Performance Analysis of Liquid Flat Plate collector and PV Cell

Dr. Ramesh B T
Assistant Professor
Mechanical Engg. Dept.
JIT-Davanagere
Email Id: rameshbt049@gmail.com
26-06-2021
Dr. Ramesh B T 1
Performance Analysis on Liquid flat plate
collectors

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• Effect of Shading
• Collect Tilt
• Fluid Inlet Temperature
• Dust on the top Cover

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Stagnation temperature
Stagnation temperature is the temperature reached when stagnation persists until the losses of the solar
thermal collectors equal the absorbed energy. The stagnation temperature depends on the ambient
conditions (ambient temperature and hemispherical irradiance) and reaches different values depending
on these conditions. The standard stagnation temperature defined by the international standard EN ISO
9806:2013 /1/ give the value for the stagnation temperature at 1000 W/m² hemispherical irradiance and
30 °C ambient temperature. This standard stagnation temperature is usually used to describe the highest
temperature reached by the solar thermal collectors
Stagnation describes the state of a solar thermal system in which (by any reason) the flow in the
collector loop is interrupted although sufficient solar irradiance is available for operation of the collector
loop. If stagnation persists and solar irradiance is still being absorbed by the collector, temperatures and
pressure in the collector loop will increase. When the temperature raises higher than the operation
temperature, two things can happen: -
The design temperature is reached: The solar thermal collectors or parts of the collector loop reach a
temperature where (parts of) the collectors (or the collector loop) are damaged. Obviously, this has to
be avoided using appropriate measures.
If the first does not apply and the stagnation persists, the collectors reach their specific maximum
absorber temperature (= stagnation temperature). This temperature depends on the collector design and
the current weather conditions (mainly irradiance and ambient temperature) and the heat transfer
medium conditions inside the collector and/or collector loop.

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Transmissivity of the Cover System

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The calculation is done in detail for one angle of incidence, viz. θ1=15◦.
Hence, θ2 =sin−1[(sin15◦)/1.52]=9.80◦
ρI =sin2(9.80◦−15◦) sin2(9.80◦+15◦) =0.047
τrI =1−0.047 1+(3×0.047)=0.835
ρII =tan2(9.80◦−15◦) tan2(9.80◦+15◦)=0.039
τrII =1−0.039 1+(3×0.039)=0.860
τr =1/2(0.835+0.860) =0.848

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τd =0.885, τr = 0.848
τ =0.848×0.885
τ =0.750

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Transmissivity-absorptivity product
The Transmissivity -absorptivity product is defined as the ratio of the flux absorbed in the absorber
plate to the flux incident on the cover system, and is denoted by the symbol (τα), an appropriate
subscript(b or d )being added to indicate the type of incident radiation. An expression for the
Transmissivity absorptivity product will now be derived.

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The symbol ρd represents the diffuse reflectivity of the cover system. It can be found by determining the
value τa (1−τr) for the cover system for an incidence angle of 60◦. From Example it is seen that ρd = 0.21 for
a two glass cover system. Similarly, for a one-glass cover system, the value of ρd can be shown to be 0.15.
Over all loss coefficient and heat transfer correlations
Where, Ul = Over all loss coefficient.
Ap = Area of the absorber plate.
Tpm = Average temperature of the absorber plate.
Ta = Average temperature of the absorber plate.

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The heat lost from the collector is the sum of the heat lost from the top, the bottom and the sides.
Thus,
Where,
qt = Rate At which heat is lost from the top.
qb = Rate at which heat is lost from the bottom.
qs = Rate at which heat Is lost from the sides.
It will be noted that the definition of each of the coefficients is based on the area Ap and the
temperature difference (Tpm−Ta). This is done for convenience and helps in giving the simple
additive equation

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The losses can also be shown in terms of thermal resistances as shown in Fig. The overall loss
coefficient is an important parameter since it is a measure of all the losses. Typical values range
from 2 to10 W/m2-K.

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Top loss coefficient

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Heat transfer coefficient between inclined parallel surfaces
Heat transfer coefficient at the top cover

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Empirical equation for top loss coefficient

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Bottom loss coefficient
Side loss coefficient

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i)From equation, sky temperature is calculated,
Tsky =Ta−6=297.2−6=291.2 K
ii)Using equation, we can calculate hw,
hw =8.55+2.56V∞ =8.55+(2.56×2.5)=14.95 W/m2−K
iii)Top loss coefficient can be found using empirical equation
Where we need to find values of f and C first,
f = (9/ hw −30/ hw2) (Ta /316.9)(1+0.091M)

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v) Side loss co-efficinet can be found using equation
Us =(L1 +L2)L3Ki /(2L1L2δs)
=(0.90×1.90)×(0.4+0.4+0.8)×0.05/0.90×1.90×0.04
Us = 0.33 W/m2−K

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Temperature Distribution between the Tubes
it is desirable to have an understanding of the temperature distribution that exists in a solar collector
constructed as shown in below Figure shows a region between two tubes. Some of the solar energy absorbed by
the plate must be conducted along the plate to the region of the tubes, thus the temperature midway between
the tubes will be higher than tube temperature in the . vicinity of the tubes. The temperature above the tubes
will be nearly uniform because of the presence of the tube and weld metal.
The energy transferred to the fluid will heat the fluid, causing a temperature gradient to exist in the direction
of flow. Since in any region of the collector the general temperature level is governed by the local temperature
level of the fluid, a situation as shown in Figure is expected At any location y, the general temperature
distribution in the x direction is as shown in Figure and at any location x, the temperature distribution in the y
direction will look like Figure.

