CHAPTER - 4 Improvement in Energy Efficiency of a Solar...

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


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


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


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

genera

ρavCpavdT/dt = qsw - qlw - qconv−Pout ...............(4.1)

ρav = Average Density of PV panel and glass

Cpav = Average Specific heat of PV panel and glass

T = Temperature of PV panel (It is assumed that temperature of PV panel and glass above

it are same)

qlw = long wave radiation

qsw = short wave radiation

qconv = Heat loss by convection

Pout = Power output of PV panel

-qlw = A σ [(1+CosƟ)/2*ЄskyTsky4 + (1-CosƟ/2)* ЄgroundTground

4 – ЄpanelTpanel

4]...(4.2)

σ = Stephen Boltzman Constant

Є = Emissivity

Ɵ = Angle between panel and ground

qsw = αΦA.....(4.3)

qconv = A (hcnatural +hcforced)(Tpanel – Tenv)....(4.4)

Substituting (4.2), (4.3) and (4.4) in (4.1)

ρav Cpav dT/dt = A σ [(1+CosƟ)/2*ЄskyTsky4 + (1-CosƟ/2)* ЄgroundTground

4 – ЄpanelTpanel

4] +

αΦA - A (hcnatural +hcforced)(Tpanel – Tenv) – Pout

Єsky = 0.736 +0.00577T

Єground = Emissivity of concrete =0.94

Єpanel = 0.85

Ɵ = 20

Chapter - 4


A = Area of panel =0.628 sq. m.

σ = 5.67 X 10-8

W/m2K

4

ρav = 3015 kg/m3

Cpav = 0.7733 J/g oC

hcnatural = 1.31 (Tglass- Tair)1/3

hcforced = 5.82 + 4.07v

The ANSYS Computational fluid dynamics software was used to simulate this model.

Assumptions made in simulating the model using ANSYS CFD tool are depicted below.

A constant water thickness of 2 mm above the panel is considered.

The flow is steady.

The water temperature varies with time (Water absorbs the solar radiation).

Infrared: 50%, Visible radiation: 40% and ultraviolet: 10% of the total incident

radiation.

Absorptivity of opaque material is 80%.

Glass transmissivity: 80%, Absorptivity: 20% and no reflectivity.

Pipe material does not absorb radiation.

Simulations were carried out applying boundary conditions with ANSYS CFD software

until the solution converges.The photovoltaic panel comprised of the following different

layers, physical properties of each layer is given in table 4.1[1, 2].

TABLE 4.1: Physical properties of the constituents of PV panel

Layer Thickness t (m)

Thermal

Conductivity K

(w/m K)

Density

(kg/m3)

Specific heat

Cp (J/kg K)

Tedlar 0.0001 0.2 1200 1250

Rear contact 10X10-6

237 2700 900

EVA 500X10-6

0.35 960 2090

PV Cell 225X10-6

148 2330 677

ARC 100X10-9

32 2400 691

Glass 0.003 1.8 3000 500

Chapter - 4


As there are perforations in the feed water pipe, the geometry was created by considering 8

inlets and 4 outlets of water from the panel. Air domain has been considered surrounding

the physical geometry. Thereafter, geometry was also created by considering 1 slit type

inlet and 1 outlet to match the experimental condition.

Figure 4.2 shows the meshed domain of 8 inlets, 4 outlets system and figure 4.3 shows the

sliced domain of this system made using ANSYS CFD software. Skewness of mesh is 0

and orthogonal quality is 1.

FIGURE 4.2: Meshed domain of 8 inlets 4 outlets system

FIGURE 4.3: Sliced domain of 8 inlets 4 outlet system

Figure 4.4A shows the schematic of model and 4.4B shows the schematic of model mesh.

Meshing becomes denser near boundaries as the software will solve equations at the

crossing points. The denser meshing near boundaries will improve the quality of solution.

Chapter - 4


4.4 Results and Discussions: Initial part of this section discusses the results with 8

inlets, 4 outlet system; the later part simulates the system with single inlet and single

outlet.

