The main port of this research is Den Helder. This may not be the most op-timum location for the main port as the Dogger Bank is in the middle of the North Sea. Due to this reason, the outcome of the best strategy may differ when the location of the main port is changed. For optimal results regard-ing the effect of changregard-ing the location of the main port, the strategy is cho-sen which operates completely from the main port, which are strategy 1 and 2. The different main ports which are compared are Den Helder and Rotterdam in the Netherlands, Hull and Aberdeen in the United Kingdom, Hamburg in Germany and Esbjerg in Denmark. These ports are terminal ports according to Searates and the marine route between the ports and the Dogger Bank is given by Marine Traffic and the distance can be seen in Table 17.
The data will be compared on the up time of the wind turbines and the as-sociated transportation costs, this can be seen in Table 18. Interesting to see is that main ports which are further away have worse results. This will be further discussed in the conclusion.
Table 17: Distance between Dogger Bank and ports Port Distance to Dogger Bank [nm]
Den Helder 174
Rotterdam 195 Hull 128 Aberdeen 196 Hamburg 298 Esbjerg 221
Table 18: Results due to different main ports
Port Up-time [%] Transportation costs [$]
Den Helder 95.0 34.4 M
Rotterdam 94.4 36.7 M
Hull 96.4 26.3 M
Aberdeen 94.2 37.9 M
Hamburg 20.4 49.3 M
Esbjerg 87.9 42.5 M
7 Conclusion
Based on this research several conclusions can be drawn regarding the transport for maintenance of large offshore wind farms. The main conclu-sion to be drawn is regarding the optimal strategy within the boundaries and requirement for this research. Next to the optimal strategy, there can be concluded certain things about the manner of logistics, number of ves-sels and place of the operation base. The results of the optimal setting of each maintenance strategies can be seen in Figure 1. This graph shows the required number of vessels with their transportation costs to achieve the required availability of the wind farms.
Figure 1: Results of the optimization of each maintenance strategies The optimal strategy is when the operation base is located at the offshore artificial island, which is in the center of gravity in between the offshore wind farms, in combination with individual logistics, indicated as strategy 5. This strategy requires 3.6 million dollars for the transportation costs to reach up to 95 % up-time of all the wind turbines.
32,1 34,4
Another conclusion which can be made is based on the location of the op-eration base. The impact of changing the location of the opop-eration base is enormous regarding the transportation costs. The strategies where the op-eration base is located onshore requires the most transportation costs as the vessels must transfer the complete offshore route for each mainte-nance operation. Strategies which operate partly onshore and offshore show less transportation costs but in the same order of magnitude due to the major replacements which are still operated from the onshore base.
The major replacements require significant higher transportation costs.
The strategy with the complete operation base offshore only requires a fraction, approximately 10 to 15 %, of the transportation costs. Therefore, it is preferred to have the operation base close to the wind farms to reduce the transportation costs.
The manner of logistics also has effect on the transportation costs. The re-sults show that individual logistics is preferred over grouped logistics when only looked at the transportation costs. However, the grouped logistics re-quires less vessels to maintain the required up-time of all wind turbines but in this research, this is not considered. This conclusion will be further dis-cussed in the discussion and recommendations.
The conclusion regarding the spare parts is that there is approximately daily need for a new spare part. These spare parts must be transferred from the main port to the wind farms. This transfer requires a vessel which can heavy lift these spare parts, such as an HLV. There are also restock vessels which can make the transfer to the offshore operation bases, but this re-quires more research regarding the size, costs and possibilities of these ves-sels.
Regarding the location of the main part is an interesting correlation notice-able. As stated, the location of the main port within the strategy where each type of maintenance is operated from onshore to emphasize the difference.
The correlation is between the distance between the main port and the Dogger Bank and the performance of the operation. Even up to the point where the overall availability of the wind turbines is down to 20 %. This re-sult stresses the importance of the location of the main port.
8 Discussion
In this section certain discussion points are listed as they possible have cer-tain (negative) effect on the research. These effects can be due to the neg-ligence of certain parameters but also regarding interesting new research topics.
The most important discussion point is regarding the transportation costs.
