Objective

In this experiment, the performance of solar cells under different working conditions are investigated. These variables include light intensity and temperature. This is achieved by studying the different current-voltage characteristic curves. Also, the relationship between short-circuit current and no-load voltage with different working conditions is studied.

Introduction

Solar Cell
A solar cell (or a "photovoltaic" cell, Fig. 1) is a semiconductor device that converts light energy in the form of photons from the sun (solar light) into electricity. Solar cells have many applications and are regarded as one of the key technologies towards a sustainable clean energy supply.
[pic]
Fig. 1 A solar cell, made from a monocrystalline silicon wafer
Silicon solar cell has a structure of a pn junction. Silicon can be doped with tri- and pentavalent atoms to make a p- or n-type semi-conductor. If we put a p-and n-type crystal together we get a junction (pn-junction, Fig. 2) whose electrical properties determine the performance of the solar cell.
[pic]
Fig. 2 pn-junction in the energy-band diagram. – acceptors, + donors, UD is the diffusion potential, EF is the Fermi characteristic energy level, and e is the elementary charge.

Photovoltaic Device Principles
Consider a pn junction with a very narrow and more heavily doped n-region, in equilibrium (with no external voltage) the Fermi characteristic energy level EF will be the same throughout. Because of the difference in the concentrations of electrons and holes in the p- and n-regions, electrons diffuse into the p-region and holes into the n-region. The immobile impurity atoms create a space charge-limited current region; the diffusion current and the field current offset one another in equilibrium. There is a built-in field E0 in this depletion layer. The electrodes attached to the n-side must allow illumination to enter the device and at the same time result in a small series resistance. They are deposited on the n-side to form an array of finger electrodes on the surface. A thin antireflection coating on the surface reduces reflections and allows more light to enter the device.
[pic]
Fig. 3 Finger electrodes on the surface of a solar cell reduce the series resistance
As the n-side is very narrow, most of the photons are absorbed within the depletion region (W) and within the neutral p-side and photogenerate electron-hole pairs (EHPs) in these regions. EHPs photogenerated in the depletion region are immediately separated by the built-in field E0 which drifts them apart. The electron drifts and reaches the neutral n+-side whereupon it make this region negative by an amount of charge -e. Similarly, the hole drifts and reaches the neutral p-side and thereby makes this side positive. Consequently, an open circuit voltage develops between the terminals of the device with the p-side positive with respect to the n-side. If an external load is connected, then the excess electron in the n-side can travel around the external circuit, do work, and reach the p-side to recombine with the excess hole there. It is important to realize that without the internal field E0 it is not possible to drift apart the photogenerated EHPs and accumulate excess electrons on the n-side and excess holes on the p-side.

The diffusion potential UD in the pn-junction depends on the amount of doping and corresponds to the original difference between the Fermi energy levels of the separate p- and n-regions. The distance between the valence band and the conduction band in silicon at room temperature is E = 1.1 eV. For silicon, the diffusion potential is UD = 0.5 to 0.7 V.

The EHPs photogenerated by long-wavelength photons that are absorbed in the neutral p-side diffuse around in this region as there is no electric field. Only those EHPs photogenerated within the minority carrier diffusion length Le to the depletion layer can contribute to the photovoltaic effect. Once an electron diffuses to the depletion region, it is swept over to the n-side by E0 to give an additional negative charge there. Holes left behind in the p-side contribute a net positive charge to this region. Those photogenerated EHPs further away from the depletion region than Le are lost by recombination. The same idea also apply to EHPs photogenerated by short-wavelength photons absorbed in the n-side. The photogeneration of EHPs that contributes to the photovoltaic effect therefore occurs in a volume covering Lh+W+Le. This current due to the flow of the photogenerated carriers is called the photocurrent.

Photons are absorbed not only in the pn-junction but also in the p-layer above it. The electrons produced are minority carriers in those areas: their concentration is greatly reduced by recombination, and with it their efficiency. The p-layer must therefore be sufficiently thin for the electrons of diffusion length LE to enter the n-layer. LE >> t, where t = thickness of p-layer.
[pic]
Fig. 4: Construction of a silicon solar cell.
If g is the number of electron-hole pairs produced per unit area and of a voltage U is applied across the pn-junction, a stream of electrons and holes of density i=e[exp(eU/kT-1)(n0Det/Le2+p0Dh/Lh)-eg is produced, where e is the elementary charge, k is Boltzmann’s constant, T is the temperature, L is the diffusion length of electrons and holes, D is the diffusion constant for electrons and holes, n0 and p0 are equilibrium concentrations of the minority carriers.

Consider an ideal pn junction photovoltaic device connected to a resistive load R. If the load is a short circuit, then the only current in the circuit is that generated by the incident light. This is the photocurrent Iph which depends on the number of EHPs photogenerated within the volume enclosing the depletion region (W) and the diffusion lengths to the depletion region. The short-circuit current density is=–e·g is proportional to the intensity of the incident light at fixed temperature. The greater the light intensity, the higher is the photogeneration rate and the larger is Iph. If I is the light intensity, then the short circuit current is Isc= -Iph = -KI, where K is a constant that depends on the particular device. For temperature changes, g becomes very slightly greater (less than 0.01 %/K) as the temperature rises. The voltage U can become as high as the diffusion potential UD but no higher as the temperature rises the no-load voltage decreases typically by –2.3 mV/K, since the equilibrium concentrations n0 and p0 increase with the temperature: n0 exp (– E/2kT).

If R is not a short circuit, then a positive voltage V appears across the pn junction as a result of the current passing through it. This voltage reduces the built-in potential of the pn junction and hence leads to minority carrier injection and diffusion as it would in a normal diode. Thus, in addition to Iph there is also a forward diode current Id in the circuit, which arises from the voltage developed across R. Since Id is due to the normal pn junction behavior, it is given by the diode characteristics Id = I0 [exp(eV/ηkT)-1], where I0 is the "reverse saturation current" and η is the ideality factor (η=1-2). In an open circuit, the net current is zero. This means that the photocurrent Iph develops just enough photovoltaic voltage Voc to generate a diode current Id =Iph. [pic]
Fig. 5 (a) The solar cell connected to an external load R and the convention for the definitions of positive voltage and positive current. (b) The solar cell in short circuit. The current is the photocurrent Iph. (c) The solar cell driving an external load R. There is a voltage V and current I in the circuit.

The overall I-V characteristics of a typical Si solar cell are shown in Figure 6. It can be seen that it corresponds to the normal dark characteristics being shifted down by the photocurrent Iph, which depends on the light intensity I. The open circuit output voltage Voc, of the solar cell is given by the point where the I-V curve cuts the V axis (I=0). It is apparent that although it depends on the light intensity, its value typically lies in the range 0.5 - 0.7V.
[pic]
Fig. 6: Typical I-V characteristics of a Si solar cell
When the solar cell is connected to a load, the load has the same voltage as the solar cell and carries the same current. But the current I through R is now in the opposite direction to the convention that current flows from high to low potential, thus I= -V/R.

The actual current I' and voltage V' in the circuit must satisfy both the I-V characteristics of the solar cell and that of the load. By solving the two equations simultaneously, we can find I' and V'. They are most easily found by using a load line construction. The I-V characteristics of the load is a straight line with a negative slope -1/R. This is called the load line and is plotted along with the I-V characteristics of the solar cell under a given intensity of illumination. The load line cuts the solar cell characteristic at P where the load and the solar cell have the same current and voltage I' and V'. The point P therefore represents the operating point of the circuit.
[pic]
Fig. 7: The current I' and voltage V' in the circuit can be fond from a load line construction. Point P is the operating point. The load line is for R=3Ω.
The power delivered to the load is Pout=I'V', which is the area of the rectangle bound by the I and V axes and the dashed lines. Maximum power is delivered to the load when this rectangular area is maximized (by changing R or the intensity of illumination), when I'=Im and V'=Vm. Since the maximum possible current is Isc and the maximum possible voltage is Voc, IscVoc represents the desirable goal in power delivery for a given solar cell. Therefore it makes sense to compare the maximum power output ImVm with IscVoc. The fill factor FF, which is a figure of merit of the solar cell, is defined as FF= ImVm/IscVoc.

The FF is a measure of the closeness of the solar cell I-V curve to the rectangular shape (the ideal shape). It is clearly advantageous to have the FF as close to unity as possible, but the exponential pn junction properties prevent this. Typically FF values are in the range 70-85 percent and depend on the device material and structure.

Light Intensity
The light intensity is varied by varying the distance between the light source and the solar cell. To determine the intensity with the thermopile it is assumed that all the light entering the aperture (dia. 2.5 cm) reaches the measuring surface. The sensitivity is 0.16 mv/mW.

By extrapolating the straight line we can determine the intensity at distances s ≤ 50 cm.
|[pic] |[pic] |
|Fig. 8 Light-intensity J at distances s normal to the light |Fig. 9 Short-circuit current is and no-load voltage Uo as a |
|source. |function of the light intensity J. |

Using the measured values in Fig.8, we obtain the relationship between the light intensity and short-circuit current and no-load voltage measured at various distances away from the light source (Fig. 9).

