Wind Power has the potential to be used in a home environment only in the right
circumstances, and has the potential to power everything your home
needs, from electric radiators to hot water. In this instance, I’m going
to focus on the electrical side of things, and how you can use mainly
use wind turbines to power the electricity in your home, and even make
money selling it back to the grid.
The Basics
Ok, so it
makes sense to begin at the beginning; that is, explain the basics of
wind power and the ideas behind it. So, wind power is the conversion of
wind into a useful form of energy e.g. using wind turbines to create
electricity. But this is not the only form of energy that it is capable
of being converted into, other forms such as using wind mills for
mechanical power, wind pumps for pumping water or drainage, or sails to
propel ships with kinetic energy are also applicable. At the end of
2010, worldwide capacity of wind-powered generators was 196.6 GW, with over 90 countries worldwide using wind power commercially.
Some,
however, are recently starting to doubt the ability of wind power to
provide enough energy on a global scale (power output vs. Needs of
nation) for it to be economically viable (see recent article in the
Telegraph).
However, it is still unquestionably one of the most
popular methods of renewable energy on a personal scale, owing to a
number of factors that will be discussed later. In terms of electrical
uses on a large-scale, wind farms are the key. These are a collection of
many wind turbines (as pictured) to collect as much wind power from one
economically-viable area as possible. Wind Farms are connected to the
electric power transmission network, whereas smaller facilities are used
to provide electricity to isolated locations. Utility companies
increasingly buy back surplus electricity produced by small domestic
turbines.
Wind park on sea |
Wind energy, as an alternative to fossil fuels,
has plenty of positive factors. It is plentiful, clean, renewable,
widely distributed, and produces no greenhouse gas emissions during
operation. However, the construction of wind farms/turbines has been
frowned upon in some communities and areas, as it can have a large
visual impact aesthetically.
Yet, with some of the most viable
areas for wind farming out to sea (and thus more wind farms being built
at sea) this could be a small complaint of the future. Any effects on
the environment, nevertheless, are generally among the least problematic
of any power source, making it a favourite amongst the more
environmentally friendly.
Generating Electricity
In
a wind farm, individual turbines are interconnected with a medium
voltage, power collection system and communications network. At a
substation, this medium-voltage electric current is increased in voltage
with a transformer for connection to the high voltage electric power
transmission system.
In small scale wind energy generation, the
surplus power produced by domestic microgenerators can be fed into the
network and sold to the utility company, producing a retail credit for
the microgenerators’ owners to offset their energy costs. This works on a
retail credit system, the same as that used in small scale solar power
generation.
Grid management
Induction generators are often
used for wind power. These systems include substantial capacitor banks
for power factor correction. Different types of wind turbine generators
behave differently during transmission grid disturbances. However,
induction generators cannot support the system voltage during faults,
unlike steam or hydro turbine-driven synchronous generators, making this
a sight weakness of the system.
Capacity factor
Since
wind speed is not constant, a wind farm’s annual energy production is
never as much as the sum of the generator nameplate ratings multiplied
by the total hours in a year. The ratio of actual productivity in a year
to this theoretical maximum is called the capacity factor. Typical capacity factors are 20–40%, with values at the upper end of the range in particularly favourable sites.
The
inherent properties of wind limit the capacity factors, unlike fuelled
generating plants. Capacity factors of other types of power plant are
based mostly on fuel cost, with a small amount of downtime for
maintenance. Nuclear plants, for instance, have low incremental fuel
cost, and so are run at full output and achieve a 90% capacity factor.
Variability and intermittency
Electricity
generated from wind power can be highly variable at several different
timescales: from hour to hour, daily, and seasonally. Annual variation
also exists, but is not as significant. Related to variability is the
short-term (hourly or daily) predictability of wind plant output. Like
other electricity sources, wind energy must be “scheduled”.
Wind power forecasting methods are used, but predictability of wind plant output remains low for short-term operation.
Wind Turbines and Personal Usage
Wind turbine for home use |
Now
that the ins-and-outs of generating electricity using wind have been
covered, it’s time to take a look at the practicalities of using it on a
personal scale. To do this we have to look at what is called
Microgeneration. This is described as the small-scale generation of heat
and power by individuals, small businesses and communities to meet
their own needs, as alternatives or supplements to traditional
centralized grid-connected power. Although this may be motivated by
practical considerations (such as unreliable grid power or long distance
from the grid) it is primarily used to describe the
environmentally-conscious and their approaches to generating power that
aspire to zero or low-carbon footprints.
Additionally, studies
have backed-up the environmental impacts of wind power on a small-scale
in the UK. A new study by the Carbon Trust into the potential of
small-scale wind energy has found that small wind turbines could provide
up to 1.5 terawatt hours (tW/h) per year of electricity (0.4% of total
UK electricity consumption). This is saving 0.6 million tonnes of carbon
dioxide (Mt CO2) emission. (This data is based on the assumption that
10% of households would install turbines at costs competitive with grid
electricity, around 12p a kW/h). These figures show it not only makes
financial sense to make use of wind power, but makes a massive
difference environmentally.
Wind turbines have been used for
household electricity generation in conjunction with battery storage
over many decades in remote areas.
Small wind turbine - basic parts |
In
terms of the practicalities, turbines should be mounted on a suitable
tower to raise them above any nearby obstacles. Another approach to
positioning a small turbine is to use a ‘shelter model’ to predict how
nearby obstacles will affect local wind conditions. Models of this type
are general and can be applied to any site. They are often developed
based on actual wind measurements (obviously preferable) and can
estimate flow properties, such as mean wind speed and turbulence levels
at a potential turbine location. They do this by taking into account the
size, shape, and distance to any nearby obstacles.
A small wind
turbine can also be installed on a roof. But installation issues then
include the strength of the roof, vibration, and the turbulence caused
by the roof ledge. Small-scale rooftop turbines suffer from turbulence
and rarely generate significant amounts of power, especially in towns
and cities.
Also, in locations near or around a group of high-rise
buildings, wind shear generates areas of intense turbulence, especially
at street-level. The risks associated with mechanical or catastrophic
failure have thus plagued urban wind development in densely populated
areas, rendering the costs of insuring urban wind systems
prohibitive. Moreover, quantifying the amount of wind in urban areas has
been difficult, as little is known about the actual wind resources of
towns and cities.
Conclusion
So it seems that whilst wind
turbines seem like a great idea for urban personal renewable energy, it
may be best left to those in areas high above sea level, or in less
densely populated urban areas, and of course the most environmentally
conscious.
However, due to factors like; ease of installation,
benefits to the environment and ability (in the right conditions) to
easily (and effectively) produce electricity in many different
environments, wind power will continue to be a popular source of
personal renewable energy.
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