Journal of Energy and Power Engineering 7 (2013) 2078-2082
Influence of Internal and External Parameters in Temperature of Hybrid PV/T Water Collector
Hanene. Ben Cheikh El Hocine and Mimia. Marir-Benabbas
Laboratory Modeling Renewable Energy Devices and Nanometric, Department of Electronic, University Constantine 1, Constantine 25000, Algeria
Received: July 10, 2013 / Accepted: August 08, 2013 / Published: November 30, 2013.
Abstract: The combination of photovoltaic system with a thermal to form the hybrid PVT (photovoltaic thermal), which together will generate electricity and heat. This energy depends on the input that is to say the energy of solar radiation, temperature and speed wind and output which is the operating temperature of the system. This production also depends on the mode of heat removal. The authors prent in this article; a study by a numerical simulation of the thermal behavior of a prototype hybrid nsor th营业执照注册号
rough the development of an energy balance that involves heat exchange between the different components of the hybrid nsor, and it will allow us to study the influence of internal and external parameters on the temperature variation in the different layers of the prototype PV/T studied.
Key words: Solar collector, photovoltaic, thermal, hybrid solar system, simulation.
1. Introduction
To improve the electrical performance of PV (photovoltaic) generator, it was brought to recover the heat dissipated by convection and conduction and when operating in a state of “hot spots” and/or normal state [1], this led us to consider the u of a conventional hybrid collector in order to operate an electrical and thermal performance for both occupied the same space.
A photovoltaic/thermal hybrid solar system (or PVT system for simplicity) is a combination of photovoltaic and solar thermal components/systems which produce both electricity and heat from one integrated component or system. The basic device of a PV system is the PV cell. Cells may be grouped to form panels or arrays.
Zondag [2] has carried out rigorous review on PV-thermal collector systems, carried out by various scientists till 2006. His review included the history
Corresponding author:Hanene Ben Cheikh El Hocine, rearcher, rearch fields: photovoltaic, solar collector and hybridsolarsystem.E-mail:*********************.and importance of photovoltaic hybrid syst
em and its application in various ctors. It also includes characteristics equations, study of design parameters, and marketing, etc..
Chow [3] has done a review on PV/T (photovoltaic/thermal) hybrid solar technology especially PV/T air collector systems. His article gives a review of the trend of development of the technology,
in particular the advancements in recent years and the future work required.
Hasan and Sumathy [4] have prented the module aspects of different PV/T collectors and their performances in terms of electrical as well as thermal output. The review covered detailed description of flat-plate and concentrating PV/T systems, using liquid or air as the working fluid, numerical model analysis, experimental work and qualitative evaluation of thermal and electrical output. Also an in-depth review on the performance parameters such as, optimum mass flow rate, PV/T dimensions, air channel geometry is prented in this study.
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Influence of Internal and External Parameters in Temperature of Hybrid PV/T Water Collector 2079
Ibrahim et al. [5] prented the state-of-the-art on
flat plate PV/T collector classification, design and
performance evaluation of water, air and combination
of water and/or air bad. Different designs feature
and performance of flat plate PV/T solar collectors
have been compared and discusd. They found that for both air and water bad PV/T solar collectors, the important key factors that influenced the efficiency of the system are the area where the collector covered, the number of pass and the gap between the absorber collector and solar cells.
Teo et al. [6] prented a comparison of the electrical efficiency of the PV module with and without cooling. By varying the air flow through the conduit, a simulation model is adapted to examine the actual temperature profile of the photovoltaic cell during operation. Without cooling, they found a yiel
d of 8%-9%. But, when the module was operated under conditions of active cooling, the temperature has dropped significantly, leading to an increa of the efficiency of solar cells between 12% and 14%.
The study prented here is the development of hybrid PVT collector model to exhibit the behavior of hybrid prototype, bad on the influence of internal and external parameters of the temperature variation in the different layers of the prototype PV/T studied.
2. Prentation of PV/T Hybrid Prototype
The concept of hybrid photovoltaic-thermal collector consists of superimposing both electrical and thermal energy functions. It is characterized by a combination sandwich between air and 满分作文500字
water (Fig. 1). The lower face is insulated.
To prent the thermal exchange between the different layers of the nsor within the prototype, the authors apply the nodal method that allows modeling electrical system analogy (Fig. 2).
