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Land Needed To Make All Our Electricity with Solar Photovoltaics

January 28, 2010

A number that comes up frequently is the “what is the percentage of US land needed to make all our electricity with PV?”

The answer is about 0.7%: approximately a square 160 miles on a side (or 25,700 square miles); or 260 km on a side (66,800 km2).

The assumptions needed to calculate this are:

1. The efficiency of the PV system (because that defines the area needed)

2. The fraction of land the modules cover within the deployed system (packing factor)

3. The output in kWh per installed W, which depends on the sunlight, tracking or not, and other losses within the system.

These numbers can vary quite a bit. For example, system efficiencies are between 5% and perhaps 15% at this time, and as they evolve, will almost certainly rise. Traditionally one is safe to choose 10% as the system efficiency, knowing full well it is likely to be better.

Packing factor varies between tracking and nontracking systems, and seems to be about three for those where land is a constraint. I assume simple, nontracking systems.

Output (kWh/W installed) depends strongly on sunlight and tracking. Assuming nontracking systems but mostly in sunny places allows one to estimate about 1.8 kWh per installed W output per year.

Calculations Showing Land Area

Assumption Amount
m2/MW modules (10% System Efficiency) 10,000
Packing factor 3
m2/MW system 30,000
km2/TW 30,000
TWh/TW 1,800
km2/TWh 16.7
Area of US (km2) 9372610
US electricity use TWh/yr 4000
% US land for All US Electricity from PV 0.7% (66,800 km2)

So, with these assumptions it would take less than 1% of US land area to make all our electricity with PV. If we put more in the sunniest places, it would take less; if we put more all around the country, more. These numbers should be about right as we evolve, but probably conservative – that is, real land area will be a little lower.

By the way, hydro produces 7% of our electricity and uses 100,000 km2 for lakes behind the dams. This is about 1% of US land area. So in comparison, hydro is about 20 times more land intensive per kWh than PV ((1%/7%) / (0.7%/100%)). This is actually a more important answer than the raw number, since it puts it in perspective. PV land area is 20 times less than hydro land area, yet we value hydro a great deal. And PV use doesn’t make any permanent alteration on the land like making artificial lakes.

Ken Zweibel

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6 Comments leave one →
  1. Sam Maloba permalink
    August 16, 2010 10:58 am

    Hi Ken,
    I read with much interest your article on land needed for PV. Well I am from Kenya in africa, the story here is disheartening, we have frequent blackouts, power bills are hitting the skies why because we depend on hydro power. Rivers are drying and so we need to use more generators to keep demand which we can produce only 1200MW. Please educate me since we have enough land to invest in PV. why is it not possible to use it as a solution…is it expensive to put a solar plant than a hydro or geothermal plant or we dig up the massive deposits of coal we have in our untapped mineral base.

    Samuel Maloba
    Mobile +254710494
    Kenya, Nairobi

    • gwsolar permalink*
      August 16, 2010 12:31 pm

      The solutions that work in the US with a responsive power grid and small amounts (to 20%) variable wind and solar don’t work as well where you lack that infrastructure. In Kenya, you should be able to integrate some percentage of solar and wind in your grid that would allow you to reduce the amount of backup fuel generation you now use. You could also convert your hydro from baseload to back-up. It would take a close study of the situation to know these amounts. No new electricity option is cheap, and present day coal, especially without the protections we assume in the US, is a lot cheaper than solar. If you have wind resource, that’d be a good first step. Meanwhile, we hope the incentives provided by developed countries will reduce the price of PV to the same level as wind.

      • Sam Maloba permalink
        August 17, 2010 5:59 am

        Thanks it is good to know the milestones the developed world has done in terms of solar energy, Developing world will still have to do much, I still have a question though for a stadium that is struggling to pay huge bills in electricity would you recommend to them to invest in Solar energy instead? and also is possible to earn carbon credits in Africa Kenya?

      • May 23, 2011 3:16 am

        Thanks alot – your answer solved all my problems after several days sturgignlg

  2. gwsolar permalink*
    August 18, 2010 9:21 am

    Perhaps one of our readers with more knowledge of Africa might comment. The incentives make the immediate cost in the US acceptable. I don’t know what you are paying for electricity or what your incentives or other help might be. If your electricity is over 20 c/kWh, perhaps it would work to substitute some solar energy. Needless to say, every situation varies. Please consult an expert in your kind of situation.

  3. Tom permalink
    January 29, 2013 5:42 pm

    Ken- Finance is also an issue that could be explored for PV relative to Hydro. The U.S. government put up the money to build these dams using long term bonds (50 year time horizons?) and guaranteed low cost electricity generation for many publicly owned utility companies for generations. What was the long term cost of the electricity? How would this compare to PV financed in a similar way? Why wouldn’t something like this be possible for PV?

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