Nuclear Energy

Nuclear energy harnesses the power of the atom to generate tremendous amounts of electricity
from a very small amount or fuel. This controversial source is non-renewable because there is a
finite amount of uranium, and while it produces no carbon emissions it is not “green” because of
the radioactive waste it produces.

Nuclear power plants use the heat created by splitting uranium atoms to create steam either by
boiling water or turning pressurized water into steam without boiling it. The steam turns turbines,
which generate electricity. In both boiling water and pressurized water systems the steam is
condensed back into water to be cycled again. 

Nuclear fission in action

Much of the controversy surrounding nuclear energy is a fear of what could happen. In the years
since nuclear energy plants began generating, there have been three major accidents- Three Mile
Island in 1979, Chernobyl in 1986, and Fukushima Daiichi in 2011. An example of what could go
wrong follows.

Three Mile Island was a loss of coolant accident. A mechanical failure prevented water from
reaching the reactor core to cool it. As pressure began to build in the core, a relief valve opened
as it should have, but remained stuck open when pressure returned to normal levels. Cooling
water poured out of the valve, but plant staff was unaware as instruments indicated the valve was
closed. Without correct information from instrument readings, staff incorrectly reduced the amount
of cooling water going to the reactor, which caused it to overheat. The zirconium cladding that
contained the uranium fuel pellets began to melt. A hydrogen bubble formed inside the containment
dome, raising fears of an explosion and containment breach. Pregnant women and small children
were ordered to evacuate, and there was a release of radiation (done intentionally to relieve pressure)
but not enough to cause any health issues. Plant staff resumed the flow of cooling water and were
able to reduce the hydrogen bubble. The reactor stabilized, and it was discovered that about half
of the core had melted. 

Three Mile Island. The cooling towers for the damaged
reactor are in the foreground. (Lancaster Online)

Safety has improved considerably at US plants. In fact, the costs associated with safety, security,
and permitting have become almost prohibitive to opening new plants. A plant in Tennessee will
be coming online in late 2016, over 40 years after construction began because low demand for
electricity and did not justify the cost of completing the plant until recently.

Aside from safety concerns, spent nuclear fuel is an issue no one is quite sure how to deal with.
Currently, spent nuclear fuel is stored on-site at power plants. First, it is stored in a cooling pool
for a minimum of five years. When it has cooled enough, it is encased in a concrete and steel cask.
However, the material will remain radioactive for thousands of years and a permanent location for
disposal has yet to be found. Reprocessing allows uranium and the resulting plutonium to be reused
as fuel, which cuts down on the amount of waste material but only delays the problem.

Spent nuclear fuel in a cooling pool (International Atomic Energy Agency)

One potential solution to the waste problem is transatomic power, which dissolves nuclear waste
into molten salt, would reduce the amount of spent nuclear fuel by using it again. It also has the
potential to reduce the half-life of waste, or amount of time that it takes for half of the mass to decay
and no longer be radioactive.

Another negative environmental impact of nuclear energy is the potential for radioactive release or
water pollution from tailings at uranium mines. Uranium tailings are radioactive, and may contain
sulfides that can produce acids. Tailings should be placed within an engineered dam and then back
inside the mine when operations conclude (World Nuclear Association, 2013).

After examining various methods of energy production, it has become clear that no source is
completely free of environmental impacts. The negative impacts are wide ranging, from localized
to single windmill to a global scale with fossil fuels. Fossil fuels have been widely panned for the
environmental damage they cause at a regional level for oil spills to the global climate change
linked to carbon dioxide emissions. They have been ruled out as the “greenest” energy, but what
about the others? 

Wind, solar, tidal, and geothermal appear to have the least negative environmental impacts but
can be limited by factors such as geology, topography, and weather. As technology advances, it
may be able to overcome these limitations. An ideal solution to the fossil fuel problem is to
increase their generating capacity and incorporate them into an improved and more efficient grid.
Since these sources, as well as hydroelectric, are mainly regional a better grid would blend all
electricity into a single network that can easily transfer energy to rapidly meet demand. Thus,
hydroelectric from the Pacific Northwest could supply power to Iowa when the wind stops blowing. 

