Introduction To Wind Turbines

    Renewables

What are wind turbines?

Windmills (now in the form of wind turbines) have been used for millennia to convert the wind’s kinetic energy into mechanical energy. As early as 200 B.C., mechanical energy was used for specific tasks including grinding grain and pumping water. Nowadays, wind turbines harness kinetic energy from the air and convert it into electricity via a generator.

Much like solar PV installations, you can purchase a domestic wind turbine to supply as much or as little electricity as you want. If you are hoping to limit your dependence on the mains as much as possible, you will need a larger turbine, or multiple smaller turbines. If you are simply looking to produce enough electricity for a light in your garden shed, you can get away with a very small turbine.

Below we look at the different types of wind turbine system you can install in your property.

Battery-less grid tied systems

Battery-less grid tied systems are the simplest, most effective and most environmentally-friendly wind turbine systems. Their role is simple: to produce the most electricity possible to provide electricity for your home and also feed into the grid. Due to the availability of grants such as the feed-in tariffs in the UK, this type of system has grown enormously in popularity in recent years. In these installations, the home owner can effectively sell the surplus energy back to the utility company. There are no batteries in the system, so this removes a lot of the system complication and maintenance. The lack of batteries also makes it cheaper to install.

If your aim is to become completely unreliant on the grid, then you need to ensure the electricity produced by your battery-less grid tied system is in excess of your total electricity usage for the year. However, this system should suit most budgets, because it will reduce reliance on the energy companies, by significantly reducing your bills. If you cannot produce all your electricity, the shortfall is simply made up with electricity from the grid.

There is one major drawback with this setup, and that is that if there is a electrical power cut then you will have no power for your home, because the inverter your energy goes through is connected to mains power, so you may require a generator (powered by diesel or oil) as a back-up policy.

Grid-tied system with battery backup

This is essentially the same as the grid-tied system above, but has a bank of batteries which means that if there is a grid power cut, the inverter can still get the electricity it requires to operate, so the installation will keep providing you with electricity. The constraints of this system are primarily associated with the batteries, which are expensive and require regular maintenance. Finally, add extra inefficiency into the system (ranging from 5 – 40%) and this is added to the constraint side.

Off-grid systems

This system has no connection at all to the grid, relying instead on batteries to operate if no wind is blowing. However if the capacity of these batteries is too low, then you could be without any power for a prolonged period of time. Having a system off-grid presents an ideal situation as you become completely independent from the grid, and you produce all the electricity you need. However, this type of system tends to be the most expensive and also is maintenance-heavy. If you have a garden shed that needs lighting then this system can work out relatively cheaply, but as soon as you are looking to upscale then it becomes very expensive.

In the next section we look at the components that you need for a successful wind turbine installation.

Benefits

Limitations

Cost

 

    Maximising Wind Turbine Return

    Renewables

Maximising wind turbine returns

To maximise the electricity contribution that a wind turbine can provide you with, two interlinked questions need to be considered:

How much electricity do you need your turbine to produce?

You first you need to decide exactly what you are trying to achieve by installing a wind turbine on your property. Are you trying to become completely independent from the grid? Are you simply trying to decrease you electricity bills having received a capital lump sum that you can invest? Do you simply want a wind turbine to power a light in your garden shed? Obviously the larger the turbine, the more electricity it will produce; however larger turbines will be more costly.

By looking at utility bills from previous quarters, you can get a feel for your total electricity usage over a year. You can get more accurate readings if you go around your property and complete an energy assessment of your current load (simply the total energy that each appliance in your house uses over a certain period of time). This involves producing a table with each appliance, its draw in watts (measured using a watt plug in meter – sometimes known as a wattmeter), and the estimated time of use in a 24 hour cycle. With all this information you can complete a much more accurate total yearly assessment of usage of your house (by multiplying usage for a 24 hour cycle by 365 days).

Having a feel for your total energy usage should help you decide what you are trying to achieve with your turbine. There are several wind turbine setups which we have described in more detail below.

How much electricity can your system produce?

It is really important that you have a target electricity figure in your mind that you are aiming to achieve, be it 50% of your total energy requirements, or becoming fully self sufficient. However, this may not be possible if there are constraints on your property, such as lack of space or low average wind speed.

Wind speed

This is the key factor and we usually use average wind speed as the measurement for your particular location. You cannot directly affect the average wind speed at your home; however your choice of site and tower height can have a dramatic impact on the wind resource. The power available for the wind that is blowing is the cube of the wind speed – this is absolutely fundamental, and this can be seen in the simple sums below:

This is excellent news, as the further you get away from the surface of the earth and its many obstructions (e.g. houses), the higher the wind speed: therefore the more power in the wind. This means it is important to try and maximise the height of any tower you use, to try to maximise the wind potential of your wind turbine system.

