Preface

A preface has the function of introducing scope, intention and method of a literary or other work. The broad scope in this book is to review in depth the prospects and opportunity for applying small- and micro-chp systems as energy providers for domestic residences and smaller institutional, commercial and industrial buildings. But you might ask ‘surely we are already well provided for in this area of services?’ We have modern gas fired hot water boilers which can be up to 90% efficient and we have a readily available mains electricity supply which we can conveniently ‘tap’ as needed, even though conversion efficiency is low.

However, we are in a time of change where ‘energy resources’ have suddenly become an important and challenging issue and the scenario needs a re-think. In the twentieth century we were provided with a stable national electricity system by the government-owned CEGB (Central Electricity Generating Board) for England and Wales and equivalents in Scotland and Northern Ireland. These systems had slowly grown from many small local generators mid century, to regional and then a national grid network. Supply was based mainly on large, typically 500 MW size per unit, coal fired electricity generators backed by ample cheap coal resources. In parallel we had moved from local ‘coal gas’ producers (with gasometers for gas storage) to a national supply pipeline fed from the extensive gas wells in the North Sea. Then both gas and electricity were privatised by the Thatcher Government in the cause of ‘competitiveness’ towards the end of the century and the ‘dash for gas’ for new cheaper generation changed the supply balance. Nearly every home is now linked to the electricity network and over 80% to the gas grid.

The twenty-first century has brought concerns about long-term sustainability of fossil fuels as our initially vast North Sea reserves are depleting and by 2020 this source may provide as little as 10% of our needs, which means reliance on long cross border pipelines and shipped LNG (Liquefied natural gas). These routes also have cost rise implications. Secondly, the major issue of ‘climate change’ has resulted in national energy policies which seek a broad and ongoing reduction in fossil fuel usage. The IPCC (International Panel of Climate Change) who operate under UN auspices, have promoted reduction of carbon discharges to atmosphere for all nations who are partners, of which there are over 190 countries. In the UK the government has responded by planning to generate a total of 15% of our energy needs through renewable sources by 2020. This is a huge challenge!

To build up adequate capacity of such renewable energy plant will take time, and so will the building of possible new nuclear plant. But fossil energy reduction and carbon discharge reductions can also come from measures such as ‘energy saving’ and ‘using energy more efficiently’. Of course, the obvious energy savers, such as insulating buildings, low energy electrical appliances and light bulbs, are already being implemented. But using energy more efficiently nearly always means more complicated systems and results in increased equipment cost which is not always readily accommodated.

However, applying CHP (combined heat and power) plant is one key example of how to increase efficiency. What happens is that electricity is produced from a conventional turbine/engine but then the waste heat is also collected for use in a process or for space heating. Overall efficiency typically rises from, say, 33% to 60-90% at peak. The problem is to find a heat demand local to the plant and cost goes up with this added equipment. But what was more expensive and more complicated and unacceptable in the days of cheap and readily available fuel may now be justified. Extra plant cost and complexity can be offset by better fuel economics and availability. As a matter of interest 2008 statistics show that the UK had installed 5569 MWe of CHP capacity of all sizes (which apart from heat duty) actually provided 7% of UK electricity supply. While units below 1 MWe only provided 218 MWe of this total, this represented only 1192 plants. There is, therefore, a huge scope for growth in this size range.

While many of the existing CHP plants in this country are of multi MW size and are mainly large process/industrial plant related, the opportunity for CHP is now also being further considered and applied in the small and micro size range which is the subject of this book. There is no strict size definition, but typically ‘micro’ size could be 2-10 kW and be aimed mainly at domestic type applications, whereas ‘small’ CHP plants cover a wider range of applications from say 50 kW up to a few MW and are directed at larger establishments such as multi-dwelling blocks, hotels, hospitals, educational and community centres, commercial buildings, etc., and may even be suitable for small industrial sites.

It is an application area where previously it would have been easier to pipe in gas and electricity, but where now it is definitely of interest to consider small- or micro-CHP, which would increase overall efficiency of fuel usage, avoid the 4-7% grid line losses and provide a measure of self sufficiency. The technology can also be used with biomass type fuels saving conventional gas and heating oil.

There are government plans towards eventually building up locally controlled supply systems, often called DES (distributed energy systems), which really means local industry and communities building up their own supply network, which can still be supplemented by the grid when needed. Small- and micro-CHP would fit well in this scenario with other local energy sources.

It should be pointed out that small- and micro-CHP is on the agenda in many parts of the world. At the ‘micro scale’ Japan and now Germany and the USA, in particular, have already marketed conventional engine technology, using neatly contained and ‘outside located’ packages for domestic use. There are many tens of thousands of installations. UK has focussed more on developing Stirling or heat pump technology for domestic ‘in house’ application, with imminent commercial breakthrough. The Netherlands, Austria and Denmark are also contenders. The latter country is particularly relevant in applications for district heating for communities. All these and many other countries are also using ‘small scale’ CHP for all sorts of industrial, commercial, community and residential applications with mostly conventional engine technology, but with growth of micro turbines in North America. Involvement on such an international scale will ensure steady growth of this technology area.

So the case for considering small- and micro-CHP in new build and even sometimes for replacement situations has been established. But there is the need for careful review and assessment of each potential application in terms of the mix and, pattern and optimisation of electricity and heat demand with time of day and year. Existing large scale CHP often has a big heat load as the main process demand and small electricity output for sale; the ratio can be as high as 6 to 1. New fuel cell designs can, however, offer a 1 to 1 ratio. Each installation can be different and has to be assessed so that the right type of equipment is installed for the duty.

The aim of this book is to provide, from a wide range of experts, the widest coverage and description that we can of the different CHP technologies available and their typical applications. In addition, the aim is to produce enough background information for a serious assessment of performance capability, so that equipment installers can identify the most likely route for their particular duty. We have also tried to clarify the ‘state of art’ of each technology area. Some processes are still in the final stages of development even though major energy suppliers have imminent plans for marketing. Others are already in the market and being applied.

The method of presentation of the book is to group the chapters into three parts. Part I includes an initial overview, followed by chapters on technicoeconomic appraisal, performance analysis and computational modelling, performance integration and possible integration into DES, and use of biomass fuels in CHP systems.

Part II goes into more detail on each of the various technologies and fuels. There are seven chapters covering such areas as internal combustion reciprocating engines, microturbine systems, Stirling cycle engine systems, Organic Rankine Cycle systems, fuel cell systems, heat-activated cooling technologies, and energy storage methods for small and micro scale systems.

Then in Part III we turn attention to areas of application with chapters on micro-CHP for residential and small commercial buildings, small CHP for community-based district heating applications, small CHP systems for commercial buildings and institutions, small systems for the food industry, biomass-based CHP systems, and thermal engine-based CHP systems for domestic applications.

It is not necessarily a book to read from cover to cover, but rather the purpose is to provide a range of information, some or more of which will be directly relevant to each reader's application, and which will then provide a positive starting point for deciding whether and how to go ahead with small- or micro-CHP. It also provides a broad background to the technology for those wishing to update their knowledge on this subject which is one of growing importance.