3. PowerPoint ® Presentation Chapter 5 Cells, Modules, and Arrays Photovoltaic Cells Current–Voltage (I–V) Curves PV Device Response Modules and Arrays

4. Chapter 5 — Cells, Modules, and Arrays The basic building blocks for PV systems include cells, modules, and arrays.

5. Chapter 5 — Cells, Modules, and Arrays Semiconductor materials with special electrical properties can be made by adding small amounts of other elements to silicon crystals.

6. Chapter 5 — Cells, Modules, and Arrays The photovoltaic effect produces free electrons that must travel through conductors in order to recombine with electron voids, or “holes.”

7. Chapter 5 — Cells, Modules, and Arrays Various PV materials and technologies produce different efficiencies.

8. Chapter 5 — Cells, Modules, and Arrays Monocrystalline silicon wafers are sawn from grown cylindrical ingots.

9. Chapter 5 — Cells, Modules, and Arrays Polycrystalline silicon wafers are sawn from cast rectangular ingots.

10. Chapter 5 — Cells, Modules, and Arrays Several steps are involved in turning silicon wafers into PV cells.

11. Chapter 5 — Cells, Modules, and Arrays Diffusion of phosphorous gas creates a thin n-type semiconductor layer over the entire surface of a p- type wafer.

12. Chapter 5 — Cells, Modules, and Arrays The different materials, processes, and manufacturing steps produce a range of PV cell types.

13. Chapter 5 — Cells, Modules, and Arrays An I-V curve illustrates the electrical output profile of a PV cell, module, or array at a specific operating condition.

14. Chapter 5 — Cells, Modules, and Arrays Open-circuit voltage is easily measured with test instruments.

15. Chapter 5 — Cells, Modules, and Arrays Using in-line and clamp- on ammeters are two methods of measuring short-circuit current.

16. Chapter 5 — Cells, Modules, and Arrays A power versus voltage curve clearly shows the maximum power point.

17. Chapter 5 — Cells, Modules, and Arrays Fill factor represents the shape of an I-V curve.

18. Chapter 5 — Cells, Modules, and Arrays Efficiency is a measure of how effectively a PV device converts solar power to electrical power.

19. Chapter 5 — Cells, Modules, and Arrays A PV device can be modeled by a current source in parallel with a diode, with resistance in series and parallel.

20. Chapter 5 — Cells, Modules, and Arrays Increasing series resistance in a PV system flattens the knee in the I-V curve, reducing maximum power, fill factor, and efficiency.

21. Chapter 5 — Cells, Modules, and Arrays Decreasing shunt resistance reduces fill factor and efficiency and lowers maximum voltage, current, and power, but it does not affect short-circuit current.

22. Chapter 5 — Cells, Modules, and Arrays Voltage increases rapidly up to about 200 W/m 2, and then is almost constant. Current and maximum power increase proportionally with irradiance.

23. Chapter 5 — Cells, Modules, and Arrays Increasing cell temperature decreases voltage, slightly increases current, and results in a net decrease in power.

24. Chapter 5 — Cells, Modules, and Arrays Modules are constructed from PV cells that are encapsulated by several layers of protective materials.

25. Chapter 5 — Cells, Modules, and Arrays An array is a group of PV modules integrated as a single power-generating unit.

26. Chapter 5 — Cells, Modules, and Arrays Several modules may be connected together to form a panel, which is installed as a preassembled unit.

27. Chapter 5 — Cells, Modules, and Arrays A junction box on the back of a module provides a protected location for electrical connections and bypass diodes.

28. Chapter 5 — Cells, Modules, and Arrays PV cells or modules are connected in series strings to build voltage.

29. Chapter 5 — Cells, Modules, and Arrays The overall I-V characteristics of a series string are dependent on the similarity of the current outputs of the individual PV devices.

30. Chapter 5 — Cells, Modules, and Arrays Strings of PV cells or modules are connected in parallel to build current.

31. Chapter 5 — Cells, Modules, and Arrays The overall I-V curve of PV devices in parallel depends on the similarity of the current outputs of the individual devices.

32. Chapter 5 — Cells, Modules, and Arrays Modules are available in a variety of sizes and shapes, including squares, rectangles, flexible units, and shingles.

33. Chapter 5 — Cells, Modules, and Arrays Bypass diodes allow current to flow around devices that develop an open-circuit or high-resistance condition.

34. Chapter 5 — Cells, Modules, and Arrays A bypass diode limits reverse current through PV devices, preventing excessive power loss and overheating.

35. Chapter 5 — Cells, Modules, and Arrays Module labels must include performance ratings for the module and may include other information used to design a PV system.

36. Chapter 5 — Cells, Modules, and Arrays Various test conditions can be used to evaluate module performance and may produce different results.

37. Chapter 5 — Cells, Modules, and Arrays Modules are added in series to form strings or panels, which are then combined in parallel to form arrays.

38. Chapter 5 — Cells, Modules, and Arrays Bipolar arrays can be constructed from a pair of monopole subarrays that are connected together in the center. The total bipolar array voltage is then twice the voltage of the individual subarrays.