Material/Equipment/Procedure

The experiment setup and the circuit is shown in Fig. 10 and Fig. 11, respectively. The current-voltage characteristics of a solar cell are measured at different light intensities by varying the distance between the light source and the solar cell. The dependence of open-circuit voltage and short-circuit current on temperature is determined.
|[pic] |[pic] |
|Fig. 10 Experimental set-up for determining characteristic |Fig. 11 Circuit for measuring the current -voltage |
|curves |characteristic. |

Measure the light intensity with the thermopile and amplifier with the equipment at different distances from the light source. The distance between the lamp and the thermopile should be at least 50 cm and it is increased by 5 cm each step until 90 cm.

Two solar cell plates will be studied in this experiment, 8-cell plate and 4-cell plate. Repeat the following steps for each plate respectively:
(1) Measure short-circuit current and no-load voltage at various distances from the light source.

(2) Measure the current-voltage characteristic at different light intensities (50 cm, 70 cm and 90 cm).

(3) Repeat no. 2 with the aid of a glass plate.

(4) Repeat no 2 with the aid of a blower. Blow hot air over the solar cell and measure the temperature directly in front of it with a thermocouple.

(5) Repeat no 2 with the aid of a blower. Blow cold air over the solar cell and measure the temperature directly in front of it with a thermocouple.

Results

The relationship between light intensity and distance to the light source was first calibrated by measuring the open circuit voltage in the circuit with the thermopile at different distances. The open circuit voltage can then be used to determine the light intensity at the different distances through the equation shown below.

The results are tabulated in table 1 and the trend is shown in figure 12.
|Distance (cm) |Voltage (mV) |Intensity (W/m2) |
| | | |
|50 |29.83 |379.81 |
|55 |26.22 |333.84 |
|60 |22.77 |289.92 |
|65 |20.38 |259.49 |
|70 |18.42 |234.53 |
|75 |16.87 |214.80 |
|80 |15.56 |198.12 |
|85 |14.46 |184.11 |
|90 |13.55 |172.52 |

Table 1 showing the variation of measured voltage at different thermopile distance and corresponding calculated light intensity
[pic]
Figure 12 showing the calculated light intensity at different thermopile distance
From the shape of the graph obtained, it is clear that the light intensity decreases with increasing distance following an inverse squared rule. This trend is expected as the number of photons reaching the thermopile aperture will decrease at further distances as the point light source becomes more diffuse, i.e. photons are spread over a larger area. This is illustrated in figure 13.
[pic]
Figure 13 showing the inverse squared law of light intensity from a point source
However, from the graph, it can be seen that at larger distances, the light intensity measured appears to approach a constant value of approximately 150 W/m2. This does not tally with the expected trend (light intensity approaches 0 at large distances), and could be due to the effect of ambient lighting, which contributes to the photons entering the thermopile and shifts the entire graph up to a minimum value. This constitutes a source of systematic error.

(2) Plot the variation of short-circuit current and open-circuit voltage with the incident light intensity.
[pic]
Tab. 2 showing the variation of short circuit currents and open circuit voltages at different light intensities

From the previous section, light intensities at different distances have been elucidated and fixed. The thermopile is then replaced by the solar cells the open circuit voltages and short circuit currents at different distances (light intensities) is measured and tabulated in table 2 above. The current-intensity and current voltage graphs are shown in figures 14 and 15 respectively.

[pic]
Fig. 14.1 showing the variation of measured short circuit current against light intensity for 8 cell solar cell

[pic]
Fig. 14.2 showing the variation of measured short circuit current against light intensity for 4 cell solar cell

From figures 14.1 and 14.2, it can be seen that the current-light intensity graphs follows the expected linear proportional relationship as provided in the lab manual where is= – e · g. The gradient of the 8 cell line was calculated to be 0.0267 compared with the 0.0543 for the 4 cell line. The 4 cell current also appears to be approximately half that of the 8 cell line, suggesting the cells are in a series connection.

[pic]
Fig. 15.1 showing the variation of measured open circuit voltage against light intensity for 8 cell solar cell

[pic]
Fig. 15.2 showing the variation of measured open circuit voltage against light intensity for 4 cell solar cell

From figures 15.1 and 15.2, it can be seen that the voltage-light intensity graphs, the slight curvature of the graph as it approaches low intensities follows the expected logarithmic relationship as deduced from the lab manual. However, the sharply decreasing curved portion of the graph is not as apparent probably due to the limited range at which the data was collected. The 8 cell voltage also appears to be approximately half that of the 4 cell, suggesting the cells are in a series connection as well.

(1) Plot the current-voltage characteristic at different light intensities.
The current-voltage characteristics can be determined by measuring the voltage and current in the solar cell circuit while varying the resistance. The current-voltage measurements under different conditions for the 3 different light intensities (50cm, 70cm and 90cm respectively) are tabulated in tables 3,4,5,6 and plotted in the figures 16,17,18,19 below.

|Resistance Level |8 Cell (Standard Conditions) |
| |Light Intensity = 379.81W/m2 |Light Intensity = 234.53 W/m2 |Light Intensity = 172.52 W/m2 |
| |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |
|2 |0.48592 |0.027 |0.27353 |0.0165 |0.17746 |0.0112 |
|3 |0.79447 |0.0267 |0.52112 |0.0164 |0.35439 |0.0111 |
|4 |1.2529 |0.0264 |0.73712 |0.0162 |0.51466 |0.0111 |
|5 |1.5918 |0.0261 |0.9935 |0.0161 |0.67469 |0.0111 |
|6 |1.936 |0.0257 |1.2395 |0.016 |0.83833 |0.011 |
|7 |2.2405 |0.0253 |1.4628 |0.0159 |0.96691 |0.011 |
|8 |2.5915 |0.025 |1.6921 |0.0158 |1.1381 |0.0109 |
|9 |2.9179 |0.0247 |1.8677 |0.0156 |1.2893 |0.0109 |
|10 |3.2137 |0.0243 |2.0662 |0.0155 |1.4333 |0.0108 |
|11 |3.4502 |0.0234 |2.243 |0.0153 |1.5775 |0.0107 |
|12 |3.5333 |0.0218 |2.4466 |0.0152 |1.7204 |0.0106 |
|13 |3.601 |0.0205 |2.6404 |0.015 |1.8589 |0.0106 |
|14 |3.6591 |0.0192 |2.8551 |0.0148 |1.9945 |0.0105 |
|15 |3.6959 |0.018 |2.9997 |0.0146 |2.1498 |0.0104 |
|16 |3.7313 |0.0169 |3.1296 |0.0141 |2.295 |0.0103 |
|17 |3.754 |0.016 |3.214 |0.0137 |2.4212 |0.0103 |
|18 |3.7797 |0.0151 |3.2994 |0.0132 |2.5603 |0.0102 |
|19 |3.7983 |0.0141 |3.3732 |0.0126 |2.645 |0.0101 |
|20 |3.8149 |0.0134 |3.4299 |0.012 |2.7765 |0.0099 |
|21 |3.8231 |0.0129 |3.4516 |0.0118 |2.8733 |0.0097 |
|22 |3.8342 |0.0124 |3.489 |0.0114 |2.9338 |0.0095 |
|23 |3.8429 |0.0119 |3.5237 |0.0109 |3.0013 |0.0093 |
|24 |3.8542 |0.0113 |3.5479 |0.0105 |3.0689 |0.0091 |

Table 3.1 showing the 8 cell current-voltage characteristics at 3 different light intensities
|Resistance Level |4 Cell (Standard Conditions) |
| |Light Intensity = 379.81W/m2 |Light Intensity = 234.53 W/m2 |Light Intensity = 172.52 W/m2 |
| |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |
|2 |0.8608 |0.0546 |0.50984 |0.0322 |0.40037 |0.0219 |
|3 |1.4995 |0.0513 |0.59085 |0.0317 |0.68702 |0.0216 |
|4 |1.7937 |0.0397 |1.3655 |0.0296 |0.97468 |0.0214 |
|5 |1.878 |0.0316 |1.5453 |0.0261 |1.2656 |0.0202 |
|6 |1.92 |0.0249 |1.6673 |0.0222 |1.4047 |0.0188 |
|7 |1.9332 |0.0221 |1.7277 |0.0191 |1.5123 |0.0168 |
|8 |1.9478 |0.0191 |1.7609 |0.017 |1.5806 |0.0152 |
|9 |1.9562 |0.0167 |1.7887 |0.0151 |1.6299 |0.0138 |
|10 |1.962 |0.0149 |1.8091 |0.0136 |1.6736 |0.0119 |
|11 |1.9675 |0.0133 |1.8238 |0.0123 |1.701 |0.0111 |
|12 |1.97 |0.0122 |1.8348 |0.0113 |1.712 |0.0106 |
|13 |1.9708 |0.0112 |1.8436 |0.0105 |1.7301 |0.0098 |
|14 |1.9743 |0.0103 |1.8569 |0.0097 |1.7422 |0.009 |
|15 |1.9761 |0.0096 |1.858 |0.009 |1.7554 |0.0086 |
|16 |1.9721 |0.0089 |1.8631 |0.0085 |1.7656 |0.0079 |
|17 |1.9727 |0.0084 |1.8678 |0.0079 |1.7732 |0.0075 |
|18 |1.9704 |0.0079 |1.8717 |0.0075 |1.7814 |0.0071 |
|19 |1.9703 |0.0074 |1.8753 |0.007 |1.7861 |0.0067 |
|20 |1.971 |0.007 |1.8788 |0.0067 |1.7917 |0.0064 |
|21 |1.9717 |0.0067 |1.8814 |0.0064 |1.794 |0.0061 |
|22 |1.9725 |0.0063 |1.8833 |0.0061 |1.8002 |0.0058 |
|23 |1.973 |0.0061 |1.8856 |0.0059 |1.8042 |0.0056 |
|24 |1.9732 |0.0058 |1.8873 |0.0056 |1.8071 |0.0053 |

