Saturday, February 26, 2011

Post # 28: Environmental Stewardship and Sustainable Energy

The spring flowers are just beginning to peep through the brown over-burden of Winter-killed vegetation here in East Tennessee.  Spring is a wonderful time of year to be out and about in the mountains and river valleys of this beautiful region of the country.  Seeing the awakenings of Spring always starts me to thinking about our responsibilities as stewards of God's Creation.  And being a good steward of the environment, while addressing the every-growing energy needs of a world seeking the quality of life enjoyed by those of us in the West is an ever-growing challenge.  That's one reason I'm such a strong supporter of nuclear power.

Nuclear power generates ~ 17% of the world's electrical energy while generating lower carbon dioxide emissions per MW-hr of energy than any other energy form except hydro power (and there are some estimates that indicate it's actually lower than everything except run-or-the-river or "kinetic" hydro power.)  If one is concerned about the amount of carbon emitted by energy production, one has to look positively on nuclear power.

Nuclear power is a frugal user of land - generating the highest energy production per acre of land used (or conversely using the least land per unit of energy produced) of any energy production resource - even when uranium mining is considered.  I recently ran across a fascinating paper from on this subject entitled   "Energy Sprawl or Energy Efficiency: Climate Policy Impacts on Natural Habitat for the United States of America," by Robert I. McDonald, Joseph Fargione, Joe Kiesecker,William M. Miller, Jimmie Powell.  It can be found at

Here's a quote from the paper relating to land-use intensity of energy production:

The land-use intensity of different energy production techniques (i.e., the inverse of power density [16],[17]), as measured in km2 of impacted land in 2030 per terawatt-hour per year, varies over three orders of magnitude (Fig. 3). Nuclear power (1.9–2.8 km2/TW hr/yr), coal (2.5–17.0 km2/TW hr/yr) and geothermal (1.0–13.9 km2/TW hr/yr) are the most compact by this metric. Conversely, biofuels (e.g., for corn ethanol 320–375 km2/TW hr/yr) and biomass burning of energy crops for electricity (433–654 km2/TW hr/yr) take the most space per unit power. Most renewable energy production techniques, like wind and solar power, have intermediate values of this metric.

So there you have it.  If one is concerned about land "consumed" in the production of electrical energy (along with associated issues such as human and biological population displacement and habitat destruction), one has to look positively on nuclear power.

An then there is water usage.  Water usage is a challenge for all large central generation power plants.  Presently, there are two dominant approaches to cooling both fossil and nuclear power plants.  The "once-through" cooling approach "borrows" water from the river or reservoir that serves as the cooling water source.  This water is heated as it cools the plant.  About 99% of the water is returned back to the river.  Federal and state regulations set limits on the allowable warming of the river or lake from which the water is drawn.  The second major approach to cooling power plants utilizes "wet cooling tower".  This approach consumes twice as much water as the once through cooling approach, and a larger volume of this water is actually "consumed" in the process (i.e. the net water lost from the river or reservoir is greater.)

According to the Nuclear Energy Institute, "Nuclear energy consumes 400 gallons/MWh with once-through cooling and 720 gallons/MWh with wet cooling towers.  Coal consumes less, ranging from about 300 gallons/MWh for plants with minimal pollution controls and once-thorough cooling to 714 gallons/MWh for plants with advanced pollution control systems and wet cooling towers.  Natural gas-fueld plants consume even less, at 100 gallons/MWh for once-through, 370 gallons/MWh for combined cycle plants with cooling towers, and non for dry cooling."  To put this in perspective, "a typical nulcear power plant supplies 740,000 homes with all of the electricity they use while consuming 13 gallons of water per day per household in a once-through cooling system, and 23 gallons per day per household in a wet cooling tower system.  By comparison, the average U.S. household of three people consumes about 94 gallons of water per day."   (Nuclear Energy Institute @ )

So,  water usage issue is actually one of the most complicated and challenging issues in energy production - especially for large nuclear and fossil-powered plants.  The reason for this complication is the numerous ways in which water is used at different points in the energy production supply chain for different energy production technologies (fossil, nuclear, solar, geothermal, etc.)  We can and we should do better.  New technology and new approaches to water management show promise for improving this picture.  This "energy – water nexus" will be subject of a future post.

Just thinking ...


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