3. Modeling of Hybrid PV/T Collector
Assume steady states established valid assumption in the ca of an analysis on a daily scale. The
objective is to model the entire PVT analytically prented before Fig. 1 Descriptive scheme for a solar photovoltaic thermal water collector.
Fig. 2 Electrical equivalent heat transfer of hybrid PV/T collector.
it by calculating the temperatures on each wall. Indeed, it is esntial to know the temperature profile
across the collector as the temperature of the PV panel in order to improve its performance.
To calculate the temperatures, it is to write the heat balance of each layer taking into account energy loss by conduction, convection and radiation.
3.1 Expression of Heat Transfer Coefficients
The radiative heat transfer coefficient exchange between the outside air and the outside glass cover.
()()
sky
og
sky
og
g
a
og
r
T
T
T
T
h+
+
=
-
2
2
,
(1) The corresponding coefficient of convective loss caud by the wind can be calculated from equation (h c) [7]:
w
conv
V
h8.3
7.5+
=(2) where, V w is wind speed on the top surface of PV/T collector. The effective temperature of the sky (T sky) is calculated from the following empirical relation [6]:
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Influence of Internal and External Parameters in Temperature of Hybrid PV/T Water Collector
20806-=amb sky T T (3)
After calculating transfer coefficients between the outer glass cover and ambient air, the authors can deduce the thermal resistance:
v
v conv a ve r I e h h R ++=
-,1
(4)
The radiative heat transfer coefficient between glass external and glass internal is calculated by:
()()⎪⎪⎭
⎫ ⎝⎛-++=
-122
2,g ig og ig og
ig og r T T T T h
(5)
Natural convection heat transfer coefficient between glass external and glass internal is given by the expression:
ig
og air u ig
og c w N h --=
, (6) N u is the Nuslt number calculated by means of a flow characteristic correlation between two flat plates
defining an enclod volume [8]:
<1,70047.8 1.013
+=r u G N (7)
()>80,000
2.50.013390
=+-r u G N (8)
Otherwi,
()[]
33
.049010.306.0r
u G N -+=- (9)
G r is the Grashof number defined by:
2
3Tb g G r ∆=
(10) : is being the thermal dilatation, for the air 1-=T ;
w air : duct depth of air;
T : temperature difference between the two plans. The thermal resistance between the glass external and glass internal is given:
g
g ig og r ig
og c II e h h R +
+=
--,,1
(11)
The radiative heat transfer coefficient term between
the glass internal and photovoltaic module:
()()⎪⎪⎭
⎫
⎝⎛-+++=
-1112
2,cell g cell ig cell ig
cell ig r T T T T h
(12) Between the glass/panel and PV brine [9], the
convective heat transfer coefficient h f is calculated according to the flow regime and the Nuslt number, in our work, it was assumed that its value is the same that for the one air channel.
The thermal resistance between the glass internal and photovoltaic module:
si
si
f
cell ig c III e h h R +
+=
-,1
(13)
The thermal resistances on the back surface of PV/T
water collector, taking into account the wind speed:
i
i
conv
IV e h R +
=
1
(14)
The heat balance at the nodes can be written [10]:
II ig
og I amb og og abs R T T R T T Q -+
-=- (15)
III
cell
ig II og
ig ig abs R T T R T T Q -+
-=- (16)
ce
IV
amb
cell III
ig
cell c E R T T R T T E --+
-=
(17) Solar flux absorbed by the glass cover outside;
calculated by:
g og abs G Q =- (18)
Solar苌弘化碧的典故
flux absorbed by the inner glass:
g g ig abs G Q =- (19)
The total energy absorbed by the photovoltaic
module:
c g c c G E 2
= (20)
Due to solar irradiation, the electrical energy, E ce ,
produced by the PV cell is expresd by the following equation:
e c g ce G E 2
= (21)
The electrical efficiency reprented as a function of the module temperature:
()()ref cell e T T --=10 (22)
3.2 Resolution of System
Solving the system of equations governing the heat
transfer in the prototype allows evaluating the
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Influence of Internal and External Parameters in Temperature of Hybrid PV/T Water Collector 2081
influence of internal and external parameters of temperature variation in the different layers constituting the prototype PV/T studied.
