Access restrictions to some wind farm sites may, in future, limit the size of blades and hence the rating of the turbines that can be used. The concept of constructing blades in two or more sections, which are then assembled on site, is assessed here through a comparison of two conceptual designs. The first is a tubular connection, which has been tested at scale model size; the second is a bolted connection, which has been manufactured and tested as a prototype sectional blade. The results are compared with the equivalent conventional blade design and an economic assessment of the viability of the sectional blade concept is presented.
A public report is available as a download.
This concept was implemented at prototype scale (23.3m blade). It was an existing LM23.3 blade without tip-brake and the connection was at 7.3m.
Step 1: Measure increase in manufacturing costs for prototype (23.3m) sectional blade compared to standard blade
Result: Cost increase (23.3m) 68%
Step 2: Estimate increase in manufacturing costs for likely full-scale implementation (60m) - these are proportionately much less since the relative proportion of the blade which must be strengthened is less
Result: Manufacturing cost increase (60m) ~19%
Step 3: Estimate saving in transport costs for typical journey (LM Denmark to Hannover, Germany)
Table showing comparison between cost price of 60m blade and transport costs (for access to a typical wind farm site)
Result: Transport cost saving ~5% (more for a less accessible site)
Conclusion: Likely cost increase for 60m sectional blade ~ 14%
In order to get a deeper understanding of the blade to blade variations and to determine the statistical distribution of the fatigue strength of rotor blades, 37 small rotor blades have been tested in static and fatigue loading. Besides these blades, a number of coupons of identical material as that of the blades has been tested statically and under fatigue loading.
Static and fatigue tests on rotor blades:
Static and fatigue tests on coupons:
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