Effect of Temperature on Solar Panel Performance

Transcription

1 Exercise 3 Effect of Temperature on Solar Panel Performance EXERCISE OBJECTIVE When you have completed this exercise, you will be familiar with the effect of temperature on solar panel performance. DISCUSSION OUTLINE The Discussion of this exercise covers the following points: Effect of temperature on the output voltage and current Effect of temperature on the output power DISCUSSION Effect of temperature on the output voltage and current The characteristics of PV panels studied in the previous exercise assumed that the temperature of the PV cells is close to room temperature, i.e., about 25 C (77 F). In this exercise, you will learn that the characteristics of PV panels are significantly affected by the temperature of PV cells. The open-circuit voltage of a PV module, or more generally the PV module output voltage, decreases significantly as the cell temperature is increased. For most PV modules made of crystalline-silicon PV cells, the output voltage decreases by about 0.3% to 0.5% for every 1 C increase in temperature (about 0.17% to 0.28% for every 1 F increase in temperature). For instance, decreases by about 6% to 10% when the PV cell temperature passes from 25 C to 45 C (77 F to 113 F). See Figure 40. Irradiance: AM 1.5, 1000 W/m C (167 F) Current (A) C (122 F) 25 C (77 F) Voltage (V) Figure 40. Characteristic - curves of a PV module operating at various cell temperatures. Conversely, the short-circuit current of a PV module, or more generally the PV module output current, increases very slightly as the cell temperature is Festo Didactic

2 Exercise 3 Effect of Temperature on Solar Panel Performance Discussion increased. For most PV modules made of crystalline-silicon PV cells, the output current increases by about 0.05% to 0.1% for every 1 C increase in temperature (about 0.03% to 0.06% for every 1 F increase in temperature). For instance, increases by about 1% to 2% when the PV cell temperature passes from 25 C to 45 C (77 F to 113 F). Effect of temperature on the output power The effect of cell temperature on the output voltage and current changes the shape of the characteristic - curve of PV modules. This results in a significant decrease in the maximum power a PV panel can produce. For most PV modules made of crystalline-silicon PV cells, the maximum output power decreases by about 0.3% to 0.5% for every 1 C increase in temperature (about 0.17% to 0.28% for every 1 F increase in temperature). In other words, the efficiency of a PV module decreases when the PV cell temperature increases. For instance, the maximum output power of a PV module decreases by about 6% to 10% when the PV cell temperature passes from 25 C to 45 C (77 F to 113 F). The temperature of the cells in PV modules installed outdoors is often higher than 25 C (77 F) when the units operate under direct sunlight and warm ambient temperatures [>25 C (>77 F)]. Under such conditions, cells in PV modules often operate at temperatures between 50 C and 75 C (122 F and 167 F). Because of this, the degradation in performance due to high temperature operation must be accounted for when evaluating (predicting) the actual amount of electrical power a PV module can produce, as this has a direct impact on the amount of electrical energy produced. For instance, when a PV module exhibiting a decrease in maximum output power of 0.4% per degree Celsius (0.22% per degree Fahrenheit) operates at a cell temperature of 60 C (140 F), i.e. (35 C (63 F) above the nominal operating temperature of 25 C (77 F), the maximum output power is 14% lower than the maximum output power obtained when the same PV module operates at a PV cell temperature of 25 C (77 F). Figure 41. With a generating capacity of 100 MW, the Perovo Solar Park in Ukraine is one of the largest solar power plants in the world (photo courtesy of Lujkin8). 38 Festo Didactic

3 Exercise 3 Effect of Temperature on Solar Panel Performance Procedure Outline PROCEDURE OUTLINE The Procedure is divided into the following sections: Setup Open-circuit voltage and short-circuit current of a PV module operating at high temperature Characteristic E-I curve of a PV module operating at high temperature Maximum power point produced by a single PV module operating at high temperature PROCEDURE Setup In this part of the exercise, you will set up the equipment in order to observe the effect of temperature on the operation of the monocrystalline silicon solar panel. 1. Refer to the Equipment Utilization Chart in Appendix A to obtain the list of equipment required to perform this exercise. a To ensure greater consistency between the results obtained during the various exercises, make sure that you are using the same Monocrystalline Silicon Solar Panel and Solar Panel Test Bench modules as in Exercise 2 (same serial numbers). 2. Install the Monocrystalline Silicon Solar Panel in the Solar Panel Test Bench then install the Solar Panel Test Bench into the Workstation. Adjust the position of the solar panel so that the short-circuit current of the lower PV module is as close to 100 ma as possible at near room temperature. Steps 4 to 9 of Exercise 2 provide detailed directions for installing the modules and setting to about 100 ma. 3. Once the Monocrystalline Silicon Solar Panel is properly positioned in the Solar Panel Test Bench, turn off the fan but leave the lamp on. This will cause the PV panel temperature to increase to a value well above room temperature [about 55 C to 65 C (131 F to 149 F)] after a warm up time of approximately half an hour. Risk of burns. The halogen lamp and the surrounding components can become very hot during this exercise. Open-circuit voltage and short-circuit current of a PV module operating at high temperature In this part of the exercise, you will compare the open-circuit voltage and short-circuit current of a PV module operating at high temperature (i.e., well above room temperature) with those measured at near room temperature. 4. Once the PV panel temperature has stabilized, measure the open-circuit voltage, short-circuit current, and the temperature of the lower PV module. Festo Didactic

