Prac 2

 

Safety and ethical issues overview

The light source will not be touched due to the heat that may accumulate during use. The method above will be followed. Resistors will be used (82-100 Ohms) as a load to create a more realistic situation. This is because a panel without a loadgenerates different amounts of power to a panel with a load.

The energy use is reduced in this design by keeping the experiment running for the minimum possible time.The experiment will be undertaken quickly and destroying apparatus will be avoided. No injury or harm is to be caused on others during the experiment. Lights should be kept off until necessary for the solar panel. The apparatus should be kept safe to avoid missing equipment. All apparatus should be returned to the designated area for others to use. No safety gear will be necessary. The electricity used for this experiment is generated as DC current from a solar panel. The refrigerator and incubator is turned off before use, reducing the need for any safety precautions.

Principles

The data was collected directly asdecimal values from measuring devices. The light sensor used resulted in an average irradiance of 0.1972 mW/cm². This is the radiant flux or power of the radiation received per square centimetre.

The calculations using the average of sixty seconds of light intensity data assumes that the units are mW/cm². The maximum value possible for this sensor was 0.9925 mW/cm².The torches were likely to generate more power if placed closer to the panel. The irradiance decreasesas the distance from a point source of radiation increases due to the receiving area becoming larger.Calibration of the sensor devices were not carried out as the digital readings was deemed correct before use.

Formulas Used

 

Hypothesis:If the temperature of the panel is lowered, the efficiency will increase compared to panels at higher temperatures.

Variables

Independent Variable:Temperature of Solar Panel

How the Independent Variable is changed:Changed by using both an incubator and a fridge to create environments in which the temperature differs

Dependent Variable:Current and Voltage

How the Dependent Variable is Measured:Using Vernier sensors

Other factors held Constant in the Experiment:

Frequency of Colour and Light

Surface Area

Dirtiness

Silicon cell type

Angle to the light

Light Intensity

·         Combination of cells

Notes: The light Intensity will be kept constant by using the same light source at similar distances. The same panel will be used for the cell arrangement to be constant. The surface area will be measured. The temperature will be controlled and monitored with sensors. No ambient light will be considered as the doors of both the incubator and the fridge will be closed.

Results

The tables below are arranged in order. The table on the left beginning with ‘Time’ is the result of one hour using the incubator while the table on the right is that of the second hour. The table below that is for the fridge attempt.

 

The data gained from the three consecutive attempts were recorded with a computer connected to the three sensors at a rate of ten measurement recordings a minute. This was completed for two hours for the set-up in the incubator and three hours for the attempt using the fridge.

Using the first formula , the power was calculated from the current and voltage measurements.

Figure 10 Multiplying Current with Voltage

Graphs were drawn and interpreted based on temperature increasing from left to right for the incubator. This was the opposite for the fridge results. Temperature decreases from right to left.

For the graph of Solar Power Generated in Incubator (1st Hour) the power generated in the first attempt in the incubator decreased as the temperature increased from 20 to 30 degrees Celsius. From 30 to 40 degrees, the power generated was stable. At 50 degrees, a rapid drop to 0.0008 Watts was observed. As the temperature increased from 50 to 60 degrees, the power peaked at 55 degrees (0.0014 W – same as the power generated at 25 degrees) and then dropped again. A gradual increase in power was found to occur from 60 to 80 degrees in the second graph above. The increase in temperature was slower for this second hour of the experiment.

The power generated from the solar panel set-up in the fridge decreased suddenly before the temperature reached 6 degrees. A steep decreasing slope can be observed from 14 to 10 degrees Celsius. From 10 to 6.5 degrees and 6 to 2.5 degrees, constant power was generated.

 

Using the second formula , the resistance of both incubator and the fridge attempts were calculated.

The resistance fluctuated during the entire experiment but was generally increasing from around 98 Ohms to 101 Ohms. The greatest difference in resistance was recorded at around 50 degrees.

In the second hour, the resistance had the greatest difference at 70 degrees. However, the general trend of the data was towards a lower resistance. The fluctuations continued until the end of the experiment.

For the fridge experiment, the resistance fluctuated and lowered during the decrease in temperature from 16 to 3 degrees.

From this it can be summarised that because the resistor was located outside the device, the resistance changes are related to the circuit within the device. As the temperature is increased, the resistance of the circuit generally increases as well. As the temperature decreased, the resistance lowered. Although solar panels are not ohmic conductors, the relationship here could be  where the I-V relationship is linear and ohmic. The slope is constant. This can be clarified with the graphs below.

 

The current–voltage characteristic was graphed for the three attempts

These graphs were supposed to be a curve. Here, they are not because the experiment was carried out with environments that continuously changed its temperature. By setting the machine to stable temperatures and recording results for each, a curve may result which can then be compared with other curves provided that the light intensity is the same. All the required values for the calculation of solar panel efficiency (maximum power point etc.) should be possible to plot on that curve.

Calculations

Using , the irradiance measured by the sensor and the actual power generated from the panel can be compared. The sensor gave an average of 0.1972 mW/cm². The initial power generated was 0.0015 W from a 50 cm² panel. So0.0015 W becomes 1.5 mW.

