Robert N. Farrugia

The wind shear exponent in a Mediterranean island climate

The difficulties in estimating the long term mean wind speed and subsequently wind turbine energy output derive from the fact that more often than not, available data is taken at a level other than machine hub height. The 1/7th power law has been recognised as a handy tool to carry out vertical wind speed extrapolation to the desired hub height. It is also understood that using an exponent of 1/7th could lead to underestimation of the actual long-term mean wind speed aloft. This paper strives to evaluate the power law with respect to wind data taken on a 25 m mast on the central Mediterranean island of Malta. Whilst deriving a site-specific factor affiliated to a typical terrain type, it also strives to determine characteristic variations of the power law exponent over appropriate sampling intervals.

Wind characteristics on the Caribbean island of Puerto Rico

Wind data was measured at a number of sites on the Caribbean island of Puerto Rico over a 24 calendar-month time frame. The wind data gathered at four sites is envisaged to shed new light on the wind characteristics of this tropical island with an emphasis on the climate’s suitability for wind energy technology applications. Characteristics such as the diurnal, monthly and annual wind speed are subjectively investigated to determine the sites’ potential for further studies in the wind measurement field. Reasonable wind conditions for wind energy conversion system installation seem to exist in and around Aguadilla and Ponce.

Analysis of wind characteristics in the Maltese Archipelago

The Maltese Islands enjoy a typical Mediterranean climate with hot, humid summers and cooler winters. The size of the islands as well as their location between Europe and the African continent makes them susceptible to wind currents induced by these comparatively huge land masses as well as to small scale localised effects induced by the islands themselves. The latter effects would be more marked in generally undisturbed conditions which enhance the formation of breezes. The wind data evaluated in this paper was gathered at Luqa International Airport (Lat. 35°51.5′N, Long. 14°28.5′E). Due to its long time frame (1947 to date), this database is appropriate for the evaluation of wind parameters on a long-term basis. Characteristics such as the diurnal trends, as well as parameters relevant to power generation will be discussed and illustrated.

The Potential and Constraints of Wind Farm Development at Nearshore Sites in the Maltese Islands

The electrical energy requirements of the Maltese Islands are met in their entirety by two oil-fired electrical generation plants. In view of this complete dependence upon fossil fuels, investigations into the prospects of diversifying electrical generation by resorting to renewable energy technologies are particularly relevant. The archipelago has peculiar characteristics such as high population density, comparatively deep coastal waters and an economy based on tourism, manufacturing, marine-sector activities and services that make the integration of wind power generation projects challenging. Local government authorities commissioned the authors to assess the constraints related to wind farm development in a shallow water coastal area, known as is-Sikka l-Bajda, which could present a wind potential worth exploiting, and to recommend adequate mitigation measures to minimize any impacts and conflicts with stakeholders. These constraints include marine navigational aspects, fishing and aquaculture, tourism and other site-specific activities. Environmental constraints exist including the fact that the site is characterized by extensive seagrass (Posidonia oceanica) meadows, that it is a priority habitat under the EU Habitats Directive, and that the site itself is a reef – another priority habitat within the same directive. The proposed near-shore site is also in the vicinity of a protected coastal bird rafting and bird nesting site for the Yelkouan Shearwater species. Submarine noise generation – particularly during the construction phase – is also of concern in view of the regular sighting of marine mammals in Maltese coastal waters. In the site evaluation exercise, another secondary site in the Maltese Islands, located off the north Gozo coast, was also assessed. Mitigation measures specific to the Sikka l-Bajda site proposed by the authors include the deployment of silt curtains, bubble screens and unobtrusive turbine lighting devices and avoiding utilisation of the reef area closest to the protected bird colony. Such measures also relate to the choice of the array design to minimise visual impact and to the period of the year when wind plant construction and deployment should take place to minimize impact on avifaunal populations. By declaring the marine area contiguous to the proposed nearshore wind facility development as off-limits to fishing vessels, a de facto ‘No-take’ Marine Protected Area can also be effectively instituted. One also expects submerged components of the nearshore wind facility to be colonized within a brief period by a diverse fouling community and that the same components act as Fish Aggregating Devices (FADs), greatly enhancing fish populations in the area. In view of the current paucity in Mediterranean nearshore wind power facilities, the proposed project could potentially serve as a pilot project for the whole region, and also become a tourist attraction.

Analysis of Low Level Wind Behaviour in Central and South East Malta

The main objective of this study was to investigate low level wind behaviour at five locations in the central and South East parts of the Mediterranean island of Malta. The datasets covered a period of 12 months spanning from November 2007 to October 2008. The results showed similar wind speed trends; a feature that may, to a certain extent be attributed to the relative proximity of the locations being studied. The monitoring height and the exposure of the wind measurement sensors were important factors to be kept in mind when comparing wind behavioural characteristics. As expected, the site with the highest instrument cluster exhibited noticeably higher wind speeds than the rest of the locations. The wind monitoring stations were in open, built or semi-built environments and the results generated should be useful to estimate performance characteristics of small wind turbines at similar locations.