Table 3.2 showing the 4 cell current-voltage characteristics at 3 different light intensities

[pic]
Figure 16.1 showing the 8 cell current-voltage characteristics at 3 different light intensities

[pic]
Figure 16.2 showing the 4 cell current-voltage characteristics at 3 different light intensities

|Resistance Level |8 Cell (Glass Plate) |
| |Light Intensity = 379.81W/m2 |Light Intensity = 234.53 W/m2 |Light Intensity = 172.52 W/m2 |
| |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |
|2 |0.29794 |0.0194 |0.21107 |0.0118 |0.12085 |0.0081 |
|3 |0.61841 |0.0192 |0.35208 |0.0118 |0.25023 |0.0081 |
|4 |0.83328 |0.0191 |0.51473 |0.0117 |0.3654 |0.008 |
|5 |1.143 |0.019 |0.68598 |0.0116 |0.4778 |0.008 |
|6 |1.4059 |0.0188 |0.85922 |0.0115 |0.59051 |0.0079 |
|7 |1.6407 |0.0185 |1.0467 |0.0114 |0.70388 |0.0079 |
|8 |1.892 |0.0183 |1.2046 |0.0114 |0.82259 |0.0079 |
|9 |2.1117 |0.0181 |1.3405 |0.0113 |0.93101 |0.0079 |
|10 |2.3534 |0.0179 |1.487 |0.0113 |1.0429 |0.0078 |
|11 |2.5757 |0.0177 |1.6517 |0.0112 |1.1512 |0.0078 |
|12 |2.8143 |0.0175 |1.7933 |0.0111 |1.2605 |0.0078 |
|13 |3.0305 |0.0174 |1.9232 |0.011 |1.3615 |0.0077 |
|14 |3.2306 |0.017 |2.0658 |0.0109 |1.4766 |0.0077 |
|15 |3.3542 |0.0164 |2.2148 |0.0109 |1.5722 |0.0076 |
|16 |3.4425 |0.0158 |2.3595 |0.0107 |1.6722 |0.0076 |
|17 |3.5152 |0.015 |2.4969 |0.0106 |1.7731 |0.0075 |
|18 |3.557 |0.0144 |2.622 |0.0105 |1.875 |0.0075 |
|19 |3.5974 |0.0138 |2.7471 |0.0104 |1.9697 |0.0074 |
|20 |3.6337 |0.0132 |2.8628 |0.0103 |2.073 |0.0074 |
|21 |3.6636 |0.0126 |2.9559 |0.0101 |2.1656 |0.0073 |
|22 |3.6843 |0.012 |3.03 |0.0099 |2.2737 |0.0073 |
|23 |3.7062 |0.0115 |3.0992 |0.0097 |2.3568 |0.0072 |
|24 |3.7315 |0.0109 |3.1522 |0.0094 |2.4439 |0.0072 |

Table 4.1 showing the 8 cell with glass plate current-voltage characteristics at 3 different light intensities
|Resistance Level |4 Cell (Glass Plate) |
| |Light Intensity = 379.81W/m2 |Light Intensity = 234.53 W/m2 |Light Intensity = 172.52 W/m2 |
| |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |
|2 |0.29794 |0.0194 |0.21107 |0.0118 |0.12085 |0.0081 |
|3 |0.61841 |0.0192 |0.35208 |0.0118 |0.25023 |0.0081 |
|4 |0.83328 |0.0191 |0.51473 |0.0117 |0.3654 |0.008 |
|5 |1.143 |0.019 |0.68598 |0.0116 |0.4778 |0.008 |
|6 |1.4059 |0.0188 |0.85922 |0.0115 |0.59051 |0.0079 |
|7 |1.6407 |0.0185 |1.0467 |0.0114 |0.70388 |0.0079 |
|8 |1.892 |0.0183 |1.2046 |0.0114 |0.82259 |0.0079 |
|9 |2.1117 |0.0181 |1.3405 |0.0113 |0.93101 |0.0079 |
|10 |2.3534 |0.0179 |1.487 |0.0113 |1.0429 |0.0078 |
|11 |2.5757 |0.0177 |1.6517 |0.0112 |1.1512 |0.0078 |
|12 |2.8143 |0.0175 |1.7933 |0.0111 |1.2605 |0.0078 |
|13 |3.0305 |0.0174 |1.9232 |0.011 |1.3615 |0.0077 |
|14 |3.2306 |0.017 |2.0658 |0.0109 |1.4766 |0.0077 |
|15 |3.3542 |0.0164 |2.2148 |0.0109 |1.5722 |0.0076 |
|16 |3.4425 |0.0158 |2.3595 |0.0107 |1.6722 |0.0076 |
|17 |3.5152 |0.015 |2.4969 |0.0106 |1.7731 |0.0075 |
|18 |3.557 |0.0144 |2.622 |0.0105 |1.875 |0.0075 |
|19 |3.5974 |0.0138 |2.7471 |0.0104 |1.9697 |0.0074 |
|20 |3.6337 |0.0132 |2.8628 |0.0103 |2.073 |0.0074 |
|21 |3.6636 |0.0126 |2.9559 |0.0101 |2.1656 |0.0073 |
|22 |3.6843 |0.012 |3.03 |0.0099 |2.2737 |0.0073 |
|23 |3.7062 |0.0115 |3.0992 |0.0097 |2.3568 |0.0072 |
|24 |3.7315 |0.0109 |3.1522 |0.0094 |2.4439 |0.0072 |

Table 4.2 showing the 4 cell with glass plate current-voltage characteristics at 3 different light intensities

[pic]
Figure 17.1 showing the 8 cell with glass plate current-voltage characteristics at 3 different light intensities

[pic]
Figure 17.2 showing the 4 cell with glass plate current-voltage characteristics at 3 different light intensities
|Resistance Level |8 Cell (Hot Blower) |
| |Light Intensity = 379.81W/m2 |Light Intensity = 234.53 W/m2 |Light Intensity = 172.52 W/m2 |
| |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |
|2 |0.72189 |0.0369 |0.40754 |0.0222 |0.24368 |0.0149 |
|3 |1.2251 |0.0362 |0.7178 |0.0221 |0.47884 |0.0148 |
|4 |1.704 |0.0355 |1.0844 |0.0219 |0.69403 |0.0147 |
|5 |2.1564 |0.0343 |1.3234 |0.0217 |0.93537 |0.0146 |
|6 |2.6244 |0.0333 |1.6517 |0.0214 |1.1069 |0.0145 |
|7 |3.0075 |0.0327 |1.9201 |0.0211 |1.3029 |0.0144 |
|8 |3.3173 |0.0314 |2.1773 |0.0208 |1.5236 |0.0144 |
|9 |3.4894 |0.0291 |2.452 |0.0205 |1.7139 |0.0143 |
|10 |3.5872 |0.027 |2.7056 |0.0201 |1.9118 |0.0142 |
|11 |3.6682 |0.0246 |2.91 |0.0196 |2.0956 |0.0141 |
|12 |3.7165 |0.0226 |3.08 |0.0188 |2.2823 |0.0139 |
|13 |3.7536 |0.021 |3.1921 |0.0179 |2.4371 |0.0137 |
|14 |3.7847 |0.0197 |3.2833 |0.017 |2.5707 |0.0134 |
|15 |3.8106 |0.0183 |3.3531 |0.0162 |2.7149 |0.013 |
|16 |3.8304 |0.0172 |3.4104 |0.0154 |2.8163 |0.0127 |
|17 |3.8459 |0.0161 |3.4596 |0.0146 |2.9017 |0.0122 |
|18 |3.8619 |0.0153 |3.492 |0.0138 |2.9766 |0.0119 |
|19 |3.8736 |0.0146 |3.5221 |0.0132 |3.0354 |0.0115 |
|20 |3.8853 |0.0138 |3.5532 |0.0127 |3.0949 |0.011 |
|21 |3.8951 |0.0132 |3.5785 |0.012 |3.1432 |0.0106 |
|22 |3.9025 |0.0126 |3.5964 |0.0116 |3.1779 |0.0103 |
|23 |3.909 |0.0121 |3.6148 |0.0111 |3.2103 |0.0099 |
|24 |3.9138 |0.0116 |3.6286 |0.0107 |3.2441 |0.0095 |

