Christophe Menezo

Hybrid solar: A review on photovoltaic and thermal power integration

The market of solar thermal and photovoltaic electricity generation is growing rapidly. New ideas on hybrid solar technology evolve for a wide range of applications, such as in buildings, processing plants, and agriculture. In the building sector in particular, the limited building space for the accommodation of solar devices has driven a demand on the use of hybrid solar technology for the multigeneration of active power and/or passive solar devices. The importance is escalating with the worldwide trend on the development of low-carbon/zero-energy buildings. Hybrid photovoltaic/thermal (PVT) collector systems had been studied theoretically, numerically, and experimentally in depth in the past decades. Together with alternative means, a range of innovative products and systems has been put forward. The final success of the integrative technologies relies on the coexistence of robust product design/construction and reliable system operation/maintenance in the long run to satisfy the user needs. This paper gives a broad review on the published academic works, with an emphasis placed on the research and development activities in the last decade.

Discrete ordinates solution of coupled conductive radiative heat transfer in a two-layer slab with Fresnel interfaces subject to diffuse and obliquely collimated irradiation

The coupled conductive radiative heat transfer in a two-layer slab with Fresnel interfaces subject to diffuse and obliquely collimated irradiation is solved. The collimated and diffuse components problems are treated separately. The solution for diffuse radiation is obtained by using a composite discrete ordinates method and includes the development of adaptive directional quadratures to overcome the difficulties usually encountered at the interfaces. The complete radiation numerical model is validated against the predictions obtained by using the Monte Carlo method.

Analysis of a Hybrid PV/Thermal Solar-Assisted Heat Pump System for Sports Center Water Heating Application

The application of solar energy provides an alternative way to replace the primary source of energy, especially for large-scale installations. Heat pump technology is also an effective means to reduce the consumption of fossil fuels. This paper presents a practical case study of combined hybrid PV/T solar assisted heat pump (SAHP) system for sports center hot water production. The initial design procedure was first presented. The entire system was then modeled with the TRNSYS 16 computation environment and the energy performance was evaluated based on year round simulation results. The results show that the system COP can reach 4.1 under the subtropical climate of Hong Kong, and as compared to the conventional heating system, a high fractional factor of energy saving at 67% can be obtained. The energy performances of the same system under different climatic conditions, that include three other cities in France, were analyzed and compared. Economic implications were also considered in this study.

An Experimental Investigation of Free Cooling by Natural Convection of Vertical Surfaces for Building Integrated Photovoltaic (BIPV) Applications

An experimental study is carried out to investigate the effect of the geometrical configuration on the thermal performance of a series of vertical heaters cooled by natural convection of air. The aim of the work is to investigate the physical mechanisms which influences the thermal behaviour of a double-skin photovoltaic (PV) facade. This results in a better understanding of the related phenomena and infers useful engineering information for controlling the energy transfers to the building where the PV system is applied. In real applications, the PV integrated double facade allows local production of electricity and heat to be employed for the building needs. Furthermore increasing the heat transfer rate from the PV surfaces increases the conversion efficiency of the PV modules since they operate better as the working temperature is lower. The test section consists in a double vertical wall, 2 m high, and each wall is constituted by 10 different heating modules 0.2 m high. The separating distance between the walls is varied from 0.03 to 0.16 m, and the convective heat flux at the wall ranges from 75 to 200 W/m. In this study, the heated section is 1.6 m in height. Different heating configurations are analysed, including the uniform heating mode and two different configurations of non uniform, alternate heating. The experimental procedure allows the wall temperature and local heat transfer coefficient to be inferred and shows that the proper selection of the separating distance and heating mode can noticeably decrease the surface temperatures and hence enhance the conversion efficiency of PV modules

Hybrid PVTh Panel optimisation using a Femlab/Matlab/Simulink approach

A PVTh hybrid solar panel, made up of polycrystalline silicon cells and a heat exchanger, has been designed and developed and its performance is now being tested. The solar cells, glued to glass and with an average yield of 16 -18% and total area of 0.69 m2, are laminated to a flat aluminium heat exchanger using the simple and cheap roll-bond reg technology. This hybrid panel works well as a solar heat collector, since it allows water temperatures in excess of 60degC to be attained, whereas the electrical characteristics of the photovoltaic module display high temperature-dependency. Our numerical approach has two aspects to it: 1)Numerical optimisation of the exchanger to minimise the effect of temperature on the electrical yield at the same time as ensuring good thermal yields. 2) Creation of a tool to aid selection of PVTh panels based on their yields under virtual operation.

