Optimising position control of a solar parabolic trough

Abstract

In today's climate of growing energy needs and increasing environmental concerns, alternatives to the use of non-renewable and polluting fossil fuels have to be investigated. One such alternative is solar energy. This study is based on the implementation of a mathematical computation -the PSA (Plataforma Solar de Almeria) computation developed at PSA (the European Test Centre for solar energy applications) -embedded in a control algorithm to locate the position of the sun. Tests were conducted on a solar parabolic trough (SPT) constructed at the Solar Thermal Applications Research Laboratory of the Mangosuthu University of Technology (Durban, South Africa) for optimal position control using the PSA value. The designed control algorithm embedded in an industrial Siemens S7-314 C-2PtP programmable logic controller compared the PSA computation to a measured position of the SPT to optimally rotate the SPT to a desired position with the constant movement of the sun. The two main angles of the sun relative to the position of the SPT on earth, the zenith angle and the azimuth angle, both calculated in the PSA from the vertical and horizontal planes, respectively, were applied to the control algorithm to generate an appropriate final tracking angle within a 0.007 radian (0° 24′ 3.6″) tolerance, in accordance to the construction specifications and solar collector testing standards of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE, 1991). These values, together with the longitude and latitude applicable to the geographical location of the SPT, were processed in the control software to rotate the SPT to an optimal position with respect to the position of the sun in its daily path, for solar-to-thermal conversion.

A Review of Parabolic Trough Collector (PTC): Application and Performance Comparison

“…During a sunny day, HTF in the tube is heated by DNI and goes to the steam power plant, then preheats water, and generates steam in the steam generator. It also superheats the vapor, then releases the heat and circulates back to the SCF to complete the cycle again, [15].…”

Dynamic Modeling and Controller Design for a Parabolic Trough Solar Collector

“…Few studies have laid focus on the tracking control for PTSC. An optimal position control has been pursued by Naidoo et al [12], data is collected from Plataforma Solar de Almeria (PSA) and fed to PLC based software to tune the controller. In a study by Palacios et al [13], solar tracking controller of PTSC has been designed using traditional PID and then with help of fuzzy logic and particle swarm optimization (PSO).…”

Sliding Mode Control of a Water-Displacement Based Mechanism Applied to the Orientation of a Parabolic-Trough Solar Concentrator

“…Several methods have been proposed for the guidance and positioning mechanisms that put the surface of the cylinder-parabolic solar concentrator perpendicular to the sun's rays, thus the incident radiation is captured. Computer algorithms that take into account the solar equations [1]- [3], and the sun's trajectory predictions [4], [5], for the purpose of tracking the sun when it is cloudy. Electromechanical systems controlled via a programmable logic control or another automatic control are used in solar tracking systems [3], [6].…”

“…However, these mechanisms become very expensive and complicated when installed in a larger cylinder-parabolic solar concentrators and some of them are only implementable in photovoltaic panels and require frequent maintenance. An interesting low-cost maintenance mechanism alternative were present by [1], where the solar tracker is passively activated by aluminium/steel bimetallic strips and controlled by a viscous damper, an unbalanced moment results, generating movement towards the sun. Similary [2] used mechanical passive trackers balanced by a water displacement mechanism.…”