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Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'Optimising measurement strategies to maximise project value: Is the industry making false economies at the expense of project value?' taking place on Tuesday, 11 March 2014 at 11:15-12:45. The meet-the-authors will take place in the poster area.

Konstantinos Gkarakis HWEA - TEI Athens, Greece
Co-authors:
Konstantinos Gkarakis (1) F P Konstantinos Loukidis (2)
(1) HWEA - TEI Athens, Marousi, Greece (2) ENTEKA SA, Chalandri, Greece

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Abstract

Evaluation of pre/post construction energy of a windfarm in complex conditions with different measurement strategies

Introduction

A resource assessment wind measurement campaign is one of the most important factors in the estimation of the energy yield of the proposed windfarm. Using longterm correction of short term measurements and special software packages, the predicted energy yield has been calculated. Also, an uncertainty study has been included. After the construction of the windfarm, it is useful to be compared the real productions with the energy estimations has been performed based on the wind resource assessment.

Approach

This study estimates and compares the annual energy production results using four different scenarios of measurement strategies (two meteorological masts – different time periods: one-three years) with the real energy production of the windfarm for two years. The estimated energy yield has been corrected using available mesoscale data. The uncertainty of the assessments was taken into account and a comparison of the probability values with the corrected real production has been additionally performed.

Main body of abstract

The windfarm has capacity of 2,7 MW and it is located in extremely complex terrain in the island of Kefallonia, Greece. In the area of the windfarm were installed two met masts of 10m and 30m in small distance between them with total operation period of seven years. Three years of data at 10m mast and one year at 30m mast have high availability. All the energy calculations have been performed using windfarm design tools WAsP 11.0 and WindPRO 2.9. The four scenarios of using different measurement strategies are the following: a) 10m mast – 3 years measurements, b) 30m mast – 1 year measurement, c) 30m mast – 3 years measurements (one year real and two from the use of Measure-Correlate-Predict- MCP – reference 10m mast) and d) parallel use of 3 years measurements of 10m mast and 3 years measurements of 30m mast (real and MCP). The most sophisticated information for oropraphy, roughness, power curve and a check of performance of design tools using RIX factor has been performed.
The using measurements are corrected longterm using mesoscale wind data from ConWx database. Based on the year variability through ConWx data for the project area, has been calculated the estimated energy production for the full two years of operation. Also, the additional losses (windturbine availability, electrical losses, availability of grid, access, environmental factors) has been calculated so to be able to have a successful comparison. Under consideration the probability values, the P(75) and the P(90) values compared to the results of performed study.


Conclusion

The results are showing a slight overestimation in the energy production and reasonable deviations in uncertainty. For a comparison of predicted energy yield with the real energy production, several aspects have to be taken into account due to the fact there is a high amount of possible reasons why a prediction is fulfilled or not. Some factors are technical availability, deviations concerning the used power curve, the differentiation of environmental terms, and the quality of wind measurement campaign. Moreover, the reliability of the long-term correction based on mesoscale data has an influence of the ratio between predicted and real energy productions.


Learning objectives
The measurement strategy has an extremely serious role in the maximization of the project value and the reliable energy assessment yield. This study presents the comparison results in energy estimations with four different measurement scenarios with the real production of a small windfarm of three windturbines in a complex condition (extremely complex terrain, proximity to the sea, influence of local wind systems). The overestimations of the design tools have some possible reasons that have been named.