Solar panels can be successfully fitted to properties in the UK and provide over half of the energy needed for usual hot water requirements.
The panels are most effective between the months of May and September and work even on a cloudy day. The best position for the panels is facing south (within 30 degrees in either direction) and a roof slope of between 25 and 70 degrees. Having said this, panels pointing within 70 degrees of south on a roof slope of between 10 and 90 degrees can still achieve 90% efficiency. The first thing to do is get a quote from two or three companies and see which will give you the best service at the best price. Don’t forget to check what is included in their guarantees.
Solar panels can be used with existing heating systems, or for best results, matched components such as a dual-mode hot water cylinder and system controller can be purchased from suppliers of solar heating appliances.
The solar panel may not work on some days during the winter so another heating system is needed as a backup. This can be a conventional boiler or another form of renewable energy.
Many customers ask if they have to clear snow from their solar panels. This is not necessary as, although the panel will not work while it is covered with snow, you will find that the snow melts more rapidly from the panel than from the rest of your roof. Temperature is also not a problem as panels on Alpine hotels work perfectly in temperatures as low as minus 30 degrees Celsius!
Although a south-facing roof gives the best performance, panels pointing within 70 degrees of south and angled between 10 and 90 degrees can still achieve 90% efficiency. Even a panel sited on an east or west facing roof with a roof slope of 20 to 40 degrees can reach an efficiency of 85%.
For south-facing panels a more steeply raked installation (towards 70 degrees) is best for year-round performance. Lower installation angles (towards 25 degrees) are better for sites where the panel does not point south. Angles of less than 20 degrees should be avoided as contamination with dirt and bird droppings can become a problem. Yes, you can go up there to clean them, but it will be a pain if you have to do that every two week!
What about planning permission? You should check with your local planning office, but generally you do not need permission to fit solar panels to an existing building.
If you are fitting solar panels as part of a new build or an extension then the panels may need to be included in your planning application – check with your local planning office before carrying out the work.
You may see a lot of hot air in the wind about the sound of wind turbines.
Here’s an article looking as dispassionaltely as possible at the issue.
Virtually everything with moving parts will make some sound, and wind turbines are no exception. Well designed wind turbines are generally quiet in operation, and compared to the noise of road traffic, trains, aircraft and construction activities, to name but a few, the noise from wind turbines is very low. Outside the nearest houses, which are at least 300 metres away, and more often further, the sound of a wind turbine generating electricity is likely to be about the same level as noise from a flowing stream about 50-100 metres away or the noise of leaves rustling in a gentle breeze. This is similar to the sound level inside a typical living room with a gas fire switched on, or the reading room of a library or in an unoccupied, quiet, air-conditioned office.
Have a listen to this video and judge for yourself:
As the video would seem to show, the sound of a working wind farm is actually less than normal road traffic or an office. Even when wind speed increases, it is difficult to detect any increase in turbine sound above the increase in normal background sound, such as the noise the wind itself makes and the rustling of trees.
The best test is always to experience the noise from a turbine for yourself. You will find that it is perfectly possible to stand underneath a turbine and have a normal conversation, without raising your voice.
What makes the noise?
Almost all wind turbines producing electricity for the national grid consist of a tower, which is between 25 and 50 metres high; a nacelle (housing) containing the gearbox and generator, which is mounted on top of the tower, and 3 blades which rotate around a horizontal hub protruding from the nacelle. This type of turbine is referred to as a horizontal axis machine.
There are two potential sources of noise: the turbine blades passing through the air as the hub rotates, and the gearbox and generator in the nacelle. Noise from the blades is minimised by careful attention to the design and manufacture of the blades. The noise from the gearbox and generator is contained within the nacelle by sound insulation and isolation materials.
Standing next to the turbine, it is usually possible to hear a swishing sound as the blades rotate; and the whirr of the gearbox and generator may also be audible. However, as distance from the turbine increases, these effects are reduced.
How is noise measured?
Noise is measured in decibels (dB). The decibel is a measure of the sound pressure level, ie. the magnitude of the pressure variations in the air. An increase of 10 dB sounds roughly like a doubling of loudness. Measurements of environmental noise are usually made in dB(A) which includes a correction for the sensitivity of the human ear.
The noise a wind turbine creates is normally expressed in terms of its sound power level. Although this is measured in dB(A), it is not a measurement of the noise level which we hear but of the noise power emitted by the machine. The sound power level from a single wind turbine is usually between 90 and 100 dB(A). This creates a sound pressure level of 50-60 dB(A) at a distance of 40 metres from the turbine, ie. about the same level as conversational speech. At a house 500 metres away, the equivalent sound pressure level would be 25-35 dB(A) when the wind is blowing from the turbine towards the house. Ten such wind turbines, all at a distance of 500 metres would create a noise level of 35-45 dB(A) under the same conditions. With the wind blowing in the opposite direction the noise level would be about 10 dB lower.
There is an increase in turbine noise level as wind speed increases. However, the noise from wind in nearby trees and hedgerows, around buildings and over local topography also increases with wind speed but at a faster rate. Wind turbines do not operate below the wind speed referred to as the cut-in speed (usually around 5 metres per second) and wind data from typical sites suggests that wind speeds are usually below this for about 30% of the time.
Preliminary recommendations from the Wind Turbine Noise Working Group*1, established by the UK DTI, are that turbine noise level should be kept to within 5 dB(A) of the average existing evening or night-time background noise level. This is in line with standard practice for assessment of most sources of noise except for transportation and some mineral extraction and construction sites when higher levels are usually permitted. A fixed low level of between 35 and 40 dB(A) may be specified when background noise is very low, ie. less than 30 dB(A).
Different Types of Turbine
Wind turbines may be designed in different ways and many of the differences have come about from a desire to minimise noise emissions:
Upwind & Downwind Machines
The majority of horizontal axis turbines are designed in such a way that the blades are always upwind of the tower. This has the effect of minimising any airflow changes as the blades pass the tower. Some turbine designs, particularly some of those installed in the USA, have the turbine blades downwind of the tower. With this type of design, a strong pulse can sometimes be heard with each passing of a blade behind the tower. However, most turbines currently operating in the UK are of the upwind design.
Twin Speed and Variable Speed Machines
Most horizontal axis turbines rotate at a constant speed, usually between 25 and 50 rpm, irrespective of wind speed. However, twin speed machines operate at a reduced speed when the wind is light. This produces less noise and means that when the noise of wind in the trees is low, the noise of the turbine is also significantly lower by up to 10 dB(A). Variable speed machines change speed continuously in response to changes in wind speed and, although noise output may be higher at higher wind speeds, it is lower at low wind speeds where the low background levels occur.
Direct Drive Machines
Direct drive turbines are the latest design concept in turbine technology. Simply put, these machines have no gearbox or drive train, and consequently no high speed mechanical (or electrical) components. Direct drive turbines are therefore much quieter than gearbox machines as they do not produce mechanical or tonal noise. An example of this type of turbine is the 1.5MW ‘Ecotricity’ turbine installed at Swaffham in Norfolk in September 1999.
While everyhting is subjective, the noise produced by typical wind farms is so low that they would not be noticeable in most residential areas in the UK. However, the areas suitable for such developments tend to be in quiet but exposed areas of countryside. A significant amount of effort is put into minimising any noise impact but it should be emphasised that typical noise levels are so low for a carefully considered site that they would normally be drowned out by a nearby stream or by a moderate breeze in nearby trees and hedgerows .