Table 5.1 showing the 8 cell with hot blower current-voltage characteristics at 3 different light intensities
|Resistance Level |4 Cell (Hot Blower) |
| |Light Intensity = 379.81W/m2 |Light Intensity = 234.53 W/m2 |Light Intensity = 172.52 W/m2 |
| |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |
|2 |1.2139 |0.0667 |0.80099 |0.0415 |0.58785 |0.028 |
|3 |1.7269 |0.0515 |1.448 |0.0404 |0.95894 |0.0278 |
|4 |1.8054 |0.0377 |1.6113 |0.0343 |1.2756 |0.0267 |
|5 |1.8409 |0.029 |1.739 |0.0266 |1.4856 |0.0232 |
|6 |1.8593 |0.0239 |1.7835 |0.0222 |1.5842 |0.0204 |
|7 |1.8712 |0.0201 |1.8061 |0.0196 |1.6463 |0.0178 |
|8 |1.8795 |0.0174 |1.8239 |0.0172 |1.6835 |0.0158 |
|9 |1.8858 |0.0158 |1.8371 |0.0153 |1.7179 |0.0135 |
|10 |1.8893 |0.0141 |1.8486 |0.0137 |1.7276 |0.0127 |
|11 |1.8938 |0.0127 |1.8569 |0.0124 |1.7416 |0.0116 |
|12 |1.8952 |0.0116 |1.8633 |0.0113 |1.7541 |0.0106 |
|13 |1.8983 |0.0106 |1.8679 |0.0105 |1.7624 |0.0098 |
|14 |1.9004 |0.0098 |1.8733 |0.0096 |1.7751 |0.0086 |
|15 |1.9011 |0.0091 |1.8767 |0.009 |1.777 |0.0085 |
|16 |1.9037 |0.0085 |1.88 |0.0084 |1.7816 |0.0079 |
|17 |1.9051 |0.0079 |1.8829 |0.0079 |1.7858 |0.0074 |
|18 |1.9068 |0.0075 |1.8852 |0.0074 |1.789 |0.0071 |
|19 |1.9074 |0.0071 |1.8874 |0.007 |1.792 |0.0067 |
|20 |1.9085 |0.0067 |1.8891 |0.0067 |1.7964 |0.0064 |
|21 |1.9096 |0.0065 |1.8916 |0.0064 |1.7989 |0.0061 |
|22 |1.9106 |0.0062 |1.893 |0.0061 |1.8004 |0.0058 |
|23 |1.9122 |0.0059 |1.8946 |0.0058 |1.8027 |0.0056 |
|24 |1.9126 |0.0056 |1.8958 |0.0056 |1.805 |0.0054 |

Table 5.2 showing the 4 cell with hot blower current-voltage characteristics at 3 different light intensities

[pic]
Figure 18.1 showing the 8 cell with hot blower current-voltage characteristics at 3 different light intensities

[pic]
Fig. 18.2 showing the 4 cell with hot blower current-voltage characteristics at 3 different light intensities

|Resistance Level |8 Cell (Cold Blower) |
| |Light Intensity = 379.81W/m2 |Light Intensity = 234.53 W/m2 |Light Intensity = 172.52 W/m2 |
| |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |
|2 |0.7169 |0.037 |0.54049 |0.0224 |0.27499 |0.015 |
|3 |1.2787 |0.0367 |0.78911 |0.0223 |0.48385 |0.0149 |
|4 |1.692 |0.0359 |1.1133 |0.0222 |0.68818 |0.0148 |
|5 |2.204 |0.0351 |1.3867 |0.0219 |0.9269 |0.0147 |
|6 |2.6627 |0.0339 |1.7236 |0.0218 |1.1183 |0.0147 |
|7 |3.0635 |0.0333 |2.0107 |0.0216 |1.3329 |0.0146 |
|8 |3.4144 |0.0323 |2.3044 |0.0213 |1.5267 |0.0145 |
|9 |3.6285 |0.0303 |2.5664 |0.021 |1.7294 |0.0144 |
|10 |3.7513 |0.028 |2.8936 |0.0206 |1.9084 |0.0144 |
|11 |3.8306 |0.0258 |3.0694 |0.0202 |2.0908 |0.0143 |
|12 |3.8993 |0.0233 |3.3335 |0.0194 |2.3023 |0.0142 |
|13 |3.9323 |0.022 |3.3661 |0.0185 |2.4782 |0.014 |
|14 |3.9677 |0.0202 |3.4771 |0.0176 |2.6652 |0.0138 |
|15 |3.9884 |0.0191 |3.5567 |0.0167 |2.7935 |0.0135 |
|16 |4.017 |0.0175 |3.608 |0.0159 |2.9355 |0.0132 |
|17 |4.0316 |0.0165 |3.6623 |0.015 |3.0275 |0.0129 |
|18 |4.0393 |0.0159 |3.7044 |0.0143 |3.1205 |0.0125 |
|19 |4.0515 |0.0151 |3.7367 |0.0138 |3.2023 |0.0121 |
|20 |4.0608 |0.0144 |3.7559 |0.0132 |3.2757 |0.0117 |
|21 |4.0695 |0.0136 |3.7821 |0.0126 |3.3309 |0.0113 |
|22 |4.078 |0.0131 |3.801 |0.0121 |3.3815 |0.0109 |
|23 |4.0838 |0.0126 |3.8189 |0.0117 |3.4215 |0.0106 |
|24 |4.0918 |0.012 |3.8373 |0.0111 |3.4667 |0.0102 |

Table 6.1 showing the 8 cell with cold blower current-voltage characteristics at 3 different light intensities
|Resistance Level |4 Cell (Cold Blower) |
| |Light Intensity = 379.81W/m2 |Light Intensity = 234.53 W/m2 |Light Intensity = 172.52 W/m2 |
| |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |
|2 |1.0535 |0.054 |0.62016 |0.0316 |0.39516 |0.0213 |
|3 |1.6433 |0.0478 |1.0525 |0.0311 |0.69653 |0.0208 |
|4 |1.8534 |0.0375 |1.4443 |0.0286 |1.0205 |0.0205 |
|5 |1.933 |0.0292 |1.621 |0.0251 |1.2696 |0.0197 |
|6 |1.9578 |0.0253 |1.723 |0.0218 |1.4433 |0.0182 |
|7 |1.9788 |0.0214 |1.7878 |0.0187 |1.5341 |0.0167 |
|8 |1.9929 |0.0184 |1.8169 |0.017 |1.6261 |0.0147 |
|9 |1.9989 |0.0167 |1.8452 |0.0152 |1.6724 |0.0133 |
|10 |2.006 |0.0149 |1.866 |0.0136 |1.6985 |0.0125 |
|11 |2.0115 |0.0134 |1.8783 |0.0126 |1.7283 |0.0115 |
|12 |2.0155 |0.0121 |1.8918 |0.0114 |1.7499 |0.0106 |
|13 |2.018 |0.0113 |1.8991 |0.0106 |1.7665 |0.0099 |
|14 |2.0212 |0.0103 |1.9079 |0.0098 |1.783 |0.0092 |
|15 |2.0226 |0.0097 |1.913 |0.0091 |1.7958 |0.0085 |
|16 |2.0238 |0.0091 |1.9182 |0.0085 |1.8044 |0.0081 |
|17 |2.0261 |0.0085 |1.9238 |0.0081 |1.8145 |0.0075 |
|18 |2.0277 |0.008 |1.9271 |0.0076 |1.821 |0.0072 |
|19 |2.0286 |0.0076 |1.93 |0.0072 |1.8278 |0.0068 |
|20 |2.0294 |0.0071 |1.9327 |0.0068 |1.8345 |0.0065 |
|21 |2.0299 |0.0068 |1.9359 |0.0065 |1.8393 |0.0062 |
|22 |2.0299 |0.0065 |1.9384 |0.0062 |1.8427 |0.0059 |
|23 |2.0309 |0.0062 |1.9414 |0.006 |1.8474 |0.0057 |
|24 |2.0318 |0.006 |1.943 |0.0058 |1.8511 |0.0055 |

Table 6.2 showing the 4 cell with cold blower current-voltage characteristics at 3 different light intensities

[pic]
Figure 19.1 showing the 8 cell with cold blower current-voltage characteristics at 3 different light intensities

[pic]
Figure 19.2 showing the 4 cell with cold blower current-voltage characteristics at 3 different light intensities

From the shapes of all the graphs above, it is apparent that the greater the intensity of light received by the solar cell (i.e. the closer to the light source), the greater the corresponding voltage and current in each case. Since the power output of the solar cell is the product of voltage and current in the circuit, the greater the light intensity incident on the solar cell, the greater power output.

