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SOLAR ENERGY BASICS
The term "solar energy" casually refers to electromagnetic radiation emitted by the Sun. It can be captured
and converted to other usable forms of energy. We have various techniques to harness this nearly limitless
resource and use it for our needs
PRACTICAL USES FOR SOLAR ENERGY
Most guides say that Sun's irradiance can be used for two things: to heat objects and to produce
electricity. In reality, it can also convert into chemical energy. In the nature, through photosynthesis,
plants utilize sunlight to grow and reproduce. Similarly, with the right equipment which implements
sort of "artificial photosynthesis", light can drive the reactions resulting in energy stored in chemical
bonds of "solar fuel". However this process is still in R&D stage and is not quite suitable for residential
applications. By the way, some articles claim that sunlight is the source for all forms of renewable
energy on our planet. This is incorrect because it neglects such forms of energy as gravitation and
geothermal. The main solar uses in today's homes are pool and hot water heating as well as
generating electricity with photovoltaic panels. In general, heating an object from sunlight may require
little more than placing it in the sun and creating a means through which the heat will remain in it.
Swimming pools can be heated by covering them with special covers that trap the heat in the water.
Generating solar electricity is more complex. It can be done in several different ways. Solar cells,
also known as photovoltaic (PV) devices, directly convert the electromagnetic radiation into electricity
in the form of DC voltage. These cells can be combined into panels, which in turn can be connected
into arrays. Solar electricity is used to feed various electric loads from small calculators to large power
plants.
Since the PV cells produce DC voltage, you need to use DC-AC inverters to feed all the conventional
equipment requiring AC power. Concentrating solar power plants also create electricity using sunlight.
However in these plants, there is an intermediate energy carrier: special thermal collectors use the heat from
the sun to warm a fluid and create steam. The steam then powers the prime mover of an electric generator,
which makes electricity via electromagnetic induction.
PROS
Like all forms of power conversion, sunlight as a fuel has its advantages and disadvantages. The
primary benefit of solar energy is its renewability. The sun shines somewhere in the globe every day.
Unlike fossil fuels, it will never be used up. Even on cloudy days, some of the radiated energy seeps
through the clouds to the surface below, providing enough power to feed, for example, hand-held
electronics. The operation of solar powered systems produces no pollution. There are various federal,
state and utility-sponsored rebates and credits for qualified grid-connected systems.
CONS
Using sunlight for water heating can be quite efficient and cost effective. Using sunlight for electricity
however, has two primary drawbacks.
First, it is not constant. You do not know from one day to the next how much energy your solar panels
will be able to generate. This is a problem especially in areas where overcast days outnumber sunny
days. Of course, you can store excess energy in batteries, but this will require a grossly oversized
system. Because of this, it is not practical to use sunlight as the prime power source unless your
power demand is very low. If you are off grid you may need to supplement solar-powered system by
other systems, such as a wind turbine and/or a diesel-fueled electric generator. Otherwise, you have
to significantly oversize the surface area of the PV array and batteries to collect and store the excess
energy to be used for days when sun does not shine. Therefore, if you have a limited space, you may
not be able to fully benefit much from this renewable resource.
Secondly, while sunlight of course is free, the equipment needed to capture and convert it to
electricity is quite expensive both for homeowners and for utilities. Likewise, while solar
generators are pollution free, some pollution are nevertheless produced in the process of their
manufacturing, transportation and installation.
Currently, in 2014 an average net cost of a PV system installation is about $7,000 per kilowatt- see
the cost distribution in dollars/watt by states. The so-called levelized cost of electricity produced on
new photovoltaic power plants is about $0.16 per kW-hour. This value is still much higher than the
cost of electricity generation from coal and natural gas. As the result, in 2010 less than 0.1% of total
US energy consumption came from photoelectric systems. However, in applications where an electric
grid is not available, like in space for instance, sunlight can be a very cost-effective source of
renewable energy.
WIND ENERGY BASICS
When you leave your home and feel the wind whip through your hair, you may view it as an annoyance, but the
fact is wind is an important form of renewable energy. With the right equipment, the kinetic energy of moving
air can be turned into electricity or usable mechanical energy.