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To model the situation shown in Figure , a number of simplifying assumptions can be made to lay the
foundations without obscuring the basic physical situation. These assumptions are as follows: _
1. Performance is steady state.
2. Construction is of sheet and parallel tube type.
3. The headers cover a small area of collector and can be neglected.
4. The headers provide uniform flow to tubes.
5. There is no absorption of solar energy by a cover insofar as it affects losses from the collector.
6. Heat flow through a cover is one dimensional.
7. There is a negligible temperature drop through a cover.
8. The covers are opaque to infrared radiation.
9. There is one-dimensional heat flow through back insulation.
10.The sky can be considered as a blackbody for long-wavelength radiation at an equivalent sky
temperature. .
11.Temperature gradients around tubes can be neglected.
12.The temperature gradients in the direction of flow and between the tubes can be., -- treated-
independently.
13.Properties are independent of temperature.
14.Loss through front and back are to the same ambient temperature.
15. Dust and dirt on the collector are negligible.
16. Shading of the collector absorber plate is negligible

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Collector efficiency factor

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Next we consider the flow of heat from the plate to the fluid. The three thermal resistances
in the path are due to the adhesive used for attaching the tubes to the absorber plate, the
tube wall and the heat transfer coefficient at the inner surface of the tube. Assuming the
thermal resistance of the tube wall to be negligible.

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Where, F0 represents the ratio of the actual useful gain rate per tube per unit
length to the gain which would occur, if the collector absorber plate where at the
temperature Tf

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Collector heat removal factor

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The term FR is called the collector heat-removal factor. It is an important design
parameter since it is a measure of the thermal resistance encountered by the
absorbed solar radiation in reaching the collector fluid. From above Eq, it can be seen
that FR represents the ratio of the actual useful heat gain rate to the
gainwhichwouldoccurifthecollectorabsorberplatewasatthetemperature Tf i every
where. As such its value ranges between 0 and 1.

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ii)Solar hour angle ωs =0,
(at mean of11:30and12:30),
iii)Solar altitude angle αa is given by,
sinαa =cosφcosδcosωs +sinφsinδ
=cos22◦cos(−23◦)cos0◦+sin22◦sin(−23◦)
=0.85−0.146 =0.7036 αa =44.7◦ ...(Ans.)
iv)Incident angle θ,
θ = π 2 −αa =90−44.7◦
θ =45.3◦ ...(Ans.)

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viii)Now,
S =HbRb(τα) =350×1.40×0.811 S
=395 W/m2
=340.62 kcal/hr m2

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Effect of various parameters on collector performance
a)Heat transfer system
b)Selective surface
c)Number of covers
d)Collector tilt
e)Spacing
f)Fluid temperature
g)Cover transmissivity
h)Dust on top of the cover
i)Performance over a day

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Photovoltaic Cell
Definition: The Photovoltaic cell is the semiconductor device that converts the light into electrical energy.
The voltage induces by the PV cell depends on the intensity of light incident on it. The name Photovoltaic is
because of their voltage producing capability.
The energises electron is known as the Photoelectrons. And the phenomenon of emission of electrons
is known as the photoelectric effect. The working of the Photovoltaic cell depends on the photoelectric
effect

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Construction of Photovoltaic Cell
The semiconductor materials like arsenide, indium, cadmium, silicon, selenium and gallium are used for making
the PV cells. Mostly silicon and selenium are used for making the cell. Consider the figure below shows the
constructions of the silicon photovoltaic cell.
The output voltage and current obtained from the single unit of the cell is very less. The magnitude of the
output voltage is 0.6v, and that of the current is 0.8v. The different combinations of cells are used for
increasing the output efficiency. There are three possible ways of combining the PV cells.

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Series Combination of PV Cells
If more than two cells are connected in series with
each other, then the output current of the cell
remains same, and their input voltage becomes
doubles. The graph below shows the output
characteristic of the PV cells when connected in
series.
Parallel Combination of PV cells
In the parallel combination of the cells, the voltage
remains same, and the magnitude of current becomes
double. The characteristic curve of the parallel
combination of cells is represented below.

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Series-Parallel Combination of PV cells
In the series-parallel combination of cells the magnitude of both the voltage and current increases.
Thereby, the solar panels are made by using the series-parallel combination of the cells.
The solar module is constructed by connecting the single solar cells. And the combination of the solar
modules together is known as the solar panel.

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Working of PV cell
The light incident on the semiconductor material may be pass or reflected through it. The PV cell
is made of the semiconductor material which is neither a complete conductor nor an insulator.
This property of semiconductor material makes it more efficient for converting the light energy
into electric energy.

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How Solar Cell Install on the Solar Power Plant?
Maximum power point tracker, inverter, charge controller and battery are the name of the
apparatus used for converting the radiation into an electrical voltage.

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Photovoltaic Applications
• Solar Farms. Many acres of PV panels can provide utility-scale
• power—from tens of megawatts to more than a gigawatt of
electricity. ...
• Remote Locations. ...
• Stand-Alone Power. ...
• Power in Space. ...
• Building-Related Needs. ...
• Military Uses. ...
• Transportation.

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Dr. Ramesh B T 54
Thank YOU

Performance Analysis of Liquid Flat Plate collector and PV Cell

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Performance Analysis of Liquid Flat Plate collector and PV Cell