(3) Plot the current-voltage characteristic under different operating conditions: 1) under standard conditions, 2) shining the light through a glass plate 3) heated with a hot blower 4) cooled with a cold blower.

2i) At 50cm (Light intensity 379.81W/m2)
|Resistance |8 Cell (Light Intensity 379.81 W/m2) |
|Level | |
| |Standard Conditions |Through Glass Plate |With Hot Blower |With Cold Blower |
| |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |
|2 |0.48592 |0.027 |0.29794 |0.0194 |0.72189 |0.0369 |0.7169 |0.037 |
|3 |0.79447 |0.0267 |0.61841 |0.0192 |1.2251 |0.0362 |1.2787 |0.0367 |
|4 |1.2529 |0.0264 |0.83328 |0.0191 |1.704 |0.0355 |1.692 |0.0359 |
|5 |1.5918 |0.0261 |1.143 |0.019 |2.1564 |0.0343 |2.204 |0.0351 |
|6 |1.936 |0.0257 |1.4059 |0.0188 |2.6244 |0.0333 |2.6627 |0.0339 |
|7 |2.2405 |0.0253 |1.6407 |0.0185 |3.0075 |0.0327 |3.0635 |0.0333 |
|8 |2.5915 |0.025 |1.892 |0.0183 |3.3173 |0.0314 |3.4144 |0.0323 |
|9 |2.9179 |0.0247 |2.1117 |0.0181 |3.4894 |0.0291 |3.6285 |0.0303 |
|10 |3.2137 |0.0243 |2.3534 |0.0179 |3.5872 |0.027 |3.7513 |0.028 |
|11 |3.4502 |0.0234 |2.5757 |0.0177 |3.6682 |0.0246 |3.8306 |0.0258 |
|12 |3.5333 |0.0218 |2.8143 |0.0175 |3.7165 |0.0226 |3.8993 |0.0233 |
|13 |3.601 |0.0205 |3.0305 |0.0174 |3.7536 |0.021 |3.9323 |0.022 |
|14 |3.6591 |0.0192 |3.2306 |0.017 |3.7847 |0.0197 |3.9677 |0.0202 |
|15 |3.6959 |0.018 |3.3542 |0.0164 |3.8106 |0.0183 |3.9884 |0.0191 |
|16 |3.7313 |0.0169 |3.4425 |0.0158 |3.8304 |0.0172 |4.017 |0.0175 |
|17 |3.754 |0.016 |3.5152 |0.015 |3.8459 |0.0161 |4.0316 |0.0165 |
|18 |3.7797 |0.0151 |3.557 |0.0144 |3.8619 |0.0153 |4.0393 |0.0159 |
|19 |3.7983 |0.0141 |3.5974 |0.0138 |3.8736 |0.0146 |4.0515 |0.0151 |
|20 |3.8149 |0.0134 |3.6337 |0.0132 |3.8853 |0.0138 |4.0608 |0.0144 |
|21 |3.8231 |0.0129 |3.6636 |0.0126 |3.8951 |0.0132 |4.0695 |0.0136 |
|22 |3.8342 |0.0124 |3.6843 |0.012 |3.9025 |0.0126 |4.078 |0.0131 |
|23 |3.8429 |0.0119 |3.7062 |0.0115 |3.909 |0.0121 |4.0838 |0.0126 |
|24 |3.8542 |0.0113 |3.7315 |0.0109 |3.9138 |0.0116 |4.0918 |0.012 |

Table 7.1 showing the 8 cell current-voltage characteristics for different experimental conditions at light intensity of 379.81W/m2

|Resistance |4 Cell (Light Intensity 379.81 W/m2) |
|Level | |
| |Standard Conditions |Through Glass Plate |With Hot Blower |With Cold Blower |
| |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |
|2 |0.8608 |0.0546 |0.60029 |0.0384 |1.2139 |0.0667 |1.0535 |0.054 |
|3 |1.4995 |0.0513 |1.1766 |0.0377 |1.7269 |0.0515 |1.6433 |0.0478 |
|4 |1.7937 |0.0397 |1.5339 |0.0334 |1.8054 |0.0377 |1.8534 |0.0375 |
|5 |1.878 |0.0316 |1.7035 |0.0282 |1.8409 |0.029 |1.933 |0.0292 |
|6 |1.92 |0.0249 |1.7889 |0.0234 |1.8593 |0.0239 |1.9578 |0.0253 |
|7 |1.9332 |0.0221 |1.839 |0.0197 |1.8712 |0.0201 |1.9788 |0.0214 |
|8 |1.9478 |0.0191 |1.8579 |0.0177 |1.8795 |0.0174 |1.9929 |0.0184 |
|9 |1.9562 |0.0167 |1.8775 |0.0157 |1.8858 |0.0158 |1.9989 |0.0167 |
|10 |1.962 |0.0149 |1.8888 |0.0139 |1.8893 |0.0141 |2.006 |0.0149 |
|11 |1.9675 |0.0133 |1.8969 |0.0129 |1.8938 |0.0127 |2.0115 |0.0134 |
|12 |1.97 |0.0122 |1.9031 |0.0117 |1.8952 |0.0116 |2.0155 |0.0121 |
|13 |1.9708 |0.0112 |1.9095 |0.01 |1.8983 |0.0106 |2.018 |0.0113 |
|14 |1.9743 |0.0103 |1.9143 |0.01 |1.9004 |0.0098 |2.0212 |0.0103 |
|15 |1.9761 |0.0096 |1.9181 |0.0093 |1.9011 |0.0091 |2.0226 |0.0097 |
|16 |1.9721 |0.0089 |1.9215 |0.0087 |1.9037 |0.0085 |2.0238 |0.0091 |
|17 |1.9727 |0.0084 |1.9242 |0.0081 |1.9051 |0.0079 |2.0261 |0.0085 |
|18 |1.9704 |0.0079 |1.926 |0.0076 |1.9068 |0.0075 |2.0277 |0.008 |
|19 |1.9703 |0.0074 |1.9285 |0.0072 |1.9074 |0.0071 |2.0286 |0.0076 |
|20 |1.971 |0.007 |1.9299 |0.0069 |1.9085 |0.0067 |2.0294 |0.0071 |
|21 |1.9717 |0.0067 |1.9315 |0.0066 |1.9096 |0.0065 |2.0299 |0.0068 |
|22 |1.9725 |0.0063 |1.9325 |0.0062 |1.9106 |0.0062 |2.0299 |0.0065 |
|23 |1.973 |0.0061 |1.9336 |0.0059 |1.9122 |0.0059 |2.0309 |0.0062 |
|24 |1.9732 |0.0058 |1.9345 |0.0057 |1.9126 |0.0056 |2.0318 |0.006 |

Table 7.2 showing the 4 cell current-voltage characteristics for different experimental conditions at light intensity of 379.81W/m2

[pic]
Figure 20.1 showing the 8 cell current-voltage characteristics for different experimental conditions at light intensity of 379.81W/m2
[pic]
Figure 20.2 showing the 4 cell current-voltage characteristics for different experimental conditions at light intensity of 379.81W/m2

2i) At 70cm (Light intensity 234.53W/m2)
|Resistance |8 Cell (Light Intensity 234.53 W/m2) |
|Level | |
| |Standard Conditions |Through Glass Plate |With Hot Blower |With Cold Blower |
| |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |
|2 |0.27353 |0.0165 |0.21107 |0.0118 |0.40754 |0.0222 |0.54049 |0.0224 |
|3 |0.52112 |0.0164 |0.35208 |0.0118 |0.7178 |0.0221 |0.78911 |0.0223 |
|4 |0.73712 |0.0162 |0.51473 |0.0117 |1.0844 |0.0219 |1.1133 |0.0222 |
|5 |0.9935 |0.0161 |0.68598 |0.0116 |1.3234 |0.0217 |1.3867 |0.0219 |
|6 |1.2395 |0.016 |0.85922 |0.0115 |1.6517 |0.0214 |1.7236 |0.0218 |
|7 |1.4628 |0.0159 |1.0467 |0.0114 |1.9201 |0.0211 |2.0107 |0.0216 |
|8 |1.6921 |0.0158 |1.2046 |0.0114 |2.1773 |0.0208 |2.3044 |0.0213 |
|9 |1.8677 |0.0156 |1.3405 |0.0113 |2.452 |0.0205 |2.5664 |0.021 |
|10 |2.0662 |0.0155 |1.487 |0.0113 |2.7056 |0.0201 |2.8936 |0.0206 |
|11 |2.243 |0.0153 |1.6517 |0.0112 |2.91 |0.0196 |3.0694 |0.0202 |
|12 |2.4466 |0.0152 |1.7933 |0.0111 |3.08 |0.0188 |3.3335 |0.0194 |
|13 |2.6404 |0.015 |1.9232 |0.011 |3.1921 |0.0179 |3.3661 |0.0185 |
|14 |2.8551 |0.0148 |2.0658 |0.0109 |3.2833 |0.017 |3.4771 |0.0176 |
|15 |2.9997 |0.0146 |2.2148 |0.0109 |3.3531 |0.0162 |3.5567 |0.0167 |
|16 |3.1296 |0.0141 |2.3595 |0.0107 |3.4104 |0.0154 |3.608 |0.0159 |
|17 |3.214 |0.0137 |2.4969 |0.0106 |3.4596 |0.0146 |3.6623 |0.015 |
|18 |3.2994 |0.0132 |2.622 |0.0105 |3.492 |0.0138 |3.7044 |0.0143 |
|19 |3.3732 |0.0126 |2.7471 |0.0104 |3.5221 |0.0132 |3.7367 |0.0138 |
|20 |3.4299 |0.012 |2.8628 |0.0103 |3.5532 |0.0127 |3.7559 |0.0132 |
|21 |3.4516 |0.0118 |2.9559 |0.0101 |3.5785 |0.012 |3.7821 |0.0126 |
|22 |3.489 |0.0114 |3.03 |0.0099 |3.5964 |0.0116 |3.801 |0.0121 |
|23 |3.5237 |0.0109 |3.0992 |0.0097 |3.6148 |0.0111 |3.8189 |0.0117 |
|24 |3.5479 |0.0105 |3.1522 |0.0094 |3.6286 |0.0107 |3.8373 |0.0111 |