So what is the “greenest” energy? It is all a matter of personal preference and an individual’s
tolerance for the different negative impacts. Bird strikes from wind energy may be a more pressing
concern for some people than fish strikes caused by tidal energy. 

This week's information comes from Duke Energy, Nuclear Regulatory Agency, Wired, Nuclear Regulatory Commission, Transatomic Power, and World Nuclear Association.

Geothermal Energy

Geothermal energy uses heat from within the earth to provide power. It is considered renewable
because of the constant supply of heat from the earth and is “green” because there are minimal
emissions.

Geothermal plants are developed after exploration for a suitable location. Plants need access to
aquifers that are adjacent to hot rock. A production well is drilled to access the heat and steam used to
generate electricity. Once brought to the surface, there are three methods used to produce electricity.
They are flash, dry steam, and binary. 

Geothermal plant (US Energy Information Administration)

A flash plant uses a steam separator to separate steam from water. Steam goes to turbines that power a
generator, while the water is reinjected into the ground where it becomes steam to start the cycle over.
A dry steam plant functions similarly, but there is no water and no need for a steam separator. Steam
alone turns the turbines. As it cools and condenses into water, it is reinjected back into the ground.

Binary geothermal plants use hot water from beneath the surface to boil another liquid, such as
isobutene, that has a lower boiling point than water. The vaporized fluid powers the turbines. The
water is reinjected into the ground, while the vaporized fluid goes through a condenser and a preheater
before returning to the vaporizing chamber and powering the turbines again.

How a geothermal plant works (Mechanical Technology)

A geothermal heat pump is similar to passive solar heating and cooling. Water circulates into the
ground to bring up the earth’s heat or to carry indoor heat underground to cool a building. Direct use
geothermal uses geothermal heat without use of a plant or heat pump. Hot water or steam is brought to
a plate heat exchanger for heating and cooling of a building.

Geothermal plants emit low levels of carbon dioxide and sulfides (hydrogen sulfide mainly) that occur naturally in the subsurface water and steam. Scrubbers can remove most of the hydrogen sulfide. Sulfide emissions are generally lower than fossil fuel plants (US Energy Information Administration, 2015).

This week's information comes from Geothermal Energy Association and US Energy Information Administration. Next week we'll be taking a break for the Species of the Month before returning to check out the pros and cons of nuclear energy.

Solar Energy

Solar power is another “clean” and renewable source that is emission-free and will never exhaust the sun. Not only do photovoltaic panels not drain the sun of energy, they do not diminish the capacity of other panels, so long as one panel is not placed on top of another.

There are two ways to use solar energy, active and passive use. Photovoltaic electricity (PV), solar heating and cooling, and concentrated solar are active systems. Passive solar building use design features capture and utilize solar radiation.

PV cells turn sunlight into electricity. This technology was accidentally discovered in 1954 when a scientist noticed that silicon created an electrical charge when exposed to sunlight. The solar powered calculator was born and eventually evolved into today’s solar panels. The early panels were made of silicon, but second generation panels use thin film and semiconductors. Thin film panels can be used as shingles, tiles, or façades and incorporate electrical generation into the design of a building. PV units can be found powering individual homes or on roadsides, collecting energy for lighting for highway signs.

How solar energy works (Sunpower)

Solar heating and cooling uses the sun’s radiant energy to heat or cool a building with the use of PV panels. A transpired collector is a black metal panel on the south-facing wall of a building that absorbs heat from sunlight. Holes in the panel allow heated air to pass through to the other side, where it is sucked into the ventilation system and throughout the building.

Solar process heating uses a solar collector (usually an evacuated tube or parabolic trough), a pump, a heat exchanger, and water tanks to heat a building. The evacuated tube is a series of glass tubes and reflectors that heat water inside. A parabolic trough is a U-shaped mirror focusing sunlight in a central tube. The focused sunlight heats water in the tube. The heated water is pumped throughout the building to warm it up. Solar cooling uses the same collection system, along with the magic of chemistry to cool the air.

