Photovoltaic Power Systems Laboratory: Practical Experiments in Solar Energy

1. ECEN 4517 ECEN 5517 POWER ELECTRONICS AND PHOTOVOLTAIC POWER SYSTEM LABORATORY http://ece.colorado.edu/~ecen4517 • Photovoltaic power systems • Power conversion and control electronics Prerequisite: ECEN 4797 or ECEN 5797 Instructor: Mr. Roger Bell

2. Experiment 1 Direct Energy Transfer System • Model PV panel • Investigate direct energy transfer system behavior • Investigate effects of shading • Observe behavior of lead-acid battery

3. Experiments 2 and 3Maximum Power Point Tracking • Design and construct dc-dc converter • Employ microcontroller to achieve maximum power point tracking (MPPT) and battery charge control

4. Experiments 4 and 5Add Inverter to System • Build your own inverter system to drive AC loads from your battery • Step up the battery voltage to 200 VDC as needed by inverter • Regulate the 200 VDC with an analog feedback loop • Change the 200 VDC into 120 VAC

5. Mini-ProjectECEE Expo Competition • Operate your complete system • Competition during ECEE Expo: capture the most energy with your system outside • Morning of Thursday, May 2 A previous year’s competition poster

6. Development of Electrical Modelof the Photovoltaic Cell, slide 1 Photogeneration Semiconductor material absorbs photons and converts into hole-electron pairs if Photon energy hn > Egap (*) • Energy in excess of Egap is converted to heat • Photo-generated current I0 is proportional to number of absorbed photons satisfying (*) Charge separation Electric field created by diode structure separates holes and electrons Open circuit voltage Voc depends on diode characteristic, Voc < Egap/q

7. Development of Electrical Modelof the Photovoltaic Cell, slide 2 Current source I0 models photo-generated current I0 is proportional to the solar irradiance, also called the “insolation”: I0 = k (solar irradiance) Solar irradiance is measured in W/m2 Full sun: irradiance is approximately 1000 W/m2

8. Development of Electrical Modelof the Photovoltaic Cell, slide 3 Diode models p–n junction Diode i–v characteristic follows classical exponential diode equation: Id = Idss (elVd – 1) The diode current Id causes the terminal current Ipv to be less than or equal to the photo-generated current I0.

9. Development of Electrical Modelof the Photovoltaic Cell, slide 4 • Modeling nonidealities: • R1 : defects and other leakage current mechanisms • R2 : contact resistance and other series resistances

10. Cell characteristic • Cell output power is Ppv = IpvVpv • At the maximum power point (MPP): • Vpv = Vmp • Ipv = Imp • At the short circuit point: • Ipv = Isc = I0 • Ppv = 0 • At the open circuit point: • Vpv = Voc • Ppv = 0

11. Direct Energy Transfer

12. Maximum Power Point Tracking (MPPT) • MPPT adjusts DC-DC converter conversion ratio M(D) = Vbatt/Vpv such that the PV panel operates at its maximum power point. • The converter can step down the voltage and step up the current. • Battery is charged with the maximum power available from the PV panel.

13. Series String of PV Cellsto increase voltage • To increase the voltage, cells are connected in series on panels, and panels are connected in series into series strings. • All series-connected elements conduct the same current • Problems when cells irradiance is not uniform

14. Bypass Diodes • Bypass diodes: • Limit the voltage drop across reverse-biased cells or strings of cells • Reduce the power consumption of reverse-biased cells

15. Apparent path of sun through sky Baseline Rd. is 40˚N Times are not corrected for location of Boulder in Mountain Time Zone Net panel irradiation depends on cos(j) with j = angle between panel direction and direction to sun So take your data quickly

16. Experiment 1 • Experiment 1: Photovoltaic System • Characterize the SQ-85 PV panels, and find numerical values of model parameters for use now and later in semester • Test the inverter provided • Charge the battery from the panel, using the Direct Energy Transfer method • Hope for sun! • Experiment 1 to be performed this week • Final report for Exp. 1 due in Canvas dropbox by 5:00 pm as listed in schedule.

17. Lab Format • Two-person groups, up to 10 groups per section • Parts kits: • Available from E Store • One kit needed per group • Cost: $180. Contains power and control electronic parts needed for experiments. • You will also need other small resistors etc. from undergraduate circuits kit • Lab: • Access via CUID card reader • Fill out Lab Policy • Computer login via CU Identikey • You may optionally store your parts in your own locked drawer in your lab bench. Lock and key deposit for the semester at E Store.

18. Lab reports • One report per group. Include names of every group member on first page of report. • Report all data from every step of procedure and calculations. Adequately document each step. • Discuss every step of procedure and calculations • Interpret the data • It is your job to convince the grader that you understand what is going on with every step • Regurgitating the data, with no discussion or interpretation, will not yield very many points • Concise is good

19. Upcoming assignments • Experiment 1: PV DET system • Do Exp. 1 in lab this week • Exp. 1 report due in Canvas dropbox by 5:00 pm. See in Schedule. • One report per group • Experiment 2: Intro to LAUNCHXL-F28027F • Do Exp. 2 in lab. See in Schedule. • Exp. 2 scoresheet initialed by your TA and uploaded to Canvas. See dates in Schedule. • Experiment 3: Buck MPPT converter • Exp. 3 prelab assignment due in Canvas dropbox by 12:00 pm. See dates in Schedule.: Buck converter power stage design. • Start Exp. See dates in Schedule.

20. Required Work • Your course grade will be based on the following: • Prelab assignments • Lab final reports • Quizzes • Project proposal and report • Expo • Attendance and lab performance • Assignments are due in the appropriate Canvas dropbox at the times listed in the course schedule page. Late assignments will not be accepted. • Weightings for assignments are listed in the course Canvas site.