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From
space, the view at night gives a good indication of how
much
electricity we humans use. With the exceptions of
North
Korea and Antarctica, you can’t find many places on
Earth
that don’t glow at night. But even at that, it would
take
20 years for us to produce the same amount of energy that
shines
on the Earth from the Sun in one day.
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Christmas has just passed and everyone has new phones, PlaySatations, drones and other gadgets. Unless your phone is nuclear or solar, it also came with a recharging cord because these tool/toys work on electricity, the very lifeblood of modern society. To illustrate - the total amount of electricity generated in the U.S. in 2012 was 4,047,765,000,000 kilowatts.
For something so important to commerce, entertainment,medicine – just about anything you can name – the average person knows shockingly little about how it comes to them. Let’s take some time to acquaint ourselves with something called the National Grid of electrical generation and distribution. Let’s consider power generation this week.
There are a couple of ways to directly generate electricity from a potential energy source. Solar photovoltaic cells turn solar radiation directly into electricity. These technologies have been around for several decades. However, even though sunlight has many wavelengths of light, most photovoltaic cells only harvest a fraction of them. Historically, this has made solar energy inefficient to use.
New cells use several different semiconducting materials,
each absorbing a different wavelength of light. According to 2014 research,
these new cells achieve an efficiency of 44%, meaning that 44% of the energy
that strikes the surface is converted to electricity. This is pretty good
compared to single junction cells that have about a 25% efficiency.
Fuel cells generate electricity by moving hydrogen ions
across a catalyst. The metal catalyst strips electrons from the hydrogen and
these electrons form an electrical current. The resulting positive hydrogen
ions combine with oxygen on another catalyst to produce water as the only by
product. The problem is that the materials (exchange membranes or electrolytes) to move the positive hydrogens to
the oxygen are every expensive.
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Fuel
cells produce water as their only byproduct. When the
catalyst
strips hydrogen of its electron, this flows as
current,
and is then replaced by an electron from oxygen.
Most
cells differ only by the electrolyte used. Upps now has
a
fuel cell on the market to power your smart phone for a
week.
I wonder how you don’t end up with a soggy phone.
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These technologies excepted, most electricity is produced
from the turning of generator turbines. The turbines spin a coil of wire in a
magnetic field. This produces electricity – thank you very much Michael Faraday.
The key is how we generate the force that turns the turbine blades that then
spin the wire coil. In most cases, we burn some sort of fuel to turn the
blades, but in a few cases turbine blades can be turned directly.
The wind turbine is an old technology use to harness the power
of air moving from areas of high atmospheric pressure to areas of low pressure (wind).
The Europeans used wind power to grind grain into flour (hence the name wind mill)
but they have been around since the time of the Greeks. American and Australian
farmers use them to pump water, but today we mostly use wind turbines to
generate electricity.
Hydroelectric generators use the power of gravity and water
under pressure to turn turbine blades. By constructing a dam between an area of
high elevation and one of lower elevation, water is put under pressure. Allowing
a controlled volume to pass through a turbine will spin it and the associated
generator will produce electricity.
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The
Three Gorges Dam and Hydroelectric Plant in China
(top)
was built to be world’s largest hydroelectric generator
system.
However, the Itaipu Dam on the Brazil/Paraguay
border
(bottom, all generators first online in 1991)
generated
significantly more electricity in 2013 and 2014.
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These direct "energy to turbine" mechanisms are helpful, and are
becoming larger players in the electricity game (along with solar power and
fuel cells). But the burning of fossil fuels - natural gas/petroleum/coal - is
still the main way we turn turbine blades turn.
Fossil fuels are non-renewable natural resources and their
importance in energy can’t be underestimated, both from the standpoints of how
helpful and efficient they are, but also in how dirty they are and how they are
running out. However, they aren’t the most important natural resource for the
generation of electricity. Can you guess what is?
Believe it or not, water is the resource used
in greatest amount so that you can charge your iPhone. Name an energy generation technique
that doesn’t use water – you can’t. Water cools power plants that burn fossils
fuels; it cools nuclear reactors too. It is used to water the fields that grow
plants for biodiesel. Water is heated for almost all generator turbines. Water
is even used to extract petroleum from the ground – ever heard of fracking? A
research report in 2008 stated that the U.S. alone uses 500 billion liters (132
billion gallons) of fresh water each day just to produce electricity.
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Frack
- expletive, energy process, or jacket? All three, actually.
In
dressage, the frack is the dress coat worn in some
competitions.
In energy circles, it refers to hydraulic fracturing,
where
water, chemicals and sand are injected into shale in order
to
fracture it and release trapped crude oil or natural gas. Some
people
are against both and use the expletive to show
their
displeasure.
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How do we produce steam to turn the blades of a generator turbine?
Nuclear fission is one way. Decay of naturally radioactive materials in a water
bath generates a lot of steam. Other ways include solar thermal energy, where
the energy of the sun is directed by mirrors at a large mass of water that then
boils, or by burning biomass (wood, sawdust, biodiesel, trash, methane).
It's beyond this discussion to explain how a spinning
magnet across a coil produces moving electrons, so you can read about it here.
The point is that whatever means is used to spin the turbine, its shaft is
attached to the magnet that spins.
In most power stations, one magnet passes three coils on
each revolution, so three alternating current lines are produced. This is the
three phase generation that will become important when we next week talk about
the electrical lines coming to your house.
contributed by Mark E. Lasbury, MS, MSEd, PhD
As Many Exceptions As Rules
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