The Green Paradox and Learning-by-doing in the Renewable Energy Sector

21 p.

Wind climate trends in the Pacific Northwest and the implications to renewable energy supply

EXTRACT (SEE PDF FOR FULL ABSTRACT): This paper examines the influence of wind climate variations on new Pacific Northwest renewable energy sources. Wind represents a potentially valuable supplemental source of energy in the region. ... The recent period of weaker winds may be associated with a stronger North Pacific Low in the last decade. This would result in winter storms more often being deflected farther north, to Canada. Also, in the last dozen years, lower SOI values were common. Other investigators have found low SOI to be associated with drier conditions in the Pacific Northwest.

Force ripple compensation in a tubular linear generator for marine renewable generation

Tubular permanent magnet linear generators are a promising generator technology for use in marine renewables. One aspect of their design relates to the conditions necessary for achieving a smooth thrust response from the generator, free from cogging and periodic variations due to spatial harmonics of the flux cutting the generator coils. This paper presents an experimental and finite element study of the sources of thrust ripple in a prototype linear generator for marine generation. A simple self-commutated control scheme is shown, which uses linear Hall-effect sensors and look-up-table based feed-forward compensation to derive the excitation currents required to drive the machine with constant force. Details of the controller's FPGA based implementation are given, including its strategy for detecting sensor failure. © 2011 IEEE.

The role for low carbon electrification technologies in poverty reduction and climate change strategies: A focus on renewable energy mini-grids with case studies in Nepal, Peru and Kenya

As a potential poverty reduction and climate change strategy, this paper considers the advantages and disadvantages of using renewable energy technologies for rural electrification in developing countries. Although each case must be considered independently, given a reliable fuel source, renewable energy mini-grids powered by biomass gasifiers or micro-hydro plants appear to be the favoured option due to their lower levelised costs, provision of AC power, potential to provide a 24. h service and ability to host larger capacity systems that can power a wide range of electricity uses. Sustainability indicators are applied to three case studies in order to explore the extent to which sustainable welfare benefits can be created by renewable energy mini-grids. Policy work should focus on raising awareness about renewable energy mini-grids, improving institutional, technical and regulatory frameworks and developing innovative financing mechanisms to encourage private sector investments. Establishing joint technology and community engagement training centres should also be encouraged. © 2011 Elsevier Ltd.

Thermal modelling of a tubular linear machine for marine renewable generation

A lumped parameter thermal model has been constructed for a tubular linear machine that has been designed for use in a marine environment. It shows good correlation to both steady state and transient experimental tests on the machine. The model has been developed for a stationary machine in a laboratory environment - the modelling techniques used and enhancements to enable the application of the model directly to marine scenarios are discussed.

Detailed thermal modelling of a tubular linear machine for marine renewable generation

A detailed lumped-parameter thermal model is presented for a tubular linear machine that has been designed for use in a marine environment. The model has been developed for a static machine, the worst-case thermal scenario, and is used to establish a rating for the machine. The model has been validated against a large range of experimental tests and shows good correlation to both steady-state and transient experimental results. The model was constructed from a mostly theoretical basis with very little calibration, suggesting that the techniques used are applicable in a more general sense. © 2013 IEEE.

Sensorless commutation of a two-phase linear machine for marine renewable power generation

A sensorless scheme is presented for a two-phase permanent-magnet linear machine targeted for use in marine wave-power generation. This is a field where system reliability is a key concern. The scheme is able to extract the effective inductance and back-emf of the machine's phases simultaneously from measurements of the current ripple present on the power electronic converter. These measurements can then be used to estimate position. An enhancement to the scheme in the presence of spatially-varying mutual inductance between phases allows more accurate and reliable tracking from indutance-based measurements than would otherwise be expected. This scheme is able to operate at any speed including, critically, when stationary. Experimental results show promise for the scheme, although some work to reduce the level of noise would be desirable. © 2013 IEEE.

Electrical machine characterisation and analysis for renewable energy applications

