Congratulations! By holding this book (or e-read equivalent) in your hands, you are very likely showing an interest in the engineering of renewable energy concepts. (And well done, too, on reading a Foreword, most people, including myself, jump straight into the technical chapters but that's another story.)

I want to urge you to keep that interest in renewable energy going. When I studied electrical engineering in the 1980s, anything renewable (wind, solar, and to some degree hydro) was classified by many scholars, industry practitioners and stakeholders as Alternative Energy. ‘Alternative’ to the might of having a standardised high voltage and low voltage grid network that delivered electricity to homes and factories from bulk sources such as coal, oil, gas and nuclear power stations. We had some hydro but this was pretty much exclusively used for peak demand management and frequency control, and virtually no other renewable energy sources existed at scale. That ‘Alternative’ badge pretty much also made anyone who was trying to explore renewable sources be tagged as anything from ‘non-mainstream’ to ‘tree hugging’ to ‘just plain crazy’. It was difficult to be different and to do anything other than the decades old ways of generating and delivering electricity. To be fair, this was for good reason, of course – when the paying of your energy bills formed a significant part of just about everyone's income it was often the cheapest way of generating electricity and delivering it reliably to ‘consumers’. Implementing significant change was deemed difficult and costly. It was easier to move in straight lines.

Now, we are in a very different age. I'm pleased the term ‘consumer’ has almost gone, and has been replaced with the word ‘customer’. The production and sale of electricity is now much more competitive and customer value is replacing monopoly product and service. Regrettably, the world still has millions of people struggling to afford to pay for energy and so the changes we want to make to improve our environment must continue to take affordability into account. Often, this requires innovative ways of doing things, finding new solutions to use existing infrastructure and challenging the age-old engineering and regulatory norms that dominate power systems around the world.

Further, the steady realisation that those who warned about the effects of noxious gases that created acidic rain, and then CO₂ contributing to climate change, were actually right as opposed to crazy, has led to global legislation to do something about it. Renewable energy, particularly wind and solar power, has made great strides. The Alternative Energy world is on a journey to becoming far more mainstream. There will always be some who deny climate change, of course. Nevertheless, what is indisputable is that fossil fuels are finite, and it's better, in my view, to generate power using sustainable resources and to either leave our fossil fuels alone or at least find far more efficient, non-polluting uses for them.

In my undergraduate days, we were taught only to be engineers. We entered the world of work with maths and physics bursting out of our heads – only to find that most places of work required, in addition to one's engineering talents, a head for economics, environmental awareness, customer service and stakeholder management. These are qualities I'd urge all engineers to be aware of if you want to see your work make the best progress.

The rapid development of renewable energy sources that are, by their nature, distributed to take advantage of local energy resources rather than being centrally located for other economic reasons, makes the future creation and delivery of electricity (and other energy products) far more challenging to forward plan but it also makes it much more interesting and exciting for tomorrow's engineers. We no longer move forwards in straight lines of “bigger equals better”. We have to think tangentially, innovatively and with a healthy mixture of focus on detail where it's due but also on wider system and regulatory imperatives. The age old rules of ‘this is how it's done’ need not always apply.

I'm delighted to see the growth of wind power, especially offshore, move forwards so rapidly in recent years, and installed volumes are forecast to grow heavily over the next couple of decades. Wind ‘power stations’ are now at a competing scale with fossil fuel plants, costs are competitive and continue to fall and reliability is ever improving. Yet, there is more to be done to keep those improvements going, using new materials to improve sustainability, improving designs to make turbines lighter, blades more aerodynamic, foundations lighter yet stronger, and cables more sea reliant. Cost-effective deep-sea solutions such as floating wind are now within our grasp. The digital age is creating more prospects for operations and maintenance to be done remotely and with less human intervention. Fewer people working in situ means a safer industry and human power will be used more to control, to innovate and to invent. Tidal, wave and even kite power solutions continue to follow on as potential sources for the future, alongside many concepts in early stages of development such as carbon from air extraction.

We need to think, too, of how our grid systems and its regulations, designed decades ago for very different ways of working, will evolve at the same time, likely with more smart grid technology, greater interconnectivity both onshore and to offshore plants as well as to other countries, with greater storage of likely not one but a few types (batteries, pumped storage, mechanical and maybe compressed air, for example). Wind and other forms of renewables are obvious candidates for providing renewable energy for heating and for transportation, finally providing a first class opportunity to decarbonise those latter sectors which, in fact, are much larger users of energy than that of electricity in our homes.

There are prospects for using renewables to process sea water into hydrogen or ammonia – creating sustainable, transportable, storable fuels. These products could provide sensible solutions to the continued usage of our electricity and gas grid networks, not to mention the highway refuelling of vehicles. When we create new renewable electricity solutions in the future we should do so with heat and transport in mind, all such systems require major innovations to decarbonise.

Finally, one other big change is clearly happening in our world of renewable energy – that of people power. The voice of the customer, especially through social media, is now a far more powerful tool in policy making and in popularising new technological successes (the latest electric cars, for example) – as well as reputation breaking when things go wrong. We must bring change to the ways we generate and use our energy sources, but we must always have customers in mind. They are key drivers to better cost reduction, energy usage efficiency and sustainability.

