Monday, July 17, 2006

Why Solar is the Long Term Energy Solution

I really like how this image from The Skeptical Environmentalist puts the various amounts of energy in perspective.

Amount of energy in Exajoules (10^18 Joules or EJ):

2,895,000 annual solar radiation
        8,960 total resources of oil
      17,280 total resources of natural gas
    114,000 total resources of uranium
    185,330 total resources of coal
           630 yearly amount of potential wind power
             90 yearly amount of potential hydro power
        1,260 plant photosynthesis
           400 annual human energy consumption

The amount of solar energy is enormous. 7000 times the amount of energy that humans currently consume. 13 times more energy comes from the sun each year than is stored in all fossil fuels currently in the ground! The sun gives of the equivalent of a 180 watt bulb perpetually lighting up every single square meter on the Earth. The tropics receive 250 watts per meter vs 100 for the polar regions.

Photosynthesis in plants only captures 1/2,300th of the total solar energy that reaches the earth. Green plants exploit on average 1-3% of solar energy that touches them compared to 15-20% for solar panels. Total agricultural biomass production from stalks and straw, making up half the world's harvests in mass, only constitutes about 65EJ.

A square area in the tropics 469km on each side (.15% of Earth's land mass) with solar cells of today's efficiency could supply all our current energy requirements. With an average solar influx of 300 W/m2 and an efficiency of 20%, 219,961 km2 of solar cells would produce 416 EJ. This could be in Sahara (which would take up 2.6%) or out at sea. At 40% efficiency you would need a square 330km on each side. This is a lot of area, but I believe it is possible.

The cheapest photovoltaic cells have become 3 times as effective since 1978 and prices have dropped by a factor of 50 since early 70s. The key to the transition to solar power will be the economics. The quicker the price drops, the quicker we will start using more solar power.

Short term I see fossil fuels (and coal in particular) being used more, but long term (next 50 years) I see a transition to solar energy as the dominant source of energy.

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