Micro-wind turbines
Last updated: June 26, 2009.
If small is beautiful, micro-wind turbines—tiny
power generators perched on a roof or mast—should be the most attractive
form of renewable energy by far. Some manufacturers have pushed the
technology aggressively, hinting to consumers about big savings on
electricity bills and major benefits for the environment. The reality
is a little different: microturbines do indeed bring economic and
environmental benefits if they're sited in reliably windy areas, but
they're less helpful in towns and cities where buildings
make "energy harvesting" more of a challenge. So are micro-wind turbines
really worth the investment? How do they compare with their big brothers?
Let's take a closer look!
Photo: A micro-wind turbine in the process of being raised into position. The propeller part is at the front and the mast is stretching away into the distance behind it. Photo by Warren Gretz courtesy of US Department of Energy/NREL (DoE/NREL).
Power to the people
Photo: Micro power to the people! Now in position, the small mast-mounted wind turbine from our top photo can produce 900 watts of power with a wind speed of 45 km/h (28mph). Photo by Warren Gretz courtesy of US Department of Energy/NREL (DoE/NREL).
Our electricity infrastructure is remarkably centralized, with
huge power plants sending electricity vast distances across grid
networks to factories, offices, and homes. It sounds good in theory:
you don't have to worry about where your energy is coming from—just
plug in your TV, pay your bill, and you'll be fine.
Most people don't realize how wasteful this centralized system can be. Large power
plants (especially old ones fuelled by coal) can be hugely
inefficient. Energy is wasted both in the plants themselves and in
the process of sending their electricity down cable to
our homes; according to a Greenpeace report
(Decentralising power: an energy revolution for the 21st century),
about two thirds of the energy produced in the first place can be lost in this way. That's a very
serious problem if you bear in mind that the vast majority of our
energy currently comes come from a very limited reserve of fossil
fuels—and every ton of coal and liter of oil or gas we burn puts the
planet at greater risk of global warming and climate change.
Centralized systems, though proven to be extremely reliable
over many decades, also lock us into a dependence on foreign energy
(oil from the Middle East, gas from Russia, coal from Colombia, and so on).
Wouldn't it be great if we could produce all our own electricity
without worrying about energy prices, global warming, oil crises, and
the rest? In theory, that's exactly the promise that renewable
energy—wind turbines, solar power, and other technologies such as
heat pumps and tidal power—is offering us.
What are micro-wind turbines?
If you've ever seen a conventional wind turbine, you'll know it's a towering
beast of a machine. A typical turbine is about 80m (260ft) high with rotor
blades about 70m (230ft) across. Imagine 40 adults standing on top of
one another and you can visualize the height; now picture them
standing with their arms outstretched in a line, all touching, and
you can visualize the rotor span as well. One single wind turbine makes
about 2-3 megawatts (MW) of electricity, which is enough to supply
about 1000-1500 homes. You need about 1000 turbines like this to
generate as much electricity as a big nuclear or coal-fired power
plant. That's why wind turbines are often built in clusters called wind farms.
Single wind turbines are effectively mini power plants that
supply whole communities. So, what we achieve by erecting a large
wind turbine is to scale down and decentralize the process of power
generation from the city or town to the community level. But why not
take that a step further? Instead of having one big wind turbine to
supply 1000 homes, why not give each home its own small wind turbine
and let it make its own power? That's the basic idea of micro-wind
turbines—scaled down versions of the towering turbines in wind farms.
How to set up your own micro-wind turbine
If you want to build your own micro-wind turbine, what do you need?
Apart from the turbine itself, you also typically need a piece
of electrical equipment called an inverter (which converts the
direct-current electricity produced by the turbine's generator into
alternating current you can use in your home) and appropriate
electrical cabling. Your turbine will also need either a connection
into the grid supply or batteries to store the energy it produces.
Photo: What else do you need? Here are the batteries, inverter, and control electronics for a micro-wind turbine. Photo by Warren Gretz courtesy of US Department of Energy/NREL (DoE/NREL).
Aside from the equipment, here are a few pointers worth bearing in mind:
- The best place to start is with a professional assessment of
your site's wind potential, which involves a series of measurements
with an anemometer. Remember that wind turbines generally work far better in
open, rural areas than mounted on rooftops in cities.
- Don't assume it will automatically be windy enough to make
the investment in a microturbine worthwhile: a recent UK study of
microturbines by Encraft found a mixed picture, with good
performance from the best-located turbines and the very worst
performing model (embarrassingly) not even producing enough
electricity to power its own electronics—in other words, using more
electricity overall than it produced. Some contribution to the environment!
- Depending on where you live, you will almost certainly need
planning consent for a wind turbine, so check that out carefully with your
local authority first.
- Sound out your neighbors before you start spending any money:
maybe you could persuade them to join you in a community green-energy venture?
- Remember that roof-mounted wind turbines could prove noisy
and cause problems with vibration.
- Don't forget that there are all kinds of other energy
technologies that might give a quicker and better return on your
investment and make more difference to the planet. Energy efficiency
measures (such as improved heat insulation) generally give the
quickest payback for least cost and make the most difference in the
short-term, and solar hot water systems work very well
almost anywhere.
Further reading
