Gero Di Piazza

As power companies research and develop unique and efficient ways of combining fuel cell technology with microtubines, PEi looks into the potential successes and the ability of such technologies to survive in a weakened market.

Earlier this year, the US Department of Energy, together with Siemens Westinghouse Corp., Southern California Edison and Ingersoll Rand teamed up to design the first hybrid fuel cell gas microturbine. The mini power plant, the size of a small caravan, passed its testing hours at the National Fuel Cell Research Center at the University of California-Irvine, USA, where it operated for 3000 hours between March and June this year.

The two technologies combine to supply 210 kW (190 kW fuel cell and 20 kW microturbine), which is enough to power around 200 homes. But it is the efficiency levels that is the real breakthrough for the technology, as tests have shown a 53 per cent efficiency rate – a world record using this combination. The target, as technological improvements surface, is 70 per cent and above. This not only lessens the risk of environmental pollution, but increases the profitability of the generator.

Emissions

Since the $16 million plant with a combined $170 million total project cost, named the Irvine system, operates on an electrochemical process, as opposed to combustion, it emits 50 times less nitrogen oxide (NOx) pollutants than a gas turbine. Natural gas carries small traces of sulphur when it reaches the fuel cell, which limits the sulphur dioxide (SO2) pollutants that are released into the air. As for nitrogen oxide emissions, this too is limited to be in the range of 0.5 parts per million. This aids its cause to be implemented almost anywhere, even in urban areas.

The project is still under experimentation with numerous tests being carried out. The final version of the plant is expected to launch in 2005/6 with a capacity of 500 kW. Because of its uniqueness, there is nothing it can be compared with. This leads to tests being carried out until the plant reaches breaking point or cannot function any longer. Therefore, the method of ‘break it, find a solution and fix it’ is vital for progression. A spokesman for Siemens Westinghouse in Pittsburgh, US, says: “Around five or six start/stops were performed from its initial operation until earlier this year. The tests were really just duration tests for the combustors, duct heaters and various operating parameters. This is the first time a fuel cell gas turbine hybrid has been tested so we’re still learning a lot.”


Figure 1. The hybrid generator, for the time being, remains a prototype
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The latest batch of experiments are trying to probe ways of improving turndown capabilities, as well as look at other gas turbine models like single/multiple shaft, air bearings and oil-based bearings. “We have to run a power system [all year], so we want a long term operating data and you just don’t get that running a few thousand hours here and there,” said the spokesman.

The fuel cell is made up of 1152 individual tubular ceramic cells which give it the power to generate 190 kW of electricity. The unit is the first to operate cells under high pressures and use the hot, pressurized exhaust gases to drive a microturbine generator which will generate an additional 20 kW of electricity at full power.

The mechanics

The fuel cell used to power this hybrid concept uses solid oxide fuel cell technology (SOFC). This uses a hard ceramic style electrolyte instead of a liquid and operates at temperatures of up to 1000°C. A mixture of zirconium oxide and calcium oxide form a crystal lattice, though other oxide combinations have also been used as electrolytes. The solid electrolyte is coated on both sides with specialized porous electrode materials. A SOFC is an electrochemical device that converts the chemical energy of a fuel (natural gas, coal-derived synthesis gas, reformed gasoline or diesel) into electrical energy without combustion.

The reason behind the inclusion of a microturbine is because a fuel cell does not use all its fuel potential. Much of the energy in the system is lost. The microturbine is able to capture some of this by using the hot exhaust gases from the fuel cell to drive a generator and thus increasing the overall efficiency of the system.

One group that is promoting the SOFC cause is the Solid State Energy Conversion Alliance (SECA), which was set up by the US Department of Energy (DOE). The year-old company has a goal to develop a SOFC between 3-10 kW and can be mass produced in modular form. SECA’s main objective is to ‘dramatically lower the cost of fuel cells’. The body tries to find new ways of doing this by introducing a research and development programme, which takes up 40 per cent of its budget. The development is, however, held up partly due to government coffers tightening their purse strings. “We report to the Whitehouse, which has priority in funding levels and they do that very wisely. On the other hand, the total amount of money put into fuel cell development to date still doesn’t compare to developing the Apollo spacecraft,” says Wayne Surdoval, programme manager for the US DOE.

On the plus side, Surdoval believes that fuel cell development does not have too many obstacles in its way compared to other renewable energy sources. “I don’t want to knock anybody’s technologies, but take solar cells for example. It is very noble and definitely the right thing to do, but I’m not entirely sure that they’re on a clear path. I think we have a fairly clear path and I don’t think there’s anything undoable, it’s just going to take time and resources,” claims Surdoval.

Drawbacks

If there were not any drawbacks in fuel cells or a hybrid implementation as a means of supplying electricity, then it would be safe to say a lot of power companies would show more than a sniffing interest in their potential. But the main factor that is generating a ten-year ‘wait and see’ approach boils down to economics. Power companies around the globe have been scared off by the cost of such a hugely untested means of producing electricity. The price of a fuel cell hybrid combination is quoted at more than ten times the cost of current uses of energy.


Figure 2. The 220 kW hybrid system consists of a SOFC generator and a downstream microturbine
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It can amount to $4000-5000 per kWh compared with $400 for microturbines. Another sting in the tail, that could deter power companies from being potential investors is that despite space missions, fuel cells are relatively unproven for energy. The largest running fuel cells for power generation or cogen have at most 20 000 hours of operation, which is a considerable amount off the intended 40 000 hours projected lifetime.

Surdoval says: “It’s a resource issue against commercialization. With the resources and their [DOE] desire to commercialize it as soon as possible, you sometimes shortchange things like in-lab testing. Therefore, they’re going to rush out and do more of a public demonstration,” he notes: “It’s unfortunate that every time something [wrong] happens it’s widely public, that’s why SECA wants to do smaller units. There are fundamentals involved when dealing with failure analysis too. Ceramics are like metals, so you always have a probability of failure and you have to have enough of them to gain experience.”

Adoption

The future, as promising as it sounds, for fuel cell and hybrid markets does not look too rosey in terms of mass demand. This belief is widespread amongst some fuel cell industry insiders themselves that believe mass adoption could take some time. Rodrigo Prudencio, principle of Nth Power, a venture capital firm dedicated to the global energy industry, says: “It will take a decade for mass adoption of these applications. Key requirements for mass adoption are lower cost, customer education and comfort with a new technology, and ubiquitous sales and service channels. It will not take a decade for early adopters to buy and use combined fuel cell and microturbine technology, but there is a difference between early adoption and mass adoption.”

Commenting on which industries are most likely to take to the fuel cell technology, Prudencio adds: “I don’t know if it will be the power companies, or the real estate managers, or some other service provider that will capture the customers. It may be too early to guess, but power companies in the US have not been so successful in selling more than power.” But two respectable power companies may already be proving Prudencio wrong as the Siemens Westinghouse spokesman revealed that contracts are due to follow within the year. He said Germany’s RWE and Italy’s Edison will each acquire from Siemens a 340 kW hybrid system this year and the following year for testing.

Unsure of the system’s future, Rodrigo notes: “Energy service companies and energy system providers have had more success, but perhaps better models will emerge and power companies will be good channels to the customer. We’ll have to see how this develops.”