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  "events": [ {
    "tStartMs": 8152,
    "dDurationMs": 3345,
    "segs": [ {
      "utf8": "The Earth intercepts a lot of solar power:"
    } ]
  }, {
    "tStartMs": 11497,
    "dDurationMs": 3082,
    "segs": [ {
      "utf8": "173 thousand terawatts."
    } ]
  }, {
    "tStartMs": 14579,
    "dDurationMs": 4721,
    "segs": [ {
      "utf8": "That's ten thousand times more power\nthan the planet's population uses."
    } ]
  }, {
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    "dDurationMs": 1650,
    "segs": [ {
      "utf8": "So is it possible that one day"
    } ]
  }, {
    "tStartMs": 20950,
    "dDurationMs": 3497,
    "segs": [ {
      "utf8": "the world could be completely \nreliant on solar energy?"
    } ]
  }, {
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    "dDurationMs": 1251,
    "segs": [ {
      "utf8": "To answer that question,"
    } ]
  }, {
    "tStartMs": 25698,
    "dDurationMs": 6261,
    "segs": [ {
      "utf8": "we first need to examine how solar panels\nconvert solar energy to electrical energy."
    } ]
  }, {
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    "dDurationMs": 4304,
    "segs": [ {
      "utf8": "Solar panels are made up of smaller units\ncalled solar cells."
    } ]
  }, {
    "tStartMs": 36263,
    "dDurationMs": 2920,
    "segs": [ {
      "utf8": "The most common solar cells\nare made from silicon,"
    } ]
  }, {
    "tStartMs": 39183,
    "dDurationMs": 4114,
    "segs": [ {
      "utf8": "a semiconductor that is the second\nmost abundant element on Earth."
    } ]
  }, {
    "tStartMs": 43297,
    "dDurationMs": 1292,
    "segs": [ {
      "utf8": "In a solar cell,"
    } ]
  }, {
    "tStartMs": 44589,
    "dDurationMs": 3978,
    "segs": [ {
      "utf8": "crystalline silicon is sandwiched\nbetween conductive layers."
    } ]
  }, {
    "tStartMs": 48567,
    "dDurationMs": 5209,
    "segs": [ {
      "utf8": "Each silicon atom is connected\nto its neighbors by four strong bonds,"
    } ]
  }, {
    "tStartMs": 53776,
    "dDurationMs": 4301,
    "segs": [ {
      "utf8": "which keep the electrons in place\nso no current can flow."
    } ]
  }, {
    "tStartMs": 58077,
    "dDurationMs": 1126,
    "segs": [ {
      "utf8": "Here's the key:"
    } ]
  }, {
    "tStartMs": 59203,
    "dDurationMs": 4683,
    "segs": [ {
      "utf8": "a silicon solar cell uses\ntwo different layers of silicon."
    } ]
  }, {
    "tStartMs": 63886,
    "dDurationMs": 3150,
    "segs": [ {
      "utf8": "An n-type silicon has extra electrons,"
    } ]
  }, {
    "tStartMs": 67036,
    "dDurationMs": 5253,
    "segs": [ {
      "utf8": "and p-type silicon has extra spaces\nfor electrons, called holes."
    } ]
  }, {
    "tStartMs": 72289,
    "dDurationMs": 1934,
    "segs": [ {
      "utf8": "Where the two types of silicon meet,"
    } ]
  }, {
    "tStartMs": 74223,
    "dDurationMs": 3699,
    "segs": [ {
      "utf8": "electrons can wander across \nthe p/n junction,"
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  }, {
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    "dDurationMs": 2057,
    "segs": [ {
      "utf8": "leaving a positive charge on one side"
    } ]
  }, {
    "tStartMs": 79979,
    "dDurationMs": 3084,
    "segs": [ {
      "utf8": "and creating negative charge on the other."
    } ]
  }, {
    "tStartMs": 83063,
    "dDurationMs": 3722,
    "segs": [ {
      "utf8": "You can think of light \nas the flow of tiny particles"
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  }, {
    "tStartMs": 86785,
    "dDurationMs": 1340,
    "segs": [ {
      "utf8": "called photons,"
    } ]
  }, {
    "tStartMs": 88125,
    "dDurationMs": 2060,
    "segs": [ {
      "utf8": "shooting out from the Sun."