FIGURE 4.4A: Schematic of the model FIGURE 4.4B: Schematic of the model mesh

Figure 4.5 shows the simulation results of temperature on the back side of the panel as well

as on the top of the panel. As there is insulation on the back side, the heat cannot escape

from the back. However, the temperature is within control with the average temperature

near 36oC at the back side except the extreme bottom corner point where the temperature

reached upto 60oC. The temperature is particularly higher at the bottom corners of the

panel where water cannot flow and remain stationary whereas; the temperature is well

under control about 27oC on the top side as visible from the image. The purpose of cooling

from top side is to cool the array surface and insulation at the back side prevents heat loss.

The results show that the cooling is effective as the average temperature does not reach

very high on the back surface.

Chapter - 4


FIGURE 4.5: Temperature of photovoltaic panel back surface and top surface

FIGURE 4.6: Velocity of water over photovoltaic panel

Figure 4.6 shows the velocity of water over photovoltaic panel. The velocity is low (less

than 0.05m/s) over the panel, however it is higher at entry and exit points. The central part

is photovoltaic panel over which the velocity profile is shown. The temperature of

photovoltaic panel as shown in Figure 4.5 shows that this velocity was good enough to

control the temperature.

Direct solar

irradiance: 800

w/m2

Inlet cooling

water

temperature:

30oC

Total Inlet flow:

1 Liter/minute

Chapter - 4


FIGURE 4.7: Temperature of cross section of photovoltaic panel

Figure 4.7 shows the temperature of photovoltaic panel across the cross-section. It is

explicit that the temperature increases at the bottom because of insulation. When the

thermal energy is transferred from top and it is not allowed to escape from bottom, it is

understandable that the temperature of the back side will increase. The insulation is

efficient to prevent heat loss and heat is transferred from top.

FIGURE 4.8: Temperature of cross section in z axis of photovoltaic panel

Figure 4.8 shows the temperature of cross section in z axis of photovoltaic panel. The

temperature varies because of natural convection of air above the panel.

Direct solar

irradiance: 800

w/m2

Inlet cooling water

temperature: 30oC

Direct solar

irradiance: 800 w/m2

Inlet cooling water

temperature: 30oC

Chapter - 4


FIGURE 4.9: Velocity vector above the PV panel surface

Figure 4.9 shows the velocity vectors above photovoltaic panel surface. Velocity is higher

at inlet and outlet. At inlet, it is higher because the flow is coming from the small opening

and at the outlet, the flow converges to a small exit.

There were number of perforations over the length of pipe. Thus, to, simulate the actual

experimental condition with more precision, the meshed domain with single inlet and

single outlet is considered as shown in figure 4.10 with the velocity remaining nearly same

as the actual experimental velocity.

FIGURE 4.10: Meshed domain with single inlet/single outlet

The meshing characteristics: Skewness: 0, Orthogonal quality: 1

The figure 4.11 demonstrates the velocity vectors along the streamline of water. The

velocity of water is low i.e. approximately 0.03 -0.06 m/s for both the cases 1 LPM and 2

Total Inlet flow:

1 Liter/minute

Chapter - 4


LPM. However, the increase in velocity is quick for 2 LPM flow when the flow converges

to the exit point.

FIGURE 4.11: Velocity vectors for the flow 1 LPM and 2 LPM at 13:00 Hrs

The snapshot in Figure 4.12A and 4.12B demonstrates the comparison of PV panel

temperature with 1 LPM and 2 LPM flow respectively at 10:00 Hrs and 13:00 Hrs. It can

be seen from the simulation results that larger area of PV panel remains at lower

temperature with increased flow rate, and higher flow rate is particularly required to

maintain the temperature when solar radiation intensity is higher at 13:00 Hrs. When

comparing the panel temperature without cooling as shown in Figure 4.13, it becomes clear

that the panel temperatures are well within control with cooling. The panel temperature

without cooling reaches upto 76oC and the changes at different locations in the panel as a

result of natural convection are indicated in figure 4.14. The panel temperature is

controlled within 40oC by cooling even with lower flow rate of 1 LPM.

