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Blue Peter

Those rooftop wind turbines again

There's a lot of interest in these rooftop turbines, but very little hard fact. A further question which I'd like to ask about them, which has come up on other fora which I subscribe to, is:

I believe that the plan is that the wind turbine connects into the grid so that if you have surplus power you can feed it into the grid (and potentially get paid for it). I think that there has to be a special sort of box to do this (and the code G83 springs into my mind thanks to Nathan). Anyway, someone suggested that because of this grid tie in, your power would go off if the grid went down. Is this true? And can a switch of some sort be put in to prevent this? (Though I think that you would need something - a dump load? - to put any excess power in such a case).

Any comments would be much appreciated. And forgive me if I've got some of the terminology wrong - if you can answer the question, you'll probably know what I'm trying to say Wink ,


Peter.
wellington womble

I think the idea of this system, is that you use the grid as your battery - so when you are making power you feed into the grid, and when you using power you draw from the grid - so yes, if the grid went down, you'd be off too. Whether you can put in short term batteries at any reasonable cost, I don't know. Batteries are expensive! it may be possible to use power straight from the source - I'm not really up on the technical bits!
dougal

W Womble puts it more succinctly than I would Very Happy

The Windsave idea is to away with the large and expensive batteries and control equipment that is needed if you want to have your own supply as a backup to the grid.

It also works on the basis that any surplus power returned *to* the grid is not going to be worth enough to cover the expense of a 2-way meter, let alone the sub-optimal tarrif that would likely imply for your own consumption...

The thing to remember with wind turbine specs is that the power generated would be proportional to the windspeed *cubed*.
IIRC Windsave is said to produce 1000w @ double UK average windspeed. Half the speed to get to UK average, and you only get one eighth of the power, 125 watts - enough for a couple of ordinary lightbulbs...
Even when its blowing a hoolie Windsave only claims to deliver one third of the power an electric kettle uses - so what might you have been hoping to do during a power cut?

One small point from computer uninterruptable power supplies - most of the small ones are less reliable than the *UK* mains... "Your mileage may vary" depending on where you live, but power cuts are generally not a major problem.
Blue Peter

Cheers for this. What's the average UK wind speed?


Peter.
wellington womble

I guess it depends where you live. I thought those box things were meant to deliver about 15 percent of a houses ekeltrickery? Or maybe it depends on the house (I wondered, you see, why you couldn't have 7!) maybe thats in gale country!
dougal

Blue Peter wrote:
Cheers for this. What's the average UK wind speed?


Better still - ask about your own!
There's a link here that wants an OS Grid Ref for the nearest town/village... Smile

http://www.almac.co.uk/proven/UKwindspeedreading1.htm

.
dougal

Blue Peter wrote:
What's the average UK wind speed?


Should have said that 12m/sec which Windsave claim gives 1kW is about Gale Force 6 - thats blowing!
Windsave themselves suggest that 6m/sec is "a fairly average UK windspeed" - which its reasonable to expect to generate just 125 watts... (but of course Windsave haven't published their own graphs, yet).

As I have previously pointed out, exemption from Planning Permission (as "Permissable Development") would depend on the whole of the turbine being *below* roof height - and that inevitably means that the turbine would be sheltered from many directions, and would be in turbulent air (less efficient, more noise and vibration) from other directions...
Lozzie

Atricle on Wind Power on a small scale

I found this (sorry, if it is already old news. It was posted on MSN Messenger's home page a couple of days ago. There is no indication of who wrote it, I'm afraid):

Introduction


Harnessing wind as a renewable energy source involves converting the power within a moving air mass (wind) into rotating shaft power which in turn generates electricity. Modern wind turbines contain rotors fitted with aerodynamic blades, which utilise lift forces caused by the wind on the blades.


Wind energy resources

In the UK we have a large potential wind resource. Although we have 40% of Europe's total wind energy resource, it remains largely untapped, currently meeting only about 0.5% of our electricity requirements.

Power from the wind is proportional to the cube of the wind speed therefore relatively minor variations in wind speed can result in large changes in potential output.

Individual turbines vary in size and power output from a few hundred watts to 2-3 megawatts (as a guide, an electrical kettle uses approximately 2,000 watts or 2 kilowatt). Uses range from very small turbines supplying energy for battery charging systems (e.g. on boats or in homes), to turbines grouped on wind farms supplying electricity to the grid.

Small Scale Wind and your home

Wind speed increases with height so it is best to have the turbine high on a mast or tower. Generally speaking the ideal sitting is a smooth-top hill with a flat, clear exposure, free from excessive turbulence and obstructions such as large trees, houses or other buildings. However, small-scale building integrated wind turbines suitable for urban locations are currently being developed and will be available to install in homes and other buildings within the next few years, Knowledge of the local wind resource is critical to designing a wind energy system and predicting output. For domestic installations a good source of information on local wind speeds is the NOABL database which can be accessed from the British Wind Energy Association alternatively you can collect
primary information by setting up your own monitoring mast to record wind speed. An ideal way of doing this is with an anemometer which can be bought online for around £120.