    } ]
  }, {
    "tStartMs": 90185,
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    "segs": [ {
      "utf8": "When one of these photons strikes\nthe silicon cell with enough energy,"
    } ]
  }, {
    "tStartMs": 94131,
    "dDurationMs": 4398,
    "segs": [ {
      "utf8": "it can knock an electron from its bond,\nleaving a hole."
    } ]
  }, {
    "tStartMs": 98529,
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    "segs": [ {
      "utf8": "The negatively charged electron and\nlocation of the positively charged hole"
    } ]
  }, {
    "tStartMs": 103321,
    "dDurationMs": 2413,
    "segs": [ {
      "utf8": "are now free to move around."
    } ]
  }, {
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    "segs": [ {
      "utf8": "But because of the electric field\nat the p/n junction,"
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  }, {
    "tStartMs": 108752,
    "dDurationMs": 2603,
    "segs": [ {
      "utf8": "they'll only go one way."
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  }, {
    "tStartMs": 111355,
    "dDurationMs": 2021,
    "segs": [ {
      "utf8": "The electron is drawn to the n-side,"
    } ]
  }, {
    "tStartMs": 113376,
    "dDurationMs": 2986,
    "segs": [ {
      "utf8": "while the hole is drawn to the p-side."
    } ]
  }, {
    "tStartMs": 116362,
    "dDurationMs": 5633,
    "segs": [ {
      "utf8": "The mobile electrons are collected by\nthin metal fingers at the top of the cell."
    } ]
  }, {
    "tStartMs": 121995,
    "dDurationMs": 2755,
    "segs": [ {
      "utf8": "From there, they flow through \nan external circuit,"
    } ]
  }, {
    "tStartMs": 124750,
    "dDurationMs": 1315,
    "segs": [ {
      "utf8": "doing electrical work,"
    } ]
  }, {
    "tStartMs": 126065,
    "dDurationMs": 1541,
    "segs": [ {
      "utf8": "like powering a lightbulb,"
    } ]
  }, {
    "tStartMs": 127606,
    "dDurationMs": 4368,
    "segs": [ {
      "utf8": "before returning through the conductive\naluminum sheet on the back."
    } ]
  }, {
    "tStartMs": 131974,
    "dDurationMs": 3093,
    "segs": [ {
      "utf8": "Each silicon cell only puts out\nhalf a volt,"
    } ]
  }, {
    "tStartMs": 135067,
    "dDurationMs": 3591,
    "segs": [ {
      "utf8": "but you can string them \ntogether in modules to get more power."
    } ]
  }, {
    "tStartMs": 138658,
    "dDurationMs": 4105,
    "segs": [ {
      "utf8": "Twelve photovoltaic cells are enough\nto charge a cellphone,"
    } ]
  }, {
    "tStartMs": 142763,
    "dDurationMs": 3601,
    "segs": [ {
      "utf8": "while it takes many modules \nto power an entire house."
    } ]
  }, {
    "tStartMs": 146364,
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    "segs": [ {
      "utf8": "Electrons are the only moving parts\nin a solar cell,"
    } ]
  }, {
    "tStartMs": 149478,
    "dDurationMs": 2376,
    "segs": [ {
      "utf8": "and they all go back where they came from."
    } ]
  }, {
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    "dDurationMs": 2028,
    "segs": [ {
      "utf8": "There's nothing to get worn out\nor used up,"
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  }, {
    "tStartMs": 153882,
    "dDurationMs": 3175,
    "segs": [ {
      "utf8": "so solar cells can last for decades."
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  }, {
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    "segs": [ {
      "utf8": "So what's stopping us from being\ncompletely reliant on solar power?"
    } ]
  }, {
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    "segs": [ {
      "utf8": "There are political factors at play,"
    } ]
  }, {
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    "segs": [ {
      "utf8": "not to mention businesses that lobby\nto maintain the status quo."
    } ]
  }, {
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    "dDurationMs": 4111,
    "segs": [ {
      "utf8": "But for now, let's focus on the physical\nand logistical challenges,"
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    "segs": [ {
      "utf8": "and the most obvious of those"
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  }, {
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    "dDurationMs": 4370,
    "segs": [ {
      "utf8": "is that solar energy \nis unevenly distributed across the planet."
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  }, {
    "tStartMs": 178852,
    "dDurationMs": 2367,
    "segs": [ {
      "utf8": "Some areas are sunnier than others."
