Solar Thermal Power to Offset Coal Plant Carbon Emissions

From the DOE online reference, CO2 Emissions Report, Table 1, you will see that in 1999 in the USA there were nearly 1.8 million metric tons of CO2 emissions from the burning of coal to create electricity, which yielded nearly 1.9 million kilowatt-hours of power. This means in that year in the USA, for each megawatt-hour of coal-fired electric power, there were .95 tons of CO2 ejected into the atmosphere. It is likely the global efficiency of coal-fired electricity plants in the USA in 2008 exceeds this standard, but for the sake of a numerically clear argument suppose for every megawatt-hour of coal-fired power, 1.0 ton of CO2 enters the atmosphere.

Currently the United States emits about 6.0 billion tons of CO2 into the atmosphere each year, and about 50% of that, about 3.0 billion tons, comes from coal-fired electricity plants. In the entire world, annual CO2 emissions approach 30 billion tons per year, and it is safe to say about half of these emissions come from coal, although worldwide, coal is used at scale for a variety of fueling applications and not just for electricity. So how much would it cost the USA or the world to replace every megawatt-hour of coal fired electricity with solar electricity, and how much does today’s global installed base of roughly 10 gigawatts of photovoltaic array cut into the annual worldwide CO2 emissions from coal?

Ameren’s Sioux Unit 1, with the first in-furnace control technology, achieving
NOx emissions below 0.15 pounds per million Btu on a coal-fired cyclone boiler.
(Photo: DOE)

Assuming photovoltaic (or solar thermal, where the global installed base is beginning to matter as they approach their first gigawatt) has a yield of 25 percent – which corresponds to about six hours of full-sun-equivalent daily light on the collectors – 10 gigawatts installed equates to 2.5 gigawatt-years of electricity annually. In turn this means solar power produces about 21.9 million megawatt-hours of electricity per year, and at 1.0 ton of CO2 per megawatt-hour of power, this means solar power offsets not quite 22 million tons of CO2 emissions from coal power per year.

What this all means is inspiring insofar as it presents solar as an opportunity that is truly in its infancy, despite some arguably overvalued stocks among photovoltaic companies. The issue isn’t these companies running out of customers. The issue is they will have to continue to double their output year upon year in an environment of continuously improving technologies and relentlessly lower prices – a challenge that can slow any company’s growth. The solar power sector is in its infancy because even if the fully amortized price for solar energy already approaches parity with coal, the entire installed base of solar electricity production worldwide would only fulfill about 0.7% of CO2 emissions for coal-fired electricity just in the USA.

For the entire world, the solar power sector would have to grow by 684 times before it would offset the CO2 emissions attributable to coal, more specifically, to offset 15.0 billion tons of CO2 emissions annually based on 1.0 ton of CO2 per 1.0 megawatt-hour of coal-fired electricity. Given the miniscule accomplishments of solar energy so far in the global power equation, and given that global energy output has to double as soon as possible, if the price keeps coming down solar energy as a sector has the potential to experience 50%+ annual growth for a very long time. How much would it cost today to install enough solar energy to offset 15 billion tons of CO2 emissions?

An all-in installed price of $5.00 per watt is still low by today’s standards, but probably represents the high end of eventual costs as technology and productivity improves in the solar sector. Increasing the 10 gigawatts of installed solar power worldwide by 684 times means installing a 6.8 terawatt distributed array producing 15 million gigawatt-hours of power per year, which at $5.00 per watt would cost 34 trillion dollars. For the perhaps 1.0 billion lucky residents of the fully developed, industrialized world to pay for this via offset fees and taxes and the like over 20 years, zero interest, would amount to $1,700 per person per year. Adding the grid and storage infrastructure should easily raise that price to $2,000 each – something like $7,500 per average household per year. And this sort of accomplishment is a vital pillar of Gore’s pledge. No more coal – twenty years. Shave a few more points on future cost and call it twenty years, twenty trillion, a trillion per year. Using these same assumptions, it would cost America $6.8 trillion to replace 100% of coal fired electricity with solar power, or about $23,000 for every person in the country.

Shaving costs any further on the future price of solar is a dangerous assumption, however. Even at a cost of $34 trillion to replace coal worldwide with solar, our calculations are based on a collection of very optimistic givens; $5.00 per watt installed including storage and distribution upgrades, a 25% yield, and 20 year zero-interest financing; resulting in $114,000 per gigawatt-hour or 11.4 cents per kilowatt-hour for future solar. We are nowhere near this, yet to precipitously phase out coal or to participate in a doubling of global energy production, or both, this is probably what the solar sector is going to have to do.

4 Responses to “Solar Thermal Power to Offset Coal Plant Carbon Emissions”
  1. Solar John says:

    The report doesn’t mention that we could cut our use of electricity by 50% through conservation efforts. I’ve already done this in my own home. I’ve also installed solar panels, and I’ll eventually eliminate my use of fossil fuel entirely, but a little help would be appreciated. Anyone can do what I’ve done, but it won’t happen on a large scale without incentives. We need leaders who think outside-the-box.

  2. Bill Woods says:

    “…resulting in $2.3 billion per gigawatt-hour or 2.3 cents per kilowatt-hour for future solar.”

    Some decimal points went astray:
    $2.3 billion per gigawatt-hour is $2,300 /kW-h, or
    2.3 cents per kilowatt-hour is $23,000 /GW-h.

  3. Ed Ring says:

    Bill – you make a great point; I have corrected the data in the report based on the following variables:
    A = $5.00 per watt installed
    B = 25% yield
    C = 20 year life & amortization period (zero interest)
    D = 8,766 hours per year
    On this basis, (B x C x D)/1,000 = lifetime kilowatt-hours per watt installed, or 43.8, and $5.00 per watt / 43.8 kWh = 11.4 cents per kWh. And of course we are assuming no interest, no maintenance, and no operating costs, which easily make up for installation costs falling well below our assumed $5.00 per watt.

    There is something else that may not add up, however. Maybe you can weigh in if you wish.

    CO2 emissions from coal are about half of the total worldwide, i.e., about 15 gigatons of CO2 per year are the result of coal burning. Referring to the DOE, it appears that a modern coal-fired electricity generating plant will release about 1.0 ton of coal for each megawatt-hour of power generated. (Table 4).

    If this coal were used to generate electricity, this suggests that 15 gigatons of CO2 emissions from coal burning each year could be offset by 15 billion megawatt-hours of electricity produced each year by solar energy.

    Converting 15 billion megawatt-hours into giga-watt years requires dividing by 1,000 (megawatts per gigawatt) and then dividing by 8,766 (hours per year), and if you do this, you’ll get a constant gigawatt output, or gigawatt-year output, of 1,711.

    Now does this pass the smell test? Because 1,711 gigawatt-years, at 33.4 gigawatt-years per Quadrillion BTUs equals only 51 Quad BTUs per year. Given the human race currently produces about 500 Quad BTUs of energy per year, is this correct? Is it correct that coal produces 10% of the energy in the world and 50% of the CO2 emissions? Just wondering.

  4. Bill Woods says:

    A kW-h of electricity takes 2.5–3 kw-h of heat, so scale up the energy released from burning coal accordingly. Of course, it’s not all used for generating electricity.


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