Concentrating Solar Thermal Energy

4Solar Receivers

Benjamin GRANGE

PROMES-CNRS, Font-Romeu-Odeillo-Via, France

4.1. Introduction

The objective of a solar receiver is to absorb concentrated solar radiation and transfer the energy to the heat transfer fluid (see Chapter 5). Depending on the considered collector field (linear or point concentration), there are two types of receivers. Section 4.2 presents the use of absorber tubes when the concentration is linear, particularly the parabolic trough concentrators, while section 4.3 describes the solar receivers used in tower power plants (point concentration).

4.2. Absorber tubes for linear concentrators

4.2.1. Description

Absorber tubes are composed of two concentric tubes: an internal metal tube through which the transfer fluid flows and an external glass tube, as shown in Figure 4.1. The external tube is made of low-iron borosilicate glass to increase its solar radiation transmittance. This tube can be used to create reduced pressure (≈ 5–10 mbar) in the annular space and thus limit thermal losses. A selective coating is applied on the metal tube in order to increase its absorption in the visible range and reduce its emission in the infrared range (see Chapter 7). The glass and metal tubes are connected by means of thermal expansion bellows. Besides tolerating the expansion of the two tubes, the latter offer a tight annular space between the two tubes to create the vacuum. The chemical getters in the ring between the two tubes allow the absorption of gas molecules ...