WHAT CAUSES WIND?
There are a number of mechanisms that cause air movement around the earth. For example, when
the surface of the earth absorbs heat from the sun, it does so at different rates. Land absorbs heat
about eight times faster than water, and the warm air over the land rises, making room for the cool air
over the water to move in. This moving air is wind. As the earth rotates and the sun "sets", the land
looses its heat faster than the water, so the winds reverse themselves. Changes in the weather can
also affect these cycles. The other major mechanism is related to latitudinal effect. The areas near
the Equator obviously get more sunlight that the areas near the poles. This causes large scale air
motions between the Equator and the poles. Mountains additionally affect the air currents.
HARNESSING THE WIND
The energy in the air molecules can be harvested by using electro-mechanical devices called wind
power turbines (read more about the turbines). These machines have blades that can turn when
exposed to the wind. The blades are connected to a drive shaft that spins an electromagnet or a
permanent magnet. This motion produces rotating magnetic field. The variable magnetic field induces
voltage in the armature of electric generator according to Faraday's law. In residential grade systems
this voltage is not regulated. It has to be rectified and converted into stabilized 120VAC 60Hz
by SMPS inverters. Wind energy can also be converted to mechanical energy in windmills.
PROS
It is always available and cannot be used up. This fact makes it a fully renewable resource. The wind
blows today, and it will blow again tomorrow regardless of whether or not we use its energy. The
process of converting this renewable resource into electricity does not create greenhouse gases or air
pollutants, which is important for our environment.
CONS
The initial monetary investment to put up a wind power plant is higher than fossil fueled options,
because the machinery is quite expensive. Wind also is not as plentiful in all areas of the country.
Unlike electricity from traditional fossil-based sources, the power flow from wind generators is erratic
as winds rise and fall. The amount of wind can also vary from day to day, so those who use it off-grid
must be able to store the electricity for days when the wind is not blowing, or have a supplementary
source of power. The constant variability of the wind power presents challenges for the grid, which
was designed to work with the relatively continuous power flow from the fossil-based plants.
There are concerns that the turbines can kill the bats and birds. Many residents do not like the way
the windmills look. The rotor blades create noise which can be heard within a few hundred feet
especially at night when background noise is low. This is a drawback in residential environments.
Finally, some of the best sources of wind are in the country, away from the urban areas that use the
most electricity. This means that the utility must find a cost-effective way to transport the electricity
long distance to the areas where it is needed.
COST
Prices of course vary widely due to many factors affecting installation. Currently the net cost of
installation of a small wind system for a private home before rebates and incentives is about $4,0006,000 per kilowatt. Such a system includes a turbine with a tower and a special grid-interactive DCAC inverter. The so-called levelized cost of electricity produced on wind power plants is about $0.150.19 per kW-hour. This is about 50-100% higher than the cost of power generation from coal and
natural gas. There is also the cost of getting the permit, which ranges from zero to $1,000 depending
on the utility. Unlike photovoltaic electricity, the cost of wind energy kept growing during the last
decade. However, in near future the prices may decrease as a result of imports of low-priced systems
from China. For reference, in 2010 only about 0.7% of total energy consumed in US came from wind
energy.
YOUR GUIDE TO GEOTHERMAL ENERGY
THE BASIC FACTS
The term “geothermal” comes from a combination of two Greek words: “geo” which means earth, and
“thermos” which means heat. So this word actually refers to “earth heat.” That's precisely what
geothermal energy (GTE) is: the thermal energy generated inside the Earth.
GTE is used primarily for electricity production or heating and can captured in a variety of different
ways. Sometimes heat pumps are also included in the category of GTE, although they utilize different
physical effects. In heat pumps commonly found in space heating systems, the Earth is used as a
huge heat exchanger whose temperature remains more or less constant. There are a number of
various physical processes that contribute to generation of GTE: the decay of radioactive materials,
volcanic activity, and even absorbed solar energy.