Swept area

The swept area is the circle that the turbine produces when spinning, so this is the diameter of the blades. The blades are driven by the power in the wind, so the larger your swept area, the more energy you can harness. Again the easiest way to illustrate this is with some more simple sums (apologies for those adverse to maths!), where the area of a circle is half the diameter2 x π. (π = 3.14)

Taking into account these two factors, you can see the maximum electricity you can produce. Remember that wind speed is free (although towers obviously cost more money the higher they are), while investing in bigger and bigger turbines gets more expensive.

What size turbine should you be looking at?

The size of your wind turbine is therefore determined by the amount of electricity you are looking to produce (but potentially constrained by windspeed and space), and secondly the amount of cash you have available.

Unlike solar photovoltaic cells that can be added to fairly easily as additional funds become available, the turbine blades would need to be replaced, and potentially the generator changed if you want to produce more power in the future. Home scale generators normally are between 8 and 25 feet in diameter (so a swept area of between 50 – 500 feet2). If you have an average wind speed of 10 mph, these could produce between 1,000 and 15,000 kWh. An average house uses approximately 4,800 kWh per year, so a 25 foot diameter turbine is going to produce a serious excess of power to sell back to the grid, or power more than one house.

Final thoughts on wind turbines

Planning permission

Contact your local council to ask about planning permission if you’re considering installing a wind turbine. The majority of local authorities are keen to encourage the installation of renewable energy systems. However it is a good idea to consult your neighbours before investing time and money into the planning phase, to allow them to voice any objections.

Average wind speed

Before you even consider investing in a wind turbine, you need to check your average wind speed. The Carbon Trust have created a tool that allows you to estimate the wind yield at your home location. You are looking for an average wind speed in excess of 5m/s. By providing simple information regarding your location and type of turbine, the tool will give you average wind speed and potential energy output.

Subsidies

In the UK, as a wind turbine owner you can benefit from the Feed-in tariffs. There are different allowances depending on the power output of your equipment. Wind turbines above 5MW are classified as commercial and alternatively benefit from the Renewable Obligation Certificates. The Feed-in tariffs basically provide you with a source of income for every kWh of electricity you produce. This is independent from any excess electricity you sell back to the grid, which you further benefit from in the form of the export tariff. This can really help a wind turbine become an economically viable system to put into your house.

    Wind Turbine Components

    Renewables

How does a wind turbine work?

When air hits the wind turbine, the blades spin, converting the wind’s kinetic energy into mechanical energy. This rotary motion then travels down the shaft and drives a generator where the electricity is produced. Typically most wind turbines are mounted in the horizontal plane (like the propeller of a plane), and therefore it is key the blades are facing directly into the wind.

The yaw angle is the difference in angle between the wind direction and the direction in which the rotors are facing. The aim is to minimise the yaw angle as much as possible, so most residential wind turbines tend to have tails which orientate the turbine to best capture the wind. Wind turbines should therefore be able to rotate 3600 on yaw bearings.

The turbine

There are 2 main styles of urban wind turbines:

Horizontal Axis Wind Turbines (HAWT)

This is a propeller type rotor mounted on the horizontal axis. As mentioned previously, the blades need to be aligned with the wind and this is done by either a simple tail, or an active yaw. These are more efficient at producing electricity than VAWTs however they are impacted more by changes in wind direction.

Vertical Axis Wind Turbines (VAWT)

These are aligned in the vertical axis (like the rotor blades on a helicopter). These are only really deployed within urban areas, where the flow of air is more uneven. Due to their alignment, wind direction has little impact on this type of turbine; however it is apparent that these are less efficient than their HAWT cousins.

In addition to HAWTs and VAWTs there are hybrid turbines that are cylindrical (imagine a gyroscope) – such as the energy ball.

At TheGreenAge, we suggest sticking with the HAWTs as they are the more proven technology, and are offered by more suppliers, so you will be able to get better value for money.

Most turbines tends to have two or three blades, two bladed turbines are cheaper but suffer from blade chatter which puts stress on the system, which can lead to increased maintenance further down the line. If you can afford to get a three bladed turbine, we suggest doing so, as these don’t suffer from this problem at all.

The tower

Three types of tower exist: tilt-up, fixed guyed and free standing. The purpose of these towers is to position the turbines in the best possible position to take advantage of the wind.

Tilt-up towers are held in position by four guy ropes one of which can be released, allowing you to lower the tower, so you can work on the turbine.

Fixed guyed towers are similar to tilt-up towers, except they are permanently fixed in place so you need to climb the tower to do any maintenance.

