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designed for those aiming for modern but sustainable living.
Here you will find articles and links looking at both the environmental and economic benefits of
systems and equipment available to those wanting to embrace sustainable living.
If you are interested in individual sustainable projects, then the links to
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Wind Turbines - selecting the right model
All wind turbine manufacturers will supply wind power data in the form of a
table, a power curve or both. Only by matching this data to your wind data will you have a
realistic idea of how much electricity you will generate.
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If you think wind power may be part of the solution for your energy needs then
there are number of questions you need to ask. How strong is the wind at your
location? How much power do you want to generate? What size and model wind
turbine do you go for? To answer the first question, the only way to know how
much wind you have is to monitor it. We have an article about
the importance of
wind monitoring that you may want to read here. The second point will depend on your
intentions. If your aim is simply to cover your own personal consumption,
thereby achieving personal sustainability and a zero carbon footprint for
electricity, then it’s simply a matter of totting up your last year’s energy
bills to see how much you use. I live in a four bedroomed house and we use
around 6,500kWh each year. The average house figure seems to range from 3,000kWh
upwards depending on whose figures you are looking at, so the only real answer
is to check what you are actually using. That brings us to the third question.
What size and model wind turbine should you have. The easy answer is one, that
based on your wind monitoring data will generate enough over the year to cover
your annual requirement (if personal sustainability is your goal).
Unfortunately things are never this straight forward. There is a plethora of machinery coming
into the market with fittings and features claiming to be better than the next
wind turbine. In this article we will try and look over the key aspects of a
wind turbine so at least we know the criteria we need to fill. The first point
is size. Assuming you are grid connected and you can take advantage of feed in
tariffs, then you might be tempted to go bigger than you need in the hope of not
only putting a big tick on your chart for sustainable living, but also making a
few quid along the way. My only comment on this is that feed in tariffs (FiTs)
rely on governments who can change there minds at a moment’s notice. Spending
more than you need in the belief that governments are honourable is a risky
business, but then maybe I’m just cynical. FiTs will take you up to a 50kWh wind
turbine so there is plenty of scope. A friend was looking at installing a 50kWh
wind turbine but after serious thought (this was going to be in excess of
£300,000) he settled on an 11kw Gaia turbine. This should still produce far more
than his personal requirement and give him a financial bonus. I remain to be
convinced but will monitor his data and update readers when it is available.
Once you have decided roughly the size you require, then it’s a matter of
sifting through the sales blurb and analysing the important points.
Evance's 5kW R9000 is one of the new breed of small wind generators susitable for domestic, agricultural and light commercial use.
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For me, the most important piece of information is the performance data as this shows how
much energy you will produce. If you have monitored the wind for a reasonable
period (at least 3 months, preferably 6 months to a year) you can use the performance data
to see how much power you would generate in your particular location from a particular wind turbine. As an
example, a 5kWh Avance wind turbine would give you 4739kWh in a year for an
average wind speed of 4m/s (9mph), 8780kWh at 5m/s (11mph) and 13186kWh at 6m/s
(13.5mph). I hope you can see the significance of small increases in wind speed from these
figures. For this reason it is essential that you monitor the speeds at your site - don't just
accept the government's wind speed figure for your grid reference - it can sometimes be rather innaccurate
for a particular site. That takes us to another crucial piece of information, the cut-in wind
speed. This is the speed where you start generating power. Staying with the
Evance wind turbine, the figure is 3m/s (6.75mph). Very little is generated at
this speed, just 14 watts an hour but from this point any increase in wind speed
will cause a large increase in power generated. For the technical types, the
available energy from the moving air molecules is proportional to the cube of
their speed. What this highlights is how misleading the rated power figure is.
For the Evance the rated power is 5kW @12m/s (26.8mph). As we don’t often get
that sort of wind speed, the 5kw is simply an arbitary figure. If you look at
the 11kW Gaia then the 11kWh is produced at 9.5kWh (21mph) with a cut-in speed
of 3.5m/s (7.8mph). I don’t want to get bogged down in figures here but
hopefully this demonstrates that you really do need to look at the power figures for individual wind turbines
and match them to your wind data. This is the only way you can compare how much
power you can generate from the different wind turbines. For example, you might assume
that a 5kW wind turbine will not produce as much as a 6kWh model but when you
analyse the date this isn’t always so.
So, now we know how much power the turbines can produce, it’s a matter of looking at other issues. Build quality
and the technology used is important but extremely hard to judge. Many of the
manufacturers claim a variety of special design features but provided the unit
is built well, is robust enough for the harsh life it’s going to take, and will
produce the power you require, then it comes down to cost and warranty. Many
offer a 5 year warranty which does give a level of comfort. On the cost side,
you will often be quoted without VAT or without foundation costs, so a £25,000
estimate can easily end up at £30,000 - be aware! Another cost to look at is
maintenance. Are there wear parts that will need replacing, does the unit
require an annual service etc? As an example, the new Nova-Wind 6kW wind turbine
requires a service after 2.5 years and then every 2.5 years. All these costs
need to taken into account. The final point on cost is that there are plenty of
installers out there so shop around. These are high cost items and savings can
be in £1,000’s.
Another aspect to consider is the rapid growth in vertical
turbines. These tend to be quieter and some feel more aesthetically pleasing
where complaints are involved. They are priced similarly to horizontal axis
machines but looking at the power curves they don’t appear to give quite the
performance. Analysis of these two turbine types will be the topic of a future article.
Getting access to the wind turbine for maintenance is an important consideration. Turbine towers that are lifted/lowered using an hydraulic ram makes the job easy.
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The last piece of the jigsaw is the tower. These come in various
heights and guises and your site may govern the type of stand you have. For
example a guyed tower may not be practical if you haven’t the space for the
guys. The important point about your tower is that you must consider
maintenance. For a small wind turbine it is important to be able to lower it to
the ground. A free standing pole may look neat but if you need a platform to
maintain it then its beauty soon wanes. Poles fitted with an hydraulic ram are
becoming popular, not requiring the space of a guyed tower and having the neat
look of a free standing pole.
Tower height is also of the utmost importance. An extra few metres on your tower can make the difference between generating the
amount of power you need and bitter disappointment. If you want to explore how
height above the ground and surface texture effects wind speed then
this site
is very handy. Don’t forget, the wind power increase will be far greater than the wind speed
increase.
Hopefully you feel a little more confident in selecting a wind turbine
now. A great place to start your hunt for the turbine that suits your situation is
the microgeneration certification site.
Want to comment or have something to add regarding wind power?
Then email with your views. Shortly we shall be introducing a comment box directly under each article. Until then, please email and we shall add your comments.