Following on from Part 2 (Energy Storage)
Using *only* solar panels to generate our electricity, it is apparent that for our household to become electrical energy independent, the long-term energy storage required is unfeasibly expensive (although not impossible).
How then to generate more energy during the autumn/winter months while there is not so much sun around?
Which brings me onto wind turbines. We all know about wind turbines - there are plenty of them dotted up and down the country already. Wind turbines are windmills that generate electricity when the wind blows them round. We live on the North West coast of England, and by 'eck it's blowy. A wind turbine would seem a very appropriate source of renewable energy.
This is the offshore wind farm at Morecame Bay, just up the coast from where we are.
This is commercial wind generation. Commercial turbines are HUGE (blade lengths up to 50m). There are a number of different models, and they generate between 1500kW and 3000kW. They are fed into the grid, and are part of the country's national energy generation.
See this link for some tech. spec. on commercial turbines:
Obviously not appropriate for domestic generation. You'd have great difficulty sticking one of these puppies in your back garden.
But there are many different sizes and designs of wind turbines. A lot of product development has gone into domestic turbines over the last few years. You can get teeny-tiny ones that you fix onto the side of your house (or motorhome or boat etc.) that generate enough electricity to charge a battery or light a few lights (50W).
Like this vertical-axis turbine. Without traditional horizontal blades they take up a lot less room. But at about £600 a go, they are a lot of money for the small amount of power you get from them.
I have identified 6 factors to consider in a domestic wind turbine:
1) How much electricity does it generate?
2) What is its operating range?
- the operating range of a wind turbine is the slowest to the fastest wind speed in which they can generate electricity (There is a minimum wind speed below which they will not generate anything at all, and there is a maximum wind speed above which they switch off to prevent damage to the generator.)
3) What is its survival speed?
- the fastest wind speed the turbine will tolerate before it is physically damaged (eg. in a storm)
4) How much does it cost / cost effectiveness? (what is its £ per kW)
5) What are the on-going maintenance/repair costs? (Turbines, unlike solar panels, are mechanical devices with moving parts that wear out, and need to be serviced/maintained to keep them operating)
6) How big is it? (Will it physically fit on your property? Will you get planning permission to install it?)
A little bit about wind speeds - there is a thing called the Beaufort scale which classifies wind speeds (primarily for nautical use, but a handy guide)
http://en.wikipedia.org/wiki/Beaufort_scale This describes wind levels in easy-to-understand terms such as 'light breeze - wind felt on bare skin, leaves rustle' etc.
In the UK, you're allowed to put a wind turbine on your property without having to apply for planning permission as long as you adhere to these conditions:
I've discounted house-mounted turbines, they're too small to be of any decent use. The most pertinent restrictions for pole mounted turbines are:
- the maximum allowed rotor diameter is 2.2m.
- the lowest point of the rotor sweep must be at least 5m off the ground. So for a 2.2m diameter turbine, it must be mounted on a pole at least 6.1m off the ground.
- the pole it is mounted on must be positioned at a minimum distance away from all your property boundaries, so that if the pole snaps at the base and falls over, it must land completely within your own property, whichever direction it falls in.
Of course, you can install wind turbines that exceed these specifications, but you'd have to go through formal planning application. And if one of your neighbours objects to the idea, it would become difficult to secure permission to do it.
On a purely geek-interest level, I've found a French company that have designed a new type of turbine blade. They use a 3D scooped design that has been engineered using fluid dynamics to produce zero wind-shear. This means they are silent in operation (well, not quite, but to all intents and purposes). Because of this engineering, they have a wider operating range than traditionally-bladed turbines. They are rudderless, and will automatically point in the correct direction to collect the incoming wind. But my goodness they do look weird. Here's one:
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This is the Nheowind 3D-50. You'd need planning permission for one of these - the rotor blades have a 3.2m diameter. It has a maximum power output of 2kW. It starts generating electricity at a minimum wind speed of 6mph, reaches its maximum output at 29mph, and has a cut off speed of 68mph. It can physically survive wind speeds up to 112mph.
