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Frequently Asked Questions
Please select your question from the list below:
What areas of the UK do SEI work in?
What type of system does SEI install?
Are SEI an independent supplier?
How much electricity will a wind turbine generate?
What proportion of my electricity will a wind system produce?
How large is a wind turbine?
Where should the wind turbine be located?
Where shouldn't a wind turbine be located?
Can I get help with project costs?
What about planning permission?
Will we organise the DNO connection (permission to connect to the electricity grid)?
How long will installation take?
What happens when little or no electricity is being generated e.g. when there is no wind?
What happens if the wind turbine is generating more electricity than is being used at that time?
Will we make an agreement with your electricity supplier for payment for electricity from the wind turbine that goes back to the mains?
How much noise does a small wind turbine produce?
What is a kWh?
When should I have a grid-connected system?
How much CO2 is mitigated per kWh generated from PV?
Why do wind turbines shut down when it is very windy?
If your question isn't listed here, try searching our website or contact one of our engineers.
What areas of the UK do SEI work in?
SEI cover all of the UK, inluding Northern Ireland for larger projects.
What type of system does SEI install?
SEI install photovoltaic systems (solar electricity), wind turbines and hydro systems.
Are SEI an independent supplier?
SEI are an independent installation company not tied to any particular supplier. SEI can therefore install whatever system you would like and best suits your site and your needs. If you do not have any specific ideas of the type of system you require, SEI will provide advice and help you to make a selection.
For small-scale installations (up to 15kW) we generally use Proven wind turbines which are manufactured in the
For larger installations, our system designers will investigate the most appropriate system on the market for your precise needs.
How much electricity will a wind turbine generate?
The amount of energy available is highly dependent on the wind speed at hub height. Below 5 metres per second (m/s), there is generally too little energy available to justify the expense of a wind turbine, while the amount of energy available above that threshold increases rapidly. An estimate for windspeed in your area can be obtained from the UK national wind database, available on-line.
If there is sufficient wind, you could then expect the following outputs from the Proven turbines we install. Note that actual output will vary, as these figures are based on optimal site conditions and an average ground wind speed of 5m/s.
|
Turbine Size |
Annual Output |
| 2.5 kW | 2,500-5,000 kWh |
| 6 kW | 6,000-12,000 kWh |
| 15 kW | 15,000 - 30,000 kWh |
1 kWh is equivalent to 1 unit of electricity on your electricity bill.
Individual outputs will vary with weather experienced. Source: Proven
What proportion of my electricity will a wind system produce?
Your electricity bills will be lower because you will be using electricity from the wind system instead of taking electricity from the mains. The exact proportion depends on the size of the wind turbine, the actual wind conditions experienced and your site consumption. You can determine your annual electricity consumption by examining one year of electricity bills. [1 unit of electricity on your bills = 1kWh]
For example, a typical UK three-bedroom family home, uses 3,300 kWh of electricity every year. This can vary considerably dependent on the household and how energy efficient any electrical appliances are. Thus a 15 kW turbine would generate electricity equivalent to the consumption of six or seven reasonably efficient three-bedroom homes.
It is important to note that a grid connection or some form of energy storage is normally still required, even if the predicted generation is higher than the planned consumption. This is for several reasons:
- Peak site consumption and wind conditions rarely coincide
- Wind speeds may be lower than average for a protracted period of time
- Consumption rates are likely to increase with time
Blade shape and size and mast sizes vary widely with the site requirements and turbine model used. Generally, the larger the turbine kW rating the taller the larger the wind-swept area of the blades and taller the mast is (to optimise the incoming energy compared to the cost of taller masts). The height of the mast or the size of the blades is often one of the restrictions in choosing a system, and our system designers will attempt to find a suitable system to comply with these requirements. Conversely, we sometimes specify taller masts than usual in order to maximise the output from the site.
With our 'standard' range of Proven wind turbines, the blade diameter of a 2.5 kW turbine is 3.5 m; the blade diameter of a 6 kW turbine is 5.5 m; the blade diameter of a 15 kW turbine is 9 m. The mast heights of our standard systems are between 6.5 – 15 m, although a 25m mast is sometimes used.
