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Friday, 27 January 2012

Small Scale Wind Power

There is a ‘Windy City’ (Chicago), the ‘Windy Isle’ (Fuerteventura), and from own experience I can vouch for the fact that there is nothing much to the west of New Zealand that would slow down a breeze. Antarctica takes some beating, though. Officially the coldest and driest place on Earth it is also the windiest. Some regions experience an average speed of 40 miles per hour (64km/h) over the year. Imagine the wind chill factor with even summer temperatures struggling to reach a not so balmy 20o Fahrenheit (-6.7o Celsius).

Moving air is a steady feature on our planet, which is why it has been used to generate electricity since the late 19th century. Despite this wind power remained a niche, mainly used on boats to recharge batteries. As a serious contender in the clean-green-energy stakes it has become a main force only over the past 20 to 25 years but goodness me it has made its mark.

RenewableUK , the British trade association for the wind, wave & tidal industry, reported that in December 2011 a peak coverage was achieved of 12.2% of the electricity demand in the country. Large potential for expanding current capacities has been proclaimed the world over, from America and Europe to Mexico and India.

A Power Station in the Garden

Is Wind Power Right for Me?

Wind’s greatest advantages are that it is ubiquitous, emission free and comes without cost to the user. On the negative side is the fact that it doesn’t blow with consistency. Therefore, output varies and sometimes disappears altogether. Battery banks can help to even out the peaks and troughs or supplement power when the turbine is not working.

Whether it is right for you or not depends on your attitude and the conditions of the site where you want to place it. Your viewpoint is important because you need to know what you want to get out of it. Go for it if you are happy with the thought that some carbon-free power is better than nothing and that it doesn’t have to earn its setting-up and maintenance costs within a flash.

Size Matters

The portion of electricity consumption that a small scale wind installation can cover is subject to your habits, where you live and the size of your machinery. Below are some examples for average household usage and the percentage of it that can be generated by wind.

1.5 kW Turbine cover of household consumption

If that is not enough it is tempting to think ‘Oh, I just get a bigger one with the added advantage of scaring the life out my neighbours’. However, wind turbines are under the strict hands of the laws of physics. An increase in size means both the rotor blades and the pylon. It is true, that raises indeed the output exponentially. Double the swept area, in other words what the blades cover when going around in a circle, and the power rises fourfold. Only, even those that RenewableUK calls micro systems tower above the average residential area at a height of 8 – 10 meters (26 – 33 feet). Their nominal power is up to 1.5 kW, which translates into a yearly total of about 3200 kilowatt hours (kWh). Really small ones with rotor diameters of a couple of meters manage about 1000 kWh per year.

If you own land or consider an installation for a commercial setting like a farm it could provide the conditions for going up in scale. Small wind turbines (another misnomer) generate between 1.5 and 15 kW for a total of 3200 to 50000 kWh per year. However, that will mean at the upper end of that range the tips of the rotor blades will touch 50 m easily.

Sorry, But Where Am I Going to Put This?

Of course the most willing mind-set counts for nothing if everything else does not fit. As you can see, the size alone is a limiting – or at the very least decisive – factor.

Also, wind is rather fickle. Not only does it come and go as it pleases, it lets itself being distracted by all manners of obstructions, for example buildings, trees, hills, etc. These cause turbulence or slower speeds that influence the efficiency considerably. This can be so bad that it makes an installation unviable. Coming back to the mathematics of it all, because air velocity goes into the formula cubed power output goes up by a factor of eight if the wind speed doubles. Turn that around and it means that very little is left at low speeds. Simply put if velocity falls by half power will only be an eighth of what it was before.

Generally, manufacturers give a required minimum average wind speed over the year of 4.5 – 6 meters per second (m/s). It is, therefore, a vital component of the planning stages to measure this over a period of time. There are some wind speed calculators on the web that work on the basis of location, but in the end these can only be good guesses. Because an accurate representation of the conditions is central to the whole project it is advisable to make the effort and get proper measurements. Once you have chosen a prospective supplier they are normally very supportive in this regard and also have the right equipment.

The general idea is to find a position that is as exposed and/or high up as possible. That is why offshore and mountains are so popular.

In the Eyes of the Law

Picking up on something I said earlier let’s hope you have not just chosen the site well but your neighbours too. In many countries a planning permission will be required for all but the tiniest systems. Instead of causing them a heart attack with a turbine the size of the Eiffel Tower you might rather want to invite those living next to you around for tea and cakes. They could be the force you have not reckoned with that will tip the scales in your favour - or not.