Inlet flow: 1 Liter/minute Inlet flow: 2 Liter/minute

Chapter - 4


FIGURE 4.12A (Top) and 4.12B (Bottom): PV panel temperature with cooling at 10:00 Hrs 13:00 Hrs

respectively

FIGURE 4.13: Panel temperature without cooling 10:00 Hrs and 13:00 Hrs

Direct solar

irradiance: 813.31

w/m2

Inlet cooling water

temperature: 30oC

Direct solar

Irradiance:

1012.28 W/m2

Inlet cooling

water

temperature:

35oC

Direct solar irradiance at 10:00 Hrs: 813.31

W/m2 at 13:00 Hrs: 1012.28 W/m

2

Chapter - 4


FIGURE 4.14: Temperature across the cross section of PV panel at 10:00 Hr and 15:00 Hrs

The figure 4.14 shows the temperature across the cross section of PV panel at 10:00 Hrs

and 15:00 Hrs. It can be seen that the temperature of the bottom layer near insulation

increases despite the panel top surface is maintained at close to 35oC. This is because the

heat is not getting wasted from the bottom on account of insulating layer at bottom. This

also ensures the heat transfer direction from bottom up across the layers of PV panel as the

day progresses.

Direct solar Irradiance: 813.31 W/m2

Inlet cooling water temperature: 30oC

Direct solar Irradiance: 856.31 W/m2

Inlet cooling water temperature: 33.5oC

Chapter - 4


FIGURE 4.15: Temperature of panel cross section without cooling at 15:00 Hrs

The figure 4.15 indicates the effect of natural convection. The air adjacent to PV panel gets

heated as the temperature of PV panel increases and the density of air decreases at higher

temperature. The light air climbs up the panel and increases the temperature at the top part

of panel as compared to the bottom as visible in figure 4.15. Thus, natural convection alters

the PV panel temperature at different places.

The ambient conditions on the days of experiment are as shown in table 4.2.

TABLE 4.2: The environmental conditions on the days of experiment

Condition 14 May 1 June

Insolation (7 Hrs- 1030 to 1730) 837.37 W/m2 838.71 W/m

2

Average wind speed 1.4 m/s 1.4 m/s

Average insolation (24 hrs) 488.60 W/m2 343.83 W/m

2

Average ambient temperature 36.51 oC 38.61

oC

The performance of PV panel is assessed by V-I Performance. In figure 4.16, the

performance of PV panel has been demonstrated, where the peak power produced by PV

panel with and without cooling are compared. It is clear that the peak power produced by

PV panel improves with cooling where about 10% improvement in power output is

observed at 13:00 hrs. The pump consumes 5 W power. Therefore, the net power produced

Direct solar irradiance: 856.31 W/m2

Chapter - 4


with cooling has to be reduced by 5 W in each case. However, the gravity operated systems

can also be designed where; net power will be the same as power produced.

FIGURE 4.16: Performance comparison of PV panel with and without cooling – Cooling water flow:1

LPM

Total energy generated over the day with cooling was 333 watt-hour, whereas the total

energy generated without cooling was 303 watt-hour.

FIGURE 4.17: Temperature of PV panel with and without cooling

It is explicit from figure 4.17 that there is a significant decline in PV panel temperature as a

result of cooling from top surface at 1 LPM flow. The experimental results are compared

0

10

20

30

40

50

60

1000 1100 1200 1300 1400 1500 1600 1700

Peak Power

produced

by Solar PV

panel

(Watt)

Time (Hours) Peak power

With Cooling

Peak power without cooling

0

10

20

30

40

50

60

70

1000 1200 1400 1600

Temperature

of PV panel

(oC)

Time of the day

Temperature of PV panel with and without cooling -Cooling water flow: 1

LPM

Avg.Temp. without

cooling

(Experimental)

Average temperature of

panel without cooling (by

CFD simulation)


panel with cooling

(Experimental)


panel with cooling (by CFD

simulation)

Chapter - 4


with CFD simulation results and found in close conformity. When temperature reaches

close to 60o C at 14:00 hrs without cooling the panel, it is controlled well below 40

o C with

cooling.

FIGURE 4.18: Performance comparison of PV panel with cooling water flow-2 LPM and without

cooling

It is evident from the figure 4.18 that the peak power produced by PV panel improves as in

the case of 1 LPM flow, however the improvement is substantial. There is 20%

improvement in peak power produced at 13:00 hrs.

