Pick up any professional journal or proceedings and one cannot but be amazed by the breadth and depth of human knowledge. Who among us can fully comprehend more than a small proportion of that knowledge? Inquisitiveness is perhaps a defining feature of human development – but that is an engineer speaking and how much can I know about human development?
Knowledge in the energy sector is also expanding rapidly. We can be equally amazed by the range and depth of research in areas where at first glance we might think we should already know the answers. Natural inquisitiveness may be a part of the driving force but for many today the key driver is to find new or improved solutions to the challenges we face in meeting the worldwide demand for energy: challenges of population growth, resource shortages, carbon and climate change; the human need to sustain and improve the quality of life for all.
The need for more knowledge is especially true in the field of renewable energy from which the four papers in this issue are drawn. With few exceptions this has been a field of serious research for only a few decades and it continues to expand rapidly. Renewable energy systems typically have a high capital cost in comparison with fossil-fuelled energy sources. With the exception of biomass, the fuel cost is at or near zero. The other key element is the operation and maintenance cost. This depends very much on the technology and can be very low (e.g. solar photovoltaics) or can be relatively high and at risk from uncertainty. For example, marine energy devices installed in harsh conditions can be at risk due to their exposure and the difficulty in gaining access for maintenance. Hence there is a need to understand fully all aspects of performance and optimise it in order to capture the maximum energy from a system and yet ensure a sound balance between capital and operations and maintenance costs. Design needs to be certain because failure is so expensive.
The papers from O’Doherty et al.1 and from Dai and Lam2 both explore performance of tidal stream turbines. There is much development work on this technology which is making rapid progress. Many device concepts are based on the horizontal axis turbine which might be thought to be well understood. However much of the difference between concepts from different developers lies in the mounting and foundations selected. Apart from the requirement to differentiate for differing seabed conditions and water depths, developers may see this as an area in which to gain advantage. The paper by O’Doherty et al. describes a system with five turbines sharing a common framework on the seabed which might not need anchoring or fixing. This would avoid expensive operations on the seabed and environmental disturbance. The paper presents the results of detailed computerised fluid dynamics (CFD) modelling to understand the potential interaction between turbines in the cluster and the sliding forces created at the interface between the framework and the seabed.
The paper from Dai and Lam also concerns CFD modelling but this time on the less well-developed concept of the vertical axis marine current turbine (VAMCT) of the straight-bladed Darrieus type. Here the primary objective is to be able to model the flow through the system in order to be able to predict the hydrodynamic performance and blade design loads. A key drawback of the Darrieus turbine is the risk of blade fatigue from the cyclical loading. The paper describes the work leading to the present state of knowledge of such turbines and the experimental modelling used to define the turbine characteristics for the subsequent CFD work.
Notable in both papers is the intensive use of large parallel computing resources to resolve the analysis.
The paper by Preene and Powrie3 brings us back to land and consideration of using ground energy systems for heating and cooling buildings. These systems are more commonly known as heat pumps although in fact a heat pump is not always the technology to use in order to exploit temperature differentials between the ground and the desired building temperature. Ground energy systems have been widely accepted in many countries but only now are becoming popular in UK. The paper provides an excellent review of the key issues for selecting a system and type of ground heat exchanger to use. It goes on to discuss barriers to their use and in particular the potential for long term degradation of the performance due to continued unidirectional transfer of heat leading to changes in the ground conditions.
The paper on low-carbon energy solutions for an ecological island in China is by Roddy et al.4 and provides interesting data on the concept of ecological development in a unified programme to provide low carbon generation to a group of three very different islands in the Yangtze delta. Chongming, the largest island, is planned to have moderate development, Changxing is heavily industrialised and Hengsha is planned to be for ecological tourism. The overall plan is to serve as a showcase for new energy technologies in contrast with Shanghai a few kilometres away. The paper reviews all the available renewable resources on and around the islands before setting out a strategy to maximise the potential for carbon reduction. A potential 30% reduction is proposed compared with conventional energy solutions. The main resources are solar and wind with a variety of biomass resources. The transportation problem for the biomass is solved by gasification and piping the gas to users. Several biomass plants and a coal or coal/biomass gasification plant would be networked. The paper clearly identifies the need for integrated and tailored solutions to take maximum advantage of the renewable resources.
These papers then demonstrate a wide range of knowledge which will be new to all of us to some degree. They also demonstrate that we need to continue to learn in order to make maximum use of our energy resources. Diversity, and adaptation to conditions and circumstances, is needed, as is integration of the available resources to achieve the best solutions.