Planning issues such as visual impact, noise and conservation issues also have to be considered. System installation normally requires permission from the local authority.

Stand-alone or grid-connected systems?

Small scale wind power is particularly suitable for remote off-grid
locations where conventional methods of supply are expensive or impractical.

Most small wind turbines generate direct current (DC) electricity. Off-grid systems require battery storage and an inverter to convert DC electricity to AC (alternating current - mains electricity). A controller is also required to ensure the batteries are not over or under-charged and can divert power to another useful source (e.g. space and/or water heaters) when the battery is fully charged. 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.

Wind systems can also be installed where there is a grid connection. A special inverter and controller converts DC electricity to AC at a quality and standard that is acceptable to the grid. No battery storage is required. Any unused or excess electricity can be exported to the grid and sold to the local electricity supply company.

Cost and maintenance

Systems up to 1kW will cost around £3000 whereas larger systems in the region of 1.5kW to 6kW would cost between £4,000 - £18,000 installed. These costs would be inclusive of the turbine, mast, inverters, battery storage (if required) and installation, however 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 service checks every few years to ensure they continue to work efficiently. For battery storage systems, typical battery life is around 6-10 years, depending on the type, so batteries may have to be replaced at some point in the system's life.

Are there grants available?

Scotland:
Householders can access capital funding of up to £4000 from the Scottish Community and Householder Renewables Initiative (SCHRI).

For more information please see the funding and advice page or contact the SCHRI Hotline on 0800 138 8858.

Rest of the UK (England, Wales and Northern Ireland)
Householders can access grants for small scale wind from Clear Skies. For more information contact the Clear Skies Helpline on 08702 430 930 or visit their website. http://www.clear-skies.org/


Smile
Lozzie

And, just to answer my own post -

this came from another discussion group I beling to:

There's a fair amount of discussion in the press about a new roof-top
wind turbine which plugs straight into your mains, reduces your
electicity bills, and is a lot cheaper than the typical system cost
quoted in the Clear Skies grant information.

http://www.telegraph.co.uk/news/main.jhtml?
xml=/news/2005/05/27/nwind27.xml&sSheet=/news/2005/05/27/ixhome.html

http://www.oilfiredup.com/news/index.asp?id=348

http://www.creatingdreamhomes.co.uk/modules.php?
name=News&file=article&sid=65

http://www.windsave.com/index.htm
dougal

Yes, there has been a lot of publicity!

Generators simply cannot "plug in" because they'd have unsafe exposed live plug 'pins' if ever unplugged... Shocked (and yes, Windsave's publicity does talk about "plugging in" Rolling Eyes )

As per your quote and my post above - the output *falls* dramatically when windspeed drops. And systems should have a "self limiter" for very strong winds - usually above force 6 - which gives the *maximum possible* output, which of course is what is quoted in the publicity!

For those of us wondering "when is windsave going to happen" - I note that the Oilfiredup story speaks of "an initial pilot" trial being "later this year" - and yes, its a 2005 story! And its now targeted at a price of £1500 inc installation.
Rikki

I'm currently installing a solar panel to heat my domestic hot water and have considered having a wind turbine connected to a heat sink imersion heater to heat the water in winter (when it's windy, but not sunny. Has anyone else done this. I reckon the recoup period on my solar panels, home made and installed, is 10 years whereas a commercial installation would take 50 years to recoup the cost. Has anyone looked at how long it would take to recoup the £1500 of an electricity turbine?
Rikki

I've just done a rough calculation based on 100W and I reckon you'd save £50 a year, so 30 years recoup period! To get a more useful amount of power you'd need a much larger turbine costing more like £15,000 (it would need it's own tower and couldn't be strapped to the chimney) but the increase in power and increase in cost are proportional so it would still take 30 years to recoup.
dougal

Rikki wrote:
I'm currently installing a solar panel to heat my domestic hot water and have considered having a wind turbine connected to a heat sink imersion heater to heat the water in winter (when it's windy, but not sunny. Has anyone else done this.

Its a simple-ish means of using wind energy, because it requires very little in the way of control systems and energy conversion, such as voltage stabilisation, transformers, inverters and mains synchronisation.
But its not common because usually folk *needing* wind energy are wanting to make the maximum/best possible use of it, and may well have access to plenty wood for water heating. Such folk, off grid would be charging batteries from the wind, and only when that store is full would they 'dump' wind energy into heating.
And if mains gas is available, using wind for water heating is unlikely to be very cost competitive.
Rikki wrote:
I reckon the recoup period on my solar panels, home made and installed, is 10 years whereas a commercial installation would take 50 years to recoup the cost. Has anyone looked at how long it would take to recoup the £1500 of an electricity turbine?

That's the answer no one knows yet.
And it'll be different, depending on the local wind conditions. Which could mean *very* local.
My understanding is that without specific planning permission, the whole turbine must be lower than the top of the roof. Which must mean the roof screening the turbine from some directions, and running it in turbulent air - further complicating any pre-calculation of its viability.
There is some concern that some rather optimistic assumptions must be made to have such things pay back financially before they are expected to wear out. And then there's the question of the energy in their production...