Concentrated solar power is a generating system that reflects and focuses sunlight to create heat and steam that turns a turbine to create electricity. Because the system converts sunlight into thermal energy, it can be stored and generate electricity even on cloudy days or at night. Concentrated solar power can accompany a traditional fossil fuel plant as a carbon offset or as a stand-alone plant.

Solar array collection system (Colorado Springs Business Journal)

Passive solar uses site, climate, and material to use the sun’s radiant energy to heat and cool a building without the use of active mechanical systems like those mentioned above. Energy efficiency measures to reduce the required amount of heating and cooling is the first step. The second step is an unobstructed south face to maximize sun exposure. Sunlight entering the south facing windows is absorbed by thermal mass- material such as concrete, stone, or brick. The thermal mass absorbs heat from the sunlight during the winter and from warm air during the summer. Conduction, convection, and radiance are natural phenomena that circulate the heat throughout the building.

Like all other energy sources examined so far, solar energy is not completely “green”; it too has negative environmental impacts. Habitat loss for large solar arrays and concentrated solar plants can be mitigated by siting these in repurposed areas such as brownfields and reclaimed mine sites. Small scale units that power a single building typically have minimal impact, especially when roof-mounted.

Water use is a concern with concentrated solar plants. The sunniest areas in the US are often the driest, and water is scarce so a massive withdrawal of 600 to 650 gallons per megawatt hour of electricity can have a negative impact on desert denizens.

An additional concern is the hazardous materials used in the manufacture of PV cells. Many are used to polish the semiconductor surface and include hydrochloric acid and acetone. Petroleum is used in the manufacture of PV cells also, so even solar energy is somewhat dependent on fossil fuels. However, new technology that uses cotton and castor beans is being developed.

Next week we'll look at geothermal energy. This week's information comes from Solar Energy Industries Association, National Renewable Energy Laboratory, Renewable Energy World, US Department of Energy, Union of Concerned Scientists, and Scientific American.

Wind Energy

Wind energy is another “clean” energy using the power of moving air to generate electricity. It is renewable because there is no shortage of air on the planet, and it is constantly in motion to a varying degree. It is not completely reliable because the wind is not always blowing, although the wind turbines are at least 100 feet above the ground to take advantage of the less turbulent and more abundant airflow, as compared to ground level.

Wind farm (US Department of Energy)

Wind energy currently makes up 4% of the US energy mix, but is growing and will eventually pass
hydroelectric as most rivers are dammed to capacity. An ideal place for wind farms in the central US
“Tornado Alley” because of nearly constant strong wind. Wind farms are compatible with the
traditional farms of the region and are an economic boon for farmers. They can lease land to energy
companies for windmill placement, and still have the ability to use nearly all of their land. Ridge tops
in the Appalachians are another great location, where topography produces adequate wind speeds.  

Developing technology has greatly improved the efficiency of windmills. Lighter blades, taller towers,
and control systems have increased the average capacity factor from 22% in 1998 to 33% in 2014. As
the race to replace fossil fuels continues, expect efficiency to increase further.

The downside to wind energy, aside from lack of wind, includes environmental impacts. Construction
of windmills in undeveloped areas requires access roads and site preparation, which can be a strain on
the environment. Leaking lubricants can pollute the soil. Birds and can be struck and killed by
windmill blades. However, fewer birds are killed by windmills than stationary buildings. Many birds
are learning to avoid areas containing windmills. Tornado Alley windfarms are away from major
flyways so migratory birds are less likely to affected in that region.

Birds and windmills are not always a good mix (NBC News)

Other negatives are aesthetics and safety. Many people believe the windmills are unsightly and ruin the
landscape. One workaround for that is to install them in developed areas, where they might actually
improve the view, especially if the view is mainly housing developments and shopping centers.
The focus then shifts to noise. The rotating blades can be noisy, depending on the distance from the
listened but the elevation above the ground helps reduce that.

Safety can be an issue when rotating blades are involved. Machines malfunction, and should a windmill
throw a blade, the potential for human death is there. A serious concern in Tornado Alley is that a
namesake tornado could destroy a wind farm and turn the blades into deadly projectiles.

