Cut-price power

Rolls-Royce claims its new low-price fuel cell technology will cost less than half that of
existing systems.

Rolls-Royce claims its new low-price fuel cell technology will cost less than half that ofexisting systems.

The company is testing its hybrid solid oxide fuel cell system, designed to serve the localised distributed power generation market.

Chief executive of Rolls-Royce Fuel Cell Systems, Colin Berns, said that whereas current systems offered by competitors such as Siemens Westinghouse could cost from $5,000 (£3,200) per kW, his company’s second-generation version would cost around $2,000 (£1,275).

The design would run on natural gas rather than pure hydrogen, said Berns, since theinfrastructure and supply is already available.

It is known as a hybrid since it would run in conjunction with turbomachinery driven by excess heat from the cell’s reaction. Hot air would enter the combustion stage of a gas turbine ‘wrapped around’ the fuel cell. It would mix with pressurised air from the compressor stage and spin the turbines to produce more electricity. The pressurised air would then continue back into the fuel cell itself.

Part of the secret of the system’s cost effectiveness is the use of commercially available ceramics similar to bathroom materials. Berns said strips of ceramics could be mass manufactured with ‘basic extrusion processes’ and then 40 anodes and cathodes could be cheaply screen printed on to each one. The natural gas fuel would flow through air holes running through the strips, aided by pressures of 5-10 atmospheres in working versions.

The strips capable of producing 40-50W each would be ‘bundled’ together into units. More specific details on the bundle design will become available early next year, but 500W configurations are already being tested.

One of the problems associated with fuel cells is management of excess heat from the reaction. This can mean that the cells are put under stress by expansion and contraction as materials warm and cool. The advantage of using ceramics throughout the system is that all the material in the cell stack is free to expand and contract at the same rate, said Berns, taking strain away from the cells themselves. The bundle configuration was designed to further alleviate expansion and contraction stresses.

Efficiency of the whole hybrid system, which would include heat exchangers to manage temperatures and power conditioners to produce usable AC electricity, could be up to 70 per cent, compared to a gas turbine or proton exchange membrane fuel cell’s 30 per cent.

Rather than trying to keep down temperatures arising from chemical reactions in the cell, Rolls-Royce is exploiting modelling and materials expertise from its traditional gas turbine products to deal with the heat itself and avoid using expensive ‘exotic’ materials. Furthermore, technology borrowed from aerospace also saves cost, weight and bulk with the pressure vessels required to contain working systems, said Berns.

Tests of a 20kW cell are planned for next year, while trials on a 10kW pressurised system would be in 2004. ‘Once this is proven,’ said Berns, ‘all you have to do is stick them together.’

The first 1mW system should be tested in 2006 and will serve as a reference plant for a production version. Berns said the whole system should be portable enough to fit on a lorry (currently only 200kW fuel cell stacks are small enough). The company would aim at the local industrial market, which does not suffer from the domestic market’s peaks and troughs in demand.

Development programmes were underway, said Berns, in order to shrink the ceramic strips (currently around the size of two chequebooks end-to-end) by a factor of five. He claimed that further work could bring costs down to $1,000 (£640) per kW.

Sidebar: What other technology companies are offering

Other companies in Europe are exploring the fuel cell’s potential for distributed power generation. In Germany, DaimlerChrysler-owned MTU is co-operating with US firm Fuel Cell Energy on the 250kW HotModule system. Several systems are already in place, for example at Magdeburg University Clinic, and are in their field testing phase.

Unlike the Rolls-Royce system, the HotModule’s excess heat (170kW) can be fed into a building’s heating system or used to heat water and produce steam for industrial processes. MTU claims that its overall energy efficiency is 90 per cent. It is ultimately aiming for $1,100-$1,500 per kW (£730-£1000). Series production could begin in 2006.

The leader is US-German company Siemens Westinghouse. It installed the world’s first fuel cell-gas turbine hybrid power plant at the National Fuel Cell Research Centre at the University of California-Irvine in 2000.

Similar to the Rolls-Royce hybrid design, the mobile home-size prototype produces 190kW, enough to power approximately 200 homes.

However, unlike Rolls-Royce’s solid oxide fuel cells, Siemens Westinghouse’s are tubular. Each is made up of an electrolyte and two electrode layers, which eliminates the need for seals required by other types of fuel cells, and also allows for thermal expansion. Air flows through the interior of the cell, and fuel flows on the outside of the cell.

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