Rikki - may I suggest you register (it costs nothing), and start a new thread on your solar system?
woody

we are looking for an effective wind turbine for our project can anyone help Very Happy
Blue Peter

woody wrote:
we are looking for an effective wind turbine for our project can anyone help Very Happy



Woody, perhaps you could tell us what your project is?

Anyway, you might take a look at the following article:

http://www.downsizer.net/Products%10Services/Sustainable_Construction%10Renewables/Big_small_wind_power!/


Peter.
dougal

woody wrote:
we are looking for an effective wind turbine for our project can anyone help Very Happy


Woody, did you spot this?
http://forum.downsizer.net/viewtopic.php?p=66541#66541

Do register, and tell us about your project!
fonant

dougal wrote:
Generators simply cannot "plug in" because they'd have unsafe exposed live plug 'pins' if ever unplugged... Shocked (and yes, Windsave's publicity does talk about "plugging in" Rolling Eyes )


Yes, they can. Any grid-connected power generation system _must_ switch itself off if the grid fails. This is so that anyone working on the disconnected part of the grid is safe.

I've seen solar PV inverters that are like a large wall-socket power supply - you do just plug it in. For example http://www.mastervolt.com/sunmaster/soladin.asp. Very cool and very portable for when you move house Smile

I love electronics - these things work so fast it makes the 50Hz mains frequency look slow!
dougal

fonant wrote:
dougal wrote:
Generators simply cannot "plug in" because they'd have unsafe exposed live plug 'pins' if ever unplugged... Shocked (and yes, Windsave's publicity does talk about "plugging in" Rolling Eyes )

Yes, they can. Any grid-connected power generation system _must_ switch itself off if the grid fails. This is so that anyone working on the disconnected part of the grid is safe.

Embarassed I already stand corrected on this! Embarassed
nathanbriggs wrote:
{22 June 2005}... there is nothing in BS7671 which precludes the use of a 13Amp plug as a source of power as long as it safe to touch... Removal of the plug and touching the pins has to be safe, the energy must be below 50V within 2 cycles and less capacity than will stop a human heart, btw its still possible to get a little tingle if you are quick.
The windsave device is fitted with a plug, having said that most people will get it installed by a competent electrician who will promptly hard wire it.
Lastly the plug is standard but the socket requires a metal cover plate


One point that hasn't been brought out is the necessary implication that such systems therefore *cannot* provide independence of the mains. During a powercut, your own generator *must* shut down too.
I'm not saying its physically impossible, just that it is the inevitable consequence of a "plug-in" system's mode of operation. (But would a power outlet on the generator side of the isolater be possible..?)

However there are a couple of points that might be taken in mitigation of my error.
1/ Isolating from the mains to protect maintenance/repair workers, does not require an *instant* disconnect. Personal safety on accidental unplugging demands a much more rapid response.
2/ While you can safely *just* isolate a solar pv panel, my understanding is that a wind turbine generator can't just be left to freewheel 'off-load' in the same fashion as one might isolate the pv panel. My understanding is that such freewheeling could destroy the turbine and/or the generator - please correct me if I've got that wrong! A mechanical brake can substitute for the braking effect of the electrical load, but I don't think such things are part of the design of these small domestic turbines. (Note that this is independent of the "self-furling" self-protection from increasing windspeed.) And dumping a kilowatt from the braking load is not exactly inconsiderable.
3/ And, Milud, I was mislead!
nathanbriggs wrote:
{23 March 2005}...this means you can directly connect the Windsave power into the mains (although not by just plugging it in it must be hardwired).
{My emphasis - Dougal}


fonant wrote:
I've seen solar PV inverters that are like a large wall-socket power supply - you do just plug it in. For example http://www.mastervolt.com/sunmaster/soladin.asp. Very cool and very portable for when you move house Smile
As above, I think solar pv isolation can be just switching off, but that its more involved with turbines. And I note that those units are handling just 1/10th of the claimed maximum output of a Windsave.

fonant wrote:
I love electronics - these things work so fast it makes the 50Hz mains frequency look slow!
I remember learning Assember programming on a 1Mhz 6502 Microprocessor system, 25 years ago. The response and stability of stepper motor control is an experience that lives with me! Shortly thereafter I was faced with the problem of measuring the quiescent current of CMOS custom chips (nanoamps) in a rather noisy RF environment. Having rather fancy test equipment, I didn't bother with shielding at all. I simply made 1k measurements (!) and averaged them by adding and shifting the "decimal" point (1k rather than 1000 so it was simply a matter of a "binary shift"). The results were brilliantly reproduceable for particular chips - it worked!
I suspect that the programming problem for the solar inverter isolater would have been in reliably and quickly recognising the difference between noise and a powercut.
I am well aware just how quickly microelectronics can respond, and how difficult this can make interfacing to the real, slow, physical world..!
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