Tuesday, September 4, 2012

A Disappointing Study of US Renewable Electricity Potential

Back in July the National Renewable Energy Labs (NREL) published a report titled U.S. Renewable Energy Technical Potentials: A GIS-Based Analysis.  Graphical Information System (GIS) data has become really popular.  Thanks to satellites and the ability to handle massive amounts of image data, the world today is better mapped than previous generations could even dream about.  Using available GIS data, the authors evaluated the potential for each of several different renewable sources of electricity in the US.  Consider one resource -- rural utility-scale photovoltaic panels.  The authors identified all of the land which met certain criteria (rural, sufficiently flat, not water, not in a national park, etc) and calculated how much power could be generated using today's PV technology if all of the identified land were used for that purpose.

 The table to the left summarizes the results from the power for ten different renewable resources.  The potential is shown in petawatt-hours; in 2010, total US retail sales of electricity were about 3.7 PWh.  The total figure is not meaningful.  The land considered suitable for concentrated solar and rural utility PV is the same land, and it can't be used for both.  Even some of the individual numbers aren't meaningful.  Much of the land suitable for rural utility-scale PV is also suitable for growing food crops, an application that can't be realistically ignored.  Most renewable resources are intermittent on some time scale.  Rural utility-scale PV may be able to provide many times the US current power consumption, but without some form of storage, it still won't keep the lights on at night. 

The authors presented their results at the state level and used the data to produce maps like the one shown to the right.  This particular map shows the potential for hydrothermal power, which is concentrated in the western states.  But state level aggregation doesn't seem particularly helpful either.  Western states are large, so energy sources can still be far from the population centers (as well as separated by the odd mountain range here and there).  Western states vary enormously in terms of their population.  California and Nevada may be in the same category in terms of hydrothermal potential; but because of the differences in their populations, Nevada's resource may be sufficient to meet all of Nevada's needs, while the same resource in California can provide only a small fraction of what is needed.

I'm seriously disappointed by the study, which I think adds very little value.  We already knew that rural utility-scale PV could potentially produce far more power than we currently consume.  I can think of a half-dozen things to do with the data that would have been much more useful.  For example, for some (or all) of the 50 largest metro areas, how far and in what pattern would rural PV need to be deployed to meet the metro areas' power needs?  Avoid mountain ranges; avoid areas that are heavily forested; avoid existing towns.  Where do the patterns overlap?  What happens if current crop land is excluded?  There are enormous amounts of GIS data of various types available, and some of the ways that it can be used would be valuable.  The results in this paper aren't one of those, unfortunately.

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