AT the dawn of the 21st century we are being faced with one of the toughest challenges ever - to secure energy supply. Energy consumption is expected to increase up to about 40 per cent by the year 2010.
An increasing world population, an enlarged global economy and an improved standard of living all contribute to greater demands for energy. At the same time, we are facing the greatest threat to our survival on planet earth: global climate change.
We urgently need alternate sources of energy that are sustainable and clean. Wind energy has an important contribution to make and is penetrating the energy market very successfully, especially in Europe which has a 70 per cent share of the global wind energy industry.
Backed by effective policies, the wind energy industry is experiencing a remarkable growth of 20-25 per cent a year. It is imperative that Malta starts playing a serious role in renewable energy, as it successfully did in other sectors, such as information technology, finance and tourism. Our small size is no excuse for keeping us lagging behind.
The Maltese islands enjoy favourable amounts of wind. Although we do not have enough land to build onshore wind farms large enough to meet our energy demands, there is plenty of space offshore.
Yet exploiting the offshore wind energy potential is not an easy task. In this article I will discuss briefly the various aspects of offshore wind energy and how these can influence Malta's offshore wind farm planning and development in the years to come.
The European scenario
It was only after a few years of operating onshore wind farms that various European countries realised the vast potential of moving offshore.
The mean wind speed out at sea is larger than on land. Also, placing wind farms offshore reduces their environmental impact onshore.
There is an enormous additional wind resource to be found in the seas around the coastline of Europe. An EU research programme carried out way back in 1993-5 estimated that the offshore wind potential far exceeded the total electricity consumption within the Union's 15 members in 1997.
Several European countries, led by Denmark, are already seeing the first large scale offshore wind farms built in their territorial waters. In 2002, the first large offshore wind farm was constructed at Horns Rev, about 20 km from the Danish North Sea coast.
Eighty turbines were installed, giving a total capacity of 160 Megawatts, which is equivalent to two per cent of Denmark's demand. In the UK, 15 wind farms with a total capacity of 7,200 MW are now being planned in three strategic areas off the country's western and eastern coasts.
Germany's offshore plans are much more ambitious. The target of the German government is to see up to 25,000 MW of offshore wind farms by 2025-30. This would satisfy approximately 15 per cent of Germany's demand. Other European countries with advanced offshore plans include the Netherlands, Ireland, Sweden and Belgium.
The offshore challenge
Going offshore meant that wind turbine technology had to meet the largest challenges ever. It meant new technical demands. The wind turbines must be firmly installed on the sea bed by using various foundation designs.
The foundations and tower should be tougher to resist the fierce waves splashing over the installations in rough sea conditions. Also, specially designed sea vessels are required to carry the wind turbine components and install them in place.
Cables must be laid on the seabed to connect each turbine generator to the grid. Operating and maintaining an offshore wind farm is also more consuming both in terms of time and money. Gaining access to the individual turbines is a major issue. A sea vessel or helicopter is required. There is no doubt that this is far more expensive than simply using a truck that is otherwise used onshore.
Health and safety measures become even more imperative, so workers need to undergo more rigorous training. All these factors contribute to additional costs, making an offshore wind farm on average 50% more expensive than one onshore.
Improved technology together with lessons learnt from operating existing wind farms will reduce the cost of wind energy in the coming years, making it more economical. There are four main factors that will help us achieve this:
1) Increase in wind turbine size - it has been shown that using larger wind turbine diameters will make wind energy cheaper. Installing and operating a single large wind turbine is cheaper than doing so with two small turbines which together have the same capacity of the large one. Also, a large wind turbine is more aerodynamically efficient than a small one. Larger wind turbines provide more energy per kilogramme of weight, leading to material savings. By increasing the rotor diameter it is possible to capture the wind flowing at higher altitudes where energy intensity is larger. All these benefits have led manufacturers to construct larger turbines, the largest being in the range of 100-120 m in diameter to provide 3-5 MW of power.
2) Improved reliability - Lightning strikes on wind turbine blades and the corrosive environment at sea are two major causes of increased turbine downtime in existing offshore wind farms. Lightning protection systems are under development to withstand the effects of lightning strikes. Manufacturers are now more aware of which turbine components are most susceptible to corrosion and will modify designs accordingly.
3) Improved maintenance planning - maintenance planning of a wind farm is different from that of a fossil-fuel power station since wind availability is quite unpredictable. To reduce wind farm cost, all effort should be made to ensure that every wind turbine is operating when the wind is blowing. Maintenance should be carried out only when no wind is available. Thus maintenance planning procedures should be conditional rather than scheduled. Modern performance monitoring technology will be helpful in detecting the onset of technical problems as early as possible.
4) Training for maintenance personnel - at the moment maintenance work on an offshore wind turbine is taking on average two to five times the time needed on an onshore wind turbine. As more experience is gained on how to operate offshore wind farms, more appropriate training courses will be organised for maintenance personnel on how to be more efficient at work in an offshore environment.
Yet we have to face a much greater challenge if we are to exploit wind potential to the full. It concerns the depth of sea. Wind farm capital cost increases with sea depth, since deep seas require taller towers and stronger foundations.
