How do solar panels work? - Richard Komp — Transcript

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1. 0:08The Earth intercepts a lot of solar power:
2. 0:11173 thousand terawatts.
3. 0:14That's ten thousand times more power than the planet's population uses.
4. 0:19So is it possible that one day
5. 0:20the world could be completely reliant on solar energy?
6. 0:24To answer that question,
7. 0:25we first need to examine how solar panels convert solar energy to electrical energy.
8. 0:31Solar panels are made up of smaller units called solar cells.
9. 0:36The most common solar cells are made from silicon,
10. 0:39a semiconductor that is the second most abundant element on Earth.
11. 0:43In a solar cell,
12. 0:44crystalline silicon is sandwiched between conductive layers.
13. 0:48Each silicon atom is connected to its neighbors by four strong bonds,
14. 0:53which keep the electrons in place so no current can flow.
15. 0:58Here's the key:
16. 0:59a silicon solar cell uses two different layers of silicon.
17. 1:03An n-type silicon has extra electrons,
18. 1:07and p-type silicon has extra spaces for electrons, called holes.
19. 1:12Where the two types of silicon meet,
20. 1:14electrons can wander across the p/n junction,
21. 1:17leaving a positive charge on one side
22. 1:19and creating negative charge on the other.
23. 1:23You can think of light as the flow of tiny particles
24. 1:26called photons,
25. 1:28shooting out from the Sun.
26. 1:30When one of these photons strikes the silicon cell with enough energy,
27. 1:34it can knock an electron from its bond, leaving a hole.
28. 1:38The negatively charged electron and location of the positively charged hole
29. 1:43are now free to move around.
30. 1:45But because of the electric field at the p/n junction,
31. 1:48they'll only go one way.
32. 1:51The electron is drawn to the n-side,
33. 1:53while the hole is drawn to the p-side.
34. 1:56The mobile electrons are collected by thin metal fingers at the top of the cell.
35. 2:02From there, they flow through an external circuit,
36. 2:04doing electrical work,
37. 2:06like powering a lightbulb,
38. 2:07before returning through the conductive aluminum sheet on the back.
39. 2:11Each silicon cell only puts out half a volt,
40. 2:15but you can string them together in modules to get more power.
41. 2:18Twelve photovoltaic cells are enough to charge a cellphone,
42. 2:22while it takes many modules to power an entire house.
43. 2:26Electrons are the only moving parts in a solar cell,
44. 2:29and they all go back where they came from.
45. 2:31There's nothing to get worn out or used up,
46. 2:33so solar cells can last for decades.
47. 2:37So what's stopping us from being completely reliant on solar power?
48. 2:42There are political factors at play,
49. 2:44not to mention businesses that lobby to maintain the status quo.
50. 2:48But for now, let's focus on the physical and logistical challenges,
51. 2:53and the most obvious of those
52. 2:54is that solar energy is unevenly distributed across the planet.
53. 2:58Some areas are sunnier than others.
54. 3:01It's also inconsistent.
55. 3:02Less solar energy is available on cloudy days or at night.
56. 3:07So a total reliance would require
57. 3:09efficient ways to get electricity from sunny spots to cloudy ones,
58. 3:14and effective storage of energy.
59. 3:17The efficiency of the cell itself is a challenge, too.
60. 3:20If sunlight is reflected instead of absorbed,
61. 3:23or if dislodged electrons fall back into a hole before going through the circuit,
62. 3:28that photon's energy is lost.
63. 3:30The most efficient solar cell yet
64. 3:33still only converts 46% of the available sunlight to electricity,
65. 3:38and most commercial systems are currently 15-20% efficient.
66. 3:43In spite of these limitations,
67. 3:45it actually would be possible
68. 3:47to power the entire world with today's solar technology.
69. 3:50We'd need the funding to build the infrastructure
70. 3:52and a good deal of space.
71. 3:54Estimates range from tens to hundreds of thousands of square miles,
72. 3:59which seems like a lot,
73. 4:00but the Sahara Desert alone is over 3 million square miles in area.
74. 4:06Meanwhile, solar cells are getting better, cheaper,
75. 4:09and are competing with electricity from the grid.
76. 4:11And innovations, like floating solar farms, may change the landscape entirely.
77. 4:16Thought experiments aside,
78. 4:18there's the fact that over a billion people
79. 4:21don't have access to a reliable electric grid,
80. 4:24especially in developing countries,
81. 4:26many of which are sunny.
82. 4:28So in places like that,
83. 4:30solar energy is already much cheaper and safer than available alternatives,
84. 4:34like kerosene.
85. 4:36For say, Finland or Seattle, though,
86. 4:38effective solar energy may still be a little way off.