dear oh dear!

[Martin]

I'm going to get known as "Martin the dream shatterer" - just fielded another phone call from someone wanting a roof-mounted turbine! He sounded bitterly disappointed when I pointed out that they were "chocolate teapots" as gently as I could!

[Chickpea]

Go on, please explain to me. Why are roof mounted turbines chocolate teapots?

[Martin]

best explained by this link -
http://www.wind-works.org/articles/Roof ... itain.html
this is written by one of the foremost US wind experts (he's written many of the textbooks)
We've had a pretty hefty hack at them too - visit our website, and read the posts in the "greening a school" -link at the bottom of the front page! 8)
I get REALLY cross about them - it's a blatant money making fiddle, which will leave a lot of people very disappointed, and heftily out of pocket - not the sort of thing we want to be associated with! 8)

[Chickpea]

It says "I've written elsewhere why roof top mounting of micro wind turbines-of any wind turbine-is a bad idea, so I won't go over the same ground again". I looked at some of the other articles and they don't explain either, but say it is complicated and explained in his books.

I'm not being funny. I know next to nothing about roof mounted turbines, except that David Cameron has one. Why are they bad? Is it as simple as "They don't produce much energy"? If that's it, why not just say so?

[Martin]

in the simplest possible terms the windflow is too low and turbulent close to the roof to work properly, and they WILL make a hell of a racket if wall/roof mounted, and cause major structural damage. I tipped the wink to our local Tory MP that he should save his esteemed leader from making a bloody fool of himself!
Chapter and verse again, this time from an English columnist
http://observer.guardian.co.uk/cash/sto ... 54,00.html
It is incredibly frustrating, because a PROPERLY sited wind turbine can be incredibly effective, and "payback" is one of the quickest in renewables

[Muddypause]

I have to say, Martin, that I'm not sure that comments simply defining rooftop turbines as pointless, are helpful. Firstly, because by far the majority of relatively poor, urban people in the UK live on a pocket hankerchief-sized patch of land, and don't have the luxury of being able to pitch a 30' tower. We have to work with what we've got, and we have to do something. Simply bemoaning the fact that we could do better if we had more land, or fewer buildings around us is a terribly negative approach. Secondly, as someone who has done a fair bit of roof level work on buildings, I can categorically state that even in a dense housing area, with roofs as far as the eye can see in all directions, there is no shortage of wind there.

I take your point about mis-selling, misleading claims, etc. And I take your point absolutely about structural problems that could be associated with mounting a turbine on a chimney stack. I can see that even bracketed to a gable wall, a weighty turbine could cause problems, especially on a lime mortared building. But this is not to say that some suitable mounting is not possible. And I don't see why mounting design cannot go a long way to reducing the noise transmission problem, too. These are problems to be addressed, not defeated by.

I can also see that the more gusty, unpredictable nature of the wind at rooftop level could be an issue. But rather than just resigning ourselves to impotence, surely we should be finding ways to deal with it. It cannot be beyond our wit to design a system around the conditions. Is anyone developing vertical axis wind turbines like the Savonius, or probably more likely, the Darrieus turbines? A changeable wind direction is irrelevant to these. Some claim that these designs can operate from lower windspeeds than a propeller turbine, and a Darrieus turbine can theoretically be as efficient as a prop. In fact with blade pitch control (which also overcomes the problem of self-starting), I would suggest there may be great potential for a practical rooftop version, propely mounted and bracketed.

I am not suggesting for one moment that a small rooftop turbine will provide all the electricity that a typical house uses - it can't possibly. But I can't help reflecting that within a mile of where I live, there are probably 1,000 or more tightly packed houses. We should look on these as a resource, rather than a problem. If only 20% of them had a device that provided a mere 10% of their needs, then repeated nationally, that would add up to a nuclear power station - the equvalent (I read) to 140 square miles of wind farm.

I'm not doubting your enthusiasm for microgeneration, but what we need is a pragmatic approach, rather than all-or-nothing idealism. Anything that empowers people, even if it is only by a lightbulb's worth, rather than just resigning themselves fully to the control of the energy companies, is a step in the right direction. And I can see other knock on advantages in this, too - people who are in some way dependant upon their own resources are more likely to be aware of the need to reduce their overall consumption. So the more people who can be enabled with some sort of turbine, the better.

[Chickpea]

I've read the "Greening A School" discussion on your site, Martin, and found it more helpful than the Gipe article. I think I understand what you're getting at now, although I take Stew's points too, but as I said I'm very ignorant about the topic so I don't really want to get involved.

One thing I try to bear in mind in my quest for self-sufficiency is the break-even time. If I had £500 to spend would I be better off getting £500 worth of solar panels, or £500 worth of loft insulation? Break-even calculations tell you where you can best put your money. It gets scary with rapidly advancing technologies because the answer might be "You're best off putting your money in the bank for a year because next year there will be a really whizzy new product that will be far better". But if some unscrupulous companies are trying to sell us a pig in a poke it becomes very difficult for the well-intentioned person to know what to do, and you can imagine that some waverers will become very disillusioned by the whole "green" project.