The transportation costs are solely calculated on the length of each mainte-nance operation. This calculation does not consider other affecting costs such as the investment costs of the vessel, maintenance costs and addi-tional costs when the vessels are not in operation. For example, the reason that grouped logistics are more expensive than individual logistics is that when a vessel arrives at the operation base it immediately has to return back to the wind farm for a new maintenance operation with additional crew and this can cost up to two times the daily price. This differs from the individual logistics because there is a higher change that a vessel will be waiting when maintenance notification arrives and prevents the additional costs. This discussion point will be further elaborated in the recommenda-tions.
As said in the conclusion the location of the operation base has enormous impact. However, during this research it was effortless to change the loca-tion of the operaloca-tion base but, this will bring a lot of issues. For example, the price of the operation bases variate and will have influence on the total transportation costs. If looked at the offshore artificial island, the results show that there will be roughly 30 million dollars available each year for other investments which potentially could cover the cost of such island.
This research differentiates three different types of maintenance and rep-resent all the required maintenance for each wind turbines. During this re-search this is a good indication of the required maintenance and is enough to distinguish the results between the strategies. However, when a research demands more realistic values regarding the exact outcome of transporta-tion costs, length of maintenance operatransporta-tions and maintenance costs, it is required to differentiate between more types of maintenance and with ad-ditional data. In short, this research indicates the differences between dif-ferent logistic strategies but not exports specific raw data regarding realis-tic scenarios.
9 Recommendations
The first recommendation is based on the transportation costs. As earlier stated, the transportation costs in this research are not completely investi-gated. For instance, the transportation costs can include the investment of vessels, the costs of operation bases and the amount of technician. This field of study requires a lot of investigation regarding different kind of ele-ments and further research will result in more realistic values regarding the transportation of maintenance operations.
The second recommendation is regarding the routing of the vessels. This research has a simplistic manner of routing the vessels. In further research, the vessels must involve the maximum duration of the vessel's operation.
When this is involved, the vessel can stay at the wind farm for this period and can maintain multiple maintenance operations during one trip. Poten-tially, this will be positive for the response time of the operation, the num-ber of required vessels and the total transportation costs.
The third recommendation is to investigate regarding the spare parts. The maintenance operation requires spare parts and within this research sev-eral assumptions were made but to be confident about the transport of spare parts and the required capacity, further research is required. The re-search can involve the exact statistics regarding the requirement of the spare parts for the wind turbines but also involve the physical characteris-tics. These characteristics can provide information regarding the capacity of the vessels, requirements of the lifting equipment. This research will re-sult in more realistic values regarding the costs and capacity of spare parts.
References
4C-Offshore, 2018. Global offshore map. Available at: <https://www.4coff-shore.com> [accessed 8 August 2018].
Carrol, J., McDonald, A. and McMillan, D., 2016. Wind Energy 19, pp. 1107.
Dewan, A. and Asgarpour, M., 2016. Reference O&M Concepts for Near and Far Off-shore Wind Farms.
Dinwoodie, I., Endrerud, O.E.V., Hofmann, M., Martin, R. and Sperstad, I.B., 2015.
Wind Engineering 39, pp. 1
Esteban, M.D., Diez, J.J., Lpez, J.S. and Negro, V., 2011. Renewable Energy 36, pp.
444.
Forewind, 2010. Environmental impact assessment scoping report.
Forewind, 2014a. Dogger bank - Creyke beck a & b, chapter 5 project description.
Forewind, 2014b. Dogger bank - teesside a & b, chapter 5 project description.
Marine Traffic, 2018. Marine traffic voyage planner. Available at: https://www.mari-netraffic.com/nl/voyage-planner > [Accessed 24 July 2018].
Martin, R., Lazakis, I. Barbouchi, S. and Johanning, L., 2016. Renewable Energy 85, pp 1226.
Scheu, M., Matha, D., Hofmann, M. and Muskulus, M., 2012. Energy Procedia 24, pp.
281.
SeaRates, 2018. Searates lp. Available at: < https://www.searates.com/maritime >
[Accessed 11 October 2018].