Solar Control System Research Articles

SOLAR CONTROL: An integrated approach to solar control techniques

In the framework of the CE JOULE III Programme, further to the SCL activities in PASCOOL Project, the project SOLAR CONTROL has been supported. The project participants, co-ordinated by Conphoebus, include also Universities of Sevilla and Ljubljana, NOA, TNO, BRE, VTT, Fraunhofer and GENEC, as well as leading manufacturers such as SOMFY and Pilkington. The project is aimed at undertaking investigations on the performance of shading devices in order to overcome the existing lack of support towards industry and final user, thus improving the dissemination of knowledge and the effectiveness of the application of these techniques. The final outputs of this project are: • ⊎ll Proposal of Prenormative Testing Standards for shading devices; • ⊎ll Upgrade of the existing simulation models by integration of new validated algorithms; • ⊎ll Design and implementation of a smart solar control assembly; • ⊎ll Design Guidelines & Shading Component Handbook. In the light of the above objectives, the main ongoing activities concern: • - characterisation of the most interesting shading devices (external, interpane and internal, isotropic and non isotropic) for the assessment of the overall performance (thermal, daylighting, ventilation) • - development, validation and integration in existing simulation tools of new algorithms of the shading devices behaviour in respect to solar radiation, visible radiation and ventilation • - development of new smart solar control systems for integration into the building envelope, with special attention on their impact on energy consumption and improvement of the indoor comfort as well • - preparation of Design Guidelines and a Shading Component Handbook for European architects and building designer.

Influence of deposition temperature on electrochromic properties of sputtered W0 3 thin films

The influence of deposition temperature on the electrochromic properties of reactively sputtered WO 3 films has been investigated. A set of W0 3 films produced in the temperature range of 47–400°C is electrochemically cycled with a constant current supply, which provides an easy control of the charge injected into the films. Optical absorption after coloration, and, hence, the coloration efficiency of the films, significantly increases with increasing deposition temperature (up to 400°C) in the wavelength range of ∼ 1000–2500 nm. Both optical absorption and coloration efficiency decrease at the highest temperatures studied (350–400°C) over most of the visible spectrum (∼ 500–800 nm). Optical modulation across the solar spectrum remains fairly constant for charge injection of 10 mC/cm 2, and the modulation is quite satisfactory for all films for electrochromic device applications. The films produced at higher substrate temperatures show smaller modulation of the visible spectrum, compared with the films sputtered at lower substrate temperatures. This could be more suitable for some applications of the solar control systems. The resistance of the films during the electrochemical process is found to increase with increasing substrate temperature. This causes difficulty in charge injection, requiring significantly larger voltages in techniques such as a cyclic voltammetry for the films deposited at higher temperatures. As a result the good electrochromic performance of the films deposited at higher temperatures can be masked by experimental conditions.

Sun tracking by peak power positioning for photovoltaic concentrator arrays

This paper details the design, development, and evaluation of a microcomputer-based solar tracking and control system (TACS) capable of maintaining the peak power position of a photovoltaic (PV) array by adjusting the load on the array for maximum efficiency and changing the position of the array relative to the sun. At large PV array system installations, inverters are used to convert the dc electrical output to ac for power grid compatibility. Adjustment of the inverter or load for maximum array output is one function performed by the tracking and control system. Another important function of the system is the tracking of the sun, often a necessity for concentrating arrays. The TACS also minimizes several other problems associated with conventional shadow-band sun trackers such as their susceptibility to dust and dirt that may cause drift in solar alignment. It also minimizes effects of structural warpage or sag to which large arrays may be subject during the day. Array positioning is controlled by a single-board computer used with a specially designed input/output board. An orderly method of stepped movements and the finding of new peak power points is implemented. This maximum power positioning concept was tested using a small two-axis tracking concentrator array. A real-time profile of the TACS activity was produced and the data analysis shows a deviation in maximum power of less than 1% during the day after accounting for other variations.