Personally I think there should be less emphasis on microgeneration and more emphasis on everyone using less energy, but I appreciate that microgeneration is your bread-and-butter Martin and I fully agree there needs to be activity on both fronts simultaneously.

[Martin]

I agree with most of what you say, BUT these manufacturers are "con merchants" selling empty promises that they've "conned" onto the grants list.
We're not talking here about "not very efficient" - we're talking UTTERLY useless! I was talking to someone "in the trade" the other day, who's actually got hold of one of the widest touted systems available - in a GOOD position it has failed to export ANY electricity over a six month period...........
Let me explain - to "grid-tie" what you produce has to synchronise for some two minutes before it can connect to export current - so every time the wind dies, back it goes to "dialup"..............then they don't tell the mug punters that although it is feeding current into the household system (whenever it gets a long run of wind, which in that position will be seldom/never), you have to be drawing that much current for it to be used by you - otherwise it wanders off "for free" into the grid!
At this very moment there is no turbine that should be mounted to a building - even vertical axis jobs cause the same structural damage if of "meaningful" size - just have a good read of Hugh Pigott's comments on the subject!
I desperately WANT to help people use renewables, that's why I'm in the business, but I cannot support roof mounted turbines in an shape or form - unless you can change the rules of physics that is!
If I sold these jokes, people would rightly be after my scalp, because they clearly, blatantly do NOT do what they say on the tin - not by a few irrelevant percent, but by several TIMES
For most urban dwellers, solar hot water heating offers far better value, DOES do what it says on the tin, so city dwellers aren't at all left out - give it a couple of years for the price falls in pv panels come along, and go for an acre of them too (but not just yet - big developments in the field will halve the cost).
SO, I see our job as being to view each project or home in an holistic way - what works, what's possible, what's affordable, what pays back swiftly - if you go to a turbine company, what are they going to sell you?..........

[Martin]

Chickpea - save it first, then generate it!
-go for the insulation! 8)

[Martin]

ps, having been heftily negative about roof mounting, there ARE some very useable systems coming along soon - one that has captured my imagination is a ludicrously simple idea - you feed a smallish battery bank from your turbine (or pv panels!), and then run all your conventional lighting circuits from an inverter powered by the batteries, and there's some clever sensing & switching which allows a seamless transition back to mains if the charge level drops too low in the batteries- that one's under test, it will be on the market in the next few months, and it will be affordable and effective!

[Muddypause]

there ARE some very useable systems coming along soon

Encouraging news.

What we seem to be encountering here is an industry that is in far more of a fledgling state than I had realised. It needs to be helped to develop, rather than be damned for its current state of incompetence. But I guess the nature of this industry is one that makes it ripe for the fraudster to try and make a quick buck.

My vision of the future is a small turbine producing a little electricity on a lot of roofs. Something say, one or so meters in diameter. I am convinced that this could easily be supported by a building, but I accept that it would take substantially more than a TV aerial mounting - it needs to be tied in to the structural fabric of the house. The real point of these is not to make anyone self-sufficient in their own generated electricity, but to reduce overall demand on the national grid.

One thing that puzzles me, that you may be able to answer, Martin, is why most small scale generators all seem to output at 12 or 24 volts. Why not 240v, thus obviating the need for a wasteful, expensive inverter, or separate low voltage circuits? I'm guessing that it may be to do with the torque load on the armature, but I really don't know enough about the physics of generator design to be sure.

[Martin]

as far as I understand it, you're right - the smaller turbines work best at the lower voltages, and are at their most efficient at those levels - again, small turbines tend to be used by amateurs/diyers and yachtsmen, and there's loads of 12v equipment that can be easily used directly from them. 8)
I really do wish I could wave a magic wand, and make the blessed things work on roofs - they are a lovely "idea", but until a LOT more work is done, I don't think the time is right for them - in theory, the vertical axis ones should be better in air that changes direction all the time as they don't have to "find" the wind, but you've still got that "synching" problem. Logically, it must be possible to somehow "smooth out the bumps" and hang onto the power generated by the gusts, perhaps by using vast capacitors - but once you start trotting off in that direction, you get the dreaded "losses" kicking in - THEN you have to face the fact that often the most low-tech solution is the best (less to manufacture and replace).......
What gives me hope is that the technologies are improving, and that there is a rising groundswell of opinion that we "have to do something", I am finding that renewables are "addictive" - we often visit people to talk turbines, who've already got solar hot water heating - once they've seen that it actually works, it encourages them to go further 8)
The other nice thing is that there are some reassuringly genuinely good people working on some really good developments (like the domestic lighting system) - I confidently predict that prices will be coming down on ALL renewables soon - (apologies for plug coming up) -we're trying our best -£2,500 for a solar hot water system, instead of the £6-8K quotes from the usual suspects, English engineeered turbines from £410..........