Elsevier

Solar Energy

Volume 144, 1 March 2017, Pages 286-294
Solar Energy

Optimal solar dish field layouts for maximum collection and shading efficiencies

https://doi.org/10.1016/j.solener.2017.01.024Get rights and content

Highlights

  • Methodology to optimize efficiencies of solar dish field layouts is presented.

  • Theoretical limits for shading and collection efficiencies are derived.

  • Variables are latitude, ground coverage ratio, dish shape, and tracking system.

  • Performance of optimized layouts is compared for 21 locations.

Abstract

We derive the limit for collection and shading efficiencies and describe an optimization methodology of solar dish field layouts based on a general 2D Bravais lattice using local irradiation data and as a function of latitude, ground coverage ratio, dish perimeter shape, and sun-tracking system.

Introduction

Two-axis tracking solar dish systems can deliver highly concentrated solar radiation for advanced solar thermal and photovoltaic applications (Schiel and Keck, 2012, Buljan et al., 2014). At low solar altitudes, the positioning of multiple sun-tracking dishes in a field inherently leads to shading from and to the neighboring dishes. Finding an optimal layout that minimizes losses due to shading poses an optimization problem based on the shaded radiant energy (Groumpos and Khouzam, 1987, Stephens and Angel, 2012), power output (Narvarte and Lorenzo, 2008, Capdevila et al., 2013, Kim et al., 2013), and/or economic aspects (Kim et al., 2013). For a field consisting of only a few dishes, the surroundings and the outline of the terrain play a major role, but the optimal layout can be determined freely using algorithms with reasonable computational efforts (Diaz-Dorado et al., 2011). With increasing field size, these optimizations quickly reach their limit and regular grids are required, such as rectangular with and without staggering of rows (Igo and Andraka, 2007, Stephens and Angel, 2012). In this work, we focus on maximizing the solar radiant energy collected by dishes in large fields at fixed ground coverage ratios and derive theoretical limits for the shading and collection efficiencies. This methodology enables rating of layouts as a function of location, ground coverage ratio, dish perimeter shape, as well as sun-tracking system. The results have a general validity and are applicable for finding optimal layouts with favorable economics. Whereas previous studies usually analyze one location only, we compare 21 different locations using modelled (Laue, 1970, Meinel and Meinel, 1976) and measured (Ohmura et al., 1998) irradiation data.

Section snippets

Maximum performance of large solar fields

Layouts of large solar dish fields are usually based on regular grids of various shapes, e.g. square, equilateral, rectangular, and rectangular with staggering of rows (Igo and Andraka, 2007, Stephens and Angel, 2012). Here we consider the most general case of a regular layout by using a 2-dimensional Bravais lattice, applied in crystallography (Bravais, 1949). Fig. 1(a) illustrates its construction. The two primitive vectors a and b, a  b = |a| |b| cos(γa,b), define the layout where the position p

Approaching the limit

After presenting the limit of efficiencies in the previous section, we analyze how close we can approach it for various layouts and locations, dish shapes, and tracking systems.

Applicability to small fields

As aforementioned, the optical analysis assumes that effects at the border of the dish field are negligible and considers only the center dish in a 19 × 19 dish field. Evidently, the resulting layout is valid for larger fields. However, for smaller fields, border effects may play a role. The most influential factor is the outer shape of the field. As the border dishes are exposed to less shading, layouts that are long in N-S and narrow in E-W favor ηs because the lowest sun positions (in

Conclusion

A simulation model of solar dish fields was developed to predict their optical performance and optimize their layouts in terms of shading and collection efficiencies. Simulations were performed for several locations using local irradiation data and as a function of latitude, grid configuration (optimized, north-south aligned square, and rectangular with no shading in north-south direction), ground coverage ratio (GCR = 10–70%), dish shape (circular and non-rotational symmetric dishes, rectangular

Acknowledgements

We gratefully acknowledge the financial support by the Swiss Federal Office of Energy and the European Union under the 7th Framework Program - Grants No. 312643 (SFERA-II) and No. 609837 (STAGE-STE). We further acknowledge the World Radiation Monitoring Center for granting access to the data of the Baseline Surface Radiation Network.

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