Current offshore wind farms are located in shallow waters close to the shore or on reefs. Horns Rev is only six to 15 m depth. Research has shown that, although technically possible, offshore sites deeper than 25 metres are still too expensive to be viable. Floating offshore wind farms are also technically possible but still not viable.
The Maltese offshore potential
Despite our relatively large territorial waters, we lack the availability of shallow waters less than 25 m deep. A look at the sea depth distribution around the Maltese islands reveals that we are surrounded by seas of about 60-190 m deep.
However, there are a few reefs close to the coast. The largest reef is known as Is-Sikka l-Bajda, which is located about 2 km east of Mellieha. Here there exist shallow waters on a stretch of approximately 7 km2 of sea.
A preliminary assessment of the area suggests that as many as 15 large wind turbines (about 100 metres diameter) may be located at this site. Such turbines would have a capacity of about 3 MW each, so the wind farm has a total capacity of 45 MW. This amounts to about 10 per cent of our energy needs, which is very encouraging.
Yet other considerations need special attention and these demand months (and even years) of research to assess the viability of building such a wind farm. First and foremost we are unaware of the wind resource at this offshore site and we need to investigate whether there is enough wind to make the installation of turbines worthwhile.
This is imperative in attracting potential investors to the development. Based on experience, offshore wind energy costs €1,500/KW. There should be scientific evidence to convince planners that the proposed site will provide a sustainable return on investment.
Wind data gathered on land in past years may be used to extrapolate wind speed distributions at offshore sites. Modern satellite technology can also help in quantifying the wind speeds.
However, nothing would be more accurate than to have a 60 to 100-m tall wind measuring mast installed on the offshore site. Certainly this is more expensive than one installed onshore. But this is a necessity if we are to reduce development risk.
Secondly, a geological survey is needed to establish what type of rocks make up the seabed and thus evaluate what type of foundation would be most suitable.
An environmental impact assessment is needed to determine what type of birds and marine creatures inhabit the site and how these may be affected with the installation of the turbines. Archaeological remains should be properly identified to ensure that they are not damaged.
Apart from is-Sikka l-Bajda, there are other sites of shallow waters around the Maltese coast that could be developed for offshore wind energy. All such sites require a similar assessment if sustainable development is to be assured.
With the availability of only very limited areas of shallow areas, Malta cannot compete with the ambitious offshore wind energy developments currently under way in other EU countries. But certainly we should keep a watchful eye on the technological progress in the years to come.
As the cost of turbines will go down, it would become profitable to construct wind farms in deeper water, thus enabling Malta to expand its potential. The time will come when floating offshore wind farms also become feasible and this will open our doors to exploit our wind resources to the full.
The future of offshore is onshore
There are many who are opposing the idea of constructing wind farms onshore, due to lack of space, but are in favour of having them offshore. Surely we cannot afford using our limited countryside for wide scale exploitation for wind energy.
I certainly agree that although this is the cheapest solution, it is environmentally unacceptable. But easier said than done. There is a long way to go for us to learn how to plan, manage and maintain offshore wind farms.
We have no experience of wind energy in this country. As already explained before, offshore wind farms are more challenging than onshore. We should therefore allow some time to accumulate enough experience and knowledge on the subject before embarking on an offshore project.
Considering our limited feasible offshore potential at the moment and the fact that we lack experience of wind farming, it is vital to start with some wind turbines onshore.
Wind energy is also more environmentally friendly than it seems to be. Unlike the ugly modern urban developments like Bugibba, wind farm development is more environmental pleasing for the simple reason that the turbines, though massive, can easily be removed, leaving practically no impact on the environment where they were installed originally.
So we can install a few turbines onshore until technology provides us with the practical solutions of how to build wind farms in our deep seas. Thereafter, the onshore wind turbines will be removed and moved to sea.
The advantages of using large-diameter wind turbines for offshore sites are also applicable for onshore developments. For onshore applications, noise emissions and aesthetic impact become major concerns.
Noise emissions per kilowatt hour of energy production for larger turbines are lower than for smaller ones. It is also more aesthetically pleasing to have a wind farm with a few turbines of larger diameter than a wind farm with a larger quantity of small diameter turbines. For the Maltese onshore environment, we cannot afford having large wind farms consisting of 15 to 20 turbines each. How and where to position the turbines requires sensitive treatment.
I personally think that it is best to have very small wind farms consisting of only two to five turbines located at different spots around Malta and Gozo. I think the onshore space in Malta can only allow for not more than 15 three-MW turbines contributing to an overall capacity of 45 MW.
Bird migration paths should be well known and land-based wind farm developments should be coupled with construction of new bird sanctuaries consisting of tall trees and fresh water ponds. Birds are attracted to tall trees and water ponds. By locating sanctuaries far away from the wind farms it is helpful to divert bird migration paths away from these farms.
Ing. Sant is an assistant lecturer in the Mechanical Engineering Department of the University of Malta. In 2003, the department started a research project in wind energy in collaboration with Delft University of Technology of The Netherlands. The project aims to develop improved simulation methods for more accurate performance prediction of wind turbines. E-mail: tsant@eng.um.edu.mt