There has been an increased use of the Doubly-Fed Induction Machine (DFIM) in ac drive applications in recent times, particularly in the field of renewable energy systems and other high power variable-speed drives. The DFIM is widely regarded as the optimal generation system for both onshore and offshore wind turbines and has also been considered in wave power applications. Wind power generation is the most mature renewable technology. However, wave energy has attracted a large interest recently as the potential for power extraction is very significant. Various wave energy converter (WEC) technologies currently exist with the oscillating water column (OWC) type converter being one of the most advanced. There are fundemental differences in the power profile of the pneumatic power supplied by the OWC WEC and that of a wind turbine and this causes significant challenges in the selection and rating of electrical generators for the OWC devises. The thesis initially aims to provide an accurate per-phase equivalent circuit model of the DFIM by investigating various characterisation testing procedures. Novel testing methodologies based on the series-coupling tests is employed and is found to provide a more accurate representation of the DFIM than the standard IEEE testing methods because the series-coupling tests provide a direct method of determining the equivalent-circuit resistances and inductances of the machine. A second novel method known as the extended short-circuit test is also presented and investigated as an alternative characterisation method. Experimental results on a 1.1 kW DFIM and a 30 kW DFIM utilising the various characterisation procedures are presented in the thesis. The various test methods are analysed and validated through comparison of model predictions and torque-versus-speed curves for each induction machine. Sensitivity analysis is also used as a means of quantifying the effect of experimental error on the results taken from each of the testing procedures and is used to determine the suitability of the test procedures for characterising each of the devices. The series-coupling differential test is demonstrated to be the optimum test. The research then focuses on the OWC WEC and the modelling of this device. A software model is implemented based on data obtained from a scaled prototype device situated at the Irish test site. Test data from the electrical system of the device is analysed and this data is used to develop a performance curve for the air turbine utilised in the WEC. This performance curve was applied in a software model to represent the turbine in the electro-mechanical system and the software results are validated by the measured electrical output data from the prototype test device. Finally, once both the DFIM and OWC WEC power take-off system have been modeled succesfully, an investigation of the application of the DFIM to the OWC WEC model is carried out to determine the electrical machine rating required for the pulsating power derived from OWC WEC device. Thermal analysis of a 30 kW induction machine is carried out using a first-order thermal model. The simulations quantify the limits of operation of the machine and enable thedevelopment of rating requirements for the electrical generation system of the OWC WEC. The thesis can be considered to have three sections. The first section of the thesis contains Chapters 2 and 3 and focuses on the accurate characterisation of the doubly-fed induction machine using various testing procedures. The second section, containing Chapter 4, concentrates on the modelling of the OWC WEC power-takeoff with particular focus on the Wells turbine. Validation of this model is carried out through comparision of simulations and experimental measurements. The third section of the thesis utilises the OWC WEC model from Chapter 4 with a 30 kW induction machine model to determine the optimum device rating for the specified machine. Simulations are carried out to perform thermal analysis of the machine to give a general insight into electrical machine rating for an OWC WEC device.

Engineering of metal oxide interfaces for renewable energy applications

Diminishing non-renewable energy resources and planet-wide de-pollution on our planet are among the major problems which mankind faces into the future. To solve these problems, renewable energy sources such as readily available and inexhaustible sunlight will have to be used. There are however no readily available photocatalysts that are photocatalytically active under visible light; it is well established that the band gap of the prototypical photocatalyst, titanium dioxide, is the UV region with the consequence that only 4% of sun light is utilized. For this reason, this PhD project focused on developing new materials, based on titanium dioxide, which can be used in visible light activated photocatalytic hydrogen production and destruction of pollutant molecules. The main goal of this project is to use simulations based on first principles to engineer and understand rationally, materials based on modifying TiO2 that will have the following properties: (1) a suitable band gap in order to increase the efficiency of visible light absorption, with a gap around 2 – 2.5 eV considered optimum. (2). The second key aspect in the photocatalytic process is electron and hole separation after photoexcitation, which enable oxidation/reduction reactions necessary to i.e. decompose pollutants. (3) Enhanced activity over unmodified TiO2. In this thesis I present results on new materials based on modifying TiO2 with supported metal oxide nanoclusters, from two classes, namely: transition metal oxides (Ti, Ni, Cu) and p-block metal oxides (Sn, Pb, Bi). We find that the deposited metal oxide nanoclusters are stable at rutile and anatase TiO2 surfaces and present an analysis of changes to the band gap of TiO2, identifying those modifiers that can change the band gap to the desirable range and the origin of this. A successful collaboration with experimental researchers in Japan confirms many of the simulation results where the origin of improved visible light photocatalytic activity of oxide nanocluster-modified TiO2 is now well understood. The work presented in this thesis, creates a road map for the design of materials with desired photocatalytic properties and contributes to better understanding these properties which are of great application in renewable energy utilization.

The potential of offshore windfarms to act as marine protected areas – A systematic review of current evidence

As offshore windfarm (OWF) construction in the UK is progressing rapidly, monitoring of the economic and ecological effects of these developments is urgently needed. This is to enable both spatial planning and where necessary mitigation in an increasingly crowded marine environment. One approach to mitigation is co-location of OWFs and marine protected areas (MPAs). This systematic review has the objective to inform this co-location proposal and identify areas requiring further research. A limited number of studies addressing marine renewable energy structures and related artificial structures in coastal waters were found. The results of these studies display a change in species assemblages at artificial structures in comparison to naturally occurring habitats. An increase in hard substrata associated species, especially benthic bivalves, crustaceans and reef associated fish and a decrease in algae abundance were the dominant trends. Assemblages associated with complex concrete structures revealed greater similarity to natural hard substrata compared to those around steel structures. To consider marine renewable energy sites, especially large scale OWFs as MPAs, the dissimilar nature of assemblages on the structures themselves to natural communities should be considered. However positive effects were recorded on the abundance of commercially important crustacean species. This suggests potential for incorporation of OWFs as no fishing, or restricted activity zones within a wider MPA to aid fisheries augmentation. The limited available evidence highlights a requirement for significant further research involving long term monitoring at a variety of sites to better inform management options.