FIGURE 4.19: Temperature of PV panel with and without cooling- Cooling water flow 2 LPM

0

10

20

30

40

50

60

1000 1100 1200 1300 1400 1500 1600 1700

Peak Power

Produced by

PV Panel

(Watt)

Time (Hours)

Peak Power - With cooling Peak power- Without cooling

0

10

20

30

40

50

60

70

1000 1200 1400 1600

Temperature

of PV panel

(oC)

Time of the day

Temperature of PV panel with and without cooling -Cooling water

flow: 2 LPM

Avg.Temp. without cooling(Experimental)

Average temperature of panelwithout cooling (by CFDSimulation)

Average temperature withcooling (Experimental)

Average temperature of panelwith cooling (BY CFDsimulation)

Chapter - 4


Fig. 4.19 indicates that the PV panel temperature decreases from 58oC to 37

oC as a result

of cooling with 2 LPM flow at 14:00 Hrs. The experimental results are in close conformity

with the simulation results.

In this way, the experimental results are in close confirmation with simulation results and it

becomes explicit that panel performance improves as a result of cooling from top as the

panel temperature is controlled below 40oC.

It is also important to know V-I performance of photovoltaic panel with and without

cooling. The results below indicate the V-I performance of photovoltaic panel with and

without cooling.

FIGURE 4.20: V-I performance of photovoltaic panel at 12:00 hrs

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 5 10 15 20

Current (Amp.)

Voltage (V)

V-I Performance of Panel at 1200 Hrs

With Cooling

Without Cooling

Chapter - 4




0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 10 20 30

Current

(Amp.)

Voltage (V)


With Cooling

Without Cooling

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 10 20 30


With Cooling

Without Cooling

Current

(Amp.)

Voltage (V)

Chapter - 4




0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 5 10 15 20 25

Current

(Amp.)

Voltage (V)


With Cooling

Without Cooling

0

0.5

1

1.5

2

2.5

3

3.5

4

0 5 10 15 20 25

Current

Amp.

Voltage (V)


With Cooling

Without Cooling

Chapter - 4




Figure 4.20 – 4.26 demonstrates that V-I performance of photovolataic panel improves at

higher resistance. At low resistance, current is slightly lower with the panel cooling, the

relative current performance of panel improves at higher resistance; moreover voltage is

substantially more with cooling. However, the actual applications are generally with higher

resistance and therefore the performance with cooling is better. These data were taken

over several days and average of the data has been reported.

0

0.5

1

1.5

2

2.5

3

3.5

4

0 5 10 15 20 25

Current

(Amp.)

Voltage (V)


With Cooling

Without Cooling

0

0.5

1

1.5

2

2.5

3

0 5 10 15 20

Current

(Amp.)

Voltage (V)


With Cooling

Without Cooling

Chapter - 4


Refraction effect and improvement of panel performance

The influence of refractive index in changing direction of the solar radiation has not been

studied earlier. The reason of improvement in energy efficiency can also be attributed to

the refraction effect because of flow of water above the panel. The angle of incident

radiation in Bhavnagar was obtained by SOLPOS calculator. The angle changes as a result

of refraction by the water layer. The refractive index of air and water and the incident

angle are known. The angle after refraction can be calculated using Snell’s law n1sin1 =

n2sin2. Water has the refractive index 1.333 [3]. Air has refractive index 1.0.

The table 4.3 indicates the effect of refraction over the solar PV panel.

TABLE 4.3: The Angle change as an effect of refraction by solar PV panel

Time Angle Ө1 Angle Ө2

09:00 -61.91 -41.58

10:00 -50.73 -35.63

11:00 -41.78 -30.09

12:00 -36.77 -26.76

13:00 37.27 27.10

14:00 43.11 30.94

15:00 52.54 36.66

16:00 63.98 42.53

17:00 76.49 47.00

From the table 4.3, it is clear that the incident angle varied from -61.91 to 76.49 from

Morning 09:00 hrs to evening 17:00 hrs. The angle changes after refraction and thus, the

angle 2 varied from -41.58 to 47.00. In this way, the span of angle reduced from 138.4 to

88.58. In other words, the incident radiations were straightened as a result of refraction as

shown in the figure 4.27. These straightened radiations helped to improve the performance

of the panel as they strike to panel at relatively larger angle as compared to the one without

water layer on top.