This week's information comes from National Renewable Energy Laboratory, Mount Holyoke College, and US Department of Energy. Next week we'll take a look at solar energy.

Species of the Month

This week we're taking a break from understanding energy sources and trying to understand a species. When you think about lizards, you probably imagine them basking under the hot desert sun or on a tropical island. If that's the case, then June's Species of the Month will surprise you by showing up in some unexpected locations. Say hello to the eastern fence lizard.

Eastern fence lizard (University of Georgia)

Scientific name: Sceloporus undulatus

Kingdom: Animalia (animals)

Class: Reptilia (reptiles)

Order: Squamata (scaled reptiles)

Range: New York south to Florida, west to the Rockies

Habitat: Grasslands and forest edges

Lifespan: Unknown, thought to be four years average

Diet: Insects, some plant matter

Predators: Birds, snakes, other larger lizards, domestic dogs and cats

Conservation Status: No special protection

Other Information: The eastern fence lizard is a widespread reptile. They live under rocks and logs
where they have protection overnight. Cold-blooded, they bask in sunlight during the day to raise their
body temperatures. Normally, they bask close to where they call home. They are little guys. Adults
only grow as long as 19 centimeters. Color varies, but they are usually gray or brown. Males have a
blue patch on the throat and belly. A male will display the throat patch to attract a mate or warn other
males away from his territory. He will also do head bobs and push ups if threatened.
Fence lizard eggs grow after hatching. Mating season begins in April, with hatching taking place from
June to September. The eggs doubles in size between laying and hatching, and babies are half the size
of adults when they emerge. There is no parental care.

Male lizard showing blue throat and belly (University of California, Berkeley)

This week's information is courtesy of the Animal Diversity Web at University of Michigan. Next week
we return to our energy series with a look at wind power.

Tidal Energy

Continuing the series on alternative energy sources, this week features tidal energy. It is similar to
hydroelectric power: it uses the same principles of water in motion and is also a “clean” energy source.
However, tidal power relies not on the temperamental flow of a river which is subject to effects of
weather and climate but on the timeless and ceaseless pull of the sun and moon on the world’s oceans.
Because of its reliance on ocean tides, this is considered a renewable energy source because it does
not diminish the amount of tides in the ocean.

Tidal power is also similar to wind power. Tidal turbines look like miniature underwater windmills.
Tidal turbines can be smaller and more densely spaced than windmills because water is denser than air;
less surface area is required to generate a comparable amount of electricity. While the wind may not
always blow, the tides are always in motion. 

Tide turbines (Forbes)

Another device to harness the energy of the tides is called a barrage. It is similar to a small submerged
dam that blocks the incoming and outgoing tides at the mouth of an estuary. A sluice in the dam opens
to collect the tidewater, which flows though and turns turbines to generate electricity.

One drawback of tidal energy is the tides themselves. Generation capacity is limited by the tidal cycle,
meaning peak demand will frequently be missed. Also, the change in tides must be at least seven
meters for this to be economically efficient. 

Barrages are limited by location. Not all estuaries are suitable sites. The equipment used for generation (either barrages or tide turbines) must be highly durable due to the unforgiving nature of the undersea environment.

Tidal barrage (Britannica)

Like the other energy sources previously mentioned, tidal power has negative impacts on the environment. However, due to limit use of this technology, these impacts are still being studied and at present are not certain to be occurring. The possible impacts include altered waves, currents, substrate, and sediment movement; loss of habitat for benthic organisms; noise that may interfere with biosonar; generation of magnetic fields; introduction of toxins in paint, lubricants, and antifouling; hindrance of fish passage; and fish being struck by blades or sucked into turbines.

This week's information comes from Marine Current Turbines, Ocean Energy Council, and Pacific Marine Energy Center. After a brief break for a look at June's Species of the Month, this series will resume with wind energy.

