A brief description about flat plate collectors is presented.

1. WELCOME

2. FLAT-PLATE
COLLECTORS
PRESENTED BY: KIRTIKA SHARMA
Department of Renewable Energy
Engineering, CTAE, MPUAT, Udaipur
(2017-18)

3. Solar collector – A device designed to
absorb incident solar
radiation and to transfer the energy to a fluid
passing in contact with it, usually liquid or air.
They can be classified in three groups:
- Flat-plate collectors,
- Evacuated-tube collectors
- Focusing collectors.
INTRODUCTION

4. FLATE – PLATE COLLECTOR
 A flat plate collector is
basically a stationary
black surface that is
placed at a convenient
path of the sun.
 Simple and effective
means of collecting solar
energy for applications
that require heat at
temperatures below 1000c.
Figure1. Flat-plate collectors

5. • However to reach higher temparatures
evacuated-tube collectors and focusing
collectors are used.
• In evacuated-tube collectors they use vacum
to reduce heat lost and to protect the absorber
coating from detereoration.By this way they
can reach temperatures up to 140 °C and they
can collect both direct and diffuse solar
radiation.
• And focusing collectors, they are not stable
and they follow the sun to get direct radiation;
they can not utilize diffuse radiation. And they
are also capable of producing high
temperatures.

6. Classification:
( based on heat transfer fluid used ):
1)Liquid heating collectors
- used for heating water and non- freezing
aqueous solutions
2) Air or gas heating collectors
- used for heating, drying or curing of
agricultural products, space heating

7. Components of a typical flat plate collector:
1)A transparent cover – one or more sheets of glass or
radiation transmitting plastic film or sheet.
2) Tubes, fins , passages or channels- integral with or
connected to the absorber plate & conduct the working
fluid through the collector.
3) The absorber plate- normally metallic or with a black
surface
4) Insulation – provided at the back & sides to minimise
heat losses
5) The casing or enclosure - encloses the other components
& protects them from the weather.

8. Fig 2. Cross section of a basic liquid heating flat-plate solar collector

9. A TYPICAL LIQUID FLATE PLATE COLLECTOR:
Absorber plate:
• Is basically a flat metal plate, usually made of highly conductive
and corrosion resistant copper or steel or aluminium or with a
black surface with high absorptivity for solar radiation.
• Is made from metal sheet 1 to 2 mm in thickness.
• Generally corrugated galvanised sheet material is widely used. As
copper is expensive, steel is widely used.
• The surface of the absorber plate determines how much of the
incident solar radiation is absorbed and how much is emitted at a
given temperature. Flat black paint which is widely used as a
coating has an absorptance of about 95 percent for incident
shortwave solar radiation.

10. • The tubings made of
copper of diameter 1 to 1.5
cm are soldered in line or
integral with the absorber
plate with the pitch ranging
from 5 to 15 cm.
Fig 3. Cross section of a absorber plate
& flow passages of a
flat plate collector
• For a copper plate 0.05 cm
thick with 1.25-cm tubes
spaced 15 cm apart in good
thermal contact with the
copper, the fin efficiency is
better than 97 percent.
Flow passages:

11. • One or two sheets of glass of
thickness 3 to 4 mm or
radiation transmitting plastic
film or sheet that is transparent
to incoming solar radiation and
opaque to the infrared re-
radiation from the absorber.
• Should have a high
transmittance for solar
radiation and should not
detoriate with time.
• It reduces convective and
radiative heat losses from the
absorber.
Transparent Cover plate:
Fig 4. Cross section of a cover part
of a flat-plate collector

12. • Thermal insulation of 5 to 10
cm thickness.
• Material is generally mineral
wool or glass wool or a heat
resistant fiber glass.
• Placed behind absorber plate to
prevent heat losses
from the rear surface.
• The collector enclosure is
usually made from galvanized
steel or aliminium.
• Slagwood, polyurethane foam,
hay in polythene bags are other
suitable insulation materials.
Insulation & Enclosure:
Fig 5. Cross Section of an
Insulation Part of a
Flat-Plate Collector

13. FLATE –PLATE AIR HEATING COLLECTORS
(SOLAR AIR HEATERS)
A conventional air heater is typically a flat passage
between two parallel plates. One of the plates is
blackened to absorb incident solar radiation. One or
more transparent covers are located above the
absorbing surface.
The air is made to pass through the passage so that it
gets heated. Insulation around the sides and base of the
unit is necessary to keep heat losses to a minimum.