Somehow, the amount of light hitting the solar panel was 6.5 times less than that measured with the sensor. But obviously not all radiation becomes electricity from the panel. This is where efficiency calculations would be useful. A simplified version of the equation looks like this:

The conversion efficiency based on a ratio of the highest power generated (in this experiment) and the power of the radiation hitting the panel from the lights has thus been calculated. This acts as an indication only and was completed due to lack of information on the specifications (fill factor,open-circuit voltage) of the solar panel used.

Discussion

The results from this experiment show a clear difference in the solar cell efficiency underconditions of low and high temperatures. The experiment was conducted to find the difference in power produced. It was hypothesized that higher temperatures result in lower efficiency while lower temperatures result in higher efficiency. The results show that for the chosen solar panel, room temperature made possible the greatest power output while lower temperatures caused a steady decrease of power output. Elevated temperatures decreased the output initially, however, it later increased, never reaching the initial reading. Compared to the expected result, the results of this experiment are one of many possible cases.The diagram below represents the expected efficiency change by temperature increase where the temperature coefficient is -0.45 %/℃.

Figure 12 Inverse relation between efficiency and temperature

The relationship between a cell’s temperature and its output power is an inverse proportion where there is a 0.4 to 1.1% drop in efficiency per ℃increase. This varies depending on the semiconductor bandgap which is reduced when hot and causes the voltage to drop with it (Alchemie Limited Inc., 2013). A greater output voltage would see less effect. It is also widely found that there is an increase of 0.12V for every ℃decrease (Hearst Communications, Inc., 2017).The increase of power beyond 50℃reveal some characteristics of the panel. At 47.9 ℃, the power dropped, indicating that both current and voltage decreased and was not the result of heat. Rather, it was likely to be due to a random error of either the light or panel. Only voltage decreases when temperature rises.

Although the hypothesis was refuted in the instance of this panel, the method of measuring power under a continuous change in temperature was tested and found to be more susceptible to random errors.

The design of this practical assisted in controlling variables in several ways. The distance between the torches and panel was determined by the stand attached to the acrylic board. The distance was set to 15 centimetres however the relative positioning and possibility of movement made this a random errorsource. Random errors caused by the reflection of light onto the panel could be avoided by using less reflective incubators. The same solar panel (model) and sensors were used for both the attempt in the incubator and the fridge. The amount of ambient light did not matter for the experiment as the doors of both the incubator and the fridge were shut.

The voltage decrease of the torch batteries would have contributed to large errors in data. The data for the fridge attempt reflects this random error. It could have been avoided with brighter lights directly connected to a sustained power supply.

The sensors used had a systematic scale factor error as they measured higher values than the actual. More precise ways to measure voltage and resistance could involve 4-point probes. Current does not flow to the instrument. Knowing the Burden Voltage would allow more accurate voltage values to be derived as it considers the error caused by the multimeter.The uCurrent Adapter measures low currents accurately of which+/- 0-1250µA is the accuracy required by minimising the effects oftolerance.

Blu-tac softened in the incubator and caused random errors. Adhesives of larger surface area such as tape would not allow any movement of test devices.

Covering the temperature sensor with tape while it was touching the solar panel could have given an accurate representation of the actual temperature of the panel.This is because the tape provides insulation for the sensor against the air surrounding it and allows it to reflect the temperature of the panel more accurately.

Figure 13 Room improvement sketch

The experiment could be improved by recording power output of the panel at different temperatures in stable intervals.The thermostat would need to be set to a lower temperature, thus taking longer time. Two temperature sensors for both the environment and the panel would be installed.A sketch of this is shown above. Larger panels in specialised rooms would eliminate many of the sources of error.

Conclusion

The polycrystalline panel used had an optimal temperature range spanning from 14.7℃ to 16.7℃as found from the fridge attempt. For the incubator attempt, 20℃ was found to be optimal. Any decrease in temperature and increase in temperature led to low power output. However, an increase at 50℃occurred possibly due to characteristics of the panel. This shows that the panel has certain intervals of better performance. As the panels were operated under torchlight instead of sunlight, the effect of temperature change was greater than expected. Application of the results involve further research into the effect of changing the resistance (for the maximum power point) on the power output under varying temperature conditions. The resistance value is likely to have affected the power change outlined in this report. Adjusting the resistance of panels to suit different environments could raise the overall efficiency of solar panels.

 

Bibliography

Sproul A. n.d., Understanding the p-n Junction, accessed 11 June 2017, <http://www2.pv.unsw.edu.au/nsite-files/pdfs/UNSW_Understanding_the_p-n_Junction.pdf>.

Hearst Communications, Inc.2017, The Effects of Temperature on Solar Panel Power Production,accessed 11 June 2017, <http://homeguides.sfgate.com/effects-temperature-solar-panel-power-production-79764.html>.

Alchemie Limited Inc.2013, Solar Panel Temperature Affects Output – Here's what you need to know,accessed 11 June 2017, <http://www.solar-facts-and-advice.com/solar-panel-temperature.html>.