Pros and Cons of Hydroelectric

Hydroelectric power generates the most electricity of all renewable energy sources in the US, about
7% of the total production. It is a truly renewable source as the same water can flow through a series of dams on a single river, and it is renewable. It is also “clean”, producing no carbon emissions outside of those during the dam building process. 

Water held back by a dam goes through an intake pipe and turns turbines as it passes through the dam.
Faster flowing water will produce more power. Hydroelectric power is about 90% efficient, making it a
great source of power. Due to controls at the dam, the flow of water can be adjusted to meet peak
demands much more quickly than at a nuclear or coal-fired plant. Some dams are equipped with a
pump and can pump water to a higher level during times of low energy usage. The water is then
released back through the dam at peak times to generate additional power.

Not all dams are generating stations, but hydroelectric dams often serve other purposes such as flood
control, irrigation, drinking water supply, and recreation. Because the water is naturally occurring and
free, hydroelectric power is among the cheapest on the market, less than a penny per kilowatt hour on
average. An electric utility can earn additional income through recreational fees, keeping utility rates
low.

Hydroelectric dam in Arizona (USGS)

Although hydroelectric power is “clean”, it is not completely “green”. Like the fossil fuels, it also has
negative environmental impacts. Dams affect fish migration, hydrology, and sediment and nutrient
movement. Flooding a reservoir also causes terrestrial habitat loss, which is traded for aquatic habitat.

Fish ladders can be built to aid anadromous fish in passing around a dam. These fish hatch in
freshwater, live as adults at sea, and return to their native streams to spawn. The journey through
natural aquatic habit frequently involves jumping over small waterfalls, which fish ladders mimic.
Different species of fish move at different speeds and therefore have different needs. Fish ladders come
in many different designs, and some even look like a natural stream rather than a flooded staircase.
Intake screens covering the intake pipes can successfully keep most fish from getting sucked into the
turbines, which can kill them.

Fish ladder (Army Corps of Engineers)

Terrestrial habitat is lost at the expense of aquatic habitat gain. However, the reservoir behind the dam
is of lower quality than a natural lake and alters downstream hydrology. Reservoir water stagnates
since there is no outlet and sediments and nutrients from upstream collect behind the dam rather than
enriching downstream areas. Downstream ecosystems can also suffer if not enough water is released
from the dam.

Sediment deposits after a dam removal in Washington (NPS)

This week's information comes from US Bureau of Reclamation, Michigan DNR, and
Union of Concerned Scientists.

Energy Alternatives

Energy is important at a biological level to sustain life, and at a societal level to sustain lifestyle. From
the discovery of fire to the Nuclear Age, energy consumption has changed over the years, and has also
changed the planet. Use of fossil fuels is largely to blame for an increase of atmospheric carbon dioxide
and accompanying changes in climate. The search for reliable, alternative energy sources leads down
many paths, each with its own strengths and weaknesses. Over the next few weeks, we will examine
several energy sources in an attempt to determine which the “greenest” is.

Before examining the benefits and drawbacks of alternative energies, a look at what they are an
alternative to, fossil fuels- petroleum, coal, and natural gas- is in order. Fossil fuels are still in use
because they are relatively cheap, easily refined, and provide many jobs.

Oil drilling (Bureau of Land Management)

The drawbacks of fossil fuels, in addition to the carbon dioxide output, is other environmental
degradation associated with extraction and transport. Finally, because it is a finite source, eventually
the supply will run out. As supply drops, more invasive techniques will be used to extract ever scarcer
supplies and price will go up.

Environmental impacts of drilling for oil and gas include habitat loss at the well site and access roads; noise pollution; air pollution from generators, vehicles, gas flaring, and particle matter; soil disturbance; increased erosion from vegetation loss; increased solid and industrial wastes; degraded water quality from runoff of soil and residues; and oil spills. There are also problems from end-use: air pollution, increased carbon emissions, contamination such as may be found at gas stations, and plastic litter (most plastics are petroleum-based).

Mountaintop removal coal mine (Center for Biological Diversity)

After all the environmental and health issues related to fossil fuels, it seems clear that we need an alternative energy source. There are plenty of green alternatives, which we will explore, starting with hydroelectric next week.