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Wind Power - there’s more to wind than you think
Committing to buy a wind turbine without monitoring the wind may give you a nasty shock both
environmentally and economically - the salesman's estimates of power generation can be far from reality.
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Anyone who has investigated fitting a wind turbine on their plot of land to take advantage of the
wind power available will no doubt have come across average wind speeds. If you haven’t then it’s
straight forward. Google average wind speed calculator for a site and type in your OS grid reference. You are then returned the average wind speed for your location. In my
case, and for this example, the average wind speed at 10 metres above ground level (agl) is 6.4m/s. If
you don’t know your OS grid reference, then there are sites that ask simply for your postcode.
Unfortunatley though, it would appear that average wind speed is the starting point of a great
deal of misunderstanding that is being promoted by renewable energy installers. I believe this
may turn out to be a serious case of mis-selling. As we delve deeper I am sure you will see why I have come to this conclusion.
Wind Power takes a bit of thinking about. A wind turbine doesn’t produce a steady amount of power. For this example, I have looked at the Evance R9000 wind turbine (previously known as Iskra). this is a 5kw wind turbine with some very impressive features. In fact, if I go ahead and install a wind turbine, then this would more than likely be the one for me. I am happy with what I have seen with the quality of the R9000, the power curve is good and its cut in speed where power is generated is a low, 3m/s. But this is where average wind speed and wind power can be deceptive. As I stated earlier, my average wind speed is 6.4m/s so, with that sort of wind power, the R9000 will produce around 1.250kw every hour or approximately 11,000kw every year. This is the sort of figure an installation company may give you, along with a neat set of calculations to show you how much money you are going to make thanks to feed in tariffs. The maths goes something like this
| Assumptions |
| The amount you pay for electricity | 0.10p/kWh (this does vary but seems reasonable) |
| % of power used you will generate yourself | 75% |
| Feed in tariff for small wind turbine | £0.267/kW |
| Payment for the power you don’t use | £0.03/kW |
| Annual electricity bill (based on my own) | £650 (6500kWh) |
| and the maths... |
| Annual saving on your electricity bill | £487.50 (75% of bill for electricity) |
| Annual income from feed in tariff | £2937.00 |
| Annual income from power sold to grid | £48.75 (25% of units sold to grid) |
| Annual revenue | £3473.25 |
Calculators on installers’ websites will work out not only these figures but also that you have a
payback in 7 or 8 years, and over the 20 years of the life of FITs you get back a whopping
£69,460. I have said it before, this sounds like a no brainer. If you left your money (£25,000)
in a savings account getting 2.5% for the next 20 years you would only get £41,000. Forget saving
the planet, this sounds like one serious earner. And, that for me is the big problem here, the
driver that is being used to get business is greed, not the environment. I understand the argument
that without incentive it won’t happen and it has created a situation where farmers and land
owners up and down the country are rubbing their hands together at all this easy money they are
going to make. But wait, This isn’t quite the ‘golden goose’ it first appears (unless you are
the installer). Let’s not forget what this article is all about, not a discussion on greed but a
look at average wind speed and it’s deceptiveness.
The R9000 wind turbine we mentioned earlier will generate almost nothing at 3m/s (6.72mph) but at
20m/s (45mph) it will pump out 5.235kWh. If you look at a power to wind speed chart you can see
that wind power doesn’t really do that much when it comes to generating electricity until the
speed gets up over 6m/s (13.5mph). The trouble with using average wind speed to estimate the
amount of electricity you will generate is that it doesn’t take into account that nothing is generated at low speeds and that the power curve of the wind turbine means to get the big numbers you need the big wind speeds.
A wide open aspect well towards the top of a mountain on the Welsh borders facing the prevailaing winds - surely this location would be ideal for a wind turbine - wrong!
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So how do we arrive at a realistic figure? Until there is enough mass of data to give a multiplying
factor that can be used (and this is one of realityGreen’s aims for the coming year), all you can
do is monitor your own site. This is essential as it is the only way you will know if installing a
wind turbine makes sense or not. That isn’t just financial sense but environmental sense as well.
After all, if a site is shown to produce so little power that the environmental impact of
manufacture, installing concrete bases, transport, installation etc is greater, then there really
is no justification. To find out just what’s happening, we monitored the wind for a six month
period from November to April. Wind speed readings were registered every 5 minutes so the amount
of actual wind power on any particular day was easy to work out. What the figures showed was quite
shocking. Rather than the 11,000kWh suggested by our average wind speed figure, we only would have
achieved 5,110kWh in a full year. That’s less than half. From the photo of the location you can
see its an open site with great exposure to the prevailing winds but even with these plus points,
the figure for actual power that would have been generated was less than half. I can only work on
the figures I have and intend to obtain data from other sites to see if this is repeated up an down
the country. If it is repeated, then I do feel with such a wide difference between the figures
being suggested by installation companies and what is actually achievable, then there could be a
serious case for mis-selling.
From an environmental standpoint, generating 5,110 kWh falls short of the 6500kWh target I have to
cover all my electrical power requirement. I was hoping the figure would be more than I require to
allow for the charging of an electric vehicle in the future. I could go for a larger wind turbine
but the figures get rather out of hand. After all, on the returns being offered you would not
cover repayments if you borrowed the money. Photovoltaics may be possible to make up the
shortfall. The challenge to achieve sustainable living will have to continue.
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.
A reader who wished to remain anonymous has passed on the foloowing figures from theri site. They
have had their wind turbine up and running ofr two years. and these are their generation figures:
Expected generation of 2500 and 5000 kWh per year at the average wind speed that
the government wind speed database predicted for their site - 10m agl = 5m/s [NB Wind Turbine is on 11m mast]
During 2008 - 1100 kWh generated
During 2009 - 1000 kWh generated
This is less than half the worst expectation.