Experimental Validation of Theoretical Heliostat Wind Loads

Abstract

In the current concentrated solar power (CSP) context central receiver systems seems to be the most promising technology with the highest cost reduction potential. In the construction of such plants the solar field represents one of the largest investments, a fact which has made cost reduction of these elements become the main target for many actors of the solar thermal sector. Therefore, the design of cost efficient heliostats has become a major interest. One of the design challenges is to develop a heliostat which is able to withstand all foreseen mechanical loads, while at the same time have reduce costs by avoiding unnecessary safety margins. To achieve this goal a good knowledge of expected wind loads onto the support structure and drive mechanism is crucial. In this paper a heliostat prototype, equipped with measuring devices, is deployed to a test site in order to measure the true mechanical stresses suffered due to varying wind loads. These data together with the information about wind speed and direction is then used to validate theoretical loads determined via formulations extracted from wind tunnel experiments. It is shown, that for low turbulence conditions the theoretical values correspond well to the measured values; however, for turbulent wind conditions a significant difference is detected. As those conditions are difficult to simulate in wind tunnels or CFD simulations, this shows the importance of on-site testing of new heliostat designs.

Heliostat structural optimization: A study of wind load effects with CFD-FEM methods

“…Figure 1 (a) shows the coordinate system used for heliostat drag and lift forces definition extracted from [9], and Fig. 1(b) shows the coordinate system used in the model.…”

“…1(b) shows the coordinate system used in the model. The coordinate system x axis of [9] corresponds with the drag force direction which is the z direction in the present CFD-FEM model (see Fig. 1(b)).…”

“…1(b)). Lift force direction corresponds with the z axis in [9] and with the y axis in the present model's coordinate system.…”

“…In this model the turbulence intensity is taken into account and is defined as the ratio of the root mean square of the velocity fluctuations, to the mean flow velocity. The estimation of the turbulence intensity has been made according to experimental data obtained in [9].CFD results are compared with the results obtained in previous studies [9, 10 and 11] and validated against [10 and 11]. In order to validate the model, simulations for an elevation angle of 0º, 10º, 20º, 30º, 40º, 50º, 60º, 70º, 80º and 90º, azimuth angle of 0º and a wind velocity of 10 m/s are run.…”

“…(a)Heliostat coordinate system used from[9] and (b) coordinate system for geometry analyzed in the model.…”