Deyou LIU*, Su GUO, Dingsheng WAN, Feng WANG1

‘Department of Power Engineering, Hohai University, Nanjing 210098, Jiangsu Province, China
* Corresponding Author, liudyhhuc@163.com

Abstract

In this paper, based on the geometrical optics theory, the function of heliostat field boundary line was deduced, and the simplified formula to calculate the receiver depression angle with the only independent variable of latitude was given. Moreover, the calculated heliostat field data were compared for different receiver depression angle by a case study, and the rationality of the formula was demonstrated. From the results, the following conclusions were drawn: For the conditions of the same heliostat dimension and arrangement, it is optimal when the receiver depression angle is at around the value calculated by the formula of receiver depression angle developed in this paper. Now, the installed capacity of plant is mainly dependent on the height of tower and the area of receiver aperture, and almost has nothing to do with the receiver depression angle in a certain range around its optimum value.

Keywords: solar energy, solar power towers, field boundary line, receiver depression angle

1. Introduction

In Solar Power Tower plants, the heliostat field layout is one of the most important parts in the plant design, including many optimization design works, such as the layout of the heliostats, determination of field boundary line and heliostat dimension, etc., as reported earlier [1-3]. Field boundary line refers to the envelope line of mirror centre coordinates of all heliostats in the field, and the heliostat at any location in this boundary line can reflect all rays into the receiver aperture. Determination of field boundary line is not only the basis of field layout design, but also the foundation of selection of plant location and design of installed capacity.

There are a lot of correlative factors effecting the heliostat field boundary line, for instance, the longitude and latitude of the plant location, the installation elavation of receiver, depression angle of the plane of receiver aperture (Receiver Depression Angle for short), shape and dimension of receiver aperture, the installation elavation and the dimension of heliostat mirror, tracking error and rocking error of heliostats, and so on, which has been reported earlier [4,5]. Under the circumstance of ignoring tracking error and rocking error of heliostats, this paper established numerical calculation method of field boundary line and simplified calculation formula of receiver depression angle with the only independent variable ‘latitude’ aiming at receivers with rectangle aperture. Finally, taking a certain plant project as the calculation case, for the condition of the configuration parameters of receiver and heliostats were determined, the influences of different receiver depression angle on the heliostat field boundary line were compared and analyzed, and rationality and validity of the developed formula were certified.

Physical model of the relationship between receiver and heliostats is shown in Fig.1. In Fig.1, x axis is towards due east, y axis towards due north (Northern Hemisphere) or due south (Southern

Hemisphere) and z axis towards vertically sky, which has been reported earlier [1]. Oi (xi, yi ,0) is the mirror center coordinates of Heliostat i. We assume that the mirrors of heliostats is rectangle, with the height Ht and the width Hw. E(0,0, Ht) is the center coordinates of receiver aperture,

and the vertical distance between point E and point Oi is Ht. aR is the receiver depression angle, that is the angle between the normal of receiver aperture plane and horizontal plane.