Solar Energy

Question 1

What are the key energy transformations that occur in a solar power cell?

Answer 1

Photon energy, thermal energy, electrical energy

Question 2

List three energy sources with a lower median power density (per unit area) than solar power.

Answer 2

Hydro, wind, geothermal

Question 3

List four energy sources with a higher median power density (per unit area) than solar power.

Answer 3

Coal, oil, nuclear, natural gas

Question 4

The first commercial solar plant was set up in Albuquerque, New Mexico. What was the power output of this plant?

Answer 4

5 MW

Question 5

If the entire world’s surface was coated in solar panels, how long would it take for the sun to satisfy our annual energy demand?

Answer 5

1:24 h

Question 6

Solar collectors are installed at an angle to maximize solar radiation ____ and minimize ____.

Answer 6

Maximize: intercepted/received. Minimize: reflection.

Question 7

What are the main energy changes in (1) a thermal solar energy system, and (2) a photo-voltaic energy system?

Answer 7

(1) photon energy to heat

(2) photon energy to electrical energy

Question 8

List three environmental factors that impact on the power output of a solar power plant.

Answer 8

Time of day, season, tilt of the earth

Question 9

True/False: Silicon (Si) is an electrical insulator.

Answer 9

False: it is a semi-conductor.

Question 10

List three reasons why silicon (Si) is used in solar cells instead of other semi-conductors.

Answer 10

Any 3 of: abundant, cheap, environmentally friendly, safe, easy to dope.

Question 11

Here are three different equations for the energy of a photon. Which one of these equations is false?

(1) E = hv
(2) E = hλ/c
(3) E = hc/λ

Answer 11

Number (2). E = hλ/c is false.

Question 12

Outline the physical mechanism that occurs in the photo-voltaic effect.

Answer 12

An incident photon impacts a surface electron and transfers its energy to that electron.

Question 13

Which current type do solar cells generate?

Answer 13

DC (direct current)

Question 14

How is a silicon solar cell doped?

Answer 14

Tiny concentrations of phosphorus and boron are added (1 part per thousand Si atoms).

Question 15

Define: n-type and p-type silicon.

Answer 15

n-type silicon is doped with phosphorus and has an excess of electrons. p-type silicon is doped with boron and has electron holes.

Question 16

What is a depletion zone in a solar cell?

Answer 16

Close to the p-n junction, where the electrons and holes combine. This area is neutrally charged.

Question 17

How does the incidence of a photon create a current in a solar panel?

Answer 17

The photon’s energy separates electron-holes pairs in the depletion zone, creating a potential difference between the p-side and n-side, driving a current.

Question 18

Which side of a solar panel should face the sun?

Answer 18

The n-type Si side (with excess electrons).

Question 19

List three pros of solar power generation.

Answer 19

Any 3 of: renewable, easily connected to the grid, scalable, Si is abundant.

Question 20

List three cons of solar power generation.

Answer 20

Any 3 of: inconsistency in cloudy weather, high installation costs, low efficiency (about 20%), panels may be damaged by extreme weather.

Question 21

What is the standard efficiency range for a new solar photo-voltaic cell?

Answer 21

Between 21% and 23% (for new models)

Question 22

Why are solar cells so inefficient?

Answer 22

Because silicon can only absorb a small piece of the spectrum of solar radiation

Question 23

How can technology meet the increasing demand for solar power?

Answer 23

Larger cells, greater efficiency, less expensive devices

Question 24

List 2 cons of floating solar farms.

Answer 24

Degradation of plastic bottoms, unknown effect on wildlife

Question 25

What is the main environmental impact of using sulfur hexaflouride?

Answer 25

Massively accelerates climate change