It's 6mph turn-on speed is equivalent to 2 on the Beaufort scale ('light breeze' - wind felt on exposed skin, leaves rustle.) Its maximum output is achieved at 29mph, or 6 on the Beaufort scale ('strong breeze' - large branches in motion, umbrella use becomes difficult, empty plastic bins tip over.) It continues to pump out 2kW all the way up to 68mph, ('fresh gale' - some twigs broken from trees, cars veer on road, progress on foot is seriously impeded). It's survival speed, 112mph, is classified as level 2 hurricane on the safir-simpson wind scale. Thankfully we have never experienced one of these on the Fylde coast.
I've found some wind speed data for our area on the met office website:
According to the data in the link above, the average annual wind speed (AAWS) for the North West varies between 7-10 knots (8mph - 11.5mph). This is measured at a height of 69m amsl (above mean sea level) which is rather high to be sticking a small turbine. More investigation needed to see how the wind speed drops at lower heights.
This data is from measurements taken between 1971-2000 at Ringway (Manchester airport). I fancy the Fylde Coast may be higher than this.
According to the datasheet for the Nheowind 3D50, using the met office figures above it will turn in about 1000 kWh over the year. Considering the additional time and effort required to get through planning, that's pretty poor compared to the solar panels, which are looking like giving me around 1800kWh for the year.
The viability of wind energy is highly dependent on what your local average wind speed is. For comparison, an AAWS of 20mph (5 on the Beaufort scale -'fresh breeze' - branches of a moderate size move, small trees in leaf begin to sway) would produce about 6000kWh over the year. I doubt the Fylde Coast average is that high, but you can see we're getting into the realms of viable investment.
Cost-wise, I've found a UK distributor charging £4400 for the 3D50 bundled with a Power One inverter
Then there is the 3D50's big brother, the Nheowind 3D100. This turbine has a rotor diameter of 4m compared to the 3D50's 3.2m, yet it turns in more than double the power: 3000kWh per year at 9mph AAWS, rising to 15,000kWh per year at 20mph AAWS.
But in the meantime I reckon it's worthwhile spending a few quid putting up a wind speed monitor for a few months to see just what we're getting. It's impossible to make a sensible judgement before knowing that.
Addendum: just found a couple of handy little resources:
- I've not read them through properly yet, but the first one has some info on how wind speed varies depending on how high off the ground the turbine is.
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Second addendum: Just found out about the qr5 - a mid-scale vertical axis turbine that has some impressive figures... http://www.quietrevolution.com/qr5/faqs-technical.htm
It is a 6kW turbine, already MCS approved and the company is working on a smaller 2.5kW version.
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Third addendum: I've found a more localised wind speed database for the Fylde Coast on the Department of Engery and Climate Change website. It is indeed higher than at Ringway.
http://tools.decc.gov.uk/en/windspeed/default.aspx
You have to enter the OS square code for the area you want to know the windspeed, and then click on 'find wind data' to search the database. AAWS results come back in m/s at various heights above sea level. Our little chunk of Fylde Coast is SD324300.
At 10m above sea level, our AAWS is 5.8m/s (12.9mph) ; at 25m above sea level, our AAWS is 6.6m/s (14.7mph).
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| A qr5 vertical axis turbine being installed on a roof |
From what I've read since last night, I'm beginning to get the impression that the vertical axis wind turbines (VAWT) like the qr5 are going to be the future of small-scale wind generation. Their design is simpler - they have no 'yaw' considerations (they don't have to turn to point in the direction of the oncoming wind - they spin on their vertical axis no matter which direction the wind comes from. This means they also capture more energy from turbulent gusts that rapidly change direction. They are visually appealing (I think so at least!) They have a much larger 'wind capture' area than an equivalently sized horizontal axis turbine (HAWT) so you get more kWh in the same space. I must confess the 3D50 scooped blade design has a charm of its own, but I think for the above reasons, VAWT is the way to go.
I've found an independent review of it, and it seems to come out very well.
http://www.bettergeneration.co.uk/wind-turbine-reviews/qr5-wind-turbine.html
However, it also includes the price, which is way out of anything we could realistically afford (£25,000 installed). Shame. I think it's a beautiful bit of tech. I look forward to investigating their smaller 2.5kW version when it comes out at.
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