Our research is mainly within the spheres of two University-wide centres: the Sustainable Energy Research Group and the Centre for Coastal Processes, Offshore and Coastal Hydrodynamics, and includes staff from the National Oceanography Centre Southampton. We use state-of-the-art research facilities and contribute to relevant education programmes.
Sustainable energy systems have much in common. Generally, they rely on the knowledge and understanding of the resource, the converter technology and the balance of system. This applies equally to the optimisation of converters and their energy yields, whether they are derived from tidal currents, waves or solar radiation. For example, in the study of energy yields from tidal currents, one needs to understand the technical and economic boundaries to the resource that can be utilised by turbines, the design of the mechanical/electrical interface (balance of system) that will deliver electrical power to the grid and the device layout within the site. Similarly, in solar photovoltaics (PV), energy yields are dependent on the analysis of the solar radiation (sunlight), the type of semiconductor photon converter that generates electrons (monocrystalline silicon, amorphous silicon thin film, etc), to the design of arrays and the balance of the system to supply power to the grid. Source–converter and converter–converter interactions are also important in renewable energy generation. We have undertaken many studies that have established new knowledge in these areas. Highlights are given below and full details can be seen at http://www.energy.soton.ac.uk/
Ocean and water energy
Ocean and water energy is increasingly recognised as an energy source that is a viable to exploit for the sustainable generation of electrical power. Our research addresses this, and fundamental as well as practical investigations are being made.
Key research on ocean and water energy is highlighted below:
- Work in the area of ocean energy has developed new knowledge, contributing to our understanding of the marine current energy conversion by horizontal axis turbines. This not only enhances baseline knowledge but also specific details on methodologies, accurate estimation of the resource, the design and optimisation of turbine blades and guidance for cavitation free turbine operation.
- We established testing methodologies for marine current turbines (MCT) and reported the first ever results of 1/30th and 1/15th scale models. Furthermore, we conducted feasibility studies for site utilisation, looking at arrays of devices in flow fields in particular around Alderney (Alderney Race). We have undertaken laboratory-based testing work on dual rotors, investigating blockage effects, device–device interactions, array design and impacts of these effects on energy yields. It is now proposed to use the knowledge gained to assess large-scale MCT prototypes. It has also been used in the validation of software tools developed by industry for the design and layout of such devices in arrays.
- We are undertaking exploratory development of a totally novel wave energy converter, Anaconda. The Anaconda is essentially a rubber tube in the sea which is filled with water. It is closed at both ends and anchored at the head to the waves. It is squeezed or enlarged locally by pressure variations that run along its length due to the waves. Localised squeezing and enlarging effects permit energy to be extracted indirectly at a power take off (PTO) point using a turbine.
- A novel hydraulic energy converter, the Hydrostatic Pressure Machine, was developed in Southampton for the cost-effective and ecologically acceptable utilisation of the so-far unused hydropower bracket with head differences below 2m, and capacities of 50-500 kW. The University of Southampton coordinates the research project Hylow which aims to optimize these machines, including their demonstration at prototype scale. Currently, two machines are in operation in Germany and Bulgaria.
Urban energy studies
Energy generation (through microgeneration technologies) and energy conservation are extremely important in our attempt to reduce carbon emissions. Urban energy generation technologies such as solar photovoltaics (PV), micro-wind turbines, micro-combined heat and power (µCHP) and ground-source heat pumps are so-called microgeneration systems. We have undertaken PV research and development that has led to the design of unique systems for powering transport refrigeration, solar roofing and building facades. The last include multifunctional PV elements that act as weather barriers, providing shading and daylighting while generating electricity. Studies were undertaken that allow an understanding of generator–generator interaction, system and maintenance costs and their effects on energy yields. This work has highlighted the impacts of PV electricity generation on energy demands in housing, its effects on occupier behaviour and its relationship to reduction in energy demand.
Research on microgeneration technologies, in conjunction with energy demand-reducing façade technologies, is giving an insight into the issues of renewable energy integration into buildings and building refurbishment in our current building stock. This research offers energy analysis to drive the promotion of low-carbon buildings. Elements of this collaborative research are funded by the EPSRC Sustainable Urban Environment programme, which links building refurbishment and occupier comfort to demand reduction and urban energy generation in the built environment. Some key research highlights in the field of urban energy studies include:
- investigating new techniques to assess converter technologies and operating environments for solar photovoltaic devices and micro-wind turbines, and their impact on the microclimate in buildings (with funding from the DTI and the Energy Saving Trust).
- site selection and analysis, including data integrity evaluation, undertaken for the UK's first micro-wind trial (funded by Energy Saving Trust)
- in PV, in collaboration with industry, development of the world first solar refrigeration system for the delivery of chilled produce on an articulated trailer, and the design, testing and development of the UK solar PV roof tile licensed to Marley Eternit. More details on PV are given in Urban Energy Studies.