14. Fig 6. Cross section of a basic air-heating flat-plate solar collector

15. PROPER ORIENTATION and
ANGLE of SOLAR COLLECTOR
Flat plate collectorts are divided in three main groups
according to how they are oriented:
• Flat-plate collectors facing south at fixed tilt
• One-axis tracking flat-plate collectors with axis
oriented north-south
• Two-axis tracking flat-plate collectors
Most favourable orientation of a collector for heating only-
collector facing due south at an inclination angle to the
horizontal equal to the latitude plus 150 (s= ø + 150) for
winter and is (s= ø - 150) for summer.

16. SELECTION OF MATERIALS FOR
FLATE PLATE COLLECTORS:
(i) Absorber plate:
High absorbtivity
High thermal conductivity
Adequate tensile & compressive strength
Good corrosion resistance
Less specific heat
Easily workable
Easy to handle
Low cost
Eg. Copper , Aluminium, Steel.

17. MATERIAL SPECIFICATION
Material Density
kg/m3
Specific
heat
Kg/KJ
Thermal
conductivity
W/m ºc
Aluminum 2707 0.896 204
Iron 7897 0.452 73
steel 7833 0.465 54
copper 8954 0.385 386

18. ii) Cover plate:
 Good strength, durability
 non-degradability
 efficient solar energy transmission
 Rigidity
 resistant to thermal shock
 Minimize convection loss
 Minimize radiation loss
Eg. Tempered glass.

19. SPECIFICATION OF TRANSPARENT
COVER
Material Thickness
(mm)
Solar
transmisivity
(%)
Thermal
transmission
(%)
Glass 3-4 91-95 3-5
Pvc 0-3 85 32

20. PROPERTIES OF INSULATING
MATERIALS
Material Density
Kg/m3
Thermal
conductivity
W/m ºc
Timber 720 0.1442
Thermocol 22 0.0314
Saw dust 188 0.0511
Glass wool 65 0.0418
Fiber glass 32 0.0372

21. A. COLLECTOR PERFORMANCE
The thermal performance of a collector can be
calculated from a first-law energy balance. According
to the first law of thermodynamics, for a simple flat-
plate collector an instantaneous steady-state energy
balance is :
• Useful energy = energy absorbed – heat loss to the
gain (Qu) by the collector surroundings

22. QU = AC HR (τ . α) - AC UL (Tp-Ta)
Equation 1. Useful energy gain equation
where
QU = useful energy delivered by collector, W (kcal/hr)
AC = Collector area, m2
HR = solar energy received on the upper surface of the
sloping collector structure, W/m2 (kcal/hr m2)
H = rate of incident beam or diffuse radiation on a
unit area of surface of any orientation
F = Factor of convert beam or diffuse radiation to
that on the plane of collector

23. τ = fraction of incoming solar radiation that reaches the
absorbing surface, transmissivity ( dimensionless)
α = fraction of solar energy reaching the surface that is
absorbed , absorptivity ( dimensionless)
UL = overall heat loss coefficient, W/m2 0c
Tp = average temp. of the upper surface of the absorber
plate, 0c
Ta = atmospheric temperature, 0c
τ . α = a transmittance-absorptance product that is weighted
according to the proportions of beam, diffuse, and
ground reflected radiation on the collector.

24. AC HR (τ . α) = Absorbed energy
AC UL (Tp-Ta) = Effective heat loss
 To improve the performance of solar collector it is
necessary either to reduce the overall energy loss
coefficient or reduce area from which energy is lost.
 That is; the maximum possible useful energy gain
(heat transfer) in a solar collector occurs when the
whole collector is at the inlet fluid temperature; heat
losses to the surroundings are then at a minimum.

