Sunday, November 11, 2007

I Want To Say One Word To You - Just One Word


If I was a young person interested in getting into a growing field either in the R&D, installation or sales area - solar energy would be my first pick of an industry that is guaranteed to grow in the coming decades.

I am including some interesting facts from a DOE funded study on solar energy utilization and basic research needs, to back up that recommendation.

  • Sunlight provides by far the largest of all carbon-neutral energy sources. More energy from sunlight strikes the Earth in one hour (4.3 × 1020 J) than all the energy consumed on the planet in a year (4.1 × 1020 J). We currently exploit this solar resource through solar electricity — a $7.5 billion industry growing at a rate of 35–40% per annum — and solar-derived fuel from biomass, which provides the primary energy source for over a billion people. Yet, in 2001, solar electricity provided less than 0.1% of the world's electricity, and solar fuel from modern (sustainable) biomass provided less than 1.5% of the world's energy.
  • The world now uses energy at a rate of approximately 4.1 × 1020 joules/yr, equivalent to a continuous power consumption of 13 trillion watts, or 13 terawatts (TW). Even with aggressive conservation and energy efficiency measures, an increase of the Earth’s population to 9 billion people, accompanied by rapid technology development and economic growth world-wide, is projected to produce more than double the demand for energy (to 30 TW) by 2050, and more than triple the demand (to 46 TW) by the end of the century.
  • Covering 0.16% of the land on Earth with 10% efficient solar conversion systems would provide 20 TW of power, nearly twice the world’s consumption rate of fossil energy and the equivalent 20,000 1-GWe nuclear fission plants.
  • Solar fuels in the form of biomass produce electricity and heat at costs that are within range of fossil fuels, but their production capacity is limited. The low efficiency with which they convert sunlight to stored energy means large land areas are required. To produce the full 13 TW of power used by the planet, nearly all the arable land on Earth would need to be planted with switchgrass, the fastest-growing energy crop.
  • To contribute significantly to global primary energy supply, a prospective resource has to be capable of providing at least 1-10 TW of power for an extended period of time.
  • The three prominent options to meet this demand for carbon-neutral energy are fossil fuel use in conjunction with carbon sequestration, nuclear power, and solar power.
  • The challenge for carbon sequestration is finding secure storage for the 25 billion metric tons of CO2 produced annually on Earth. At atmospheric pressure, the yearly global emission of CO2 would occupy 12,500 km3, equal to the volume of Lake Superior.
  • Producing 10 TW of nuclear power would require construction of a new one-gigawatt-electric (1-GWe) nuclear fission plant somewhere in the world every other day for the next 50 years. Once that level of deployment was reached, the terrestrial uranium resource base would be exhausted in 10 years.
  • The third option is to exploit renewable energy sources, of which solar energy is by far the most prominent. United Nations (U.N.) estimates indicate that the remaining global, practically exploitable hydroelectric resource is less than 0.5 TW. The cumulative energy in all the tides and ocean currents in the world amounts to less than 2 TW. The total geothermal energy at the surface of the Earth, integrated over all the land area of the continents, is 12 TW, of which only a small fraction could be practically extracted. The total amount of globally extractable wind power has been estimated by the IPCC and others to be 2-4 TWe. For comparison, the solar constant at the top of the atmosphere is 170,000 TW, of which, on average, 120,000 TW strikes the Earth (the remainder being scattered by the atmosphere and clouds). It is clear that solar energy can be exploited on the needed scale to meet global energy demand in a carbon-neutral fashion without significantly affecting the solar resource.
The next time someone suggests carbon sequestration, switchgrass or nuclear as a viable option for meeting the world's growing energy demands you can whip out some of these factoids.

Carbon sequestration needs a leak-free storage facility with the volume of Lake Superior.

Switchgrass would need to be planted on all arable land in the world.

Nuclear power plants with a 1 GWe capacity would need to built every other day for the next 50 years.

According to the DOE report, covering 0.16% of the land on Earth with 10% efficient solar conversion systems would provide 20 TW of power, nearly twice the world’s consumption rate of fossil energy.

Boeing Spectrolab has developed new technology solar cells that surpass 40% efficiency.

If you take the DOE's estimate for a solar array that covers .16% of the Earth to provide 20 TW, and use 200 million square miles for the earth's landmass - you come up with 320,000 square miles, an area that is approximately 565 miles by 565 miles. Using the 4X greater efficiency of the Boeing-Spectrolab cells brings this down to 80,000 square miles, an area approximately 282 miles by 282 miles.

I've seen estimates that a solar array placed in the U.S. desert that was in the range of 2,500 square miles (50 miles by 50 miles) to 10,000 square miles (100 miles by 100 miles) would provide all the U.S. energy needs. None of these figures are exact, since they require assumptions regarding energy use, solar cell efficiency and available sunlight - but at least they give us an idea of what size a solar array would need to be. Putting a 50x50 mile or even 100x100 mile solar farm in the desert sounds good to me when we consider the alternatives.

The complete DOE report is a 276 page PDF file which you can access at Basic Research Needs for Solar Energy Utilization

I've posted a condensed 10 page PDF file over here.


Note: For you young whipper-snappers, the "I want to say one word to you..." quote is from the movie The Graduate (1967).

Back in the 60's the word was "plastics".

Mr. McGuire: I want to say one word to you. Just one word.

Benjamin: Yes, sir.

Mr. McGuire: Are you listening?

Benjamin: Yes, I am.

Mr. McGuire: Plastics.

Benjamin: Just how do you mean that, sir?

Mr. McGuire: There's a great future in plastics. Think about it. Will you think about it?

Benjamin: Yes I will.

Mr. McGuire: Shh! Enough said. That's a deal.

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