IEEE TRANSACTIONS ON SUSTAINABLE ENERGY, VOL. 6, NO. 1, JANUARY 2015 281 Automatic Contour-Based Road Network Design for Optimized Wind Farm Micrositing Huajie Gu, Jun Wang, Senior Member, IEEE, Qin Lin, and Qi Gong Abstract—Constructing the access roads between wind turbines Aop Overlapping fraction of a wake with a down- requires a significant cost when a wind farm is built in hills or wind turbine rotor plane. mountains. An optimized design of road network can substantially AEP(z) Annual energy production of a turbine layout z. reduce construction costs and increase investment returns. In this paper, we consider a challenging problem of the road network ci Label of the ith node (contour) in a contour tree. design for a wind farm with complex topography. An automatic Ct Turbine thrust coefficient. contour-based model is developed for road network design, and Da Rotor diameter of turbine “a”. is incorporated into the optimization of wind farm micrositing to Eij Edge between the ith node Vi and the jth node maximize investment returns of the wind farm. The directions of V in a graph. access roads are first deduced from a contour tree, the route pro- j jections are then designed by a gradient-bounded algorithm, and G(V , E) Complete graph with nodes V and edges E. the most cost-effective road network is finally obtained by the min- gr Road gradient. imum spanning tree algorithm. The topographic speedup, wind hwt Hub height of a wind turbine. resource grid and Park wake model are incorporated to accurately LRN(z) Total length of a road network for a turbine evaluate the power production of the wind farm. Both the profit of layout z. wind energy sales and the cost of access roads are combined into a cost function called net present value, which is optimized using MST(V , S) Optimal road network represented by the mini- genetic algorithms. Simulation results illustrate that the length of mum spanning tree with nodes V and edges S. access roads is decreased significantly while the locations of wind Nd Number of wind sectors (directions) on a wind turbines are optimized. The proposed method simultaneously opti- rose. mizes the turbine layout and road network of the wind farm, N Number of generations in genetic algorithms. therefore achieving a more practical and profitable wind farm gen micrositing. Npop Population size in genetic algorithms. Nt Number of wind turbines. Index Terms—Access roads, contour tree, micrositing, road Turbine power output at wind speed network, wind farm. P (v) v. R Radius of the auxiliary circle used in route NOMENCLATURE projection. T (V , U) Spanning tree with nodes V and edges U. α Wake decay constant. v Wind speed. δ Topographic speedup or speeddown of wind in xyi v ,v Incident wind speed at turbines “a”and“j”, the ith direction at the location (x, y). a j respectively. ∆h Contour interval. c v Cutin wind speed of a turbine. ∆v Wake deficit. in v Cutout wind speed of a turbine. κ Shape parameter of Weibull distribution in the out i v Mean wind speed for a pair of Weibull parame- ith wind direction. i ters κ and λ . λ Scale parameter of Weibull distribution in the i i i v Mean wind speed in the ith wind direction at the ith wind direction. xyi location (x, y). ρ Frequency of wind occurrence in the ith i V ith node of a graph. direction. i Wc1,cM Road direction between the contour c1 and the Ab Area of rotor plane of turbine “b”. contour cM . Manuscript received February 04, 2014; revised May 28, 2014 and August xab Downwind horizontal distance between turbines 28, 2014; accepted October 11, 2014. Date of publication December 08, 2014; “a”and“b”. date of current version December 12, 2014. This work was supported in part by the National Natural Science Foundation of China under Grant 61075064 z0 Surface roughness length of a wind farm. and in part by the International Science and Technology Co-operation Program z Layout of turbines. of China under Grant 2011DFG13020. (Corresponding author: Jun Wang.) Paper no. TSTE-00048-2014. H. Gu, J. Wang, and Q. Lin are with the Department of Control I. INTRODUCTION Science and Engineering, Tongji University, Shanghai 201804, China (e-mail: [email protected]). IND ENERGY is nowadays widely used as a promis- Q. Gong is with the Department of Applied Mathematics and Statistics, W ing renewable energy. A wind power generation station, University of California, Santa Cruz, CA 95064 USA. also called a wind farm, usually consists of a large number of Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. wind turbines. Once a suitable site is allocated for a wind farm, Digital Object Identifier 10.1109/TSTE.2014.2369432 empirical or systematical methods can be utilized to optimize 1949-3029 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. 