Numerical simulation of a submerged cylindrical wave energy converter

In this study, a numerical model based on the complete solution of the Navier–Stokes equations is proposed to predict the behavior of the submerged circular cylinder wave energy converter (WEC) subjected to highly nonlinear incident waves. The solution is obtained using a control volume approach in conjunction with the fast-fictitious-domain-method for treating the solid objects. To validate the model, the numerical results are compared with the available analytical and experimental data in various scenarios where good agreements are observed. First, the free vibrations of a solid object in different non-dimensional damping ratios and the free decay of a heaving circular cylinder on the free surface of a still water are simulated. Next, the wave energy absorption efficiency of a circular cylinder WEC calculated from the model is compared with that of the available experiments in similar conditions. The results show that tuning the converter based on the linear theory is not satisfactory when subjected to steep incident waves while the numerical wave tank (NWT) developed in the current study can be effectively employed in order to tune the converter in such conditions. The current NWT is able to predict the wave-body interactions as long as the turbulence phenomena are not important which covers a wide range of Reynolds and Keulegan-Carpenter numbers.     

An integrated system of the floating wave energy converter and electrolytic hydrogen producer

The amount of energy produced now by the world community and that of energy flows caused by natural phenomena demonstrates commensurability of both power sources. Power production based on the conventional technologies is accompanied by environmental pollution, greenhouse and overheating effects resulting in biosphere degradation. It is apparent that the most intelligent solution of the problem of power production growth is the development of environmentally compatible power system using the regional renewable power resources. A system consisting of sea wave energy converter and electrolytic installation for hydrogen production is under consideration in this article.A potential candidate for wave energy conversion is an offshore Float Wave Electric Power Station (FWEPS), which is in the development stage. The second component of the system is the hydrogen producing facilities based on sea water electrolysis. Hydrogen as an ecologically safe fuel can be used in different branches of economy. The tentative studies showed that direct sea water electrolysis is technically feasible and is a perspective procedure for an environmentally-clean commercial production of hydrogen and associate products.Real performance of the system components allow to treat it as realizable.     

Quantifying the uncertainty of wave energy conversion device cost for policy appraisal: An Irish case study

Wave Energy Conversion (WEC) devices are at a pre-commercial stage of development with feasibility studies sensitive to uncertainties surrounding assumed input costs. This may affect decision making. This paper analyses the impact these uncertainties may have on investor, developer and policymaker decisions using an Irish case study. Calibrated to data present in the literature, a probabilistic methodology is shown to be an effective means to carry this out. Value at Risk (VaR) and Conditional Value at Risk (CVaR) metrics are used to quantify the certainty of achieving a given cost or return on investment. We analyse the certainty of financial return provided by the proposed Irish Feed-in Tariff (FiT) policy. The influence of cost reduction through bulk discount is also discussed, with cost reduction targets for developers identified. Uncertainty is found to have a greater impact on the profitability of smaller installations and those subject to lower rates of cost reduction. This paper emphasises that a premium is required to account for cost uncertainty when setting FiT rates. By quantifying uncertainty, a means to specify an efficient premium is presented.     

A linearized model for estimating the performance of submerged resonant wave energy converters

A realistic performance analysis of oscillating water column wave energy converters (WECs) addresses to a set of non-linear differential equations that need to be integrated in time, by using a stochastic approach, under the hypothesis of random wind-generated sea waves, for all the sea states which characterize the location of the system. Non-linearities of the differential equations have several origins:

• minor and major losses of the unsteady flow of water and air;

• compressibility of air and heat exchange with the walls of the air chamber;

• non-linear characteristics of the turbine.

Under the hypothesis of random sea waves with Gaussian distribution, the authors propose an original methodology for linearizing the differential equations that describe the flow motion inside a wholly submerged WEC. Under such hypothesis, the linearized model can be used for predicting the power output by means of the calculations in the frequency domain and for control design. The developed methodology has been applied to the estimation of the performance of the new “resonant sea wave energy converters”, called REWEC, patented by Boccotti in 1998, and consisting of several caissons, characterized by a structure similar to the caissons of the traditional breakwaters and placed on the seabed, close one to each other, to form a submerged breakwater. Each caisson is connected to a vertical duct wholly beneath the sea level, where a hydraulic Wells turbine is placed.The matching between turbine and resonance characteristic of the system is carefully analysed in order to maximize the energy conversion efficiency.Some results, given for a small installation in the Mediterranean sea, confirm that the REWEC system is able to absorb a large share of the incident wave energy due to a very simple regulation system which permits the tuning on sea states with different significant heights.     

