Chapter - 4 Hiren D. Raval 52 PhD Thesis CHAPTER - 4 Improvement in Energy Efficiency of a Solar Photovoltaic Panel by Thermal Energy Recovery Summary: As explained in chapter 2, the electrical efficiency of solar photovoltaic (PV) panel decreases with increase in its temperature because of its negative temperature co- efficient. The conventional solar PV panel has the conversion efficiency of only 5-17%; this means, about 83- 95% of incident energy is wasted and the proposition of recovering energy from solar PV panel can tap more thermal energy than electrical energy generated by PV panel itself. The heat was transferred by direct contact heat exchange with flowing water from top of the panel and bottom of the panel. Direct contact heat exchange from top surface was found more efficient in recovering energy as well improving the performance of PV panel. The refraction of light as it passes through the water layer straightens the incident radiation. The straightened radiation along with lower temperature of PV panel synergistically increases photovoltaic conversion efficiency. The computational fluid dynamics simulation of PV panel temperature closely resembled the experimental data. There is a potential to recover energy at larger scale for large scale solar PV installations. Thus, the present work proposes the win-win scenario of improved panel performance by controlling its temperature and recovery of thermal energy for alternate applications.
24
Embed
CHAPTER - 4 Improvement in Energy Efficiency of a Solar ...shodhganga.inflibnet.ac.in/bitstream/10603/118235/6/15chapter 4.pdf · energy efficiency of a solar photovoltaic panel by
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Chapter - 4
Hiren D. Raval 52 PhD Thesis
CHAPTER - 4
Improvement in Energy Efficiency of a Solar
Photovoltaic Panel by Thermal Energy Recovery
Summary: As explained in chapter 2, the electrical efficiency of solar photovoltaic (PV)
panel decreases with increase in its temperature because of its negative temperature co-
efficient. The conventional solar PV panel has the conversion efficiency of only 5-17%;
this means, about 83- 95% of incident energy is wasted and the proposition of recovering
energy from solar PV panel can tap more thermal energy than electrical energy generated
by PV panel itself. The heat was transferred by direct contact heat exchange with flowing
water from top of the panel and bottom of the panel. Direct contact heat exchange from top
surface was found more efficient in recovering energy as well improving the performance
of PV panel. The refraction of light as it passes through the water layer straightens the
incident radiation. The straightened radiation along with lower temperature of PV panel
synergistically increases photovoltaic conversion efficiency. The computational fluid
dynamics simulation of PV panel temperature closely resembled the experimental data.
There is a potential to recover energy at larger scale for large scale solar PV installations.
Thus, the present work proposes the win-win scenario of improved panel performance by
controlling its temperature and recovery of thermal energy for alternate applications.
Chapter - 4
Hiren D. Raval 53 PhD Thesis
Published peer-reviewed International Journal paper:
Hiren D. Raval*, Subarna Maiti*, Ashish Mittal (2014) “Computational fluid
dynamics analysis and experimental validation of improvement in overall
energy efficiency of a solar photovoltaic panel by thermal energy recovery”,
Journal of renewable and sustainable energy 6, pp. 033138-1-12, ISSN 1941-
7012.
4.1 Research gap identification
As discussed in literature review (chapter-2), many researchers have attempted
photovoltaic panel cooling. Despite the extensive research on heat transfer from solar PV
panel, modelling and experimental validation of solar panel heat transfer with water
cooling from top surface with overall energy perspective remains the research gap. This
chapter addresses the heat transfer aspects from photovoltaic panel cooling to increase the
panel efficiency and develop understanding on energy recovery aspects to address the
following research questions:
1. Can the temperature of solar photovoltaic panel be validated with theoretical
temperature based on the computational fluid dynamics simulation with and
without cooling of the photovoltaic panel?
2. Can the overall energy efficiency of converting solar radiation to electricity and
captured thermal radiations be calculated with cooling and the same can be
compared without cooling?
3. Is there any other phenomenon apart from cooling that may lead to increase in
energy efficiency?
4.2 Experimental
Heat transfer from solar photovoltaic panels poses the challenge that the panel efficiency
should improve, understandably there should not be any obstruction in incident solar
radiation over the panel.
Chapter - 4
Hiren D. Raval 54 PhD Thesis
The direct contact heat exchanger system was designed with the coolant being water since
radiations are incident from top; the heat exchange from was planned to control the
temperature of PV panel. All the sides and back surface of the panel were properly
insulated with calcium silicate insulation. Rationale was to utilize the maximum thermal
energy and minimize the losses of thermal energy, at the same time achieve higher
photovoltaic conversion efficiency.
4.2.1 Materials
Solar PV panel -70 Wp, frame structure, Rheostat, water tank, Thermocouples,
pyranometer (Kipp & Zonen CM4 pyranometer).
4.2.2 Method
The PV panel was kept at 20o
inclination in southward direction to get the optimal access
to solar radiation with reference to the location Bhavnagar, India, Co-ordinates: 21.7600o
N and 72.1500o E as shown in figure 1. One PV panel was provided cooling from top,
whereas the other panel was kept without cooling. The variable resistance system
(Rheostat) was used to measure the V-I (Voltage- Current) performance of PV panel.
As shown in figure 4.1, the system where, cooling was provided from top comprised of the
perforated pipe over its length at top, perforations being 2 mm in diameter. The flow rate
of cooling water was varied from 1 liter per minute to 2 liter per minute and the V-I
performance of the PV panel was evaluated. The water at outlet was drained out in a tank
open to atmosphere and was then recirculated using a DC (direct current) Kemflo make
pump. The nominal flow rate of the pump was 1 Lmin-1
. Two pumps are operated for
getting flow of 2 Lmin-1
.
FIGURE 4.1: Water flowing from top of the solar photovoltaic panel
Chapter - 4
Hiren D. Raval 55 PhD Thesis
4.3 CFD Simulation
PV panel was exposed to solar radiation out of which a fragment is getting converted into
electricity. The energy balance across the solar PV panel is given by,
Rate of accumulation of heat = Rate of heat input – Rate of heat output + Rate of heat