A wind turbine should be located in an open non-sheltered space where it will experience as much wind as possible. There should be few nearby obstructions to the path of the wind (e.g. buildings and trees) to cut down on turbulence, as this can reduce output and shorten the life of the turbine. Ideally any obstructions should be ten times their height away from the turbine. In particular, the area to the south-west should be clear of obstructions, as this is the prevailing (but not only) wind direction in the UK. The electrical connection is likely to be made within your building; hence the maximum distance from the building is approximately 500 m. The total length of land required to raise and lower the turbine is just over twice the height of mast (13m for our smallest turbines); this space must be kept free for maintenance.
It is possible to locate wind turbines on the roof of large buildings in some cases, and SEI has experience with installing building-mounted systems. There are significant structural implications, and we do require that a structural engineer is commissioned to assess the suitability of the building before issuing a fixed-price quotation as there may be additonal requirements for the mounting.
Where shouldn't a wind turbine be located?
Unfortunately, while a lot of people would like to generate electricity from the wind, not all sites are feasible. The following is a list of commonly requested types of site for which our engineers normally recommend another technology.
- Low wind: While subjective, anecdotal evidence may suggest a site is windy compared to its surrounding area, this might not mean it has sufficient wind to generate power. When this might be the case, a long-term wind study is suggested at the site (SEI can perform this study).
- Little space: As with any mechanical machine running all year round, wind turbines require regular maintenance. For tilt-up masts this means a clear, unobstructed area for raising and lowering of the mast must be reserved for the lifetime of the equipment.
- Urban areas: Wind in urban areas, especially at or near roof level is both slowed by friction and highly turbulent. This means there is less energy to harvest and the turbine is stressed, reducing its working life. In addition, in residential areas a potential for noise and visual flicker can cause complaint.
- Forests: As with urban areas, dense areas of tall trees can result in slow, turbulent wind
These are not hard and fast rules, but if your site might fall into one of the above categories, it may be to your advantage to consider another renewable technology.
Can I get help with project costs?
There are grants available for most projects, whether they are for domestic, public sector or commercial clients, through the government's Low Carbon Buildings Programme. Some projects are also eligible for additional funding from other sources. SEI can advise you on the funds available and assist you with the grant application process. Please see our Grants page for more information.
If you have any queries we are of course happy to help. Further details on the grant scheme are available from the Low Carbon Buildings Programme or by calling the grants helpline free on 0800 915 0990. Please note that SEI is a member of TLCP, a consortium accredited for Phase 2 (public sector) projects.
What about planning permission?
Planning permission will need to be obtained from your local planning office for all wind turbines installed by SEI. With standard products we can provide a planning pack to aid with this; with larger turbines SEI will produce tailored documentation as requested by the planning authorities.
Yes, we will apply on your behalf when you place a confirmed order with us.
How long will installation take?
For standard Proven wind turbines, installations take 2-3 days for a 2.5 kW turbine, or 3-5 days for a 6 or 15 kW turbine. Larger turbines will take appropriately longer periods of time, depending on site conditions.
What happens when little or no electricity is being generated e.g. when there is no wind?
For a grid-connected system, when there is little or no electricity being generated by the wind turbine, electricity is automatically taken from the National Grid. You will not need to turn the system on or off - the service to you will be seamless.
If you do not have a grid connection, we will specify a design with batteries to suit your predicted demand pattern so that your electricity supply is continuous. These batteries must be adequately sized and maintained after installation, otherwise there may be insufficient stored energy and the site will be without power for a period.
What happens if the wind turbine is generating more electricity than is being used at that time?
If your system is grid-connected, the electricity will be fed back to the mains. Grid-connected systems use an electrical rectifier and inverter combination to generate grid-synchronised electricity so they can be connected to the mains. There are no batteries.
A stand-alone system has batteries which will be charged by any excess electricity that you generate that you are not using at the time. When these batteries are fully charged, excess energy is discharged via a dump load (generally a resistive heater) to prevent damage to the generating equipment or batteries.