Prototype testing of the wave energy converter wave dragon

The Wave Dragon is an offshore wave energy converter of the overtopping type. It consists of two wave reflectors focusing the incoming waves towards a ramp, a reservoir for collecting the overtopping water and a number of hydro turbines for converting the pressure head into power.In the period from 1998 to 2001 extensive wave tank testing on a scale model was carried at Aalborg University. Then, a 57×27 m wide and 237 tonnes heavy (incl. ballast) prototype of the Wave Dragon, placed in Nissum Bredning, Denmark, was grid connected in May 2003 as the world's first offshore wave energy converter.The prototype is fully equipped with hydro turbines and automatic control systems, and is instrumented in order to monitor power production, wave climate, forces in mooring lines, stresses in the structure and movements of the Wave Dragon.In the period May 2003 to January 2005 an extensive measuring program has been carried out, establishing the background for optimal design of the structure and regulation of the power take off system. Planning for deployment of a 4 MW power production unit in the Atlantic by 2007 is in progress.     

Investigation of the potential of wind–waves as a renewable energy resource: by the example of Cesme—Turkey

There are opinions claiming that 70% of the world energy consumption could be provided from renewable resources by the year 2050. These resources are needed, because fossil fuels both cause pollution of the environment and will be depleted in the near future. In this regard, the objective of this study was to determine the wave energy potential and the costs associated with its application to Turkish waters. To this goal, the wave energy potential in Cesme–Izmir was investigated. Cesme is known to have abundant wind, which plays the primary role in the formation of sea waves. For this purpose, the Solar Energy Institute of Ege University carried out wind velocity measurements within the period from 05.11.1998 to 05.11.1999 at an altitude of 10 m in Cesme. The measured values were regarded as if they were taken at an altitude of 19.5 m from seawater level. With this approach, the Pierson–Moskowitz wave energy spectrum was constructed. Through this wave energy spectrum, wave energy that is to be obtained at the measurement area within one year was determined. The variation of wave energy according to each month was evaluated. Hence, the unit cost of electricity to be produced by a turbine (with a width of 1 m), assumed to be installed at the area of measurements, was calculated.     

Numerical modeling of the effects of wave energy converter characteristics on nearshore wave conditions

Modeled nearshore wave propagation was investigated downstream of simulated wave energy converters (WECs) to evaluate overall near- and far-field effects of WEC arrays. Model sensitivity to WEC characteristics and WEC array deployment scenarios was evaluated using a modified version of an industry standard wave model, Simulating WAves Nearshore (SWAN), which allows the incorporation of device-specific WEC characteristics to specify obstacle transmission. The sensitivity study illustrated that WEC device type and subsequently its size directly resulted in wave height variations in the lee of the WEC array. Wave heights decreased up to 30% between modeled scenarios with and without WECs for large arrays (100 devices) of relatively sizable devices (26 m in diameter) with peak power generation near to the modeled incident wave height. Other WEC types resulted in less than 15% differences in modeled wave height with and without WECs, with lesser influence for WECs less than 10 m in diameter. Wave directions and periods were largely insensitive to changes in parameters. However, additional model parameterization and analysis are required to fully explore the model sensitivity of peak wave period and mean wave direction to the varying of the parameters.     

Effective education for energy efficiency

A lot of today's world vices can be eliminated if certain targeted modules and adapted curricula are introduced in the schooling system. One of these vices is energy squandering with all its negative consequences for the planet (e.g. depletion of finite energy sources and the subsequent climate change). This paper describes the results of an energy-thrift information and education project taking place in different levels of education in Crete—Greece, which records 321 students’ and their parents’ routine energy-related behavior and proves that this behavior changes to a more energy efficient one, after the dissemination of relevant information and the participation into the energy education projects. Namely, response percentages indicating the energy-efficient behavior increased after project participation while the ones indicating an energy-squandering behavior decreased. The Wilcoxon signed rank test was statistically significant in all energy behavior questions related to students and to most questions related to parents.     

Financial impact of energy efficiency under a federal combined efficiency and renewable electricity standard: Case study of a Kansas “super-utility”

Historically, local, state and federal policies have separately promoted the generation of electricity from renewable technologies and the pursuit of energy efficiency to help mitigate the detrimental effects of global climate change and foster energy independence. Federal policymakers are currently considering and several states have enacted a combined efficiency and renewable electricity standard which proponents argue provides a comprehensive approach with greater flexibility and at lower cost. We examine the financial impacts on various stakeholders from alternative compliance strategies with a Combined Efficiency and Renewable Electricity Standard (CERES) using a case study approach for utilities in Kansas. Our results suggest that an investor-owned utility is likely to pursue the most lucrative compliance strategy for its shareholders—one that under-invests in energy efficiency resources. If a business model for energy efficiency inclusive of both a lost fixed cost recovery mechanism and a shareholder incentive mechanism is implemented, our analysis indicates that an investor-owned utility would be more willing to pursue energy efficiency as a lower-cost CERES compliance strategy. Absent implementing such a regulatory mechanism, separate energy efficiency and renewable portfolio standards would improve the likelihood of reducing reliance on fossil fuels at least-cost through the increased pursuit of energy efficiency.     