Optimal temperature control of solar energy systems

In this paper the application of dynamic optimization techniques to the design of solar energy temperature control systems is reviewed. Emphasis is placed on the application of Pontryagin's Maximum Principle to solar control system design. Included in the review are topics in optimal control of special interest to solar systems, i.e. Pontryagin's Maximum Principle, linear-quadratic optimization, on-off/singular control, periodic optimization, stochastic and adaptive control, and sampled-data and microprocessor control.

Optimal solar pressure attitude control of spacecraft—I: Inertially-fixed attitude stabilization

This paper is divided into two parts. Part I presents the development of a solar pressure control system to impart arbitrary inertially-fixed attitudes to nonspinning axisymmetric spacecraft. A controller configuration consisting of two rotatable mirror-like surfaces, representing the minimum hardware implementation, is proposed. A control strategy involving nominal controls to counter the gravitational torques and optimal feedback controls to provide stability to the system is developed. The feasibility of employing suboptimal controls resulting in reduced software requirements is explored. The validity of the system is established for all times of the year and in orbits that encounter the Earth's shadow. In Part II of the paper, the capability of the same controller is extended to accomplish large-angle attitude maneuvers of the spacecraft. The entire approach leads to a versatile semipassive attitude control system.

Solar Pressure Attitude Stabilization of Earth-Pointing Spacecraft

The development of a solar pressure control system for three-axis attitude control of Earth-oriented spacecraft is presented. A controller configuration consisting of two rotatable mirrorlike surfaces, representing the minimum hardware implementation, is considered. Optimal control theory is applied to synthesize a feedback control law directly governing the differential rotation of the control surfaces. The system performance is evaluated through the response analysis of a satellite subject to destabilizing gravity gradient torques as well as external disturbances. Even under such adverse conditions, the results indicate a moderately sized controller to be quite effective in maintaining the desired Earth-pointing spacecraft orientation. The validity of the optimal control law is established for all times of the year, and the feasibility of implementing suboptimal control policies is also examined.

Frequency Response Analysis of Fluid Control Systems for Parabolic Trough Solar Collectors

Previous studies of solar collector fluid control systems have utilized computer simulations of collector and piping dynamics to evaluate stability and response characteristics. To obtain reasonable simulation accuracy requires substantial computer memory and time and is well beyond the capability of small, desk-top computers. This paper derives a linearized steady-state frequency response for parabolic trough collectors and for connecting piping, which can be used in standard gain-phase analyses to evaluate system stability and closed loop frequency response. The frequency response characteristics of a typical collector string and piping are used in a gain-phase analysis to get some insight into the effect on system stability of various system parameters such as controller gain, sensor and controller time constants, and sensor location.

Manufacture in space: the MINOS system

The manufacture in Space of products for use on Earth is a possibility for the 1990s. The MINOS project is based on the idea of a free-flyer station for the current medium-level production of either unique products (which cannot be made on Earth), or of economic yields of products which cannot be obtained in sufficient quantities on Earth. At present, only the main system may be defined from general specifications: electrical power (10 kW), residual acceleration (10 −5 g), processing cycle duration (10 hr). The launch vehicle is Ariane I and its improved versions (models II, III and IV). The outer structure of the spececraft is described with solar panels, energy storage (battery and inertial storage) and control systems. The definition of orbital parameters capable of accommodating the basis specifications, especially the high energy level and the re-entry conditions on the Guiana base, is a major problem. The re-entry vehicle is studied from a pure ballistic trajectory point of view. From the results of orbital performance, the mass of the spacecraft and also the mass of the ascent vehicle are evaluated. For this latter value, its determination is directly related to the cost of space-processed materials. A general overview is given of the other spacecraft sub-systems such as satellite tracking, communications, ground stations, resources requirements, telemetry, onboard computing system etc.

Field experience with solar concentrating collector control systems

Field experience with solar concentrating collector control systems