Eqs. (15)-(17) of the thermal energy balance have been computed by the Matlab program for the external temperature of cover (T og), internal temperature of glass (T ig) and solar cell (T cell) tempe
rature in the PV/T collector.
The typical results of computer simulation program under the sample conditions of耳朵烫是怎么回事
Table 1.
4. Results
A parametric study was performed on the temperature of the various layers of the collector by varying the wind speed, the thickness of the air-water channel, the radiation and the ambient temperature.
The following graphs show the evolution of the temperature of each collector layer PVT. Taking as an example:
G = 1,000 W/m2, T amb = 300 K,
V w = 1 m/s, w air = w water = 0.01 m, the authors find:
T og = 340.9079 K = 67.9079 C;
T ig = 389.5016 K = 116.5016 C;
T cell = 398.8565 K = 125.8565 C.
Fig. 3 (A and B) shows the variation of temperature in the various layers of the hybrid collector for two values of the wind speed, the value of radiation varies 200 W/m2 to 1,000 W/m2, an ambient temperature of 300 K, while keeping the other values constant, note that the temperature of the different layers decreas as the wind speed increas.
At an ambient temperature of 300 K and a wind speed equal to 2 m/s, temperatures of each layer increas with increa of the widths of the air and the water channel, as shown in Fig. 4 (B and C).
From the prented results of Fig. 5 (C and D), it can be en that the temperature of each layer increas when the ambient temperature increas, for example, For the cell temperature reaches 400 K its value at an ambient temperature equal to 300 K and an illumination of 1,000 W/m2, for the same value of the Table 1 Ambient conditions and design ud in simulations.
Solar PV/T collector parameters Value
Water flow 76 m3/h Collector angle 36
The emissivity of glass g0.83
The thickness of glass cover e g0.003 m
The conductivity of glass cover g0.93 W/mK The absorptivity of glass g0.066 Transmittivity of glass cover g0.88
The emissivity of cell, module cell0.95
The absorptivity of cell, module c0.85
The thickness, back insulation e i0.05 m Thickness, silicon solar cell e si0.0003 m Conductivity, silicon solar cell si0.036 W/mK The electrical efficiency at the
reference conditions
00.12 Conductivity of back insulation i0.035 W/mK The packing factor of solar cell c0.83
Fig. 3 Effect of the wind speed on the temperature of each layer PVT collector.
A: V w = 1 m/s, B: V w = 2 m/s
A and
B for w air = w water = 0.01.
Fig. 4 Effect of the width of the channels (the air channel and the water channel) on the temperature of each layer PVT collector.
B: w air = w water = 0.01, C: w air = w water = 0.05.
Fig. 5 Influence of ambient temperature on the temperature of PVT collector.
C and
D for w air = w water = 0.05.
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Influence of Intern在家做什么挣钱
al and External Parameters in Temperature of Hybrid PV/T Water Collector 2082
Fig. 6 Effect of solar radiation on the temperature of PVT collector.
E and
F for w air = w water = 0.01.
radiation and ambient temperature equal to 323 K, its value reaches 415 K, keeping the other constant values. The Fig. 6 (E and F) shows the variation of temperature in the various layers of the collector according to the ambient temperature for two different values of radiation. The temperature of each layer increas with increasing irradiation.
5. Conclusions
An interesting alternative to ordinary photovoltaic modules is to u photovoltaic cells combined with thermal collector to form the hybrid collector, the nsor can thus achieved simultaneously produce electricity and heat.
A parametric s面包的做法
tudy was conducted to evaluate the influence of certain factors on the temperature of the layers constituting the system.
The authors have found the expected trends at different temperatures as a function of wind speed, ambient temperature, the thickness of the channel (air channel and that of water) and the received radiation. The results obtained in this study show the increa in temperature of a photovoltaic panel due to warming of its upper surface.
Knowledge of this temperature variation allows us to project the amount of electrical energy that can be extracted from our module.
A synergistic effect can be obtained in a structure combining the two devices wily to tho of thermal and photovoltaic system installed parately, the goal is twofold, increa efficiency electric
generator, that is to say, it’s electrical efficiency lowering the operating temperature and us the same heat for the thermal collector.
Both air and water can be ud as the coolant in a PV module to lower down the solar cell operating temperature and hence to improve the electricity conversion performance.
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