Choosing and Siting a Turbine 

Choosing the right turbine for your needs can be a daunting task.  Not only are there different makes to consider, each manufacturer may have a range of sizes!  How do you decide which one is best for you?

Energy Yield

The first step we would always suggest is to analyse you present energy consumption.  Dig out your last years worth of electricity bills (more if you have them) and work out your average annual electricity consumption.  Your electricity bill will show kWh or units of electricity, often at different charging rates, especially if you have an off peak tariff, storage heaters, "White Meter", "Economy 7", etc. 

A turbine is ideally suited to displace the expensive rate electricity, that is the electricity used for lighting, sockets, cooking etc.  Once you have worked this out, you need to decide at some point in the process if you need a turbine that will meet all your annual demand, just part of it, or an excess that can be sold to the grid.

Next, you need to determine what the windspeed is at your site.  To do this properly requires erecting a mast with an anemometer, ideally for a year or more.  This can be expensive, and a delay you perhaps don't want before you get your turbine up and running!  An alternative is to estimate the windspeed at your site using the NOABL database.  This gives estimated windspeed at 10, 25 and 45m above ground level for each of the 1 km squares on the UK Ordnance Survey mapping.  Whilst only an estimate, this is a useful tool to help assess your site.  We recommend you access the database through the BWEA Website NOABL page and read up the notes on assessing wind speed before trying to put in your co-ordinates!

Once you have an estimated wind speed, and idea of how much of an impact you want to make on your electricity bill, you can see how the different turbine makes and models will produce in your estimated windspeed.  One easy way to do this is to use Eoltecs power estimating spreadsheet.  This is Microsoft Excel based and you can download this for their 6 kW Scirocco, or if you need a larger turbine for a commercial or community project, their 25 kW Windrunner  

We also recommend that you look at actual production which other owners are getting, as there can be inaccuracies in using the NOABL model, especially if you have a lot of trees or other obstructions around your proposed site.  One place to look for real life data from other turbine owners is on the renew-reuse-recycle.com website, where the turbine owners have been logging their monthly production data for a range of different turbines in a variety of windspeeds.  A graph of relative production figures is shown here.

Now you should have an idea how big a turbine you need, and how much energy it is likely to produce!  Don't worry that the power rating might seem low.  Some people have said to us that a 2.5 kW turbine would never do them, as their kettle alone is 3 kW!  But bear in mind that the turbine will run for 24 hours a day, and the kettle only needs a few minutes to boil!  At times of higher demand, the grid will make up the shortfall!

As a rough rule of thumb, a 2.5 kW turbine in a good windspeed site will capture enough energy to meet the annual electricity demand of a typical house, whilst a 6 kW turbine will generate enough energy to do the heating as well.  However, if your windspeed is not so good, you might need a 6 kW turbine just to meet the annual demand for the non heating electricity.

You can also estimate the amount of energy produced by multiplying the turbine rating (in kW) by 24 hours in a day, 365 days in a year, and the Capacity Factor.  Capacity factor is a measure of how productive the wind turbine will be on your site.  A very good site (like Orkney!) might have a capacity factor of 50%, whilst a poor site only 10%.  If the Capacity Factor was 30 for a 5 kW turbine, the annual energy yield would be

5 x 0.3 x 24 hours x 365 days = 13,140kWh per year.  

This is also a good time to assess your overall energy efficiency.  Visit the Energy Savings Trust's website for hints and tips on reducing your energy demand and making your home or business more energy efficient.

The turbines that we supply vary in size ranging from 2.5kW to provide power for an average household, to 250kW turbine for larger community scale projects, schools or business premises.

Choosing a turbine very much depends on what you want the turbine to provide power for and on your budget, however there may be a grant from a funding stream to assist you in financing your wind turbine.

Funding and Grants.

It’s important to remember that costs always vary depending on location and the size and type of system. Turbines can have a life of up to 20 years but will require regular servicing and maintenance checks to ensure they continue to work efficiently.

Financial Examples.