Thankfully, renewable energy projects on a smaller scale are widely encouraged now. The regulatory powers are actually often on your side with accreditation schemes such as the Microgeneration Certification Scheme in Britain  (see also MCS – Does it Matter?)  or the Small Wind Certification Council in America.

It helps to include as much detailed information as possible. For example:

  • Photos of the site
  • Photos of the turbine/s
  • Technical details of the installation, including noise levels
    • The latter has been a concern and complaint often cited in the past but turbines have become much quieter than they used to be
  • Distance from buildings, dwellings, neighbours, etc.

Once again, an accredited and experienced installer will have it in his own interest to guide and help you at every step. One other important consideration is the connection should you produce enough energy to sell any surplus on to the grid. Speak to the relevant authorities and suppliers at the earliest opportunity.

What’s Available?

A wind turbine consists of various parts that do not change dramatically from type to type. There are the rotors that convert wind into movement. Behind the rotor assembly is the nacelle with a gearbox and a generator. The gearbox increases the slow speed of the blades into higher speeds for the generator. In addition you would find an inverter for changing direct current (DC) to alternating current (AC) and electronics that make sure the power generated is suitable for use or the grid. Of course, there is also the shaft holding everything up.

Horizontal and Vertical

Wind Turbine - Horizontal Axis 240pxApart from these components there are two main types. The one you will be most familiar with is the horizontal axis turbine. It is well developed but needs to be pointed into the  wind. For very small models a simple vane does the trick. In larger applications sensors and a motor take over that job. However, most of them need to be started, as wind cannot provide the initial power required to get the moving parts going.

Wind Turbine - Vertical Axis 240px

 

 

 

 

 

 

 

 

Slightly more unusual is the vertical axis turbine. It has the huge advantage that it does not need to be turned into the wind and some of them are self-starting. In addition, because all the major parts can be placed at ground level with the axis of rotation being in line with the shaft it makes maintenance easier. Problems can be caused by higher and less even loads on the drive train, although the latest versions have addressed this to a degree.

Both kinds are available for small scale applications. As they have their individual pros and cons it will depend on your site and personal preference which one you will choose. Sometimes vertical axis turbines are said to be better for domestic or small commercial operations because they can work with lower wind speeds and are self-starting. Demonstration runs I have seen seemed to confirm that. Whether it would stand up in a real life situation I cannot say.

Roof-top Installations

If you are thinking of the top of your roof as the best place for a turbine because it looks so exposed and there is no space elsewhere I am afraid the prognosis is not good. So far these installations have delivered disappointing results compared to ground based systems (see, for example, the Warwick Wind Trials. This was generally a consequence of buildings being surrounded by other buildings, trees, pylons, etc., which all interrupt the air flow. This would be different if a property were standing more isolated from these obstacles, but in such cases there often will be sufficient space to construct a ground-based turbine without the added complications of having to integrate it into the roof structure.

The Financial Side of Wind Turbines

And now you will want to know how much it all costs. The answer is, of course: ‘It depends’. For a start components such as labour and transport vary from country to country, not to mention the actual purchase price with a rising number of cheaper imports from China.

I am sorry I am unable to narrow it down further but installation costs per kW vary from £2000 – £5000, €2000 - €10000 or $3500 - $6000. As so often, economies of scale mean the higher you go in capacity the cheaper it will become relative to output.

What you have to take into account as well are

  • Site preparation
  • Planning application
  • Creating access
  • Connection (to buildings, storage or grid)
  • Maintenance
    • Checks
    • Overhauling or replacing inverters
    • Replacing batteries
    • Parts and labour

Payback

However, there are not just expenses. Depending on where you live there might be incentives such as the Feed-in-Tariff in the UK. Similar schemes exist in Germany, France and some American states. Most importantly, your requirement for power from a utility supplier drops and with it the payments to them.

If you are really courageous you can even build your own. Hugh Piggott has written a number of books about it and assembled all the necessary information on his website.

How Does the Wind Blow?

All in all, small scale wind generation has its uses where the conditions are right. On the other hand we have not even begun to approach its full potential. Interest is growing and that is very encouraging. It takes its rightful place among other renewables like anaerobic digestion or photovoltaic panels that can be brought into a domestic or small commercial setting.

 

See you next week

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