1st Wind Farm Siting Challenge - Assessment part 1
To determine the best technical and economic area several datasets were required to provide information about the options to develop offshore wind turbines. Datasets were searched to support the following objectives:
- An economical and viable development needs a market for the electricity it produces. This means the presence of cities, ports or large industrial sites. Alternatively, high voltage connection points can also be used to transport the electricity to a market. Currently existing connection points are often located near cities, ports, large industrial sites and power stations (conventional/nuclear/etc.);
- Developing offshore wind energy also requires facilities like ports, quays and cranes to support the activities of building, operating and maintaining the turbines and the supporting infrastructure of cables and transformer platforms. This also means the necessary on-shore availability of motorways, railways and airports, e.g. to allow specialized persons or replacement parts quick access to the area.
Locations that satisfy objectives 1 and 2 are presented in Table 1 and figure 1.
Table 1 Locations representing both the presence of a market and infrastructure available for offshore wind energy development (data from a.o. Wikipedia and other websites of municipalities and ports). Suitability or presence of infrastructure is indicated as follows: 0 absent/unsuitable; 1 present/suitable; 2 with limitations.
|Name||Inhabitants||Port Maint||Port Cons||Heavy Ind||Grid Connect||Railroad||Motorway||Airport||Country|
Figure 1 Map of the Norwegian Sea and Barents Sea showing the locations from the table above, based on assessment 1 and 2. Yellow-to-orange colours indicates the identified area is suitable for offshore wind farm development, darker colours signify higher mean wind strength.
Once the locations with suitable market and infrastructure are identified, two further datasets become important:
- Bathymetry (water depth, metres) (GEBCO 2014 gridded bathymetry 0.0083 degrees)
This indicates locations with suitable water depths that are compatible with either a fixed or a floating offshore wind turbine.
- Wind strength (m/s) (Copernicus Marine Environmental Monitoring Services or CMEMS)
CMEMS has a set of satellite-derived datasets (with global coverage 0.25 degrees) available covering six recent years of monthly wind climatology. Data is available for a total of 59 of the 72 months of the six year period. To ease the analysis an average wind resource was calculated and applied.
The data collecting instrument on the satellite, a scatterometer, comes with its own limitations. One of these is that a scatterometer cannot determine wind speeds over land or over an ice-covered sea. Thus the average wind resource dataset has no data where sea ice has prevented observations during the observation period. However this is not a severe problem given the current technology.
There is sufficient data available for the wind resource dataset. The available wind resource for the Norwegian Sea and, where data is available, the Barents Sea, is comparable and possibly somewhat larger than that for the North Sea. This dataset also provides the resolution used in the analysis. By combining the market and infrastructure datasets with coastline geography datasets (Arctic countries coastlines), a third important dataset was developed, Distance to port and market
This is useful to determine how far it is possible to develop an offshore wind farm. This distance is an important economical factor as it determines many costs, such as length of the HV-cables that bring the generated power to the market, and the travel time required when building, operating and maintaining the wind farm.
Assessment Part 1
To properly interpret the datasets outlined above it is necessary to make some realistic assumptions about offshore wind technology options: .
- How far from port and market it is economic to attempt to develop OWE.
The maximum distance within the North Sea, currently one of the best developed OWE areas, is a little over 200 km (close to the centre, on the Doggerbank). For the purpose of this study the upper limit was set at 250 km.
- How water depth is likely to interact with offshore wind turbine technology.
- Fixed OWT can be built to water depths to about 50 m deep, with several construction options including monopoles, tripod, jacket and gravity-based (concrete) foundations structures. This choice more or less follows the current state of technology in the North Sea
- Floating turbines can be built in water depths starting from ca. 100 m. to ca. 500 m. deep. These numbers match with pilot installations and early wind farm developments for turbines such as the HyWind (SPAR-type) and WindFloat (floating jacket). This technology is still in its infancy and not many such turbines are currently in operation.
Data assembled by the EU-project ACCESS on a.o. SPAR-type platforms (D 4.21) shows that these are reasonable assumptions
Sea ice and offshore wind turbines
Offshore wind parks have not yet been built in (sub-)Arctic waters, where sea ice (or larger ice floes) can occur. Technically it is possible to build wind turbines strong enough to withstand the forces exerted by sea ice. It increases their cost for which the economics of offshore wind turbines do not allow. Icing of the turbines blades can form one more complication that requires both technical attention and increases costs of maintenance. The pragmatic choice made for this study to not suggest OWE development in ice covered waters due to the lack of satellite wind speed data over ice covered sea areas is therefore also justified by economics.
While technology options to construct ice-resisting OWT do exist (see reports of ACCESS), the increased costs make them not currently viable. This is an active field of research within wind turbine development.