Free standing towers have no guy ropes. As such they require a very solid foundation. Therefore these are certainly the most expensive, but may well be the most aesthetically pleasing.

The inverter

Most wind turbines produce AC current, so this should be able to be directly fed into your home and the grid, however the voltage and frequency of the power produced is very erratic, so an inverter is used to convert the erratic AC to DC, then back to a smoother AC which can be synchronised with the grid, or for use directly into your home. Battery-based wind turbines normally operate at 12 or 48 Volts, and therefore the inverter must also act to convert this relatively low voltage to high voltage (UK mains is 240 volts). Battery-less systems may produce electricity with a voltage significantly higher (100 volts or more). Therefore in this situation, the inverter needs to be able to handle this higher voltage.

Batteries

In most wind turbine systems, the electricity does not power any appliances directly. Instead the electricity produced is stored in deep-cycle lead acid batteries which look very similar to the ones found in most cars today (although structurally different). The two most popular types of battery are GEL and Absorbed Glass Mat (AGM), which store the charge very well and do not degrade nearly as fast as the common lead acid (wet cell) battery. Both types of batteries are designed to gradually discharge slowly and recharge 80% of their capacity hundreds of times.

An automotive battery is a shallow-cycle battery, and this is designed to discharge only about 20% of its electricity so is unsuitable for solar photovoltaic cell set-up. The reason is that if any more than 20% is drawn more than a few dozen times, it will get damaged and no longer take charge.

Wind turbine batteries tend to operate at 12v, and can be arranged in banks (multiple batteries), increasing the storage potential of your wind system set up. A bank of batteries organised in a series increases the capacity of your storage but also increases the voltage delivered from your bank; while multiple batteries organised in a parallel circuit increase the capacity, but the voltage stays the same.

Charge controllers

Charge controllers are used in wind turbine systems to prevent the batteries from being overcharged. If you decide to implement a grid tie system, a charge controller is not necessary, as any excess electricity that you don’t use at any particular moment is sold directly back to the grid. However, for any battery setup, a charge controller is necessary as it prevents damage to the battery by monitoring the flow of electricity in and out. If your system overcharges the battery it will damage it. The same is also true if you completely discharge all the charge held within the battery.

Most charge controllers associated with wind turbines have dump load capability associated with them. This allows any additional charge to be diverted from the batteries when they are full, potentially to a hot water heating system (so the electricity is not completely wasted). Obviously if you are connected to the grid, this electricity would instead be sold there, providing you with an additional income stream.

Most charge controllers are also equipped with maximum power point (MPPT) charging. The principle of MPPT is to extract the maximum available power from the wind turbine by making them operate at the most efficient voltage (known as the maximum power point voltage). The algorithm included in the MPPT charge controller compares the output from the wind turbine with the battery voltage and then fixes it at the best charging voltage, to get the maximum charge into the battery.

Safety equipment   

Disconnects are simply switches that allow you to isolate parts of the system so you can troubleshoot or repair faulty parts without the risk of being electrocuted. In addition many wind turbine systems are grounded, so that if there is surge in current anywhere in the system it is safely dissipated rather than damaging the system or more importantly you!

Installing a wind turbine

Are you thinking about installing a wind turbine at home? We have scoured the country for the best tradespeople, so that we can make sure we only recommend those we really trust.

If you would like us to find you a local installer to help install a wind turbine at home, just fill in the form below and we will be in touch shortly!


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    Planning permission for wind turbines

    Renewables

General guidance for wind turbines

Planning permission for wind turbines depends on which region you live in the UK. If you live in England or Scotland, then certain wind turbines are permitted without planning permission, but they require adherence to strict conditions.

In England, building-mounted wind systems were relaxed as part of 2011 legislation, but in Scotland you will still require planning permission for this.

Permitted development for wind turbines in England

It is possible to install a wind turbine as a permitted development, although it needs to fulfil all of the following criteria:

A wind turbine mounted on a building:

 A wind turbine installed as a stand-alone installation:

Can also be considered as a permitted development if the following criteria are adhered to:

Permitted development of wind turbines for Scotland

In Scotland a building mounted development requires planning permission, but on the other hand, a standalone development doesn’t, unless it contravenes the following points:

You also need to make sure that the developer that is building the wind turbine speaks to the local authority and gets clearance for the size and type of wind turbine being installed.

Planning permission for Wales & Northern Ireland

If you live in Wales or Northern Ireland you will require planning permission no matter what the type of system you are going for.

Concluding comments on planning permission

With any wind turbine it is worth checking with your local planning authority to find out whether your proposed installation will require planning permission.

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