Reversal flow in an inclined heated channel inside a closed cavity: application to integrated collector storage solar water heaters (ICSSWH)

The storage tank of an integrated collector storage solar water heater (ICSSWH) is represented by a rectangular glass cavity partially heated on the upper wall. In order to improve the thermal stratification within the cavity that characterizes the storage performance, a rectangular plate is placed parallel to the heated wall and will be called ‘stratification plate’ in the following. However, under certain conditions, a reversal flow may appear and this phenomenon tends to reduce the thermal storage volume. Both numerical and experimental studies have been carried out to study the natural convection phenomenon inside the cavity with a focus on the reversal flow. A parametrical study on heat transfer and fluid flow inside the cavity has been done with CFD simulations. The influences of the position of the heating zone and the stratification plate have been analysed both on the thermal stratification aspect and on the velocity ones with profiles showing the presence of the reversal flow for certain configurations. The numerical study has led to the design of a new experimental bench. This bench provides the possibilities of testing different configurations by varying parameters including the channel width, the position of the heated area, and the injected power. The experimental set-up is instrumented for measurement of temperature by thermocouples and velocity by Particle Imaging Velocimetry.

Impact of Environmental Conditions on the Performance of a 300 kWp Solar PV Plant in Djibouti

The impact of environmental conditions (temperature, dust) on the performance of a 300 kWp PV power plant operating in Djibouti since 2012 is presented in this work. The final yield (Yf) ranges from 3.5 h/d and 5.3 h/d giving and annual final yield of 4.5 h/d. The performance ratio (PR) ranges between 71 and 90%. An observation based on the evolution of the PR with ambient temperature increases showed that an increase of the temperature of 1°C induce a decrease of 1% of the PR. The dust accumulation has a real impact on the PV performance. In order to evaluate this impact, we observed the PR of PV array before and after a rainfall and it was found an improve of PR of 7.4%. In addition, we present in this work a TRNSYS model based on a model from standard library to predict the array performance. A comparison between model and measurements provide a gap of 2.36 kW. Also it was found that the predicted module temperature underestimates the measured temperature at low irradiance (less than 250 W/m2) and overestimates for high irradiance.

NATURAL CONVECTION HEAT TRANSFER FROM STAGGERED DISCRETE THERMAL SOURCES: STATE-OF-THE-ART

ABSTRACT. The enhancement technique for natural convection systems based on staggering vertical thermal sources has been reviewed and discussed. The potential for the heat transfer enhancement of an array of staggered, discrete, vertical surfaces is ascribed to the systematic interruption of the boundary layer caused by the short length of the discrete sources. Considering a system of uniformly heated vertical surfaces as a reference, the use of staggered, discrete surfaces gives rise to higher average heat transfer coefficients. This enhancement strategy has been adopted to increase the natural convection heat transfer from vertical channels as well as from arrays of vertical surfaces. Main applications include the thermal control of electronic equipment, solar system devices and the design of heat sink and/or heat exchanger. The most significant results presented in relevant papers are discussed and compared for the purpose of drawing the guidelines for the optimal design of such advanced thermal systems.

Influence des données incertaines sur la simulation du milieu thermique

ABSTRACT These studies present a model on behaviour of heat exchanges between human body and indoor thermal ambient to predict thermal comfort, taking account thermal building parameters and thermal human parameters with time. Authors present standard model and metamodel. In the second step, authors develop an uncertainty study of results of computation due to data uncertainties, to increase the quality of prediction criteria. Two methods permitting to reach uncertainty range are used: the first is a classic probabilistic (Quasi Monte Carlo) which need a large computation time, the second is a determinist (Finite Differential Differences Analysis) more fast than the first and easy to program. We conclude the same range size for the two methods, with the advantage of the second to apply on various models. Then, we comment uncertainty areas around model and metamodel.