Automated classification of simulated wind field patterns from multiphysics ensemble forecasts

In this study, we have proposed an automated classification approach to identify meaningful patterns in wind field data. Utilizing an extensive simulated wind database, we have demonstrated that the proposed approach can identify low‐level jets, near‐uniform profiles, and other patterns in a reliable manner. We have studied the dependence of these wind profile patterns on locations (eg, offshore vs onshore), seasons, and diurnal cycles. Furthermore, we have found that the probability distributions of some of the patterns depend on the underlying planetary boundary layer schemes in a significant way. The future potential of the proposed approach in wind resource assessment and, more generally, in mesoscale model parameterization improvement is touched upon in this paper.     

What scope for integrating land management policies,land administration processes and data infrastructures for housing production in Nigeria?

Existing knowledge reveals that land as a resource is not currently managed efficiently and effectively in most countries of the world. One of the factors considered important in understanding the inefficiencies and ineffectiveness is the level of integration between agencies. The objective of this paper is to determine the level of this inefficiency in order to improve our understanding of the inter-relationship between agencies that perform land administration functions. The research methods include a synthesis of past studies and the use of case study approach. It uses as context, Lagos, in Nigeria. This approach involves a mixed method: interviews and online survey. The results revealed limited integration of processes and collaboration of agencies in the management of land for housing production. We conclude that policies are not sufficiently informed by data and there is a noticeable disconnection between agencies, and formulated policies.     

Comparative study of performance degradation in poly- and mono-crystalline-Si solar PV modules deployed in different applications

Data on long-term performance and degradation of field-aged solar photovoltaic modules is widely recognized as necessary for continued technological improvement and market confidence. It is also important that such research should cover various geographical regions of the globe. This paper presents a study on twenty-nine (29) crystalline silicon modules deployed in grid-connected, battery-charging and water-pumping applications. The modules, installed at six different locations in Ghana were aged between 6 and 32 years. Peak power (P_max) losses ranged from 0.8%/year – 6.5%/year. The P_max losses were dominated by losses in fill factor (FF) and short-circuit current (I_sc). Visually observable defects are also reported.     

Modes of housing production in developing countries: the contemporary role of land, labour, and capital in Lagos, Nigeria

The strategies of participants in housing production, in developing countries, are diverse and not fully understood. Governments in most developing countries have not been able to, sufficiently, explore how the production factors: land, labour and capital, impact on housing production. As a result, many policies formulated by governments aimed at stimulating housing production are found to result in unintended outcomes: they do not always align with the way housing is actually created. This study uses the production factors to assess how motivations are shaped and different modes of housing production result. The aim is to gain an improved understanding of how housing developers, builders and government, impact modes of production. The method includes synthesis of past studies on factors of housing production in Lagos. In parallel, it also involves visits and interviews with some selected developers and agencies to allow a deeper engagement with their activities. This is in addition to direct observation and interviews undertaken through purposeful selection of some autonomous (on-site) builders. As an exploratory study, it observes that a better approach to land supply is significantly beneficial in shaping the modes and capacity of housing. The study helps understand the strategies of participants in housing production in developing countries, especially in Lagos. It recommends that efficient land supply to the autonomous on-site builders should be a focus for policy makers. This will contribute to the production of more housing thereby facilitating an improved production of present and future housing needs of the population.     

Damage identification in gravity dams using dynamic coupled hydro-mechanical XFEM

In order to maximize efficiency and reduce the risk of failure in operational dams, an effective and efficient method which employs the inverse analysis of a dynamic coupled hydro-mechanical problem is proposed. The numerical model is based on the extended finite element model. The proposed method is able to identify cracks which may be detrimental to structural performance and reliability. An attempt is made using both deterministic and heuristic based strategies to solve the ill-posed inverse problem and identify the location, dimension and orientation of the crack. More so, the influence of the search space and conditioning of the cost function in identifying crack parameters are investigated. The proposed method shows promising results in the identification of cracks in a fully operational dam.     

