The evolution of wind farms from land-based to offshore locations is gradual but surely significant. Stronger winds, better technologies and less impact on real estate value make offshore wind farming the ‘sexiest’ side of this industry in its attempts to meet the high electricity demands of heavily populated coastal areas.
To date, most offshore wind farms have been in shallow waters just off the coast and locations have been largely dictated by the shallowness of the sea bottom because the foundation technology has focused on a limited depth solution. Innovaxin Consulting is working on a design that will eventually push the depth threshold to 120m of water using ‘conventional’ technology from the oil and gas industry where jack-up platforms have been in use for a number of years. The proposed designs are purpose-built jack-ups using the same principles as those in the oil and gas industry but different weight parameters.
Stronger winds, better technologies and less impact on real estate
value make offshore wind farming the ‘sexiest’ side of
this industry in its attempts to meet the high electricity demands
of heavily populated coastal areas (Courtesy Corbis.com)
Jack-up platforms designed for the task can be built at a very attractive price. Initial estimates for an operational depth of 30m jack-up housing a 2.6 MW WTG are in the region of US$ 2 million or even less and that includes delivery with a WTG and on-site commissioning. This price is very competitive with conventional land-based operations and also with constructions in shallower waters using either gravity foundations or drilled monopoles.
There is no need for expensive on-site installation. Jack-ups can be
towed into place and sited during a brief weather window (Courtesy Corbis.com)
Jack-ups have several advantages, as listed below:
However, jack-ups have the following disadvantages:
Going to deeper waters also means longer shoring cables. However, this may be a blessing in disguise and the technology is available to shore back cables over any distance. Over a 20 km distance from the shore the wind farm will be seen as a hazy blotchy line on the horizon and the noise signature will be irrelevant.
It may also be pertinent to note that offshore wind farms using a three-legged jack-up can also be used to house fish farming cages between the legs of the wind farm. Production of edible fish would be beneficial to the economics of the farms.
A jack-up design is in the process of being finalised to meet American Bureau of Shipping (ABS) standards, this being the de facto authority working with these platforms for a number of decades. The design is patented. Innovaxin Consulting, along with other partners, is in the process of rolling out two such farms, one in North America and another offshore from Malta, although details of the latter are still on the drawing board.
Without the need for heavy lift equipment, the building
process is quicker and cheaper. (Courtesy Seacore)
A modular approach to jack-up construction using low-cost building facilities in the Far East and the final assembly as near as possible to the site reduces the cost of production substantially and thus has benefits for the economics of the wind farm. The price of the platform is a function of the price of steel and the labour costs for assembly. However, a currency risk exists where funding is not in US dollars as most steelworks in the Far East only accept payment in US$.
Insurance costs based on actuarial statistics on jack-ups in the hydrocarbon industry built to ABS standards are highly competitive given the good historical records of these structures.
The evolution of deep offshore wind farms will mean bigger areas of no-go navigation for commercial shipping. New lanes have to be devised and proper lighting initiated. The radar signature of a jack-up is far more specific than that of a monopole. Given the proximity of the legs to each other, gangways to link the platforms above sea level are possible. These gangways can also be used to connect all the platforms to the final point from which the shore cable will leave the farm.
A jack-up platform-mounted WTG will stand some 20higher than a similar WTG sited on a monopole. This additional height would mean additional wind energy.
According to hydrographical research conducted in ten countries’ coastal waters by Innovaxin Research and Consulting, there is good potential for wind farms in coastal waters within a range of 50km from the shore. We are confident that a significant amount of energy can be obtained through this method, and with wind farms stretching across several kilometres and connected to the national grid at different points as much as 20% of typical national electricity need can be met this way.
So far, only a few countries have asserted jurisdiction on wind as a national resource. Most projects we are familiar with have been ‘entrepreneur-driven’. The maze of regulations to master is significant. Given the innovative aspect, size and importance of these investments several constituted authorities have a vetoing say in the developments. For governments to encourage use of this resource much has to be done on jurisdictional, legal, fiscal, financial, regulatory and economic aspects of offshore wind farming.
When the price of oil and gas is soaring because of structural demand shifts, government action in this direction is fundamental, urgent and necessary to promote these key renewable sources of energy.
The prospects for deep offshore wind farming are very bright indeed. As the industry matures, costs continue to come down and the 5 MW WTG becomes more stable, the benefits of siting wind farms offshore become clear. We are approaching a point where the benefits are tipping the challenges of deep offshore wind farming at a rapid rate. We reckon that during the next 36 months this alternative and innovative way of generating renewable energy will become the norm rather than the exception.
This article appeared in the volume 1, Nr. 8 / 2005 issue of Windtech International and is republished with permission of the authors and publisher.
German Wind Energy Association BWE e.V.
http://www.wind-energie.de/de/themen/offshore/
German Federal Ministry for Environment
http://www.erneuerbare-energien.de/inhalt/4591/
dena-Offshore-Webpage, Germany with further links (focus: Germany)
http://www.offshore-wind.de
Offshore Windenergy Europe, based in the Netherlands
http://www.offshorewindenergy.org/