Renewable energy test 2

Who first observed the photovoltaic effect, and in what year was it first noted?

Edmond Becquerel first observed the photovoltaic effect in 1839.

4. Why do many monocrystalline cells have rounded or clipped corners, and what effect do the resulting gaps have on a module?

Monocrystalline cells are cut from round silicon crystals, so trimming them into module-friendly shapes can leave gaps around the corners.

Do the Monocrystalline gaps produce electricity?

No

how quickly do monocrystalline silicon cells normally degrade each year?

less than about 0.5% per year, depending on conditions.

6. Why can polycrystalline cells be more resource-efficient to manufacture than monocrystalline cells?

requires less trimming and waste. Its manufacturing process is also simpler than producing a single pure silicon crystal.

7. What manufacturing feature allows amorphous silicon cells to be used on flexible or building-integrated surfaces?

is very thin. This allows it to be made flexible, semitransparent, or integrated into roofing, and siding

8. Why does increasing the temperature of a photovoltaic cell generally reduce its efficiency?

As temperature rises, PV cells become less efficient, so some of the extra absorbed energy is lost as heat rather than converted into useful electrical output.

how many individual cells are typically assembled into a photovoltaic module

about 36 to 72 individual cells.

11. Why are many small PV arrays wired with modules in series rather than using large parallel currents?

Series wiring increases voltage while keeping current lower. Lower current allows smaller conductors and can reduce wiring cost.

12. Why do larger PV arrays often use two or more series strings connected in parallel?

voltage limits, so very large arrays cannot simply keep adding modules in one series string. Multiple series strings connected in parallel increase total power while keeping string voltage within acceptable limits.

13. What is the simplest type of photovoltaic system described in the chapter, and what is its main limitation?

DC water pump. the load can operate only when enough sunlight is available.

14. Besides supplying energy when sunlight is unavailable, how can a battery bank help an off-grid PV system handle electrical loads?

A battery bank can supply short-duration peak loads that may be greater than the instantaneous output capacity of the PV array.

15. List three advantages of fixed-mount photovoltaic systems

Approximately how much additional annual energy can single-axis and dual-axis tracking collect compared with a fixed array?

20–25% more annual energy for single-axis tracking and about 30–35% more for dual-axis tracking compared with fixed arrays.

17. Why is the tracking mechanism of a PV array normally powered by the grid or a battery rather than directly by sunlight?

Using the grid or battery allows the tracker to reposition even when sunlight is weak or absent, such as moving into position before sunrise.

18. List four system losses that can reduce the actual electrical output of a photovoltaic system.

dust on modules, resistance in wires and connectors, inverter losses, battery losses, and reduced cell performance

19. Why does the chapter multiply the calculated PV array size by 1.25 when allowing for typical system losses?

20. What does the off-grid homestead case study show about the importance of conservation and careful management of electrical loads?

off-grid living depends on reducing unnecessary loads, choosing efficient appliances, avoiding phantom loads, monitoring battery use, and planning consumption around available energy.

Which device is used to measure energy both imported from and exported to the utility?

Bidirectional utility meter

What is the primary purpose of a PV combiner box?

To connect the outputs of multiple PV strings in parallel

What is an important consideration when an isolation disconnect is opened in a PV system?

Conductors on the source side of the disconnect may remain energized

What does Maximum Power Point Tracking allow a charge controller to do?

Operate the PV array near the point of greatest available power

What normally happens to a basic grid-connected PV inverter when acceptable utility conditions are lost?

It stops supplying power until acceptable utility conditions return

Which statement best describes a PV string?

A group of PV modules connected in series

What is the primary function of a transfer switch?

Change a load from one electrical source to another

Which connection would be used to increase the voltage of a battery bank?

Connecting batteries in series

A grid-connected home is using 3 kW while its PV system is producing 7 kW. What may happen to the additional 4 kW?

goes to the utility grid

What is the basic function of an inverter in a photovoltaic system?

Convert DC electrical energy into AC electrical energy

Which characteristic distinguishes a stand-alone PV system from a basic grid-connected PV system?

It operates without relying on a utility connection

Where would a recombiner be most likely used?

In a larger system to combine outputs from multiple combiners

Which type of inverter creates its own AC voltage and frequency without requiring a utility connection?

Stand-alone inverter

What are the three types of silicon solar cells?

Monocrystalline, polycrystalline, and amorphous.

What does photovoltaic (PV) mean?

The direct conversion of sunlight into electricity.

What is the photovoltaic effect?

Light excites electrons, and an electrical imbalance directs them through an external circuit.

What is a semiconductor?

material that allows electrons to move freely when they are in an excited state.

5. Q: What is doping?

Adding small amounts of impurities to pure silicon to change its electrical behaviour.

Which impurity creates n-type silicon?

Phosphorus adds extra electrons.

Which impurity creates p-type silicon?

Boron creates an electron deficiency.

What does n-type mean?

Negative-type semiconductor containing extra electrons.

What does p-type mean?

Positive-type semiconductor with a deficiency of electrons, called holes.

Are n-type and p-type silicon electrically charged before they are joined?

No. Both layers are electrically neutral.

11. Q: What is a p-n junction?

The boundary where n-type and p-type semiconductors meet.

What happens when n-type and p-type silicon are joined?

Electrons migrate from the n-type side into holes on the p-type side, creating an electrical imbalance.

Why is the p-n junction important?

It creates the electrical imbalance that helps drive light-excited electrons through an external circuit.

What happens when sunlight strikes a solar cell?

Electrons absorb energy, become excited, and can move freely through the external circuit.

16. Q: How does recombination affect a solar cell?

It reduces the cell's efficiency.

What is the purpose of the antireflective coating?

A: To reduce reflected sunlight and increase light absorption.

19. Q: What do the top metal contacts do?

A: Collect electrons from the n-type surface and direct them into the external circuit.

20. Q: What does the rear metal contact do?

A: Completes the circuit at the p-type side.

21. Q: What is the purpose of the p-type silicon substrate?

A: It provides the thicker base layer and receives returning electrons through the circuit.

22. Q: What is the purpose of the n-type silicon layer?

A: It provides the surface where electrons are collected and directed into the external circuit.

24. Q: What is the typical efficiency of monocrystalline cells in this chapter?

A: 15–20% or more.

Q: What are the advantages of monocrystalline cells?

A: High efficiency, durability, reliability, and slow degradation.

How are polycrystalline cells manufactured?

A: Molten silicon is poured into a mold, cooled, sliced into wafers, polished, and doped.

29. Q: Why are polycrystalline cells less efficient than monocrystalline cells?

A: Crystal boundaries impede electron movement.

30. Q: What are the advantages of polycrystalline cells?

A: Simpler manufacturing, lower cost, less waste, and lower embodied energy.

31. Q: What are amorphous solar cells?

A: Cells made from noncrystalline silicon deposited in very thin films.

32. Q: What is the typical efficiency of amorphous silicon cells?

5–8%.

36. Q: Which of the three silicon cell types is generally the most efficient?

A: Monocrystalline.

Why can't silicon solar cells convert all sunlight into electricity?

A: Some wavelengths cannot excite electrons, excess energy becomes heat, some light reflects, and some electrons recombine.