Fuel for thought

In the past, residential communities have built up around privately owned power plants created to serve industrial sites. However the localised generation, transmission and switching of such distribution systems resulted in enormous voltage fluctuations. The subsequent development of an integrated transmission system that allows numerous utility power plants to be paralleled on-line and provide an enormous reservoir of power, in conjunction with surge arresting equipment at the point of utility intake, has resulted in reasonably stable supplies.

But stability of the supply can still be affected. Lightning strikes on overhead transmission lines, high-voltage system faults, switching of grid high-voltage equipment, switching of reactive loads and certain power electronic circuits can all be factors. Such high magnitude transient over-voltages are usually very short in duration (milliseconds) and the amount of energy generated depends on the surge source.

Segregation from the utility supply provides a solution to the problem of externally generated transients but is not usually practical since the main alternative source of power has traditionally been privately owned diesel fuelled standby generators. These protect against the potential loss of power supply and are usually used in conjunction with uninterrupted power supplies (ups), which have the two-fold benefit of providing a clean and conditioned source of power during normal use, and also a battery back-up. The ups systems protect critical equipment by bridging the time delay between loss of main supply and the start up of the standby generator and also by filtering the utility supply.

Maintaining a secure electrical supply is not only economically prudent but also a necessity in buildings occupied by the public. Systems are generally categorised into: essential, life safety and desirable.

The alternative
Fuel cells are probably the most exciting technology in development, and are poised to replace both conventional standby generation and ups systems for ensuring both security and integrity of power supplies within commercial and even residential applications.

Serious development of fuel cell technology, which was first constructed in 1839 by Sir William Grove, only began in the 1960s when technologies in general were being pushed to the limit by the desire to conquer space. Fuel cells proved considerably safer than nuclear power and cheaper than solar power. Their early success in the Apollo missions spawned confidence and they have proved successful enough to be used up to present day in space shuttle missions. Also their potential is beginning to be fully realised as an environmentally friendly alternative power source.

Chemical process
Fuel cells are electrochemical devices that work by converting hydrogen and oxygen into water, a process that produces electricity (figure 1). Hydrogen is fed into an anode catalyst, with oxygen (air) entering the cathode catalyst. The anode catalyst encourages the hydrogen atom to split into its constituent parts. The proton (ion) passes through the electrolyte and the electron takes an external route before recombining with the oxidant to produce water in an extremely efficient chemical process. The electron flow is harnessed in an external circuit and converted to an ac supply before being utilised.

There are various types of fuel cell but all operate on the same basic principle, the main difference being the type of electrolyte used. The electrolyte is the main governing influence on the performance and characteristics of the fuel cells and is either solid ceramic, liquid, or solid polymer.

Fuel
In reality this process of power generation is a zero emission process, apart from water of course, if pure hydrogen is used. However, for commercial usage hydrogen must first be extracted from a hydrocarbon fuel in a process using a fuel reformer. Typical fuels used in this way are natural gas, methanol, ethanol, diesel and gasoline, these fuels are reformed into hydrogen rich gas, not pure hydrogen. The fuel reformer not only enables the use of existing fuels but more importantly negates the need for a brand new fuel storage and transportation infrastructure.

There are several methods of fuel processing, the first being endothermic steam reforming where fuel is combined with steam at extremely high temperatures with membranes used to separate the hydrogen. Another method is the partial oxidation reformer, a process that produces CO₂ and while this is not a desirable by-product it is certainly not as distasteful as the conventional fossil fuel emissions.

Currently, when hydrogen is required in its pure form production is achieved by combining methane (CH₄) with water (H₂O) to produce hydrogen (H₂) and carbon dioxide (CO₂). However, various other production methods have been explored in an effort to achieve a solution that dispenses with the use of fossil fuels altogether; these being:

• Bacteria – hydrogen is produced as a by-product of the metabolic process of a single cell organism, cyanobacteria, which flourishes in either air or water and feeds on solar energy.
  
• Photovoltaic cells and wind generators – the energy produced is used to electrolyse water, thus producing hydrogen.

In both the above methods hydrogen is used as the energy carrier and the end waste product is water allowing the process to continue in a never-ending utopian cycle of energy production.

Suitability of application
Conventional standby generators do what they say; provide standby power, usually during utility power failure, and are not usually used continuously due to noise and the production of undesirable emissions. Fuel cells are extremely quiet in comparison, produce almost negligible levels of emissions, are more efficient, and have no moving parts. For these reasons they can be sited almost anywhere and used continuously and in tandem with the main power supply if the system is designed accordingly. If a separate distribution system is provided to compliment the alternative power source then the inconvenience of externally generated and potential disastrous voltage transients is eliminated, which means connection of electronic equipment can be made directly dispensing with the need for a separate ups system in appropriate circumstances. However, if reactive loads are supplied from the alternative power source then the problem of internally generated transients must be addressed and the appropriate suppression and filtering systems employed.

An alternative to designing separate distribution systems within the building would be to connect the fuel cell in parallel with the utility power supply (figure 2). Another advantage of having a site based fuel cell is that heat is produced during the process, and when harnessed improves the fuel cell efficiency from between 40% and 60 % up to 85%. When utilised as a replacement for a standby generator as well as a heat source, a payback period of as low as three and half years may be achievable. Also, if a permanent natural gas connection is available then the need for expensive and bulky fuel storage tanks is eliminated.

Environmental impact
There has been an enormous focus on the impact mankind has had, and will continue to have on the environment, particularly since the industrial revolution, the discovery of ac power generation and the subsequent explosion in the use of fossil fuels. It is also becoming apparent that governments are taking the problem, or are being coerced into taking the problem seriously, and are investing in renewable power generation technologies accordingly. It could, of course, be argued that we could do more but converting a well established multi-billion pound power generation and distribution network into a 'green machine' has an associated cost and could not be achieved rapidly even if a free and totally green fuel source was discovered.

Populations will continue to expand, as will economies, and since hydrogen is an abundant and renewable energy source and fuel cells make efficient use of existing fuel reserves and also the associated infrastructure, they seem to be obvious solution. Of course, efficiency increases and emissions reduce the purer the hydrogen source, but we have an immediate solution that will become greener as time passes and using fossil fuels in this way reduces significantly levels of NOx, SOx, CO, hydrocarbons and particulates.

The future
Opinion seems divided as to whether the development of fuel cells has progressed far enough for them to be considered a replacement for utility produced power, and with fuel cells costs at approximately $3000/KW (£1933/kW) there is a strong case to back this argument. Using a fuel cell in lieu of a standby generator and/or ups system enables realisation of a payback period in the order of less than five years and for this reason alone we should see an increase in the installed capacity of fuel cells over the next decade. Only when costs fall below $1500/KW (£966/kW) will we really see the fuel cell begin to compete with combustion generation, and this will only become a reality when mass produced units hit the marketplace. Until this happens it is not only the government's responsibility (in the form of tax incentives and grants), but also corporate responsibility to ensure that the initial capital investment is made in this form of alternative/standby power generation.

Even the petroleum industry is admitting that the days of the combustion engine are numbered, and that its successor, a 'green' technology that can actually generate power from processed fossil fuel, must be an answer to their prayers, in the short-term at least.