Table 8.1 showing the 8 cell current-voltage characteristics for different experimental conditions at light intensity of 234.53W/m2
|Resistance |4 Cell (Light Intensity 234.53 W/m2) |
|Level | |
| |Standard Conditions |Through Glass Plate |With Hot Blower |With Cold Blower |
| |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |
|2 |0.50984 |0.0322 |0.3817 |0.0226 |0.80099 |0.0415 |0.62016 |0.0316 |
|3 |0.59085 |0.0317 |0.66945 |0.0222 |1.448 |0.0404 |1.0525 |0.0311 |
|4 |1.3655 |0.0296 |1.0035 |0.0219 |1.6113 |0.0343 |1.4443 |0.0286 |
|5 |1.5453 |0.0261 |1.3084 |0.0206 |1.739 |0.0266 |1.621 |0.0251 |
|6 |1.6673 |0.0222 |1.4464 |0.0188 |1.7835 |0.0222 |1.723 |0.0218 |
|7 |1.7277 |0.0191 |1.5562 |0.0165 |1.8061 |0.0196 |1.7878 |0.0187 |
|8 |1.7609 |0.017 |1.6182 |0.0147 |1.8239 |0.0172 |1.8169 |0.017 |
|9 |1.7887 |0.0151 |1.6502 |0.0137 |1.8371 |0.0153 |1.8452 |0.0152 |
|10 |1.8091 |0.0136 |1.679 |0.0126 |1.8486 |0.0137 |1.866 |0.0136 |
|11 |1.8238 |0.0123 |1.7042 |0.0116 |1.8569 |0.0124 |1.8783 |0.0126 |
|12 |1.8348 |0.0113 |1.724 |0.0106 |1.8633 |0.0113 |1.8918 |0.0114 |
|13 |1.8436 |0.0105 |1.7398 |0.0099 |1.8679 |0.0105 |1.8991 |0.0106 |
|14 |1.8569 |0.0097 |1.754 |0.0091 |1.8733 |0.0096 |1.9079 |0.0098 |
|15 |1.858 |0.009 |1.766 |0.0085 |1.8767 |0.009 |1.913 |0.0091 |
|16 |1.8631 |0.0085 |1.7753 |0.008 |1.88 |0.0084 |1.9182 |0.0085 |
|17 |1.8678 |0.0079 |1.783 |0.0075 |1.8829 |0.0079 |1.9238 |0.0081 |
|18 |1.8717 |0.0075 |1.7904 |0.0071 |1.8852 |0.0074 |1.9271 |0.0076 |
|19 |1.8753 |0.007 |1.7958 |0.0067 |1.8874 |0.007 |1.93 |0.0072 |
|20 |1.8788 |0.0067 |1.8009 |0.0064 |1.8891 |0.0067 |1.9327 |0.0068 |
|21 |1.8814 |0.0064 |1.8057 |0.0061 |1.8916 |0.0064 |1.9359 |0.0065 |
|22 |1.8833 |0.0061 |1.8096 |0.0058 |1.893 |0.0061 |1.9384 |0.0062 |
|23 |1.8856 |0.0059 |1.8126 |0.0056 |1.8946 |0.0058 |1.9414 |0.006 |
|24 |1.8873 |0.0056 |1.8165 |0.0054 |1.8958 |0.0056 |1.943 |0.0058 |

Table 8.2 showing the 8 cell current-voltage characteristics for different experimental conditions at light intensity of 234.53W/m2

[pic]
Figure 21.1 showing the 4 cell current-voltage characteristics for different experimental conditions at light intensity of 234.53W/m2

[pic]
Figure 21.2 showing the 4 cell current-voltage characteristics for different experimental conditions at light intensity of 234.53W/m2

2i) At 90cm (Light intensity 172.52W/m2)
|Resistance |8 Cell (Light Intensity 172.52 W/m2) |
|Level | |
| |Standard Conditions |Through Glass Plate |With Hot Blower |With Cold Blower |
| |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |
|2 |0.17746 |0.0112 |0.12085 |0.0081 |0.24368 |0.0149 |0.27499 |0.015 |
|3 |0.35439 |0.0111 |0.25023 |0.0081 |0.47884 |0.0148 |0.48385 |0.0149 |
|4 |0.51466 |0.0111 |0.3654 |0.008 |0.69403 |0.0147 |0.68818 |0.0148 |
|5 |0.67469 |0.0111 |0.4778 |0.008 |0.93537 |0.0146 |0.9269 |0.0147 |
|6 |0.83833 |0.011 |0.59051 |0.0079 |1.1069 |0.0145 |1.1183 |0.0147 |
|7 |0.96691 |0.011 |0.70388 |0.0079 |1.3029 |0.0144 |1.3329 |0.0146 |
|8 |1.1381 |0.0109 |0.82259 |0.0079 |1.5236 |0.0144 |1.5267 |0.0145 |
|9 |1.2893 |0.0109 |0.93101 |0.0079 |1.7139 |0.0143 |1.7294 |0.0144 |
|10 |1.4333 |0.0108 |1.0429 |0.0078 |1.9118 |0.0142 |1.9084 |0.0144 |
|11 |1.5775 |0.0107 |1.1512 |0.0078 |2.0956 |0.0141 |2.0908 |0.0143 |
|12 |1.7204 |0.0106 |1.2605 |0.0078 |2.2823 |0.0139 |2.3023 |0.0142 |
|13 |1.8589 |0.0106 |1.3615 |0.0077 |2.4371 |0.0137 |2.4782 |0.014 |
|14 |1.9945 |0.0105 |1.4766 |0.0077 |2.5707 |0.0134 |2.6652 |0.0138 |
|15 |2.1498 |0.0104 |1.5722 |0.0076 |2.7149 |0.013 |2.7935 |0.0135 |
|16 |2.295 |0.0103 |1.6722 |0.0076 |2.8163 |0.0127 |2.9355 |0.0132 |
|17 |2.4212 |0.0103 |1.7731 |0.0075 |2.9017 |0.0122 |3.0275 |0.0129 |
|18 |2.5603 |0.0102 |1.875 |0.0075 |2.9766 |0.0119 |3.1205 |0.0125 |
|19 |2.645 |0.0101 |1.9697 |0.0074 |3.0354 |0.0115 |3.2023 |0.0121 |
|20 |2.7765 |0.0099 |2.073 |0.0074 |3.0949 |0.011 |3.2757 |0.0117 |
|21 |2.8733 |0.0097 |2.1656 |0.0073 |3.1432 |0.0106 |3.3309 |0.0113 |
|22 |2.9338 |0.0095 |2.2737 |0.0073 |3.1779 |0.0103 |3.3815 |0.0109 |
|23 |3.0013 |0.0093 |2.3568 |0.0072 |3.2103 |0.0099 |3.4215 |0.0106 |
|24 |3.0689 |0.0091 |2.4439 |0.0072 |3.2441 |0.0095 |3.4667 |0.0102 |