282 IEEE TRANSACTIONS ON SUSTAINABLE ENERGY, VOL. 6, NO. 1, JANUARY 2015 TABLE I results in a more technically feasible and economically benefi- INITIAL INVESTMENT BREAKDOWN OF TYPICAL ONSHORE cial micrositing of wind farms. The remainder of this paper is WIND FARMS [1]–[5] organized as follows. Section II proposes an automatic model for road network design. The problem of wind farm microsit- ing is formulated in Section III. Section IV gives the simulation results. Finally, Section V makes some concluding remarks. II. AUTOMATIC ROAD-NETWORK DESIGN MODEL The configuration of the road network for accessing the the turbine layout in terms of energy production and/or finan- turbines on a farm from its entrance is similar to a tree cial income by considering the effects of local wind resources, structure. It can be transferred into an undirected graph by wake effects, terrains, etc. mapping the turbine layout z into the nodes V ,andthe In the micrositing process, the number and the type of wind roads between them into the edges U.Therefore,asolution turbines, civil works, and electrical infrastructure all influence to the road network is an undirected graph T (V , U),where the economy benefits of a wind farm project. Table I shows V = V1,V2,...,VNt , U = U12,U13,...,Uij ,... , i, j the initial investment breakdown of typical onshore wind farms 1, 2,...,N{ , i = j with} N be{ the total number of turbines.} ∈ { t} ̸ t [1]–[5]. As wind turbines account for a major proportion of The edge Uij of the graph represents the road between the ith the wind farm initial investment, previous researches mainly and jth turbines. The most cost-effective road network can be focused on optimizing the number and locations of wind tur- found by calculating the corresponding minimum spanning tree bines. In [6] and [7], the genetic algorithm was proposed to with assigned weightings for each edge. For a wind farm on a iteratively optimize gridded turbine layouts on flat terrains. In flat terrain, straight lines directly connecting any two wind tur- [8] and [9], the greedy algorithm was introduced to search bines can be considered as edges [2], [3]. However, for a wind for the optimal gridded turbine layouts on hilly wind farms. farm built in hills or mountains, roads are usually polylines or The modified particle swarm optimization algorithm [10] was curves, and topographic constraints should be considered in the applied to solve the turbine layout optimization problem in a design so that a feasible route can be built and reasonable road continuous solution space. cost can be evaluated. The civil works include the construction of access roads, In civil engineering, a feasible route between the starting and turbine foundations, crane hard-standings, cable-trenching, and end points is selected by establishing a series of control points substation buildings. Their cost can be substantial. Access roads on the terrain. Using these control points as an initial align- are greatly influenced by topographic characteristics, and their ment, the horizontal and vertical curves are then located, subject cost is much higher for hilly or mountainous wind farms than to the road design constraints including geometric specifica- plain ones [1]. A comparative strategy [2] and the minimum tions and environmental requirements. Heuristic optimization spanning tree [3] were proposed to search for the shortest road algorithms such as the genetic algorithm, the Tabu search, and network for wind farms in flat areas. In [11], the Euclidean the simulated annealing algorithm [13]–[15] have been applied Steiner tree was introduced to further reduce the length of to optimize horizontal and vertical alignments of roads. These the road network. However, these methods are not directly algorithms depend on a high-resolution digital elevation model applicable to hilly or mountainous wind farms where the road to support the analysis of road design features such as ground gradient must be considered to build winding roads capable of slopes and other landform characteristics. The calculation of an accommodating significant weight. optimal route between two given locations is time consuming Wind farms are generally constructed in rural areas with and could even take several hours. challenging topography. With the rapid expansion of wind The micrositing optimization process usually involves hun- farms, new farms have to be built in hills or mountains, where dreds or thousands of iterations to evaluate the wake effects designing suitable access roads for construction, turbine erec- between turbines and to update the turbine layout. The pro- tion and maintenance is not straight forward. It is necessary cess without road design is already intensive [2], [3], [6]–[10], to know roughly which route should be chosen to connect tur- [16].