Definition and Interpretation of Wind Farm Efficiency in Complex Terrain: A Discussion

[+] Author and Article Information
Davide Astolfi

Department of Engineering,
University of Perugia,
Via G. Duranti 93,
Perugia, 06125, Italy
e-mail: davide.astolfi@unipg.it

Francesco Castellani

Department of Engineering,
University of Perugia,
Via G. Duranti 93,
Perugia, 06125, Italy
e-mail: francesco.castellani@unipg.it

Ludovico Terzi

Renvico srl.,
Via San Gregorio 34,
Milano, 20124, Italy
e-mail: ludovico.terzi@renvico.it

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received May 15, 2018; final manuscript received December 31, 2018; published online January 18, 2019. Assoc. Editor: Christopher Niezrecki.

J. Energy Resour. Technol 141(5), 055501 (Jan 18, 2019) (7 pages) Paper No: JERT-18-1344; doi: 10.1115/1.4042447 History: Received May 15, 2018; Revised December 31, 2018

The exploitation of wind turbines in complex terrain has recently been growing. The comprehension of wind flow, especially in the downstream area, is by itself a challenging task in complex terrain: even more so, it is difficult to account for the mixing between terrain effects and the wake interactions between nearby turbines. Efficiency is one of the simplest and meaningful metrics for quantifying the impact of wakes on wind farm production, but its definition is well established basically only for offshore wind farms. In this work, the definition of wind farm efficiency is, therefore, discussed, based on the critical points arising in complex terrain, where there can be at the same time a considerable variation of free wind flow along the layout and a directional distortion of the wakes, induced by the terrain. In this work, operational data of a test case wind farm sited in a very complex terrain, featuring 17 multimegawatt wind turbines, are elaborated and inspire a discussion and a novel definition of efficiency, that restores in the complex terrain case the meaning of the efficiency.

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Grahic Jump Location
Fig. 3

The wind direction rose of WF1 at reference wind turbine: frequency distribution

Grahic Jump Location
Fig. 4

The wind direction rose of WF2 at reference wind turbine: frequency distribution

Grahic Jump Location
Fig. 5

Efficiency (according to Eq. (2)) of WF1 as a function of average nacelle position along the wind farm

Grahic Jump Location
Fig. 6

The distribution of efficiency measurements (according to Eq. (2)) for WF1

Grahic Jump Location
Fig. 7

The difference Δ of wind turbine average nacelle wind speed with respect to wind farm average, in units of standard deviation

Grahic Jump Location
Fig. 8

Efficiency of WF1 (according to Eq. (3)) and of WF2, as a function of wind direction at reference wind turbine

Grahic Jump Location
Fig. 9

Efficiency of WF1 (according to Eq. (3)) and of WF2, as a function of nacelle wind speed at reference wind turbine

Grahic Jump Location
Fig. 10

Efficiency of WF1 (according to Eq. (3)) as a function of wind direction and nacelle wind speed at reference wind turbine

Grahic Jump Location
Fig. 11

Efficiency of WF2 as a function of wind direction and nacelle wind speed at reference wind turbine



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