How to measure and optimize the efficiency of a wave power converter

A method by which one can measure the hydrodynamic efficiency of a wave power converter is discussed. Provided one measures both the horizontal and the vertical wave motion, it is sufficient to have measurements at one point closely in front of the converter and at another point behind it. Good estimates of the efficiency can be obtained without a Fourier analysis of the waves. The method should be useful both for measurements in the laboratory and in the ocean.     

Economical considerations of renewable electric energy production—especially development of wave energy

Investments in renewable energy plants normally only take standard economic key figures into account, such as installed rated power, the market price of energy and the interest rate. The authors propose that the degree of utilisation, i.e. the ratio of yearly produced energy in the installation to the installed power, must be included due to its significant impact on the present value of the investment. A site with a limited average wave height could be of economic interest if the utility factor for the installation is high, since the investment cost (associated with the power installed) can be better adjusted to conditions at the particular site. In the case of wave power from the Baltic Sea with its limited variation in wave height (and limited average wave height), this indicates that the economic potential is best for smaller units.     

Measurements of the slow drift dynamics of a model Pelamis wave energy converter

The Pelamis wave energy converter (WEC) is moored with a clump-assisted wire catenary of high compliance that, coupled with the displacement mass of Pelamis, has a resonant frequency an order of magnitude lower than the wave frequencies. The mooring is thus decoupled from first-order wave excitation, and is excited by second-order slowly varying drift forces, which are mainly due to the wave momentum transferred to the device as wave power is absorbed. The slow drift motion is damped by a combination of drag and wave-drift damping. This paper describes an experimental investigation of the slow-drift excitation and damping.     

Analysing the interactions between renewable energy promotion and energy efficiency support schemes: The impact of different instruments and design elements

CO₂ emissions reduction, renewable energy deployment and energy efficiency are three main energy/environmental goals, particularly in Europe. Their relevance has led to the implementation of support schemes in these realms. Their coexistence may lead to overlaps, synergies and conflicts between them. The aim of this paper is to analyse the interactions between energy efficiency measures and renewable energy promotion, whereas previous analyses have focused on the interactions between emissions trading schemes (ETS) and energy efficiency measures and ETS and renewable energy promotion schemes. Furthermore, the analysis in this paper transcends the “certificate” debate (i.e., tradable green and white certificates) and considers other instruments, particularly feed-in tariffs for renewable electricity. The goal is to identify positive and negative interactions between energy efficiency and renewable electricity promotion and to assess whether the choice of specific instruments and design elements within those instruments affects the results of the interactions.     

An econometric analysis of residential expenditures on energy conservation and renewable energy sources

Economic theory suggests that residential expenditures on energy conservation and renewable energy sources will be determined by the ability of households to purchase conservation inputs, their incentive to invest in conserving energy, the energy efficiency of existing homes and miscellaneous factors such as climate and age of the home-owner. Empirical analyses of energy-related expenditures reported on individual income tax returns confirm the importance of household income, energy price increases and climate conditions in determining energy conservation investments. Income tax credits are also found to have stimulated residential spending on conservation and renewable energy.     

Developments in the design of the PS Frog Mk 5 wave energy converter

This paper describes one of the innovative wave energy converters under development by the Lancaster University Renewable Energy Group. An offshore point-absorber wave energy converter, PS Frog Mk 5 consists of a large buoyant paddle with an integral ballasted ‘handle’ hanging below it. The waves act on the blade of the paddle and the ballast beneath provides the necessary reaction. When the WEC is pitching, power is extracted by partially resisting the sliding of a power-take-off mass, which moves in guides above sea level. Totally enclosed in a steel hull, with no external moving parts, PS Frog Mk. 5 is at least as robust as a ship and the survivability of the device is currently under investigation, though such work is beyond the scope of this paper. Such a device could be very economic in terms of power output per unit of capital cost. New inventive steps with experimental results and computer studies have led to promising improvements to the hull shape. The WEC is maintained in a resonant state by the use of special means to maintain a high dynamic magnifier in irregular seas. A robust feedback control system has been developed to ensure stability and maintain efficient power take-off. Some of these developments are described and illustrated with the results of computer simulations that show power outputs and device motion over a range of conditions. It is shown that useful advances have been made, with the power capture bordering on 2 MW in an increasing proportion of sea states.     