Technical Considerations

OK, so you have determined you need a 6 kW turbine - But there are loads of manufacturers out there saying their 6 kW turbine is the best!  How can you cut through all that, and find the best turbine?  Well, follow our technical guide below, based on many years of installing many different kinds....

The best turbines have the following features - Put all of the below points to your turbine supplier and check their responses.   If they don't know, or give you some other answer, be worried!

•  Designed and built of IEC Class 1 rating - This means the turbine can cope with the most extreme wind conditions.
• Do not require any intervention in either strong winds or loss of grid conditions.  Can you assure yourself that you will have the time, or even be home, to take down a cheap turbine that says in the manual "Lower to the ground if strong winds are forecast"?  What if the grid fails at 4 am on a windy night when you are asleep?  The only solution is a turbine that can completely look after itself in any wind or load conditions.
• Upwind design.  This is where the blades are on the windward side of the tower.  Have you ever seen a windfarm scale turbine where the blades are downwind of the tower?  If not, ask yourself why....  Perhaps it is something to do with the effects of the blades passing by the wake of the tower?
  
• Sychronised blade pitch - All windfarm scale turbines have pitch synchronised to within a fraction of a degree.  Pitch mismatches bring significant loss of production and stresses on turbines.  Check that your proposed turbine has a reliable means of synchronising blades to each other, by means of a solid interconnection.
• Inherent overspeed protection - Any turbine needs to have overspeed protection built in to ensure safety.  Only the best and safest turbines have a mechanism where speed is controlled directly at the turbine head.  If a turbine depends on load to keep speed under control, what happens if the load is lost as can happen in any of the following scenarios....
• Generator burn out (common on cheap turbines, especially when it gets windy!)
• Loss of connection between turbine head and load in house
• Slipring failure
• Grid failure (in grid connected turbines)
  
• Load burn out (common with cheap turbines where the diversion load is unable to cope with sustained high production)
• Operation of circuit or thermal protection - i.e. operation of a fuse or circuit breaker, or thermal overload of diversion load - If your supplier suggest installing a divert load without electrical safety protection or overtemperature protection, ask why!
• Inherent overvoltage control.  Some turbines with poor speed control produce excessive voltage when offloaded, and depend on divert loads to try and keep the output voltage within an acceptable tolerance.  Without these, inverters can have their DC inputs overloaded, resulting in spectacular damage (Guy Fawkes would have been proud!) If your chosen turbine depends on a divert load to keep the voltage within safe limits, what happens if that divert load fails, electrical protection operates or it gets too hot?  Insist only on turbines where if everything fails, the voltage coming into the house is maintained within safe limits, automatically and inherently by the turbine regulating its speed.
• Marine grade corrosion protection.  Insist only on turbines that utilise substantial non corrosive materials such as fibreglass, stainless steel, aluminium alloy (marine grade non corrosive types) and hot dipped galvanised steel.  Ask your supplier if any parts of their turbine are simply painted steel, and if so, avoid!  The best turbines have all working parts fully sealed from the elements.  This is essential in marine environment.  With some turbines, all the "workings" are either exposed directly yo the elements, or allow salt air to pass through them, with obvious effects on corrosion and reliability.  Insist on turbines where all components are within sealed enclosures, with only the bare minimum of moving components (i.e. blades!) exposed.  Beware of turbines that only have flimsy plastic covers over key components, which do nothing to exclude salt air.
• Substantial fixings and fixtures.  Some turbines are merely held together with cable ties.  What would you trust in a high wind environment?  Cable ties or nuts and bolts?
• Effective braking system.  Check your proposed turbine has the minimum of moving parts in the brake system, and that they are all protected from corrosion.  A turbine brake is perhaps only used once a year during servicing, and is no use if it seizes up before then.  The best braking systems are aerodynamic / electric as they have no wearing parts like brake pads or discs, and no parts to seize up.
  
• An extensive track record in a high wind environment.  We have seen many "guinea pigs" over the years, who have found that being the first to install a turbine in a good wind site, leads to problems that those in low wind speed sites have yet to experience.  Save yourself the grief, and ask your installer for reference sites in winds at least as good as your site.  Check the wind data for where your turbine was tested in.  If your proposed turbine was tested in winds lower than those on your site, would you be comfortable?
  