Geothermal power is generally clean, renewable, and sustainable. Therefore, it's considered a
“green” type of energy. It is also more cost-effective than other renewables. There are several
available geothermal resources: the heat in shallow ground, hot water and rock a few miles below the
Earth's surface, and high-temperature magma deep in the Earth. Scientists estimate that every 328
feet below the Earth's crust the temperature of the rock increases about 5.4 degrees Fahrenheit.
What this means is that the temperature of the rock can be high enough to boil water about 10,000
feet below the crust. This is the same heat that causes volcanoes, hot springs, and geysers to form.
What geothermal systems do is take this heat and use it to power things that would normally be
fueled by traditional fossil fuels that are considerably more harmful to the environment.
HOW CAN HEAT ENERGY OF THE EARTH BE CAPTURED?
GTE power plants generally use the hot water or steam from the ground to spin a turbine of an
electric generator, which produces electricity in the process. Wells can be drilled into the ground,
tapping underground reservoirs to produce electricity that way. Currently, most of utility-scale plants
are so-called flash steam plants. They use hot water at temperatures over 360ºF (182 oC). When it
flows up to generation equipment at the surface, its pressure drops and it boils into steam. The steam
is then used to produce a kinetic energy in a turbine that powers an electric generator. Any leftover
water and condensed steam is returned back to the reservoir. In the so-called binary system, the
underground water heats another “working fluid” by using heat exchanger. This working fluid
vaporizes and drives the turbines. By using working fluids with lower boiling point than water, binary
systems can operate in the areas with lower water temperatures (225°F to 360°F). The third type of
the plants is dry steam plant. It uses underground steam that goes directly to a turbine. Moderatetemperature water is a more common geothermal resource, so in the future most GTE power plants
will likely be binary-cycle type.
PROS AND CONS
Since all GTE generators use steam or water as a “fuel”, their power source can be constantly
renewed. Given the fact that geothermal systems have practically no external fuel requirements, the
fuel has little bearing on the cost of geothermal electricity. On the other hand, such systems used to
have a relatively large startup cost. This was the major drawback to using the underground heat as a
primary source of power. However, the latest EIA energy outlook for 2014 indicates that this year
GTE has the lower LEC. Costs notwithstanding, it is one of the cleanest forms of energy available. A
GTE system doesn't rely on fossil fuels to power it, and the renewable nature of the energy means
that it'll be available for years to come. Being a green power and highly sustainable makes it a
popular resource to use for as electricity for small towns and larger cities alike. The lower
maintenance costs may allow for the power plant to pay for itself over time, but the initial investment
keeps cost-sensitive communities out of the running. The so-called levelized energy cost of GTE that
takes into account expected power generation over its life, is currently about $0.05/kw-hr. This value
is lower than LEC of coal and natural gas technology. For reference, in 2009 only about 0.4% of total
US energy consumption came from GTE. However, as a type of renewable energy, geothermal will
likely become more prevalent in the future if the initial costs become lower.
HYDROELECTRIC POWER: THE BASICS
Water is one of the earth's most abundant resources, which can be utilized to produce convenient forms of
energy. The mechanical use of falling water to turn wheels of machinery has been known thousands of years
ago. Since the end of 19th century hydropower, or the power of water, is also being exploited for the
production of electricity. Today hydropower is an important renewable resource widely used to create electricity
in the United States and all over the world. In 2009 about 3% of total US energy consumption came from
hydroelectricity.
USING WATER TO GENERATE ENERGY
Water that moves quickly in a river or descends over a great distance possesses a large amount of
usable kinetic energy. To harness it, the fast moving water can be sent through a pipe called a
penstock. Inside the pipe, the water causes blades in a turbine to spin. The turbine's mechanical
energy is then transferred through a drive shaft to the electric generator. In the generator, the
rotational energy is transformed into electricity. Sometimes a penstock is added to a natural source of
moving water, like a stream or waterfall. The water flow can be made artificially through dams that
release it into the pipes when electricity is needed. The systems can be “run-of-river” without a
reservoir, or can include reservoir storage capacity.