Will we make an agreement with your electricity supplier for payment for electricity from the wind turbine that goes back to the mains?
No, we leave the choice of supplier up to you. SEI is independent of all electricity suppliers. Different electricity suppliers have different arrangements for billing, and these arrangements often change. We will give you up-to-date information on the different electricity suppliers to help you make your choice. Even without making a specific payment agreement with an electricity supplier, e.g. a net metering arrangement, your electricity bill will be lower because you will not be using as much electricity from the mains.
This depends on the blade shape and size, site wind conditions and turbine technology used. Where a turbine noise is expected to be a restriction our system designers will attempt to account for this when specifying the turbine model.
Our standard small Proven wind turbines are designed to produce very little noise. The blade tips are designed to reduce noise. There is no gearbox and hence no gearbox noise. The sound emitted from the turbine is low swishing noise from the blades. Noise outputs at wind speeds of 5 m/s (a gentle breeze) and 20 m/s (50 mph) are shown in the table below. For comparison a passing car 20 m away driving at 40 mph produces 70-80 dBA
|
Proven Wind Turbine |
2.5 kW |
6 kW |
15 kW |
|
Noise @ 5 m/s |
40 dBA |
45 dBA |
48 dBA |
|
Noise @20 m/s |
60 dBA |
65 dBA |
65 dBA |
What is a kWh?
kWh stands for Kilo-Watt Hour, and this is a measure of energy (in this case electricity) used or generated.
1 kWh is the same as 1 unit on your electricity bill, and is enough power to light a 100W light bulb for ten hours (or fifty hours for a typical 20W low-energy light bulb). 1 kWh costs approximately 7p for domestic customers.
Can I heat my hot water using a wind turbine system?
A wind turbine system is not necessarily the most efficient method of heating water. The electricity generated can be used for this purpose but it is unlikely to supply all your hot water needs.
However, in off-grid systems the dump-load could feasibly be used to heat water, thereby reducing the amount of energy 'wasted' when the batteries are full.
When should I have a grid-connected system?
In the majority of installations, it makes sense to connect to the electricity grid and operate the wind turbine system in parallel with it. There are a number of reasons for this, which include the following:
- In most circumstances, it is both expensive and space-demanding to size a system that will be able to provide sufficient power through all months of the year
- Batteries currently require a lot of space, are heavy and expensive, and require a lot of maintenance
- You can use the grid in a similar way to a near-infinite battery: You can often sell unused power to your provider, and buy it back when you need it most
In general, unless the site is to be extremely remote and away from a grid connection, it is almost always cheaper to have a grid-connected system. Please see our article on grid connection for more information.
How much CO2 is mitigated per kWh generated from PV?
The exact amount of CO2 mitigated by a wind turbine system is hard to measure, as the mix and efficiency of fuels used to generated grid electricity changes constantly. However, the standard figure used for the Building Regulations is 0.568kgCO2/kWh.
Why do wind turbines shut down when it is very windy?
As the wind gets stronger, the wind ‘pushes’ the blades harder (i.e. increasing the torque and forces on the blades). Most turbines (including ‘conventional’ turbines) are designed to operate in a range of wind speeds typically this is from 4.5 m/s to 14 m/s.
As the wind is constantly changing speed, several methods have been developed to overcome this. One of these is to use gears to change the torque and thereby the speed at which the wind can push the blades, the electrical generator speed remains constant. Another method for large wind turbines is to use an additional generator to act as a variable brake/resistor. The Proven wind turbines SEI supply as for small projects can adjust or ‘trim’ the blades dependant on the amount of wind blowing. This method is also used on some of the larger wind turbines to keep the generator speed at a constant.
Ultimately, there is a limit to how much you can ‘slow down’ the turbine. During extremely high wind-speed periods (termed the ‘cut-off’ wind speed), a turbine will have a mechanism to turn the blades so that they either stop turning or slow down so reducing the likelihood of damage to the turbine. A good design will account for this, choosing a turbine with cut-in (the minimum operating speed) and cut-out wind speeds to operate in most expected local conditions.