Siting and planning considerations

The optimum site for a wind turbine is a smooth-top hill with a flat, clear exposure, free from excessive turbulence and obstructions such as trees, houses or other buildings. However, other areas may have a sufficient wind resource to make an installation worthwhile.

Wind speed increases with height so it is best to have the turbine high on a mast or tower. 

Planning issues such as visual impact, noise and conservation issues also have to be considered. System installation normally requires permission from the local authority. Normally, we would recommend that you consider siting your turbine at least 20 rotor diameters (blade tip to blade tip) away from the nearest third part property.  Less than this may be problematic at the planning stage.  More than 20 or even 30 rotor diameters is much more likely to be viewed favourably.  For a 6 kW Eoltec Scirocco turbine, this equates to 112m, although 150m would be preferable.  In any case, one of the over-riding factors is making sure that the turbine can perform well by escaping the effects of building turbulence.  Any turbulence will reduce yield, and siting a turbine 150m away from buildings minimises the losses that will arise from this turbulence.

We would advise that you seek the advice on planning permission from your local authority at an early stage.

Grid connected Wind turbines

During periods of windy weather you might produce more power than you are using. Power generated by a grid-tie turbine can be exported into the grid when it is not required; therefore the power is never wasted.   It also means you don't need any changeover switches to switch back to the grid in times of light winds.  The changeover happens seamlessly and automatically.

No battery storage is required. A special inverter and controller converts raw power output by the wind turbine, DC electricity, to AC at a quality and standard that is acceptable to the national grid and is fed directly into the house or business fuse board.

Any unused or excess electricity that is exported to the national grid can be sold to the local electricity companies generating an income. A connection agreement is required with the electricity company.

On the other hand if you are using more than the turbine is producing at any particular instant, or if there is not enough wind, the electricity flows from the National Grid connection and is drawn from the grid as normal, switching back again automatically when the wind speed resumes.

Grid connect systems are cheaper and require less space and a bit less maintenance than battery systems.  They are also easier to sell the Renewable Obligation Certificates from.

Stand alone / Off grid turbines

Wind turbines are particularly suitable for remote locations that aren’t connected to the national grid (off-grid) where conventional methods of energy supply are expensive or impractical.

Designed to operate where there is no mains supply, an off grid wind turbine together with a battery / inverter system, to convert DC electricity to AC (alternating current -mains electricity), provides a renewable energy system where it is possible to have a continuous reliable source of power at 240 volts AC. 

The size of the battery bank determines the time appliances can be run if there is no wind. The size of the inverter installed determines the number of appliances that can be run at the same time from the stored electricity.

A controller is also required to ensure the batteries are not over or under-charged and can divert power to provide heating through storage heaters or hot water radiators.

It is common to combine this system with a diesel generator for use during periods of low wind speeds. A combined wind and diesel system gives greater efficiency and flexibility than a diesel-only system. It allows the generator to be used at optimum load for short periods of time to charge batteries when there is little wind, rather than by constant use at varying loads.  

An off grid system is not normally recommended when the grid is available.  The grid provides an excellent back up supply for times of no wind, and is like a huge battery!  You can sell surplus electricity into it, and buy it back when you are short!  And unlike most batteries, the grid doesn't need replacing after 10 years!

Direct Heating turbines

One of the largest costs to households or buildings is heating. At night or anytime that not all the power from a turbine is needed, the excess can be "charging up" storage radiators or heating up a water tank to supply a conventional central heating system.

If no suitable electric heating system is already installed, then this may also be required, which may make the entire project more expensive than a grid connect.  The Eoltec Scirocco direct heating system is unique amongst small wind turbines in that it can fully comply with the requirements of OFGEM approved metering, and is therefore eligible for ROC's / Feed in Tariffs.

If after reading all this, you are still uncertain what size or type of turbine you need, please call us and we'll help you decide!  

Return to the Wind Turbines Page

This page was last updated on 9/11/2009