B&Q Wind Turbines (Merged Thread)

gromituk

BaJi wrote:

Most of the time, actually. Given that the weather is becoming more irregular. My, you are a doubting thomas.

One has to be in the face of what looks like evangelism from someone who has spent some money on something and hence has to convince himself that it's perfect.

Unfortunately "most of the time" has no more meaning than the "savings of up to..." figures used by the high pressure salesmen to dupe people into buying unsuitable things in the first place. Cold hard facts are the only thing that matters.

The servicing comment above is a little naive. How many machines or materials are there that don't need servicing? It's a simple machine.

I don't service my kettle, my toaster, my bread machine, my telephone, my washing machine, my dishwasher, my computer, my television...

PS it's good to be able to read from top to bottom, rather than starting at the top, not understanding what the context is, and then finding what it's all about because the quote to which it refers is below. Thanks.

Cardew

BaJi wrote:

The servicing comment above is a little naive. How many machines or materials are there that don't need servicing? It's a simple machine.

How is the servicing comment naive?

I wasn't suggesting that it is unreasonable for it to require servicing, merely that the costs need to be taken into account in calculating potentional savings - or more realistically losses!

It is very difficult to get any appliance serviced for less than £50 these days; and that is for everyday easily accessible household appliances with plenty of local tradesmen. How much then will it cost for a device mounted on top of a roof or above the roofline, from a specialist firm? £150?

Or if they are so reliable, why don’t the firm offer a maintenance package and tell us the price?

kittiwoz

Phil_L wrote:

With regard to wind turbines, we have been looking closely at these for sometime at work. The thing to remember is that the system works by extracting energy from the air and there is a cube law involved in the ratio of wind speed to extracted energy. If the generator is rated at full load at 9m/s at 4m/s it may give 10% not the 50% you think you will get.

Nearly right. The relationship between wind speed and energy is square not cubic, it is the relationship between wind speed and power which is cubic. This is for the relationship between the energy/power of the wind and its speed where air density is assumed constant.

While this does mean much lower power at low wind speed conversely it also means the power increases dramatically in high windspeeds. This is why turbines are rated at higher than average wind speeds in order to be able to take advantage of the higher energy density of high winds. Cut in speeds are normally set such that very little energy would be extractable below that speed anyway. Still it is necessary to understand that most of the time a wind turbine will be operating below its rated power. It is also necessary to understand that the power output of the turbine at average windspeed will usually be significantly lower than the average power output of the turbine.

BaJi wrote:

The wind changes direction frequently, although output is still pretty good from the turbine (enough to keep the lights on in the house). Hence my question about vertical axis windturbines (something like the ventulators you see on top of white vans). As I understand it, they are less affected by wind from varying directions (turbulance). They have disadvatages on the large scale but on the small scale they seem to be practical.

Horizontal axis machines are able to re-orientate themselves to face into the wind. This is not necessary with vertical axis machines. However they create a lot of force in the support tower and are generally larger and heavier per kW rated output so not suitable for roof mounting. Turbulence is not the same as change of wind direction but is another problem altogether and one which would affect vertical axis turbines as well as horizontal axis machines. The turbulence problem is greater in more built up areas both in terms of density of buildings and building height. This is a major limiting factor on suitable sites for roof mounted turbines.

gromituk wrote:

I don't service my kettle, my toaster, my bread machine, my telephone, my washing machine, my dishwasher, my computer, my television...

In that case it is probably high time you took the side off your computer and hoovered the fan. You really should clean it regularly to keep your PC operating efficiently. It'll probably run quieter too because the dirt tends to build up slightly irregularly and create an off-centre force that causes vibrations. Of course you should also run regular virus checks which is a kind of routine maintanence but I suspect you do actually do that even if you claim not to. I don't think wind turbines are brilliantly analogous to wind turbines so don't bother looking for a metaphor in that. I'm just suggesting if you genuinely don't do any routine maintanence to your computer then you might like to start.

I'm not personally a fan of the Windsave turbine. The Swift turbine from Renewable Devices seems a better machine in every aspect except for initial outlay. If one of these turbines is ever going to become a real money saver it'll be the Swift. Increased manufacture could see Renewble Devices reduce the unit cost of their turbines but however many turbines Windsave sell they'll never achieve the Swift's level of performance or longer lifespan. Also it is well publicised that the Swift turbine is "harm neutral" over its 20 year expected lifecycle because it should produce as much energy as is used in its materials and manufacture. With no such claims and a lifecycle half that of the Swift it seems a fair bet that the Windsave uses more energy in it's production than it will ever create.

BaJi_2

gromituk wrote:

One has to be in the face of what looks like evangelism from someone who has spent some money on something and hence has to convince himself that it's perfect.

