Monday, January 22, 2007

U.S. Renewable Energy Consumption

I recently came across data sets on Renewable Energy Consumption from the U.S. Census. Besides recent Consumption rates, we will examine historical rates and trends. Consumption gives a good proxy for the growth in investments in particular types of renewables: the more projects get funded, the more energy is available for consumption.

The U.S. Census defines renewable energy as:
... obtained from sources that are essentially inexhaustible unlike fossil fuels of which there is a finite supply.
Using this definition, the U.S. Census included the following sources:
  • Biomass: Organic nonfossil material of biological origin constituting a renewable energy source.
  • (Conventional) Hydroelectric: Power produced from natural streamflow as regulated by available storage.
  • Geothermal: As used at electric power plants, hot water or steam extracted from geothermal reservoirs in the Earth's crust that is supplied to steam turbines at electric power plants that drive generators to produce electricity.
  • Wind: Energy present in wind motion that can be converted to mechanical energy for driving pumps, mills, and electric power generators. Wind pushes against sails, vanes, or blades radiating from a central rotating shaft.
  • Solar: Includes small amounts of distributed solar thermal and photovoltaic energy.
We quickly plot the total consumption (in Quadrillion BTU's) over the 2003-2004 period. (To enlarge a particular image, click on it.)

A drawback in the U.S. Census data set is that it ends in 2004: there has been a surge in interest in renewables, over the last 2 years, among the general public, policy makers, and the private sector. Rising oil prices, articles about "peak oil", instability in oil producing regions, and increasing concern about climate change have all contributed to the overall interest in renewables. I'm particularly interested in Wind and Solar, which the graph shows are small relative to the other sources. How fast have consumption in Solar and Wind grown in the last decade? Recent media coverage in Wind and Solar energy included pending/current projects, interesting start-ups, and increased interest from VC's. Based on the volume of media reports, one gets the sense that Wind and Solar projects and companies have gone mainstream.

The bar graph gives us an idea of the total 2003-2004 consumption in the different sources of renewable energy. What about growth rates and recent trends? The problem with using regular time-series graphs is that the difference in magnitudes (Biomass is much larger than Solar) will hide trends for the smaller energy sources (Geothermal, Wind, Solar). A common trick is to normalize all the time-series, so they start at a common value (say 100), then use their respective year-over-year growth rates to plot the rest of the graph:

Using the normalized values, we expect the smaller sources to display faster growth rates. Nonetheless, Wind Energy consumption has skyrocketed since 1998. The American Wind Energy Association has an "installed capacity" graph which shows a similar post-1998 growth spurt. What happened in the Wind Energy sector during the late 1990s? A combination of contract negotiations with Utilities, new turbine technology, and geographic diversification:
In the 1990s, the California wind farm market began to be affected by the expiration or forced re-negotiation of attractive power purchase contracts with the major California utilities: Southern California Edison and Pacific Gas and Electric. And much of the existing inventory of 1980's wind turbines were really an albatross around the wind industry's neck. Renewal was needed, and -- bouyed by "green power" initiatives in Colorado, Texas and elsewhere -- U.S. wind energy development resumed in 1999, with a much broader geographical base.
Since the growth in Wind Energy distorted the graph, here is a view minus Wind Energy:

I was suprised by the slow growth in Solar Energy consumption. From 1989 to 2004, Solar Energy consumption grew a paltry 15%, compared to a 550% increase in Wind Energy consumption. Based on tax incentives made available over the last two years, I am inclined to believe that Solar Energy consumption grew rapidly in 2005-2006. I look forward to updating these charts to include years after 2004.

So which states are the leading producers of renewable energy? In an earlier post, I listed the top ethanol producing states. The American Wind Energy Association has a nice map showing Texas and California as the top 2 states in terms of megawatts derived from Wind Energy. I hope to address this question in more detail in future posts. For now, here is renewable energy production, as compiled by the U.S. Census:

Given that production was measured in millions of kilowatt hours, I wonder if this data came from utility companies. Note that the aggregation by type, looks quite different from the earlier consumption bar chart.

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