The link between political decision-making and energy options: Assessing future role of renewable energy and energy efficiency in Finland

European Union and Finland are confronted with much the same kind of challenges in energy policy. Because of much higher importance on energy, these issues escalated earlier in Finland including vital political decision-making. Several alternative energy paths to the future can be identified with fairly similar projected costs. The more in-depth analysis in the Finnish case suggests that, e.g., an integrated approach consisting of renewable energy sources and energy efficiency measures would be one competitive alternative to satisfy both increasing energy demand and CO₂ emission reductions already by 2020. The study shows that meeting environmental, energy security and economical targets may not as such be adequate for the future success of an energy option. There is a more profound link between the energy options and the political decision-making, implying a much broader range of criteria than just the 3 Es reflecting thus politicians’ priorities and concerns. For example, in the Finnish case renewable energy sources and energy efficiency did not match optimally the parliamentary majority's preferences when deciding on future electricity direction in 2002. The methodology suggested here can be used to improve the strategic positioning of alternative energy paths.     

Factors which influence Nova Scotia farmers in implementing energy efficiency and renewable energy measures

Improvements in energy efficiency and renewable energy use can reduce farm operating costs and reduce greenhouse gas (GHG) emissions. Responses (n=224, representing a 32% response rate) from a mail survey were used to assess use and interest in energy efficient and renewable energy options on farms in Nova Scotia, Canada. Energy efficiency options used the most were behavior, insulation, and lighting. Few farms used renewable energy options. Approximately 78% of farmers indicated an interest in implementing energy efficiency and renewable energy options. Interest varied by farm type and size. Interest increased with farm size. The two main efficiency options of interest were lighting (60.8%) and insulation (43.7%), while wind power development (55.5%) and solar water heating (24.5%) were the main renewable options of interest. Farmers concerned about power and equipment reliability were less likely to be interested in implementing options. Farmers concerned about the environment were more likely to be interested in implementing options. Current use of certain energy efficiency technologies, such as efficient lighting, influenced implementation interest.     

Invention in energy technologies: Comparing energy efficiency and renewable energy inventions at the firm level

Many countries, especially in Europe, have ambitious goals to transform their national energy systems towards renewable energies. Technological change in both renewable production and efficient use of energy can help us to make these targets come true. Using a panel of German firms linked to the PATSTAT patent data, we study inventions in both types of energy technologies and investigate the role prior inventions as technology-push factors play for both types of technologies. In addition and more importantly, we study whether previous inventions in non-energy technologies also stimulate technical change in energy technologies and whether this effect differs between energy conservation and renewable energy technologies.     

An overview of ocean renewable energy resources in Korea

Korea relies on imported fossil fuels to meet its energy consumption demands. As such, there is a need to investigate alternative energy resources such as renewable energy. In this paper, assessments of the potential of various ocean renewable energy resources in the sea around Korea; potential sources of energy including wave energy, tidal energy, tidal current energy and ocean thermal energy. Tidal energy and tidal current energy are likely to play an important role in meeting the future energy needs of Korea, whereas the potentials of wave energy and ocean thermal energy for the same are relatively low. The level of technical development and the renewable energy market in Korea is currently in an early stage. The government will have to be more aggressive in the promotion of renewable energy to achieve sustainable development in Korea.     

Adaptability of a generic wave energy converter to different climate conditions

This study evaluates the influence of wave climate tunability on the performance of a generic Wave Energy Converter (WEC) for different climate scenarios. The generic WEC is assumed to be composed of an array of heaving, floating cylinders. In this study, two natural periods for the cylinders of 4 s and 8 s (typical of enclosed seas and the mean Atlantic swell, respectively) and a location-tunable cylinder are considered to evaluate the influence of tuning on the power performance of the cylinder. The WEC power matrix is computed using a frequency domain model, and the performance of the WEC is evaluated along the global coasts; the met-ocean data originated from the global reanalysis database (GOW) from Reguero et al. (2012). The performance of the WEC is evaluated using two parameters: the capture width ratio (CWR), which evaluates the efficiency of the converter at each location, and the kW/Ton (KWT) parameter, which evaluates the efficiency of the converter using “economic” terms. Tuning a converter for each location displayed a positive CWR; however, the KWT was low after WEC tuning because of the weight of the structures required to tune the converter that experiences high peak periods.