Improving the maneuverability and thermal efficiency of modern cogeneration systems based on gas turbine power plants

The paper is devoted to the issue of increasing the maneuverability and efficiency of modern cogeneration systems based on gas turbine power plants. Promising solutions for increasing the maneuverability of GTU-CHPP by using heat accumulators and the formation of a preheating circuit of the network water are considered. It is shown that in the non-heating period, it is possible to increase both the thermal efficiency and the generated electric power by installing a heat exchanger in front of the compressor. The calculation results show that this provides an increase of 0.4% in the net electrical efficiency by and an increase 3.3% in the annual electricity generation.

Improving The Efficiency of Photovoltaic Cells by Using the Distilled Water Immersion Method

Photovoltaic panels can convert solar irradiance into (electrical and thermal) energy. The (PV / T) system was developed, created, and its performance tested in this experimental analysis. The main objective of this study was to design, manufacture and evaluate the work of the PV/T system as a thermal collector to enhance heat transfer, by using distilled water as a working fluid used to cool (PV/T) system. The experiment was performed with flow rate of water from (1 L / min to 5 L / min) on the PV / T collector channel. A theoretical and practical study was conducted on the effect of cooling the panels by immersing (PV) from (upper and lower) in a distilled water parallel flow forced circulation. Numerical result obtained by using Comsol Multiphysics program have been used as a computational fluid dynamic (CFD). The numerical study was conducted to determine the optimal depth of immersion of the panel to experiment with it, simulation results showed that the optimum depth of immersion is (5mm). The experimental results were conducted at the Technical Engineering College of Najaf with indoor test conditions that were controlled, Tin=20 °C, h=5mm. The results have been shown that the electrical efficiency of traditional photovolatic panel without cooling varied between (10.5-11.6) %, while the electrical efficiency of PV/T system varied between (14.6-14.7) %.

Photovoltaic Module Electrical Efficiency Enhancement Using Nano Fluids and Nano-Paraffin

Today, photovoltaic modules have become accepted by the public and scientists in the production of clean electricity and as a possible alternative to electricity produced from fossil fuels. These modules suffer from a deterioration in their electrical efficiency as a result of their high temperature. Several researchers have proposed the use of high-efficiency hybrid photovoltaic (PV/T) systems that can cool PV modules and also produce hot water. Improving the PV modules’ electrical efficiency increases the investment attraction and commercialization of this technology. The possibility of restoring the electrical efficiency of the photovoltaic panel that was lost due to its high temperature was investigated in this study. A PV/T system designed to operate with a paraffin-filled thermal tank attached to the PV module was used. Inside the paraffin is a heat exchanger that circulates inside a nanofluid. This design is adopted to cool down the PV module temperature. The study was carried out in the climatic conditions of the month of May in the city of Baghdad - Iraq. The proposed PV/T system’s electrical efficiency was compared with similar systems from the literature. The proposed system has achieved an obvious enhancement as its electrical efficiency was 13.7%.

The Efficiency of Obtaining Electricity and Heat from the Photovoltaic Module under Different Irradiance Conditions

This paper proposes a modification to the design of a standard PV module by enclosing the skeleton space and using forced ventilation. The purpose of this research was to develop a method for calculating the amount of heat gained during PV module cooling. A simplifying assumption was to omit the electrical energy consumed by the fans forcing the airflow. For testing at low irradiance, a prototype halogen radiation simulator of our own design was used, which is not a standardized radiation source used for testing PV modules. Two measurements were also made under natural, stable solar radiation. The modified PV module was tested for three ventilation rates and compared with the results obtained for the standard PV module. In all tested cases, an increase in electrical efficiency of about 2% was observed with increasing radiation intensity. The thermal efficiency decreased by about 5% in the analyzed cases and the highest value of 10.47% was obtained for the highest value of cooling airflow rate. In conclusion, the study results represent a certain compromise: an increase in electrical efficiency with a simultaneous decrease in thermal efficiency.