Table 9.1 showing the 8 cell current-voltage characteristics for different experimental conditions at light intensity of 172.52W/m2

|Resistance |4 Cell (Light Intensity 172.52 W/m2) |
|Level | |
| |Standard Conditions |Through Glass Plate |With Hot Blower |With Cold Blower |
| |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |Voltage (V) |Current (A) |
|2 |0.40037 |0.0219 |0.2589 |0.0155 |0.58785 |0.028 |0.39516 |0.0213 |
|3 |0.68702 |0.0216 |0.49909 |0.0153 |0.95894 |0.0278 |0.69653 |0.0208 |
|4 |0.97468 |0.0214 |0.68928 |0.015 |1.2756 |0.0267 |1.0205 |0.0205 |
|5 |1.2656 |0.0202 |0.89675 |0.0148 |1.4856 |0.0232 |1.2696 |0.0197 |
|6 |1.4047 |0.0188 |1.0853 |0.0145 |1.5842 |0.0204 |1.4433 |0.0182 |
|7 |1.5123 |0.0168 |1.234 |0.0138 |1.6463 |0.0178 |1.5341 |0.0167 |
|8 |1.5806 |0.0152 |1.3364 |0.013 |1.6835 |0.0158 |1.6261 |0.0147 |
|9 |1.6299 |0.0138 |1.4147 |0.012 |1.7179 |0.0135 |1.6724 |0.0133 |
|10 |1.6736 |0.0119 |1.4737 |0.0111 |1.7276 |0.0127 |1.6985 |0.0125 |
|11 |1.701 |0.0111 |1.52 |0.0103 |1.7416 |0.0116 |1.7283 |0.0115 |
|12 |1.712 |0.0106 |1.5477 |0.0097 |1.7541 |0.0106 |1.7499 |0.0106 |
|13 |1.7301 |0.0098 |1.5743 |0.0089 |1.7624 |0.0098 |1.7665 |0.0099 |
|14 |1.7422 |0.009 |1.5982 |0.0083 |1.7751 |0.0086 |1.783 |0.0092 |
|15 |1.7554 |0.0086 |1.6162 |0.0079 |1.777 |0.0085 |1.7958 |0.0085 |
|16 |1.7656 |0.0079 |1.633 |0.0074 |1.7816 |0.0079 |1.8044 |0.0081 |
|17 |1.7732 |0.0075 |1.6469 |0.007 |1.7858 |0.0074 |1.8145 |0.0075 |
|18 |1.7814 |0.0071 |1.6585 |0.0066 |1.789 |0.0071 |1.821 |0.0072 |
|19 |1.7861 |0.0067 |1.6681 |0.0063 |1.792 |0.0067 |1.8278 |0.0068 |
|20 |1.7917 |0.0064 |1.6759 |0.006 |1.7964 |0.0064 |1.8345 |0.0065 |
|21 |1.794 |0.0061 |1.6823 |0.0057 |1.7989 |0.0061 |1.8393 |0.0062 |
|22 |1.8002 |0.0058 |1.6892 |0.0055 |1.8004 |0.0058 |1.8427 |0.0059 |
|23 |1.8042 |0.0056 |1.6967 |0.0052 |1.8027 |0.0056 |1.8474 |0.0057 |
|24 |1.8071 |0.0053 |1.7028 |0.005 |1.805 |0.0054 |1.8511 |0.0055 |

Table 9.2 showing the 8 cell current-voltage characteristics for different experimental conditions at light intensity of 172.52W/m2

[pic]
Figure 22.1 showing the 4 cell current-voltage characteristics for different experimental conditions at light intensity of 172.52W/m2

[pic]
Figure 22.2 showing the 4 cell current-voltage characteristics for different experimental conditions at light intensity of 172.52W/m2

From the shapes of the graphs above, it is apparent that the use of the glass plate had the most significant effect on the power output of the solar cell, greatly reducing the current and voltage for each point with respect to the experiment conducted under standard conditions for all the graphs. This is expected as the glass plate will to some degree reflect some of the light from the source, reducing the photons incident on the solar cell. With a reduction in the light intensity, fewer photons are able to impart their energy to excite the electrons in the semi-conductor to the conduction band, causing a correspondingly lower power output. Another possible effect that could explain the drop in performance when the plate was introduced would be that the solar cell sensitivity to infrared radiation could be high. Although the glass panel was relatively transparent (not very reflective), it could have absorbed/reflected wavelengths of infrared radiation instead of transmitting the photons to reach the solar cell. This absorbtion of infrared radiation is analogous to the greenhouse effect.

From the 4 cell set-up graphs, all 3 light intensities yielded similar trends, where the cold and standard conditions had similar voltage-current characteristics, while the hot conditions showed the highest current at lower voltages. At high voltages however, the cold conditions yielded the highest current and the hot conditions showed the lowest current, although the divergence is not readily noticeable.

The 8 cell set-up also indicated a significant drop in the voltage-current characteristic of the solar cell with the addition of the glass plate, reducing the power output. However, there was an unexpected trend observed. Unlike the 4 cell set-up, the standard conditions showed a markedly lower voltage-current characteristic curve compared with the experiment performed under the hot and cold conditions. This is an anomalous result because the standard conditions employed an intermediate temperature between the hot and cold conditions, keeping all other variables constant. This anomaly can be explained by the fact that the experiments were conducted on different days. The data for the standard conditions for the 8 cell set-up was obtained on day 1 while the hot/cold conditions were obtained on day 2. Because the entire set-up was dismantled and reassembled, the different wires and connections used could have contributed significantly to the internal resistance of the circuit, a source of systematic error. This could explain why the standard condition curve is lower at all corresponding points when compared to the data obtained for hot/cold conditions.

Comparing the hot/cold condition curves for the 8 cell set-up, a similar trend was observed as the 4 cell set-up, where at high voltages, the cold conditions appeared to give a correspondingly higher current than the hot conditions. At lower voltages, there does not appear to be a significant difference between the currents.

In summary, cold conditions result in higher current in high voltage regions; while hot conditions result in higher current in low voltage regions. The 4 cell setup showed large divergence in the low voltage region and little divergence from the standard in the high voltage region. On the contrary, in the 8 cell setup, the large divergence was in the high voltage region and little divergence from the standard was observed for the low voltage region.

Discussion

(1) Discuss the dependence of the device performance on the light intensity.

To measure the device performance at different light intensities, several parameters will be analysed under the standard conditions (irrespective of temperature or the glass plate). Table 10 tabulates the short-circuit current, open circuit voltage and maximum power output of the solar cell with varying light intensities. Figure 11 plots the variation of each parameter with light intensity.

|Distance |Intensity |8 Cell |4 Cell |
|(cm) |(W/m2) | | |
| | |No-Load Voltage (V)|Short Circuit Current |Power (W) |No-Load Voltage (V)|Short Circuit Current |Power (W) |
| | | |(A) | | |(A) | |
|55 |333.84 |4.0280 |0.0237 |0.0954636 |2.0572 |0.0468 |0.096277 |
|60 |289.92 |3.9821 |0.0206 |0.0820313 |2.0312 |0.0415 |0.0842948 |
|65 |259.49 |3.9386 |0.0184 |0.0724702 |2.0061 |0.0364 |0.073022 |
|70 |234.53 |3.8982 |0.0164 |0.0639305 |1.9818 |0.0323 |0.0640121 |
|75 |214.8 |3.8587 |0.0149 |0.0574946 |1.9602 |0.0291 |0.0570418 |
|80 |198.12 |3.8276 |0.0135 |0.0516726 |1.9386 |0.0263 |0.0509852 |
|85 |184.11 |3.7972 |0.0123 |0.0467056 |1.9192 |0.0240 |0.0460608 |
|90 |172.52 |3.7659 |0.0114 |0.0429313 |1.9016 |0.0222 |0.0422155 |

Table 10 showing the variation different parameters with different light intensities

[pic]
Figure 23 showing the relationship between light intensity and power output of the solar cell

As illustrated in figure 23, there exists a positive relationship between maximum possible power output of the solar cell and the light intensity. Both 8 cell and 4 cell set-ups displayed the exact same characteristics. This suggests that the performance of the solar cell is proportional to the light intensity.

The variations of short circuit current and open circuit voltage have been expounded on previously, where there exist a linear relation for intensity-current and a logarithmic relation for intensity-voltage. From figures 14.1 and 14.2, it can be seen that the current-light intensity graphs follows the expected linear proportional relationship as provided in the lab manual where is= – e · g. From figures 15.1 and 15.2, it can be seen that the voltage-light intensity graphs, the slight curvature of the graph as it approaches low intensities follows the expected logarithmic relationship as deduced from the lab manual. However, the sharply decreasing curved portion of the graph is not as apparent probably due to the limited range at which the data was collected.

Furthermore, the introduction of the glass plate caused a noticeably drop in the power output of the circuit, shifting the characteristic curve downwards in all cases. The screening effect caused by the glass reflecting incoming light will serve to reduce the photons incident on the solar cell, thereby illustrating the effect that light intensity has on the performance of the device.

Using the experimental data from the 8 cell standard condition set-up, the data points which correspond to the highest measured power output for each of the light intensities was determined and shown in table 11 below.

|Distance (cm) |Intensity (W/m2) |
|Figure 24 (left) showing the experimental relationship temperature and short circuit current/open circuit voltage |
|Figure 25 (right) showing the theoretical relationship temperature and short circuit current/open circuit voltage |

From figure 24, by extrapolation, the short circuit current under both hot and cold conditions is approximately 0.037A. For the open circuit voltages, they were approximated to be 4.0V for hot conditions and 4.2V for cold conditions. In short, hot conditions caused a drop in open circuit voltage compared with cold conditions. The short circuit current remained relatively insensitive to temperature. Since the magnitudes of the differences are disproportionate, an increase in open circuit voltage has a larger effect in causing a corresponding increase in the maximum power output of the cell. Thus, low temperatures will result in better performance.