- new approaches for sustainable refurbishment, as well as assessment of energy flows and comfort in buildings, and tools that address future climate scenarios and their impact on building performance
Offshore and coastal hydrodynamics
Wave- and current-induced flows around natural and artificial structures in the coastal and offshore environments present many challenging problems that demand an understanding of some fundamental fluid mechanics. Particular topics being studied include:
- Disturbed-laminar flow over an oscillating cylinder: The flow around a cylinder oscillating at small amplitude in fluid otherwise at rest is subject to instabilities that trigger a remarkable regime of three-dimensional disturbed-laminar flow. In the literature there are several accounts of experimental and theoretical studies of this problem, which is relevant to the hydrodynamic damping of large floating offshore structures. But there are conflicts between analytical predictions and laboratory measurements relating to the onset of three-dimensional flow, and resulting changes in the loading. Recent experiments have enabled us to make some progress in understanding the causes of this disagreement.
- Splashing and bubble generation in breaking waves: Air bubbles and spray generated by breaking waves in the sea strongly influence many processes, including wave impact forces on coastal structures, ship resistance, white-water wakes, and air-sea exchanges of heat, momentum and gas. The ocean provides a sink of anthropogenic CO2 emissions and accurate estimates of bubble-mediated gas transfer are required for global climate modelling. Owing to the complexity of flow in breaking waves, fundamental studies on air entrainment and splashing are often conducted under laboratory conditions in facilities filled with fresh water. But the results may not be directly applicable to oceanic breakers because considerable differences have been observed in some cases between fresh water and seawater in the total volumes and size distributions of bubbles entrained, and little is known about scale effects. Members recently completed measurements of time-dependent void fractions in the region of laboratory breaking waves in fresh water, artificial seawater, and natural seawater using novel fibre-optic probes. The results demonstrate that total volume and distribution of entrained air and the spatial and temporal evolution of the bubble plumes are almost identical in all three water types, suggesting that observed differences between breaking waves in fresh water and in seawater are due more to scale than differences in physical, chemical and biological composition.
- Vortex-induced vibrations of risers: The offshore oil industry needs to know how to design tensioned pipes (or 'risers') that reach from the oil rig at the sea surface almost vertically down to the sea bed, a vertical distance that may be as much as 3000m. One of the problems is that over this length ocean currents can cause risers to vibrate like guitar strings. Vibrations can lead to metal fatigue and can also cause adjacent risers in an array to clash into each other. Both fatigue failures and clashing can have disastrous and expensive consequences. Understanding the mechanism of excitation is part of the solution of the problem of knowing how far apart the risers should be in order to avoid clashing. Following large-scale experiments in which we measured the response of a 13m-long model vertical riser in a non-uniform current, an ongoing project is concerned with the complicated fluid mechanics of two or more risers in close proximity simultaneously undergoing multimode responses over a wide range of frequencies.
Coastal structures are exposed to the action of waves, which can produce extreme loadings. Wave impact-induced forces can enter joints and fissures of structures, generating internal bursting pressures. Wave loadings on coastal structures are investigated using physical model tests, whereby novel experimental techniques (eg photoelastic modelling of wave loadings) are utilised to record a cause–effect relationship between wave action and structural response. Small-scale or micromodels are currently under development in order to simulate large sections of the coastline and/or to prepare large scale 3D tests.
Some key research highlights are: novel methods to map the surface of a wave field using particle image velocimetry to determine surface flow velocities and wave length, and linear wave theory to establish wave heights; and photoelastic modelling of wave structure interaction. In addition, breaking waves not only cause wave impact, bursting and downfall pressure but overtopping and toe scouring (the latter constitutes the main reason of failure of coastal structures). Using the results from a variety of different studies, the concept of 'exposure' was developed for coastal structures. This implies that the exposure of structures to the main damage mechanisms is a function of the joint probability of waves and water-level elevations and may have significant consequences for the development of current design philosophy.
Morphology, risk and adaptation
This area of research integrates expertise from a range of disciplines in Engineering and the Environment and has strong collaborative links with the National Oceanographic Centre Southampton. Work ranges from surveying, monitoring and modelling physical processes (from the littoral zone to the offshore) to assessing risk and adaptation along the coast. A key theme is the effects of climate change on coastal areas and we lead the coastal research of the Tyndall Centre for Climate Change Research.
Some key research highlights:
- The assessment of erosion and flooding along the English Channel coast, including historic sea-level rise, wave climate and flooding, with a strong emphasis on the Solent.
- The development of a range of integrated tools and methods for assessing impacts of climate change and coastal management strategies. Examples include local-scale assessments (e.g. Tyndall Centre Coastal Simulator, EU InterReg BRANCH project), regional scale assessments (Defra-funded RegIS tool considering East Anglia and North West England) and global scales (eg the DIVA tool for assessing the global impacts and possible responses of sea-level rise and the OECD-funded global port cities assessment of coastal flooding).
These tools have had important policy impact, especially the global-scale assessments, and commissioned work has informed national and international policy (eg the Stern Review, the EU Green and White Paper on Adaptation to Climate Change, the OECD on coastal implications of climate change, the UNFCCC, and the World Bank on the possible costs of Coastal Adaptation).