An experimental study on the effects of winglets on the tip vortex interaction in the near wake of a model wind turbine

An experimental study of the near wake up to four rotor diameters behind a model wind turbine rotor with two different wing tip configurations is performed. A straight‐cut wing tip and a downstream‐facing winglet shape are compared on the same two‐bladed rotor operated at its design tip speed ratio. Phase‐averaged measurements of the velocity vector are synchronized with the rotor position, visualizing the downstream location of tip vortex interaction for the two blade tip configurations. The mean streamwise velocity is found not to be strongly affected by the presence of winglet tip extensions, suggesting an insignificant effect of winglets on the time‐averaged inflow conditions of a possible downstream wind turbine. An analysis of the phase‐averaged vorticity, however, reveals a significantly earlier tip vortex interaction and breakup for the wingletted rotor. In contradistinction, the tip vortices formed behind the reference configuration are assessed to be more stable and start merging into larger turbulent structures significantly further downstream. These results indicate that an optimized winglet design can not only contribute to a higher energy extraction in a rotor's tip region but also can positively affect the wake's mean kinetic energy recovery by stimulating a faster tip vortex interaction.     

Cost-competitiveness of distributed grid-connected solar photovoltaics in Ghana: case study of a 4 kWp polycrystalline system

Driven by improvements in solar photovoltaic (PV) technology, policy initiatives and module cost reduction, electricity from solar PV is becoming increasingly cost-competitive with conventional energy systems. In this paper, an economic assessment is conducted on a 4.05 kWp, polycrystalline silicon photovoltaic system installed at the College of Engineering of the Kwame Nkrumah University of Science and Technology, Kumasi, Ghana, located at latitude 6°40′N and longitude 1°37′W, and elevation of 250 m, with a hot and humid climatic condition. The concept of grid-parity, which compares the levelized cost of electricity (LCOE) from solar PV to the retail price of electricity is used in this assessment. The results show, that, at installed cost of €3567/kW and an LCOE of €0.28/kWh, the non-residential category of electricity consumers requires investment support/subsidy of up to 22.9% to achieve parity. Solar PV is already competitive for non-residential customers consuming above 600 kWh in a month, without any support. Residential electricity consumers require investment support of 40.6–92.5% to attain parity with grid electricity, while special load tariff customers (> 100 kVA maximum demand) require between 4 and 50.5% subsidy on capital investment to reach parity. This paper concludes by recommending a two-pronged approach (incentive- and legislation-based) for promoting distributed grid-connected solar PV energy system in Ghana.     

Performance and near wake measurements of a model horizontal axis wind turbine

The performance characteristics and the near wake of a model wind turbine were investigated experimentally. The model tested is a three‐bladed horizontal axis type wind turbine with an upstream rotor of 0.90 m diameter. The performance measurements were conducted at various yaw angles, a freestream speed of about 10 m s ^?1, and the tip speed ratio was varied from 0.5 to 12. The time‐averaged streamwise velocity field in the near wake of the turbine was measured at different tip speed ratios and downstream locations. As expected, it was found that power and thrust coefficients decrease with increasing yaw angle. The power loss is about 3% when the yaw angle is less than 10° and increases to more than 30% when the yaw angle is greater than 30°. The velocity distribution in the near wake was found to be strongly influenced by the tip speed ratio and the yaw angle. At the optimum tip speed ratio, the axial velocity was almost uniform within the midsection of the rotor wake, whereas two strong peaks are observed for high tip speed ratios when the yaw angle is 0°. As the yaw angle increases, the wake width was found to be reduced and skewed towards the yawed direction. With increasing downstream distance, the wake velocity field was observed to depend on the tip speed ratio and more pronounced at high tip speed ratio. Copyright © 2011 John Wiley & Sons, Ltd.     

Distribution and temporal variability of the solar resource at a site in south-east Norway

Globally, solar energy is expected to play a significant role in the changing face of energy economies in the near future. However, the variability of this resource has been the main barrier for solar energy development in most locations around the world. This paper investigated the distribution and variability of solar radiation using the a 10-year (2006 to 2015) data collected at Sørås meteorological station located at latitude 59° 39′ N and longitude 10° 47′E, about 93.3 m above sea level (about 30 km from Oslo), in south-eastern part of Norway. It is found that on annual basis, the total number of days with a global solar radiation of less than 1 kWh/(m²·d) is 120 days while the total number of days with an expected global solar radiation greater than 3 kWh/(m²·d) is 156 days (42.74%) per year. The potential energy output from a horizontally placed solar collector in these 156 days is approximately 75% of the estimated annual energy output. In addition, it is found that the inter-annual coefficient of variation of the global solar radiation is 4.28%, while that of diffuse radiation is 4.96%.