Chapter - 4


FIGURE 4.27 Radiation at a given point straightened as a result of refraction

The experiment was performed to justify this finding. Ice was placed on the back side of

the PV panel and water layer on the top of the other identical panel to maintain the

temperature of PV panel at 35oC in both cases. The peak output observed with ice on the

back side was 50.22 Watt, whereas the peak output with water layer on top was 54.04 Watt

at same time 13:00 Hrs (7.6% increase in power output). This made it clear that the

refraction effect played its role to improve the panel performance. Typically, if the increase

in power output is about 20%, 7.6% may be attributed to refraction effect and 12.4% may

be attributed to cooling.

Overall energy efficiency: The energy efficiency with and without cooling was worked

out as a case to understand the effect of cooling on overall energy efficiency. It has been

observed that the efficiency was raised from 6.68% to 40.42% with cooling as shown in

table 4.4.

138.40o

88.58o

Chapter - 4


TABLE 4.4: Energy efficiency calculations (For 1 Liter per minute flow)

Time 12:00 Hrs 14:00 Hrs 16:00 Hrs

Inlet water temperature(Twin) 37 36 34

Outlet water temperature(Twout) 39 38 35

Energy contained by water(watt) 139.56 139.56 69.78

Peak power without cooling (watt) 34.51 25.29 14.22

Peak power with cooling (watt) 41.73 28.57 16.3

Difference (watt) 7.22 3.28 2.08

Total power saving (watt) 146.79 142.85 71.86

Watt/m2 1020 732 348

Solar panel area (sq.m) 0.61 0.61 0.61

Power incident on the panel (watt) 624.24 447.98 212.98

Energy efficiency without cooling 5.53 5.64 6.68

Energy efficiency with cooling

(electrical + thermal) 29.0421 37.531 40.417

In this way, there is a significant improvement in overall energy (thermal + electrical)

efficiency with the cooling from top. The heated water can be used for some application

e.g. feed water to reverse osmosis. The higher temperature feed water improves

permeability of membrane and more product water can be generated from given membrane

area.

4.5 Conclusion

The following conclusions can be derived from the experiments to control the photovoltaic

panel temperature and theoretical study by computational fluid dynamics analysis.

Photovoltaic panel demonstrates the poorer performance at higher temperature, thus

cooling of photovoltaic panel is necessary to retain/enhance its efficiency. The

panel temperature could be effectively controlled by transferring heat from top at

low flow rate of 1 and 2 Liters per minute. Insulation at the back surface and sides

ensured that heat is not lost and transfer of heat is bottom-up in the photovoltaic

Chapter - 4


panel. CFD analysis is in close confirmation with experimental validation for the

panel temperature.

It is demonstrated that the refraction of incident solar radiation while striking to PV

panel through the water film is beneficial. Refraction narrows the span of incident

radiation over the panel and narrowing the span of angle variation is better from the

point of view of panel performance. This is proven by increased power output in

the panel with water flowing from top.

The rise in water temperature reported indicates that there is a potential to tap the

thermal energy. The higher temperature water can be used for desalination systems

like membrane distillation, reverse osmosis etc. Reverse Osmosis water flux

increases with increase in feed water temperature. It is prudent to utilize the feed

water to Reverse Osmosis as cooling water and utilize the captured thermal energy

as soon as possible. Interdisciplinary approach of tapping thermal energy from

photovoltaic panel and thereby controlling its temperature along with utilizing the

tapped thermal energy for useful application such as Reverse Osmosis can increase

the overall energy efficiency of photovoltaic powered Reverse Osmosis.

In this study, the overall energy efficiency has been increased from about 6% to

40% by direct cooling the array surface of PV panel from top at 1 liter per minute

flow.

References

1. S. Armstrong, W.G. Hurley (2010) A thermal model of photovoltaic panels under varying

atmosphetic conditions, Applied thermal engineering, Volume 30, p. 1488, ISSN 1359-4311.

2. G. Notton, C. Cristofari, M. Mattei, P.Poggi (2005) Modeling of a double glass photovoltaic

module using finite differences, Applied thermal engineering, Volume 25(17-18), p. 2584,

ISSN 1359-4311.

3. X. Han, Y. Wang, L.Zhu (2011) Electrical and thermal performance of silicon solar cells

immersed in dielectric liquids, Applied energy, Volume 88, p. 448, ISSN 0306-2619.

CHAPTER - 4 Improvement in Energy Efficiency of a Solar...

Documents

Transcript of CHAPTER - 4 Improvement in Energy Efficiency of a Solar...