient in stationary applications than the Proton Exchange Membrane cell being developed for cars. In SOFCs solid electrolytes are used in the place of liquids, as they are more stable and do not need special containers.

SOFCs operate at high temperatures, typically around 900 degrees C, although some within the industry are looking to develop systems that operate at around 500 degrees C, making them cheaper to manufacture. Working at these high temperatures means SOFCs can split natural gas into hydrogen without the need for a reformer, and the devices also produce usable heat as well as electricity.

Companies such as US-based Siemens Westinghouse and Mitsubishi of Japan are developing SOFCs, while in the UK Rolls-Royce is working on an SOFC-gas turbine hybrid. The gas turbine’s combustor is replaced by a SOFC stack, and the hot exhaust produced is then passed through the turbine. As both the fuel cell and turbine produce electricity, the overall efficiency is extremely high, reaching over 70%.

Rolls-Royce believes it has a world-beating technology, and plans to have a commercial demonstrator, with an output of 250kW, available by 2005. The device will be transportable, and four units can be connected to generate 1MW of power, says Charles Coltman, corporate adviser to Rolls-Royce on fuel cells.

But the device’s main selling point is likely to be its lower cost, he claims. The company screen prints the cells on to a flat ceramic substrate, which is a much cheaper process than the electron-vapour deposition required for the tubular cell design being developed elsewhere. ‘We can apply the chemistry in a cost-effective manner. Clean technology that denies people access to affordable power will not survive: we have to find an economical solution, and our approach has been based on that theory.’

Like most devices the Rolls-Royce hybrid system converts natural gas into hydrogen, while fuel cells can also run on propane, butane, bio-gas and methane or methanol. Using these fuels means carbon dioxide is produced as a by-product, although the high efficiency levels mean less of the harmful greenhouse gas is emitted than from existing diesel engine generators. In the future experts believe the CO2 could be captured when the natural gas is converted into hydrogen, and disposed of elsewhere.

Of course, fuel cells ideally run on pure hydrogen, which many experts consider to be the fuel of the future, as it does not produce any CO2. But although fuel cells run on the gas would be emission-free, the cost of changing the infrastructure of the country over to a hydrogen-based economy could be extremely high, while the gas is still only as ‘clean’ as the method used to produce it in the first place.

The solution could be to use hydrogen produced from a renewable energy source, such as wind farms or tidal power generators. One such tidal power system, being developed by Imperial College spin-off RVCO, is already undergoing trials off the UK coast. The system, capable of generating electricity at a low cost, uses some of this electricity to extract hydrogen from the salt water by electrolysis.

Whatever fuel is used investment in distributed power is at first likely to focus on installing relatively large generators in small local power plants, providing heating and electricity to sports centres, hotels, and estates of up to 300 houses.

But ultimately it will be feasible for much smaller devices to be installed in individual homes. Units generating around 1kW could be installed in each house, and could be used not only to provide electricity and heat to the home, but also to generate additional power that could then be sold back to the distribution company.

This would require replacing an existing boiler’s cast-iron fuel burner, a £10 component, with a fuel cell costing up to £300, and while the cost could deter some home-owners, the savings in electricity bills alone would make the investment worthwhile, says Kevin Kendall, professor of chemical engineering at Birmingham University. ‘We estimate the payback timescale is between two and four years.

People could save around £150 a year in electricity bills at current rates.’Fuel cells would again be the most suitable technology for these devices, as they have no moving parts, while in comparison the maintenance costs of a combustion engine are far too high to make them economical on such a small scale, says Kendall. ‘We believe that a solid state technology like a fuel cell offers significant benefits over engines with moving parts. And they have double the efficiency of a micro turbine.’

Existing demonstrator devices are far too heavy to be suitable for use in homes, weighing up to half a tonne each, so engineers still have work to do to design a more acceptable unit, weighing just a few kilograms. Decisions on what fuel to use in the units, whether it is natural gas, methane or even hydrogen, must also be made before a truly distributed power system can be introduced in the UK.

But aside from the technical issues, it is likely to be between 10 and 20 years before a widespread network of fuel cells within homes is established, as the government has yet to introduce incentives for their uptake, says Kendall. ‘It really depends on regulation. If there was the same sort of incentive for fuel cells as there is for photovoltaics, subsidies of around 50%, I’m sure people would put them in straight away. It is not really an engineering issue, but it does depend on the wider understanding of the possible engineering benefits.’

And therein lies the rub. The UK has yet to grasp the benefits that combined heat and power generation, whether through small local plants or within individual homes, can offer.

In the Netherlands, around 30 per cent of power is produced by CHP from gas engines, while in the UK it is just 1%.

Kendall despairs: ‘People in the UK don’t think it’s important, even though the technology is great, and the benefits are obvious. We are lagging way behind Scandinavia and Holland in conventional technology, never mind the new technology.’