Wrong sorry, I don't have one. I wouldn't think it was perfect either, so wrong again. As you are in your analysis of the cold hard facts. Like I said before, and if you have been paying attention, the point of these products is to reduce carbon dioxide output. If we take a town in Italy for example. The reason for this choice is that most Italian homes are are limited to 3kW. The B&Q machine produces 1kW. So at full output power (and don't start harping on about if the wind is blowing strong enough for full output power) then that's one third of the power supply for that home. If there are 10,000 homes and each has a wind turbine (from the Italian version of B&Q) then that's a 10 MW reduction in the power needed from some distant power station. Nice reduction in carbon output. Please watch 'An Inconvenient Truth' by Al Gore, if that's not too inconvenient.

gromituk wrote:

I don't service my kettle, my toaster, my bread machine, my telephone, my washing machine, my dishwasher, my computer, my television...

I haven't needed to look at the alternator on my car for ten years either and that's 'pretty much' the same as a wind turbine. I'd check the drain filters on your washing machine and dishwasher if I were you and if you live in a hard water area keep an eye on their heating elements. Point is, all machines and materials need servicing, you just need to wait a little longer for the items you listed above to break down.

gromituk wrote:

PS it's good to be able to read from top to bottom, rather than starting at the top, not understanding what the context is, and then finding what it's all about because the quote to which it refers is below. Thanks.

How's that?

BaJi_2

Cardew wrote:

How is the servicing comment naive?

I wasn't suggesting that it is unreasonable for it to require servicing, merely that the costs need to be taken into account in calculating potentional savings - or more realistically losses!

Fair enough. But again at this point in time it's more an issue of reducing carbon dioxide output. If you're thinking of the costs and savings you also need to include the question; what will be the likely inflation in fuel costs? Who knows what that will be in terms of general economic stability, will the debt mountain and housing bubble (world wide) cause inflation to rise? Will energy production costs from coal, gas, oil and nuclear sources increase? Who knows? It's a difficult question to answer and one that everyone will have varying degrees of comfort over. If the cost of fuel does rise and you've installed a wind turbine, then you can pat yourself on the back because it is likely that you will be saving money. If the cost of fuel stays the same price, then you spent out a lot of money but hopefully that has gone some way to reducing the output of carbon dioxide into the atmospere.

Cardew wrote:

It is very difficult to get any appliance serviced for less than £50 these days; and that is for everyday easily accessible household appliances with plenty of local tradesmen. How much then will it cost for a device mounted on top of a roof or above the roofline, from a specialist firm? £150?

No idea. But I do these things myself usually to save cash. If I had one I would learn any servicing procedures myself. I understand that that won't help most people though.

Cardew wrote:

Or if they are so reliable, why don’t the firm offer a maintenance package and tell us the price?

Best ask the firm.

BaJi_2

kittiwoz wrote:

Horizontal axis machines are able to re-orientate themselves to face into the wind. This is not necessary with vertical axis machines. However they create a lot of force in the support tower and are generally larger and heavier per kW rated output so not suitable for roof mounting. Turbulence is not the same as change of wind direction but is another problem altogether and one which would affect vertical axis turbines as well as horizontal axis machines. The turbulence problem is greater in more built up areas both in terms of density of buildings and building height. This is a major limiting factor on suitable sites for roof mounted turbines.

Can you give some more information on how you define turbulance? Could a horizontal axis machine be incorporated into the roof apex? This I imagine would be hard work when retro-fitting the machines but should be easy on new homes.

kittiwoz

A flow may be termed laminar, transistional or turbulent. A laminar flow is a smooth, predictable flow where viscous forces are dominant while a turbulent flow is full of chaotic eddies and is dominated by inertial forces. A transitional flow has elements of both.

The Reynold's number is used to define turbulence. The Reynold's number above which a flow becomes turbulent varies according to circumstance but one would generally consider it safe to say a Reynolds number above 1*10^5 indicates a fully turbulent flow. The Reynolds number is calculated: characteristic length times velocity divided by kinematic viscosity, the kinematic viscosity being dynamic viscosity divided by density. You should see from this that faster flows tend to be turbulent. This should make intuitive sense. Consider a simple chanel flow such as a river. A slow flowing river will have a smooth surface and all the water will be flowing in the same direction. If you throw a stick into the river it will be swept downstream along a roughly straight flowline. A fast flowing river is turbulent, it has vortices and eddies. If you throw in a stick it will ultimately move downstream but it will take a more complicated path, being swept around and back on itself. Another important aspect in causing turbulence is surface roughness. If you image a set of white water rapids you see the flow is extremely turbulent. This is not just because of the speed of the water but also because of the rough surface of the channel, there are rocks sticking up. This roughness can "trip" the flow into a turbulent state. In the context of a wind turbine the surrounding landscape is the base of the channel and buildings are a form of roughness.

Turbulence makes a big difference to flow behaviour. Generally it increases drag but reduces the likelihood of flow seperation (stall). It would mean constantly changing forces on the turbine so I guess would increase noise and vibration and probably reduce the lifespan of the turbine. I'm afraid I don't remember too much and I don't much want to go and dig my notes out since they are all packaged up in the cellar. Advanced fuid mechanics wasn't really my hot topic I'm afraid. I think an aero probably would know more than a mechie in so far as it relates to aerofoils anyway.