This relationship is congruent with the theoretically expected results illustrated in figure 25. The sensitivity of the curves to higher temperatures is due to the following factors. - Decrease in the band gap i.e. energy difference between the valence and conduction bands. This reduction means less energy needs to be imparted by the photon to the electron, to photo-excite the electrons to the conduction band where they can act as charge carriers. - Reduction in the p–n junction’s built-in voltage, allowing high energy carriers to cross the p-n junction, affecting the junction’s ability to separate electrons from holes in the photo-generated pairs.

Assuming the solar cell is under working conditions, the band gap is 1.1eV (room temperature, from lab manual), the relationship between the band gap (Eg) and temperature (T) is linearly approximated with the equation, [pic]. [pic] is assumed to be -2.3 x 10-4 eV/K.

When temperature increases, ΔT is positive, which results in the decrease in the band gap Eg(T). Having a smaller band gap allows electrons to be more easily photo-excited to the conduction band. Since the short circuit current is given by the equation [pic]. Where Nk is quantity of photons (having wavelength k) illuminating the photocell in the time unit, and [pic]λ is the quantum efficiency (spectrum response). Increasing the temperature will cause a corresponding increase in the number of photons with energy sufficient to photo-excite the electron. This increase in Nλ results in the increase in the short circuit current observed for the high temperature curve in the low voltage regions in figure 25.

However, there are other factors affecting the short circuit current. At higher temperatures, there will be a significant drop of the built-in voltage and the separation ability of the p–n junction. This is due to the thermally agitated charge carriers possessing too much energy, which allows them to overcome the potential barrier and cross over the p–n junction in both directions. Because illumination and charge separation by the potential barrier causes the presence of excess negative charge on the n-type side and holes on the p-type side, a charge imbalance exists in the cell and at opposite ends of the cell, a condition necessary to drive a current through the circuit. By overcoming the potential barrier, this charge imbalance is cancelled out to a certain extent, weakening the short circuit current. This effect is antagonistic to the band gap effect on short circuit current, and accounts for the decrease in the short circuit current observed for the high temperature curve in the high voltage regions in figure 25, and also why the net increase in the low voltage regions is small.

For the open circuit voltage, from the lab manual, the relationship with temperature is approximated to be linear with a coefficient of -2.3mV/K. This suggests that the open circuit voltage will decrease with increasing temperatures. This decrease can be accounted for with the generation of the reverse bias leak current. As earlier discussed, high temperatures cause a decrease in the band gap from the dependence of the leak current given by the equation [pic], a smaller band gap and higher temperatures will generate an exponentially large leak current. The open circuit voltage dependence on the leak current is given by the equation [pic] , thus with greater leak current, there will be a great reduction in the open circuit voltage, implying that high temperatures will cause a decrease in open circuit voltage.

It is also noted that the ‘ideal’ relation as described in figure 25 was not observed in all the data sets obtained. In general, the 8 cell set-up showed better correspondence to the theoretical model whereas the 4 cell setup deviated with the short circuit current higher than expected in low voltage regions. This could probably be due to the 4 cell set-up having a smaller potential drop in series connection across each cell, which to some extent negates the current reducing charge-separation effect; when the potential energy barrier across each cell becomes higher, the carriers are unable cross over easily, thus the high short circuit currents.
Also, several other factors can affect the results obtained. Random errors, the inability to maintain temperature throughout the experiment and ambient lighting all could compromise the results obtained. Thus, the experimental setup could be placed in a controlled environment such as in a thermostatically controlled dark chamber. This will reduce the random fluctuations of the measurements due to external influences. Additionally, the readings could be repeated to obtain a more representative average since the readouts from the voltmeter and ammeter tend to fluctuate.

(3) Discuss approaches to enhance the open-circuit voltage and short-circuit current
In enhancing the open circuit voltage/ short circuit current, the goal is to increase the maximum output of the solar cell. In designing a solar cell there are 3 main approaches in attaining this objective, namely reducing optical losses, reducing electron-hole recombination (increasing minority carrier lifetime) and by altering ambient conditions such as temperature and light intensity.

Firstly, as part of the experiment performed, reducing the temperature was found to have caused an increase in the open circuit voltage leading to an appreciable increase in the power output of the cell. Thus, by reducing the temperature at which the solar cell functions, it could result in better performance. This reduction in temperature could be achieved through specially designed mounting racks with installations promoting heat dissipation through air or water thermal carriers. Heat dissipation allows the cell to function at a lower temperature, increasing the open circuit voltage (dominating effect) and improving performance.

Also, increasing the light intensity incident on the solar cell will improve the device performance. By increasing light intensity, the number of photons that could be potentially absorped by the electrons and holes will be increased, hence enhancing the open-circuit voltage and short-circuit current. Additionally, the specific wavelength of the light as well as the sensitivity of the cell to those particular wavelengths will affect the absorption characteristics. For instance, in plants, chlorophyll is sensitive to red and blue wavelengths, but not to green. Similarly, in silicon, different engineering techniques will result in solar cells with different band gaps, tuned with different sensitivities to specific wavelengths. Tandem cells using combinations of these different cells can then be used to increase the spectrum of wavelengths which contribute to the generation of electron-hole pairs, making the system as a whole sensitive to the entire solar spectrum and raising short circuit current and open circuit voltages.
Optical losses through reflection also contribute to lowering the incident light intensity/sensitivity. These losses can be reduced through the use of anti-reflection coatings, thin films on the surface of the cell which cause destructive interference of reflected rays. This reduces the net energy loss through reflection. Furthermore, surface texturing through etching will reduce potential reflective losses. The rough surface obtained scatters light more efficiently to other sections of the surface where it can be absorped rather than reflecting it. Alternatively, a reflective Lambertian coating can be put on the back of thin film solar cells which essentially acts in tandem with the rough surface to trap light within the cell. The optical path of the light becomes several times that of the device thickness through total internal reflection, increasing the chances of absorption and generation of electron-hole pairs. With more electron hole pairs generated, the greater the short circuit current and open circuit voltages.

Recombination losses, in which electron and holes recombine, affect both the short circuit current and open circuit voltage. The recombination is controlled by the number of minority carriers at the junction edge, hence minimising the equilibrium minority carrier concentration reduces recombination via increased doping will affect the leakage current developed and increase open circuit voltage.

Recombination losses can also be reduced by passivation of the surface of the solar cell with silicon nitride. Since the surface of the solar cell is also the region where most of the charge carriers are generated, a high recombination rate at the surface will be undesirable. The passivating layer thus acts to reduce the recombination rate by removing localised recombination sources within a diffusion length of the junction, thereby enhancing the short-circuit current and open circuit voltage.

Lastly, the geometry of the cells and other practical improvements can be considered in maximizing the output of the cell through manipulating the light intensity. For instance, an array of mirrors could be used to focus light into bowl shaped array of silicon nano-rods, which increases the local light intensity, absorbtion probability and reduces reflective losses. Novel approaches such as solar concentrators (specially formulated dyes) which work together to absorb light across a range of wavelengths, which is then re-emitted at a different wavelength to waiting solar cells. In a similar principle, nano-cups can also be engineered to absorb light from many directions and re-emitted in a single direction, enhancing the absorption profile in terms of directions and wavelengths. The increase in light intensity/sensitivity will translate into better short circuit currents and open circuit voltages.

Conclusion

In this experiment, the effects of various variables like light intensity and temperature on solar cell performance were studied. In studying these effects, the theoretical mathematical models and relationships employed in describing the photovoltaic phenomena were better understood. In addition, much of the practical engineering principles behind the design of a solar cell were considered, giving us a holistic understanding on the design process, and not just the scientific principles.

References
S.O.Kasap. Principles of Electronic Materials and Devices

http://hyperphysics.phy-astr.gsu.edu/hbase/forces/isq.html

M.A. Green, General Temperature Dependence of Solar Cell Performance and Implications for Device Modelling, Progress In Photovoltaics: Research And Applications, (2002) DOI: 10.1002/pip.496

E. Radziemska, The Effect Of Temperature On The Power Drop In Crystalline Silicon Solar Cells, Renewable Energy 28, (2003) 1–12

http://pveducation.org/pvcdrom/design/solar-cell-design-principles

http://www.alternative-energy-news.info/nanocups-could-improve-solar-cell-efficiency/

http://web.mit.edu/newsoffice/2008/solarcells-0710.html

A. N. Tiwari, G. Krypunov, F. Kurdesau, D. L. Bätzner, A. Romeo, H. Zogg, Cdte Solar Cell In A Novel Configuration, Progress in Photovoltaics 12, (2004) p33-38