Corn ethanol and wind are two renewable energy sources being pursued in the United States. A research paper on "Energy Sprawl" released in August 2009 indicates that energy efficiency is as important a strategy in energy policy as pursuing land-intensive renewable energy sources like biofuels. Photo: brooklyn/flickr
A key challenge for renewable energy like biofuels, solar, and wind becomes the large amount of land needed to produce electricity and liquid fuels at large scale.
Fossil fuels coal, oil, and natural gas are energy dense because they contain concentrated ancient sunlight. Created from carbon-rich plant residues laid down millions of years ago, fossil fuels carry via those plants the energy of millions of years of sunlight densely packed into energy-rich rocks, liquid, and gas.
On the other hand, renewables depend on current sunlight -- today’s sun and wind, this year’s growing season -- to produce their power. Consequently the energy density of renewables is much lower than fossil fuels.
Fossil fuels are supply limited, renewables are flow limited. Fossil fuels eventually will run out as we burn coal and oil created over millions of years in just a few hundred. Renewables are just that, renewable, but their energy flow, or yield, is limited because plants can create stalks and leaves only so quickly from the sun’s energy, windmills can only spin so quickly, solar electricity is limited to the power captured from that day’s sunshine.
It is possible to produce more energy from renewables by improving yields of energy crops and efficiency of windmills and solar energy panels, but the greatest increases in renewable energy output will come from increasing capacity, devoting more land to crops, windmills, and solar installations.
So how much land will be needed to produce enough energy from current sunshine renewables to significantly reduce our need for ancient sunshine coal, oil, and natural gas?
Rob McDonald and other researchers at the Nature Conservancy have been studying this question, trying to determine how much land renewables need. Their results were published in August in the journal PLoS One in a paper called Energy Sprawl or Energy Efficiency: Climate Policy Impacts on Natural Habitat for the United States of America.
They estimate that all biofuels use a lot of land for the amount of energy produced, wind and solar use less, and solar thermal is more land efficient than natural gas. The greatest gains in energy production come not from adding renewables but improving efficiency. Their research shows that more efficiently using the electricity and liquid fuels we have now is far preferable to adding more renewables like biofuels because efficiency both saves land and reduces carbon emissions.
Regardless, they estimate that the push in the United States towards removing carbon from our energy supply likely means that by 2030 renewable energy production will require that we devote to renewables a land area equal to the state of Nebraska.
The graphic below, adapted from the TNC PLoS One research paper, shows the number of square kilometers needed to produce, on average, a terawatt hour of energy per year in year 2030. Error bars in the original graphic are not included here, the numbers in each case show the midpoint between highest and lowest land requirements for each type of energy.
Signs From Earth: Quandary for Renewables: Energy Sprawl
TNC Cool Green Science: Energy Sprawl and The Importance of Fact
TNC Cool Green Science: New Energy Production and Nature: What Will the Impacts Be?