Electrical Efficiency Increase in CPVT Collectors by Spectral Splitting

Concentrating photovoltaic-thermal (CPVT) collectors have to face the challenge of contrary temperature requirements in the single receiver parts. The PV cells require low temperatures to achieve high efficiency, whereas the thermal part should generate high temperatures for providing industrial heat. The approach of “Spectral Splitting” can offer a solution for compact CPVT receivers; however, a clear quantification of the expected conversion efficiency is difficult. Therefore, this paper describes a modelling methodology for obtaining electrical and thermal performance parameters for a Spectral Splitting configuration using semiconductor-doped glass combined with appropriate heat transfer fluid. The PV technologies c-Si, CIGS and CdTe are considered. The presented model yields distinct results for maximising the electrical efficiency, calculates the reduction in waste heat dissipation within the cells and assesses the impacts of concentration factor and cell temperature. An optimised configuration could be found with CIGS cells, impinged by a selected wavelength spectrum between 868 nm and 1100 nm, where the theoretical efficiency reaches 42.9%. The waste heat dissipation within the cells is reduced by 84.9%, compared to a full-spectrum operation. The depicted CPVT receiver design using bendable thin-film PV cells will be realised as a prototype in a subsequent project phase.

Numerical Modelling of a Photovoltaic Thermal (PV/T) System Using Nanofluid With Parallel Flow Thermal Absorber

In the present study, a numerical model of photovoltaic thermal (PV/T) system using alumina (Al2O3) nanofluid, and pure water are used as working fluid. The proposed PV/T model consists of parallel riser tubes that are connected to two header tubes and it is attached to an absorber plate to simulate the conduction and convection heat transfer mechanism of a conventional PV/T system. The energy efficiency of the PV/T model is analyzed by varying the solar radiation (Heat Flux), inlet fluid velocity, and the volume percentage of the nanofluids. The numerical simulation is performed by using a conjugate heat transfer method with a computational fluid dynamics (CFD) software. According to the simulation data, the energy efficiency and the heat transfer coefficient of the PV/T system increased by increasing the inlet fluid velocity. In comparison with water, alumina nanofluid showed better thermal and electrical efficiency due to its high thermal conductivity. The thermal efficiency increased by 5.55% for alumina, compared to pure water and the electrical efficiency increased by 0.15% for alumina. Moreover, the effect of inlet fluid velocity ranging from 0.04m/s to 0.2m/s was also evaluated, and the results showed that the increase in thermal efficiency for pure water and alumina are 18.15% and 25.77%, respectively. Subsequently, the electrical efficiency increased by 0.52% and 0.56% for pure water and alumina using the new parallel flow thermal absorber, respectively.

Electrical Efficiency of SECE-based Interfaces for Piezoelectric Vibration Energy Harvesting

Piezoelectric energy harvesting (PEH) interfaces have been widely investigated during the last decades in order to maximize the harvested power. Among the energy extraction circuits proposed in the literature, some of the most effective ones consist of extracting the electric charges from the piezoelectric elements in a synchronous way with the vibrations and within a very short portion of the vibration period (SECE, SECPE, FTSECE, etc.). For these strategies, most previous studies take the electrical efficiency (i.e., the electrical losses between the energy extracted from the piezoelectric element and the energy which is finally transferred in a storage element) into account in an ad-hoc and case-by-case manner. In this brief, we propose a unified analysis that applies to model the electrical efficiency of these SECE-based strategies taking into account losses introduced by the electrical interface. We identify the main loss mechanisms by demonstrating that the electrical efficiency mainly varies with two parameters: the quality factor of the electrical interface and the voltage inversion ratio of the considered strategy. Measurements on the FTSECE strategy show that our model predicts the stored power with a good accuracy and allows a better optimization of the harvesting interface (up to 5.4 times more stored power at off-resonance frequencies, and 30% larger harvesting bandwidth).