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Last Post 16 Oct 2012 09:43 PM by  Kelly Larson
Sun/solar power/heat
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16 Oct 2012 01:07 PM

    Drk (SRE)

    Q # 7

    How much solar power and heat do we get from the Sun, and why is solar power so expensive still?

    Tags: Solar Panels, solar power

    Kris Sigsbee

    Basic Member

    Basic Member

    16 Oct 2012 03:19 PM


    Scientists use a unit called a Watt (W) to measure energy output per second. The solar energy flux averaged over just the sunlit half of the Earth's surface is about 680 W m−2. 1 meter (1 m) is just a little over 1 yard. This means that If you make a square 1 meter on each side, it would have 1 m of area and there would be about 680 Watts of solar energy flowing into it at the top of the Earth's atmosphere. This would be just about the energy of 7 100 W light bulbs in the 1 meter square. The surface area of the sunlit half of the Earth is roughly 257,000,000,000,000 m2 so that would add up to an awful lot of light bulbs! However, only about 70% of this energy is absorbed by the ground - the rest gets reflected back into space.

    The reason why solar power is so expensive is because solar panels that convert the Sun's energy into electricity are still fairly expensive to make. We get lots of energy from the Sun, but we also cannot cover the entire surface of the Earth with solar panels, and some populated areas are better suited for using solar energy than others. You can read more about the costs of solar energy here:


    Kelly Larson

    New Member

    New Member

    16 Oct 2012 09:43 PM


    I am an electrical contractor that specializes in designing and installing solar electric systems. The main reason that solar power seems expensive is that we have conventional energy sources that are subsidized, and those sources have high energy density.

    For instance, a gallon of gasoline has a great deal of energy, (47 MJ/KG). This is an amazingly densly packed energy source. Compare that to dynamite which is 4.6 KJ/KG. Problem is, it's use also causes polution, and the supply is decreasing. (No one disputes these facts). We don't pay at the pump what it costs for a future of gasoline, nor do we pay for the "externalities", which include the effects of polution, and any needed actions to secure the fuel. So even though gasoline is "cheap" it is only so in the short run.

    Contrast that to when we buy a solar module that makes electricity from the sun. When we buy them they seem expensive, but we are buying the ability to harvest free energy into the future. Once the solar equipment is paid for, (which is often 3 - 10 years), the energy is free for the remaining 15 - 25 years. To recognise that takes long-term thinking! And in places where electricity is 25 cents/KWh, (like Hawaii), solar is cheaper than buying electricity from the utility!

    So if you think long-term, (which only means 10 years in this case), solar is much cheaper than any conventional sources, (like gasoline, coal, natural gas, or nuclear), especially if you count all the "externalities"!

    Sunny day,


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