WAVE AND TIDAL ENERGY
Other forms of renewable water energy are waves and tides. Winds and temperature differences
caused by uneven heating of the ocean contribute to the formation of waves. Their movement must
be transferred to some swinging system and converted to the mechanical energy of turbines or other
hydraulic or pneumatic engines, which drive a generator. The waves can be focused into small
channels in order to increase the amount of captured energy. Although the wave energy technology is
still in an early stage, the first commercial wave farm has been already opened in Portugal in 2008.
Tides are caused by the interaction of the gravitational forces and the movement of the sun, moon
and earth. The ocean moves toward the moon on the side facing the moon. This results in an up-and
down movement of water along the coast. The seawater can be trapped with a dam in a bay at high
tide. During low tide, it can be released from the bay to the ocean. As it falls, it can turn the turbine of
an electric generator. Typical conversion efficiencies for tidal power are 10-25%.
PROS OF HYDROPOWER
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The main benefit is that it is renewable. There are plenty places on this earth that have moving water,
and we can also create moving water on our own.
It is a fairly clean way to produce electricity, while releasing little pollution into the air through the
process.
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Conventional hydropower (in opposite to wave and tidal power) is a mature technology that does not
require big technological breakthroughs in order to develop it further.
Conventional hydroelectric technologies are highly efficient (about 90%).
CONS OF HYDROPOWER
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It does affect the environment, although not in the form of greenhouse gases and air pollutants. Many
types of fish and underwater organisms are killed in the process of generating hydroelectricty. Creating
an electricity-producing dam, for instance, can change the temperature, flow, and water chemistry in a
body of water, disrupting the natural balance of life. In areas where salmon must swim upstream to
spawn, electricity plants make it impossible for the fish to do so. The challenge then comes to find a
way to use the energy in water responsibly. In salmon spawning areas, the addition of fish ladders
allows the fish to get to their natural spawning grounds, while still allowing the energy to be tapped and
used. This is just one example of the ways in which scientists are working to make hydropower a more
environmentally safe electricity option.
Water reservoirs can occupy large areas of land.
A hydroelectric-based power system is vulnerable to large variations in rainfall and therefore is very
dependent on power transmission from other energy sources.
An estimated levelized cost of electricity produced on new hydroelectric power plants is about $0.12
per kilowatt-hour. This is 50% times higher than the electricity cost on conventional combined cycle
natural gas-fired plants and 20% higher than that of conventional coal plants. Note that these are US
national average numbers: there are significant local variations depending on the markets and the
availability of the water resources. Energy costs on large hydro plants can be as low as $0.030.05/kWh.
USING BIOMASS AS A RENEWABLE ENERGY SOURCE
THE DEFINITION
The term biomass casually refers to biological material that can be used as fuel. It can be something
as simple as a wooden log or more complex like alcohol. Biomass for millennia has been the primary
energy source on the planet.
Although it is considered that all fossil fuels such as coal and oil are originated from buried ancient
organisms, they are usually excluded from the definition of biomass.
Plants are a common source of biomaterials. Corn, for instance, can be processed to make liquid
automotive fuel, and wood can be burned for heat energy. Other sources include residue from
forests, such as grass clippings and fallen leaves. Many plants can be turned into industrial fuel,
including willow, corn, and hemp. Structures like these can be harnessed and used for energy. Since
they can be grown again, this energy source is fully renewable. Another important source of biomass
in the home is garbage, which is approximately 60% biomass.
HOW CAN BIOMASS BE USED TO GENERATE ENERGY?
The easiest and most efficient way to use biomass as energy is to burn it. When it is burned, a part of
the internal chemical energy convers to heat. For some homeowners, certain types of garbage can be
burned to heat their homes, although this is not always a practical in a modern home.
Biomass can also be burned in special plants called waste-to-energy plants. These plants use the
heat energy to create steam, which is then used to either heat buildings or create electricity. In the
about one hundred waste-to-energy plants currently operating in the United States, garbage is burned
to create enough electricity to power about 3 million homes.
Not only do waste-to-energy plants create electricity using a renewable resource, but they also allow
us to cut down on the amount of trash placed in the landfills each year. Since the average American
creates over 1,600 pounds of waste each year, this is an even more important benefit of waste-toenergy plants than the electricity they produce. In addition to creating electricity and heat, biomass
can also be used to create methane gas, ethanol, and biodiesel. Methane gas, the primary
component of natural gas, comes from rotting waste, and this gas can be harvested.
