Ultimate CHP power source
Fuel cells could revolutionise the way we power our world, offering a cleaner, more efficient alternative to the combustion of gasoline and other fossil fuels, says John Lidderdale
A fuel cell works in the same way as an electrolyser except backwards. Feed it with hydrogen and oxygen (air), force it through a suitable membrane and a chemical fusion results that produces water. The electrochemical process that achieves this generates electrons and heat so that the output is electricity and hot water.
Because a fuel cell converts an input fuel directly into heat and electricity without having to turn the input fuel into thermal energy and use that to drive machinery, it is far more efficient than any generator that produces power mechanically.
A typical fuel cell will have an electrical efficiency in the mid 40 per cent and upwards. Overall efficiency will depend on how clever we are at using the heat as with any CHP or CCHP scheme. There are applications where we have achieved overall efficiencies above 85 per cent.
Different fuel cell technologies have different characteristics in use that influence the choice of technology by application. Some follow electrical load immaculately with a turn down that can be 100 per cent without affecting the plant in any way. Others are base load units only, essentially 'fit and forget' plants that will not live follow electrical load.
In crude terms fuel cells fall into two thermal categories - low temperature and high temperature. Low temperature technologies have thermal outputs ranging between 63 and 140 deg C. High temperature technologies have thermal outputs that range between 350 and 1,000 deg C.
There is great scope here to find a power plant that best suits the application requirement, but also great skill and experience required to optimise he
outcome. There is an additional advantage a fuel cell confers on a system designer that is not available to anyone designing a reciprocating engine based system and has tremendous implications for overall efficiency. With a fuel cell you are free to extract as much of the heat as you can profitably use.
Regardless of the technology, a fuel cell is fundamentally a generating device and thus follows electrical load far more readily than it will heat load.
Because of the additional efficiency inherent in these technologies, a fuel cell powered installation reduces the carbon emissions of an installation, even when run on fossil fuels, and virtually eliminates products of combustion emissions such as NOX, SOX and particulates, as the process is electrochemical and not combustive. We routinely reduce the carbon emissions by better than 40 per cent compared to conventional grid-based systems.
Fuel cells do cost more than other, more conventional, CHP plant. However, whole life costs will always be lower, maintenance will always be cheaper, and availability (usually > 95 per cent) will always be higher.
Where our customer is a modern enlightened organisation focused on whole life costs and not still tied to the inefficient notion of simple payback, we have little difficulty achieving acceptanceof these technologies. In some cases the carbon reduction has been the swing factor in the decision making process. We have installations where the fuel cell enabled the granting of planning permission and was the only practical way in which the customer could achieve the carbon reduction requirement necessary to obtain planning consent. In other parts of the world the picture is very different, most particularly in Korea, Japan and the US, where the governments see fuel cells as an essential element of their future energy strategies and have invested heavily in these technologies over many years. Unlike most renewables, a fuel cell produces power so long as it has fuel and the fuels it requires, hydrogen, or a hydrogen rich fuel, and oxygen are two of the commonest elements on the planet and both are themselves renewable.
A few years ago fuel cell manufacturers had factory gate costs that were in the region of $15,000 per installed kilowatt. The present generation of units are less than $3,000 per installed kilowatt.
The viability of fuel cells is also affected by the spark gap and by the cost of hydrogen. Most fuel cells presently obtain their fuel by reforming a hydrocarbon, most commonly natural gas or LPG. How quickly they become cost effective in all conditions in a straight commercial fight depends to some extent on what happens to the spark gap in future and to what extent custom and practise (or legislation) drives the adoption of C(C) HP, district heating/cooling.
Most pundits appear to agree that the spark gap will widen over time. Presently, it is clear that the cost of oil is not going to fall below $75 within the next five or so years. Indeed, if it follows the 10 to 15 year cycles that it has followed for the last 100 then we are looking at high rates for five or six more years. Whatever your view, there is no question that the electrical distribution industry has to spend an enormous amount of money in the short to medium term to replace obsolete generating plant and to make the network able to handle the renewable obligation, which is distributed generation trying to feed a unidirectional grid. All of these pressures will conspire to force the spark gap wider and thus assist to make the case for all forms of distributed generation including fuel cells.
Logan Energy operates a number of fuel cell installations as part of hospital CHP schemes. Hospitals are ideal candidates for CHP and fuel cells are extremely efficient in this mode. Hotels also often make very good fuel cell installations especially where they have fitness facilities such as swimming pools. The daytime requirement to heat the pool often mirroring the night time heat requirement and making the use of the fuel cell very efficient.
Mixed use commercial/retail/residential facilities often produce excellent balanced loads that ideally suit the output profiles of FCCHP schemes. We are installing just such a system in central London based on the site base load, which will be over 85 per cent efficient.
I have tried to show some cases where the fuel cell competes particularly well but there are many others where for some reason or other the fuel cell makes an impact that is not always directly cost related. Logan Energy operates systems running golf clubs, telecommunication switch centres, fire stations, mobile telephone cell masts, air traffic control centres, and refinery control rooms. The list goes on.
// The author is managing director of Logan Energy //
1 February 2012