    } ]
  }, {
    "tStartMs": 181219,
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    "segs": [ {
      "utf8": "It's also inconsistent."
    } ]
  }, {
    "tStartMs": 182859,
    "dDurationMs": 4369,
    "segs": [ {
      "utf8": "Less solar energy is available \non cloudy days or at night."
    } ]
  }, {
    "tStartMs": 187228,
    "dDurationMs": 2410,
    "segs": [ {
      "utf8": "So a total reliance would require"
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  }, {
    "tStartMs": 189638,
    "dDurationMs": 4464,
    "segs": [ {
      "utf8": "efficient ways to get electricity \nfrom sunny spots to cloudy ones,"
    } ]
  }, {
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    "segs": [ {
      "utf8": "and effective storage of energy."
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  }, {
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    "segs": [ {
      "utf8": "The efficiency of the cell itself\nis a challenge, too."
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  }, {
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    "segs": [ {
      "utf8": "If sunlight is reflected \ninstead of absorbed,"
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  }, {
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    "segs": [ {
      "utf8": "or if dislodged electrons fall back into\na hole before going through the circuit,"
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  }, {
    "tStartMs": 208130,
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    "segs": [ {
      "utf8": "that photon's energy is lost."
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  }, {
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    "segs": [ {
      "utf8": "The most efficient solar cell yet"
    } ]
  }, {
    "tStartMs": 213241,
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    "segs": [ {
      "utf8": "still only converts 46% of \nthe available sunlight to electricity,"
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  }, {
    "tStartMs": 218634,
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    "segs": [ {
      "utf8": "and most commercial systems are currently\n15-20% efficient."
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  }, {
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    "segs": [ {
      "utf8": "In spite of these limitations,"
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  }, {
    "tStartMs": 225529,
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    "segs": [ {
      "utf8": "it actually would be possible"
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    "segs": [ {
      "utf8": "to power the entire world \nwith today's solar technology."
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  }, {
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    "segs": [ {
      "utf8": "We'd need the funding \nto build the infrastructure"
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  }, {
    "tStartMs": 232984,
    "dDurationMs": 1987,
    "segs": [ {
      "utf8": "and a good deal of space."
    } ]
  }, {
    "tStartMs": 234971,
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    "segs": [ {
      "utf8": "Estimates range from tens \nto hundreds of thousands of square miles,"
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  }, {
    "tStartMs": 239440,
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    "segs": [ {
      "utf8": "which seems like a lot,"
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  }, {
    "tStartMs": 240976,
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    "segs": [ {
      "utf8": "but the Sahara Desert alone is over\n3 million square miles in area."
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  }, {
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    "segs": [ {
      "utf8": "Meanwhile, solar cells are getting\nbetter, cheaper,"
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  }, {
    "tStartMs": 249039,
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    "segs": [ {
      "utf8": "and are competing \nwith electricity from the grid."
    } ]
  }, {
    "tStartMs": 251986,
    "dDurationMs": 4981,
    "segs": [ {
      "utf8": "And innovations, like floating solar farms,\nmay change the landscape entirely."
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  }, {
    "tStartMs": 256967,
    "dDurationMs": 1989,
    "segs": [ {
      "utf8": "Thought experiments aside,"
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  }, {
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    "segs": [ {
      "utf8": "there's the fact \nthat over a billion people"
    } ]
  }, {
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    "segs": [ {
      "utf8": "don't have access \nto a reliable electric grid,"
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  }, {
    "tStartMs": 264481,
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    "segs": [ {
      "utf8": "especially in developing countries,"
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  }, {
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    "segs": [ {
      "utf8": "many of which are sunny."
    } ]
  }, {
    "tStartMs": 268842,
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    "segs": [ {
      "utf8": "So in places like that,"
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  }, {
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    "segs": [ {
      "utf8": "solar energy is already much cheaper\nand safer than available alternatives,"
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  }, {
    "tStartMs": 274979,
    "dDurationMs": 1600,
    "segs": [ {
      "utf8": "like kerosene."
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  }, {
    "tStartMs": 276579,
    "dDurationMs": 2067,
    "segs": [ {
      "utf8": "For say, Finland or Seattle, though,"
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  }, {
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    "segs": [ {
      "utf8": "effective solar energy \nmay still be a little way off."
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