25. B. COLLECTOR HEAT REMOVAL FACTOR (FR):
A quantity that relates the actual useful energy gain of a
collector to the useful gain if the whole collector
surfaces were at the fluid inlet temperature.
The quantitiy FR is equvialent to the effectiveness of a
conventional heat exchange, which is defined as the
ratio of the actual heat transfer to the maximum
possible heat transfer.
Equation.2 . the collector heat removal factor FR
Where;
m’ = Fluid mass flow rate, kg/s
Cp = Fluid specific heat, J/kg °C

26. C. OVERALL HEAT LOSS COEFFICIENT (UL):
In equation 1. UL is the collector overall loss
coefficient and it is equal to the sum of the top,
bottom,and edge loss coefficients :
Equation 3. Overall loss coefficient UL
UL = Utop+Ubottom+Uedge , W/m²K

27. 92% of the total sunshine reaches to the copper absorber.
8% of the total sunshine is reflected from glass.
5% of the sunshine is emitted from the panel.
12% is lost through convection and conduction.
Fig.6. Energy diagram of typical flat flate collector

28. D. COLLECTOR EFFICIENCY
It is the measure of collector performance and is
defined as the ratio of the useful gain over any time
period to the incident solar energy over the same time
period.
The basic method of measuring collector
performance is to expose the operating collector to
solar radiation and measure the fluid inlet and outlet
temperatures and the fluid flow rate.
ƞ=
ƪ
QU dƮ
𝐴𝐶
ƪ 𝐻𝑇 𝑅dƮ
Equation.7. Collector efficiency equation

29. INSTANTANEOUS SOLAR COLLECTOR EFFICIENCY
can be defined as the ratio of the actual solar energy
collected to the solar energy incident on or intercepted by
the collector.
   
T
aiLR
R
Tc
u
i
H
TTUF
F
HA
Q
n

 .
 
Tc
ip
i
GA
TTCm
n


0'
Equation 8. Instantaneous solar collector efficiency formula

30. METHODS TO IMPROVE EFFICIENCY
OF FLATE-PLATE COLLECTOR:
• By increasing the transmission of energy through
the collector to the working fluid.
• By decreasing the thermal losses from the collector
to the ambient by reducing conductive, convective
and radiative losses.
• Conductive losses can be reduced by using a
sufficiently thick layer of thermal insulation & also by
increasing the thickness of the air gaps.
• Convective losses can be eliminated by evacuating the
space between the absorber and the cover plate.
• Radiative losses can be reduced by a spectrally
selective coating on the absorber plate.

31. APPLICATIONS
A) Domestic applications
• Domestic hot water
• Air conditioning
• Cooking
B) Commercial applications
• laundromats
• car washes
• military laundry facilities
• Space heating
• Power generation
• Water pumping

32. Figure 7. Flat plate collectors used for heating buildings

33. Figure 8. Flat-plate collectors used for heating swimming pools

34. COMPARISON OF LIQUID AND AIR HEATING
FLAT PLATE COLLECTORS
S.NO. PARAMETRS LIQUID HEATING
TYPE
AIR HEATING TYPE
1. Volume of storage
required
1/3rd of vol. of rocks
necessary to store
equal quantities of heat
for air systems
Roughly 3 times as
much vol. as for
water heat-storage
(due to low density of
air as working fluid)
2. Noise level Less noisy Higher noise level
3. Energy requirements
for pumping working
fluid
Much less Much more(require
blowers)
4. Energy supply to
absorption air-
conditioners
Easily adapted Has difficulty
5. Fluid circulation costs Low high

35. CONCLUSION
Flat-plate collectors which are used for water heating,
are long lasting, and also in long term they are cheaper
than other water heating systems.However,they requires
large areas if high energy output is a requirement.
Than solar energy is free if we do not include the initial
cost for installation and the maintenance.
Finally; besides these we should remember by using
solar energy we can protect nature.