Quantity of solar energy

Advocates of renewable energy often cite the enormous amount of energy passing from the sun to the earth as evidence that their preferred electricity sources can serve all human needs. While feasibility remains an issue, the general claim is unassailable. Indeed, it can be derived from first principles:

  1. We have been merrily burning coal, oil, and natural gas for hundreds of years.
  2. This has produced both heat (which does work and eventually dissipates into the atmosphere) and greenhouse gasses.
  3. The latter increase the share of solar energy that remains trapped in the atmosphere, thus significantly heating the planet.
  4. While local heating can arise from the direct heat of fossil fuel burning, this is not a significant planetary phenomenon.
  5. Thus, the extra solar energy being retained by the planet because of greenhouse gasses is much greater than the amount of energy being added to the planet by the burning of fossil fuels and the fission of uranium.
  6. As such, the total energy incoming from the sun must be much greater than the total energy being produced through fossil fuel burning.

Of course, the energy in fossil fuels also came from the sun in the first place – back before the organic matter that comprises them got buried underground and chemically altered through heat and pressure.

To make things a bit numerical, consider this. The total amount of incoming solar energy at any point in time is about 174 petawatts (10^15 watts). That is 1.524 zettawatt (10^21 watt)-hours per year of energy. In comparison, global electricity production from thermal sources is about 11.4 petawatt-hours. That is 130,000 times less than the quantity of solar energy, despite the fact that we are burning far more fossil fuels each year than are formed during that span of time.

Author: Milan

In the spring of 2005, I graduated from the University of British Columbia with a degree in International Relations and a general focus in the area of environmental politics. In the fall of 2005, I began reading for an M.Phil in IR at Wadham College, Oxford. Outside school, I am very interested in photography, writing, and the outdoors. I am writing this blog to keep in touch with friends and family around the world, provide a more personal view of graduate student life in Oxford, and pass on some lessons I've learned here.

7 thoughts on “Quantity of solar energy”

  1. “Solar radiation along with secondary solar resources such as wind and wave power, hydroelectricity and biomass account for over 99.9% of the available flow of renewable energy on Earth. The total solar energy absorbed by Earth’s atmosphere, oceans and land masses is approximately 3,850 zettajoules (ZJ) per year. In 2002, this was more energy in one hour than the world used in one year. Photosynthesis captures approximately 3 ZJ per year in biomass. The amount of solar energy reaching the surface of the planet is so vast that in one year it is about twice as much as will ever be obtained from the all of earth’s non-renewable resources of coal, oil, natural gas, and mined uranium combined.”

  2. According to the second linked diagram above, only 89 petawatts is actually absorbed by land and oceans. That’s 779 exawatt-hours per year: just 68,333 times the total world thermal electricity production. Fossil fuels are also used as a major energy source for things other than producing electricity, such as transport.

  3. The incoming energy of the atmosphere is not 174 PW it is 191 PW.


    This means the area of solar absorption is much greater, if you are using the surface area of the planet surface for your heat input calculation you are doing wrong.

    G Hughes

  4. My reference card from the MIT Physics of Energy 8.21 (2011-12) lists the level of solar power incident on Earth as 174 PW.

    Above the atmosphere, each square metre gets an average of 1,366 watts of solar energy.

    The key fact in all this is that the sun puts out enough power continuously to power human civilization. The challenge is building the hardware to collect the energy.

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