4 Exercise 3 Effect of Temperature on Solar Panel Performance Procedure Open-circuit voltage V Short-circuit current A PV panel temperature C ( F) 5. How does the open-circuit voltage measured at high temperature compare with that measured at near room temperature in step 12 of the previous exercise? 6. Using the open-circuit voltages measured at high temperature and at near room temperature, calculate the percentage decrease in PV module voltage per degree Celsius (per degree Fahrenheit). Percentage decrease in PV module voltage % 7. How does the short-circuit current measured at high temperature compare with that measured at near room temperature in step 9 of the previous exercise? 8. Using the short-circuit currents measured at high temperature and at near room temperature, calculate the percentage increase in PV module current per degree Celsius (per degree Fahrenheit). Percentage increase in PV module current % 40 Festo Didactic

5 Exercise 3 Effect of Temperature on Solar Panel Performance Procedure Characteristic E-I curve of a PV module operating at high temperature In this part of the exercise, you will plot the characteristic - curve of a PV module operating at high temperature (i.e., well above room temperature). 9. Connect the lower PV panel as shown in Figure 42. Figure 42. Circuit used to determine the characteristic - curve of a PV module. 10. Using the potentiometer of the Solar Panel Test Bench, vary the output voltage from minimum to maximum by increments of 0.5 V. For each voltage setting, record the output voltage and the corresponding current in Table 4. Enter the cell temperature in the appropriate cell of Table 4. Festo Didactic

6 Exercise 3 Effect of Temperature on Solar Panel Performance Procedure Table 4. Characteristic - curve of a PV module measured at high temperature. Voltage (V) Current (ma) Power (W) Voltage (V) Current (ma) Power (W) Temperature of the PV panel during the measurements C ( F) 11. Using the values in Table 4, plot the characteristic - curve of the PV module in Figure Current (ma) Power (W) Output voltage (V) Figure 43. Characteristic - curve of a PV module operating at high temperature. 42 Festo Didactic

7 Exercise 3 Effect of Temperature on Solar Panel Performance Conclusion Maximum power point produced by a single PV module operating at high temperature In this part of the exercise, you will compare the maximum power point produced by a single PV module operating at high temperature (i.e., well above room temperature) with that measured when operating at near room temperature. 12. Calculate the output power of the PV module for each measured - point. Enter your results in Table 4. Plot the curve of the PV module output power versus PV module output voltage on the characteristic - curve graph, and identify the maximum power point (MPP) on the curve. 13. How does the maximum power point determined at high temperature compare with that measured at near room temperature in the previous exercise? 14. Using the maximum power points determined at high temperature and at near room temperature, calculate the percentage decrease in PV module output power per degree Celsius (per degree Fahrenheit). Percentage decrease in PV module output power % CONCLUSION In this exercise you learned that the performance of photovoltaic panels is affected by the temperature. You saw that the output power produced by a PV module decreases when the operating temperature is increased because the output voltage decreases significantly while the output current increases very slightly. REVIEW QUESTIONS 1. Describe the effect of temperature on the output voltage of a PV module. 2. Determine the output voltage variation of a PV module when the cell temperature passes from 10 C to 60 C (50 F to 140 F) if the PV cell datasheet shows a voltage reduction of 0.5%/ C (0.28%/ F). Express your answer as a percentage value. Festo Didactic

8 Exercise 3 Effect of Temperature on Solar Panel Performance Review Questions 3. Describe the effect of temperature on the output current of a PV module. 4. Describe the effect of temperature on the output power produced by a PV module. 5. Determine the output power variation of a PV module when the cell temperature passes from 60 C to 10 C (140 F to 50 F) if the PV cell datasheet shows a power reduction of 0.3%/ C (0.17%/ F). Express your answer as a percentage value. 44 Festo Didactic