Sugar cane and corn are converted into ethanol, a fuel used to power vehicles. Leftover oils and fats
are used to make biodiesel, another fuel used to power vehicles.
PROS AND CONS
The main benefit of biomass is it's a renewable fuel. Not only does this give us a renewable source of
energy to heat our homes, power our vehicles, and produce electricity, but it also helps us eliminate
some of the waste we are throwing out there for the next generation to deal with. However, if not
managed carefully, biomass can be harvested at unsustainable rates, damage ecosystems, and
consume large amounts of water. Technically, biomass is the only renewable source that theoretically
can be depleted. Another drawback of using biomass as a fuel is this process produces air pollution
such as of carbon monoxide, nitrogen oxides, and volatile organic compounds.
While it is not unusual for homes to be heated with firewood, other types of bio-materials are not as
common, and their commercial-scale use is currently very limited. In 2010 only about 0.5% of total US
energy consumption came from biomass waste and 1.6% from biofuels. Aside from high utility-scale
cost, our energy demand is outpacing biomass production even with the fastest-growing known
energy crops. Meeting a significant portion of the growing primary energy demand with the use of
existing types of plants would require unreasonably large land areas. It is therefore important to
explore the ways of designing bio-organisms that could be transformed into usable energy in a more
effective way while keeping the pollution levels low.
Nuclear Power
Nuclear power is once again considered a prominent alternative, despite the disregard it was met with in the
1970s. This is because it’s now being touted as a more environmentally beneficial solution since it emits far
fewer greenhouse gases during electricity generation than coal or other traditional power plants.
It is widely accepted as a somewhat dangerous, potentially problematic, but manageable source of generating
electricity. Radiation isn’t easily dealt with, especially in nuclear waste and maintenance materials, and
expensive solutions are needed to contain, control, and shield both people and the environment from its harm.
The dialogue about using nuclear power – and expanding it – centers on weighing these risks against the
rewards, as well as the risks inherent in other forms of power generation. These are just some of the issues
involved.
PROS
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Lower carbon dioxide (and other greenhouse gases) released into the atmosphere in power generation.
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Low operating costs (relatively).
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Known, developed technology “ready” for market.
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Large power-generating capacity able to meet industrial and city needs (as opposed to low-power
technologies like solar that might meet only local, residential, or office needs but cannot generate
power for heavy manufacturing).
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Existing and future nuclear waste can be reduced through waste recycling and reprocessing, similar to
Japan and the EU (at added cost).
CONS
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High construction costs due to complex radiation containment systems and procedures.
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Subsidies and investment could be spent on other solutions (such as renewable energy systems).
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High-known risks in an accident.
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Long construction time.
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Target for terrorism (as are all centralized power generation sources).
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Waivers are required to limit liability of companies in the event of an accident. (This means that either
no one will be responsible for physical, environmental, or health damages in the case of an accident or
leakage over time from waste storage, or that the government will ultimately have to cover the cost of
any damages.)
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Nuclear is a centralized power source requiring large infrastructure, investment, and coordination where
decentralized sources (including solar and wind) can be more efficient, less costly, and more resilient.
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Uranium sources are just as finite as other fuel sources, such as coal, natural gas, etc., and are
expensive to mine, refine, and transport, and produce considerable environmental waste (including
greenhouse gasses) during all of these processes.
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Radioactive Waste lasts 200 – 500 thousand years.
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There are no operating long-term waste storage sites in the U.S. One is in development, but its
capacity is already oversubscribed. Yucca Mountain is in danger of contaminating ground water to a
large water basin, affecting millions of people. It’s difficult, if not impossible, for the U.S. to impose its
will on the state of Nevada (or other places) if they don’t want to host long-term storage of waste.
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Shipping nuclear waste internationally poses an increased potential threat to interception to terrorism
(though this has not happened yet with any of the waste shipped by other countries). Increasing the
amount of waste shipped, particularly in less secure countries, is seen as a significant increase in risk
to nuclear terrorism.