So, what does all this mean? It means engineering challenge and plenty of innovation opportunity. That's a great thing for new engineers. This book, written by two of the most gifted professors who are as passionate about the world of renewable energy as I have ever had the pleasure of meeting, will provide a solid foundation for you to move forwards. It's up to you as to whether you move forwards in straight engineering lines or in more innovative ways!

There is worldwide agreement on the need to reduce greenhouse gas emissions, and different policies are evolving both internationally and locally to achieve this. On 10 January 2007, the EU Commission announced an Energy Package that was endorsed by the European Council. The objectives are that, by 2020, EU greenhouse gases are to be reduced by 30% if a global agreement is arrived at or by 20% unilaterally. One of the vital components in the achievement of this goal is the intention to provide a 20% share of energy from renewable energy (RE) sources in the overall EU energy mix.

At present, wind power is the leading source of new renewable energy. World wind power capacity has been growing rapidly at an average cumulative rate of 30% over the last 10 years. About 20 GW of new capacity was installed in 2007, bringing the world total in that year to 94 GW. This annual investment represents around €25 billion by an industry that employs 200, 000 people and supplies the electricity needs of 25 million households. This considerable expansion has attracted investment from major manufacturing companies such as General Electric, Siemens, ABB and Shell, as well as numerous electricity utilities, notably, E.ON and Scottish Power. The future of wind power over the next two decades is bright, indeed.

Generation of electricity from the sun can be achieved directly using photovoltaic (PV) cells or through solar concentration to raise steam and drive conventional turbines. Over the last few years, considerable progress has been made in the reduction of the cost of PV generated electricity, with 2006 seeing the total value of installed capacity reaching €15 billion and with cell global production in that year approaching 2.5 GW. It is expected that further technology improvement and production cost reduction over the next decade will result in wide scale competitive generation from this source.

Marine energy is an exciting, but less well-developed technology. Tidal barrages, tidal stream turbines and wave energy devices are all in the experimental and pre-commercial stage but are expected to make a significant contribution by around 2015. Geothermal energy is now established in countries like Iceland, with a significant accessible resource, and as the technology develops could be taken up more widely. Last but not least, there are bioenergy and biofuels, important because they offer many of the advantages of fossil fuels, in particular, being easily stored. Not surprisingly, they are receiving much attention from policy makers and researchers both in the EU and North America.

Most of this renewable energy will be converted into electricity. The renewable energy resource will be geographically highly distributed and, being mostly dependent on changing weather and climate, cannot be directly controlled in the way fossil fuelled generation is. Electrical power networks were designed to operate from electricity generated in a few large power stations fuelled by coal, gas or uranium fuels, readily available on the international market and, to varying degrees, controllable. Significantly increasing the input from renewable energy sources requires a revision of the way power systems are designed and operated in order to accommodate these variable sources better. This book is an introduction to this important topic.

The material in this book is largely based on a Master's course module taught for over 10 years at the Centre for Renewable Energy Systems Technology (CREST) at Loughborough University. The course, as a whole, was designed to provide general technical education in all major electricity generating renewable energy sources and their integration in electrical networks. Students taking this course normally have first degrees in numerate topics ranging from Physics or Engineering to Environmental Science. The course modules are, therefore, designed for students who, although they may be very knowledgeable in their speciality, will only have elementary knowledge of other topics.

Likewise, this book assumes no previous knowledge in power systems engineering and guides the reader through the basic understanding of how a power system is put together and the way in which it ensures that the consumer demand is met from instant to instant. The characteristics of traditional and renewable energy (RE) resources are described with special reference to the variability of the latter and the way this impacts on their utility. These resources are available in a form that either has to be converted into electricity and/or their electrical output has to be conditioned before it can be fed into the grid. The book covers these aspects and stresses the importance of power electronic technology in the process of power conditioning. The power flows in an electricity network have to be appropriately controlled and the book addresses the way this is achieved when these new sources are integrated. The economics of renewable sources will determine their take-up by the market, and this issue is also addressed, and in some detail. Finally, an eye is cast on the future development of RE technologies and the way that power systems may evolve to accommodate them. An Appendix is available for readers who require a more mathematical coverage of the way electricity is generated, transported and distributed to consumers.

This second edition includes much material from the first that was developed by colleagues from CREST at Loughborough University when both the authors were working there. In particular, Dr Murray Thomson provided much of the power electronics material of Chapter 4 and most of the contents of Chapters 5 and 6. His comments and criticisms during the initial development of the book were invaluable and strongly informed the structure of the first edition, which has been retained. Professor Simon Watson of CREST, now with Delft University of Technology, provided key contributions to Chapter 7. In addition, the dynamic demand control example in Chapter 3 was taken from a CREST Master's dissertation by J. A. Short. The illustration of frequency response contributions from wind was taken from the PhD work of Lei Wu while at the University of Strathclyde, now a Lecturer at Nanjing Institute of Technology. The many other researchers and organisations who allowed us to reproduce material are acknowledged in the text.

We are also grateful to the Wiley staff at Chichester and elsewhere who have supported us in the production of the manuscript.

Last, but certainly not least, we would like to dedicate this edition, as we did with the first edition, to our respective partners, Marion Peach and Delphine Freris, who have accepted the times we were often distracted from family life by the demands of the writing.