Turbulent flow is by it's nature unpredictable. The behaviour of turbulent flows is known for simple pipe flows and can be predicted using empirical equations. However for most flows computational fluid dynamics would have to be employed. This is also used to compute laminar flows but the computation of turbulent flows poses significantly more difficulty. In computational fluid dynamics the area to be modelled is broken down using a mesh to create a vast number of tiny control volumes. The flow through these control volumes is modelled using transport equations which describe the behaviour of the flow in a way which is appropriate to the scale but which are not physically correct. The data is stored at the nodes of the cell. Then some sort of convection scheme is applied to re-distribute the values. The corrected values are then used as starting values and the computer iterates until the values converge (or it crashes). There are various different models and convection schemes but the models for turbulent flows are necessarily more complicated than those for laminar flows. They contain unknowns such as turbulent kinetic energy and dissipation rate or turbulent length scale which have to be guessed and which will also go through iteration so as to hopefully produce a "right" answer. (In this context by right I mean a good approximation. The mesh will then be refined to produce the best possible approximation within the limits of available computational power.) There are a lot of potential variables and if you get them wrong you can get an answer which is totally rubbish. It is best to have some known data for the situation you can compare your results with.

Cardew

BaJi wrote:

As you are in your analysis of the cold hard facts. Like I said before, and if you have been paying attention, the point of these products is to reduce carbon dioxide output. If we take a town in Italy for example. The reason for this choice is that most Italian homes are are limited to 3kW. The B&Q machine produces 1kW. So at full output power (and don't start harping on about if the wind is blowing strong enough for full output power) then that's one third of the power supply for that home. If there are 10,000 homes and each has a wind turbine (from the Italian version of B&Q) then that's a 10 MW reduction in the power needed from some distant power station. Nice reduction in carbon output. Please watch 'An Inconvenient Truth' by Al Gore, if that's not too inconvenient.

In case it has escaped your notice, this is a 'money saving' site and this is forum is entitled Green and Ethical MoneySaving

If people 'invest' in alternative energy devices the majority do so with the intention of saving money - and in the vast majority of cases they won't!

10,000 homes in Italy all producing maximum output from their wind turbines – wow. I have visions of the engineers in the ‘distant power station’ yelling “switch down output by 10 MW now as there is a large gust of wind in Reggia”

BaJi_2

Cardew wrote:

In case it has escaped your notice, this is a 'money saving' site and this is forum is entitled Green and Ethical MoneySaving

Nope it hasn't espaced my notice but thank you for pointing it out. The simple fact is with green or ethical living most costs when shopping, etc. are higher than existing products to which they are the alternatives to. Therefore my dear boy, when we talk about money saving for green and ethical living. We are discussing the savings for that market alone. If you want to live green/ethically you will undoubtly end up spending more than somebody who doesn't. It is mostly about morals, capisci?

Cardew wrote:

If people 'invest' in alternative energy devices the majority do so with the intention of saving money - and in the vast majority of cases they won't!

Yes you are correct, however, they will be investing in the people around them and to help preserve our resources (oil, coal and gas which are very useful) and the environment. You might also create a few jobs in the green/ethical market too. Sit down and have a little think about the costs associated with global warming. I think you might need to do a little research on this subject too.

Cardew wrote:

10,000 homes in Italy all producing maximum output from their wind turbines – wow. I have visions of the engineers in the ‘distant power station’ yelling “switch down output by 10 MW now as there is a large gust of wind in Reggia”

Now you are being silly. What do you think happens during football matches during half time when everybody switches on their kettles to make a cuppa? I think you know the arguement isn't that simple. There is always plenty of demind in another part of the country or another country.

If you don't like wind turbines don't buy one. Look at the alternatives if you are serious about home power generation, which is what this discussion is about. If you live near a river or stream then hydro power is an excellent source of power. If you wait a couple of years then fuel cells are supurb. You will even be able to generate the hydrogen you need for them via PV cells. Otherwise it will arrive via your existing gas connection if you have one. There are CHP boilers and PV cells. Be constructive and put a little effort into saving power and providing solutions to the problem of global warming. That unfortunately, isn't solely about money saving.

BaJi_2

kittiwoz wrote:

Turbulence makes a big difference to flow behaviour. Generally it increases drag but.

Eh, thanks. You could have just written the paragraph that begins with the above sentence and I would have known what you were talking about then saved yourself half an hour's typing. But thanks anyway.

You didn't answer my question about vertical axis machines. I spoke to an Engineer friend of mine today who is Dutch. He said that wind turbines are very popular in Holland (of course) and he thinks there may be vertical axis ones for homes. He believes the extra forces generated on them aren't a problem. In fact the Dutch think home wind turbines are great. The only warning was not to buy a cheap one because the bearings tend to go early.