Innovative optics for concentrating photovoltaic/thermal (CPVT) systems – the case of the PROTEAS Solar Polygeneration System

The aim of this work is to review the current status of photovoltaic (PV) power generation, focusing on concentrating PVs mainly as regards their typology, market and state-of-the-art feature. The incorporation of a heat recovery system can increase the overall efficiency by exploiting the waste heat. The proposed solution is a Solar Polygeneration System (PROTEAS System) for the simultaneous production of electricity, hot water and air-conditioning. The core of the PROTEAS System is the innovative set-up of total internal reflection reflectors made of plastic (primary optical system), with the potential to concentrate solar rays up to 5000 suns, while specially designed total internal reflection homogenisers (secondary optical system) later homogenise the radiation to 1000 suns. The engineering of the system is an ongoing task, while some of the subsystems have been successfully developed.     

A Methodology for Dynamic Utility Interactive Operation of Dispersed Storage and Generation Devices

This paper is introducing a new methodology for the dynamic integration of dispersed storage and generation devices into the electric utility distribution network operations. The dispersed source is viewed as an active device contributing towards the regulation of real and reactive power flows while improving the stability of the power system. Conceptual means are developed for an effective DSG-utility grid interface. Computer models of appropriate interconnection and control equipment are used in simulation studies to test the effectiveness of control strategies and optimize design parameters. Simulation results indicate that load frequency control and voltage regulation may be effectively accomplished with dispersed generators within a fraction of the time required for conventional regulating units. Appropriate modulation and conditioning of the DSG-output power can assist in damping out undesirable power oscillations. Implementation of the proposed policies may result in reduced load following requirements for conventional power generating units, increase the value and acceptability of new energy technologies, and improve power quality and stability of the interconnected system.     

A Hybrid Photovoltaic Simulator for Utility Interactive Studies

An analog-digital photovoltaic (PV) array simulator is considered. The analog section is designed on the basis of an equivalent solar cell model while the digital section is constructed realizing the mathematical representation of the array. Fast time responses achieved by the analog section make this part suitable for the study of transient phenomena associated with the interconnected operation of PVs and the utility grid. Its digital counterpart is more appropriate for long-term experimental investigations due to its inherent accuracy and reliability. The combined hybrid simulator offers a versatile and flexible piece of apparatus capable of simulating the performance of any PV array under a variety of operating conditions. The device can be constructed with low-cost components in a compact arrangement offering transportability and ease of operation. Experimental results derived from a laboratory constructed prototype match closely the theoretically computed characteristics.     

Introduction of a new simple dynamic phantom for physical BOLD effect simulation

Magnetic Resonance Materials in Physics, Biology and Medicine - To propose a new method of simulating the BOLD contrast using a dynamic, easy to construct and operate, low-cost physical phantom. A...     

A server database system for remote monitoring and operational evaluation of renewable energy sources plants

The development of a server database system for monitoring and operational evaluation of remote Renewable Energy Sources (RES) plants is presented. Meteorological and operational parameters of multiple RES systems are measured and transmitted in real-time to a database (DB) server. An integrated data management system, comprised of programs running on the DB server, displays the received data on screen, stores them on local disk and inserts them in the DB in real-time. Remote clients access the DB using the TCP/IP protocol in order to create charts, calculate statistical and operational parameters regarding each RES plant and perform DB administration actions. The proposed system can be used for the exploration of the available RES potential during the design of RES systems, the development of statistical models describing the spatial variability of RES resources and the remote monitoring and control of RES plants.     

Design of a maximum power tracking system for wind-energy-conversion applications

A wind-generator (WG) maximum-power-point-tracking (MPPT) system is presented, consisting of a high-efficiency buck-type dc/dc converter and a microcontroller-based control unit running the MPPT function. The advantages of the proposed MPPT method are that no knowledge of the WG optimal power characteristic or measurement of the wind speed is required and the WG operates at a variable speed. Thus, the system features higher reliability, lower complexity and cost, and less mechanical stress of the WG. Experimental results of the proposed system indicate near-optimal WG output power, increased by 11%-50% compared to a WG directly connected via a rectifier to the battery bank. Thus, better exploitation of the available wind energy is achieved, especially under low wind speeds.     

Methodology for optimal sizing of stand-alone photovoltaic/wind-generator systems using genetic algorithms

A methodology for optimal sizing of stand-alone PV/WG systems is presented. The purpose of the proposed methodology is to suggest, among a list of commercially available system devices, the optimal number and type of units ensuring that the 20-year round total system cost is minimized subject to the constraint that the load energy requirements are completely covered, resulting in zero load rejection. The 20-year round total system cost is equal to the sum of the respective components capital and maintenance costs. The cost (objective) function minimization is implemented using genetic algorithms, which, compared to conventional optimization methods such as dynamic programming and gradient techniques, have the ability to attain the global optimum with relative computational simplicity. The proposed method has been applied for the design of a power generation system which supplies a residential household. The simulation results verify that hybrid PV/WG systems feature lower system cost compared to the cases where either exclusively WG or exclusively PV sources are used.     

Size optimization of a PV system installed close to sun obstacles

The assessment of the optimal size of a PV-array/battery-storage system, when the incident solar radiation is considerably obstructed, is presented in this article. An optimal dimensioning method is proposed based on a new procedure for the calculation of the actual solar radiation on the array surface, for installations located near obstacles. The optimum tilt of the PV array is also computed and the resulting optimal PV-array/battery-storage system is evaluated by an appropriate routine. The results of the application of the complete algorithm for a real case study inside a gorge are illustrated.     

Design of a Power Conditioning Unit for Nonlinear Source-Load Systems

This paper describes the development, design, and operation of an electronic device which performs dynamic matching between electric energy sources and their respective loads. This matching is achieved by monitoring the output power of the energy source and modulating a control signal which, in turn, regulates appropriately the operation of a source-load interface device. This device is characterized by a simple structure and an ability to continuously match the characteristics of the source to those of the load, for maximum power transfer, even when these characteristics are randomly time-varying. The device may be used with existing energy systems, without significant changes, and operates effectively even when the utility grid substitutes for the load. Its operation is described in terms of a configuration involving renewable energy sources, such as wind electric conversion systems and photovoltaic arrays, as the primary energy generators. The latter are attracting the growing interest of many investigators recently.     

Development of a microcontroller-based, photovoltaic maximum powerpoint tracking control system

Maximum power point tracking (MPPT) is used in photovoltaic (PV) systems to maximize the photovoltaic array output power, irrespective of the temperature and irradiation conditions and of the load electrical characteristics. A new MPPT system has been developed, consisting of a buck-type DC/DC converter, which is controlled by a microcontroller-based unit. The main difference between the method used in the proposed MPPT system and other techniques used in the past is that the PV array output power is used to directly control the DC/DC converter, thus reducing the complexity of the system. The resulting system has high-efficiency, lower-cost and can be easily modified to handle more energy sources (e.g., wind-generators). The experimental results show that the use of the proposed MPPT control increases the PV output power by as much as 15% compared to the case where the DC/DC converter duty cycle is set such that the PV array produces the maximum power at 1 kW/m² and 25°C