Warwick Wind Trial Results (to date 11 Dec 2007)

These comments summarise some of the responses I have written over the last month to people in the microwind and smallwind industry who have been asking about the results of the Warwick Wind Trial, which spill over into a lot of related areas. Fundamentally Ampair supported this trial because we felt it was right to get hard facts into the public about the difficulties with urban grid connected microwind.

The WWT trial has had a difficult two years to get to where it is, namely the world’s first public domain trial of multiple models of grid connected small wind turbines on different sites especially urban sites. Just getting to this point has obviously been a mammoth task for the WWT team given the very limited resources they have had. All credit to them, especially to Mathew Rhodes and David Hailes. But they are now only one third of the way through (turbines up, data coming in) and they have the other two thirds still to come (capture one year of data, analyse data, write up and clean up). At this point they have only got one month of data (for Nov 2007) from all 24 sites (they have longer data runs from some sites) including the following manufacturers and products:

• Ampair (Ampair 600)
• Eclectic (Stealthgen D400)
• Renewable Devices Swift (Swift Mk2)
• Windsave (WS1000 c/w Plug’n’Save)
• Zephyr (AirDolphin)

There were going to be FuturEnergy turbines installed but they have failed to deliver as far as I gather. In fact an important learning point from the trial is that originally it was going to be of just Windsaves and Swifts but they both pulled out (as manufacturers). To date the only manufacturer that was prepared to commit to public datalogging was Ampair. All the other turbines have been ‘volunteered’ for the trial by clients. A list of the turbines that ought to be in the trial but are not yet (i.e. ones that are being marketed for building mounted including steel frame buildings) would include:

• Quiet Revolution (QR6 or QR5)
• FuturEnergy (1kW)
• SouthWestWindpower (various)
• Ropatec (various)
• Samrey (Wren)
• Aerovironment (Architectural Wind)

The results as presented at the 11 December 07 seminar are on the WWT site here except for the picture of the RD Swift that shed blades at BRE.

Quick advert: Yes we are very pleased with the relative performance of the Ampair 600. But we are not perfect and we have a lot to learn.

The context of the WWT trial is that several manufacturers have recently (last 5 years) entered the small wind turbine market with the initial marketing vision of low cost wind power for everyone (which by definition has to mean 0.5-1.5kW turbines; urban locations; grid connected; often building mounted). This is exemplified by Windsave and all credit to them for their laudable marketing ambitions. The industry incumbents then spent a few years trying to ignore the newcomers and then started to get serious about a response. From now on I’ll use Windsave as the exemplar of the newcomers since they’re the first to try breaking into the mass market with B+Q.

Quick advert: The media are trying to set us Ampair as being the 'rivals' of Windsave in a sort of mirror image way that media like to do. This is absolutely not what we are.

The main industry issue is the potential reputational threat to the industry arising from the over ambitious marketing claims of the newcomers. So as an industry we have become very serious about standards and testing, and in both the BWEA and the AWEA there are responsible manufacturers doing serious work in this respect (the AWEA effort seems to be mostly SouthWest and Bergy as manufacturers; the BWEA effort includes the following manufacturers: Ampair, Proven, Iskra, Gaia, Marlec, Quiet Revolution, and Windsave – I’m listing the ones I have seen taking standards committees seriously and yes that includes Windsave who are being very supportive in that respect). So the new entrants have done us all a favour in forcing us to take testing etc seriously and this is where Ampair have been putting its emphasis.

Soon people will be able to start publishing results in accordance with the new standards and that will be a dramatic step forwards. In the meantime there are already changes arising as a result of this - for example several manufacturers now have test sites in a way they did not have until recently. Also the new Ampair catalogue contains information we did not previously give.

Similarly the whole resource issue is being studied much more rationally than before. I think that within a year we will be able to predict actual windspeeds in post code grids (i.e. 10 house packets) to a fair degree of accuracy (much much better than NOABL). This work is being triggered by the new entrants but in truth it will be most use for people in the 5-15kW range. Early results are coming out in the form of adjustment factors in MIS 3003, the BRE assessment FB17, and the Loughborough CREST work and within a year these and the Warwick trial and EST trial and some other stuff in the pipeline will all be integrated.

Now coming to the particular commercial business case implicit in Windsave 'a wind turbine for every home' yes I would agree that these results objectively illustrate that this is not a good idea on electricity production grounds. The reason why we as Ampair agreed to participate in the Warwick trials when Windsave pulled out was because we felt intuitively that it was a bad thing for the industry to rush headlong into this in the way Windsave were (at the time they had just started their B+Q marketing campaign). Also at the time both Paul Gipe and Hugh Piggott were quite correctly raising serious concerns on both product performance and resource availability grounds with both of them doing useful work in informing the debate. At Ampair we decided to put our effort into the whole standards business and hoped that others would run the trials and expose their turbines to the reputational risk involved. But when Windsave pulled out of the WWT (by not supplying turbines) we felt that it was vital that somebody filled the gap and we stepped forwards. We'd only just got our grid-tie system working on the Ampair 600 so this was a huge risk to us. Also we were not exactly keen on house mounting (and still aren't) and definitely did not have the resources to actually go and do installs (and still don't – installation is what our distributors are supposed to do). So we were risking our reputation to disprove something we didn't in any case agree in and doing so on behalf of the wider industry.

Because of this we pushed to get the tower block sites included in the Warwick trial. As we expected the wind on these is very different than the suburban roofscape wind. In fact we are probably seeing more wind up there than at 5m height on Lands End. So far we cannot usefully convert all that wind into energy (because we are limited by our inverter, and because we are limited by noise production) and so we cannot yet reach any firm conclusions about the power production utility on these sites. But it is obviously a dramatically different prospect than suburban roofs.

So far the Warwick results only represent one month of data so it is simply too early to start doing much statistical crunching. And even when there is a year of data we can only crunch it so far as it is deliberately quite poor resolution data (to keep instrumentation costs down) and so the WWT team themselves are very sensibly trying not to over-analyse the data. In due course a higher resolution data set will become available from the EST trial which will include about 100 turbines but that is running about a year behind the WWT (there is some overlap) and then more analysis can be done.

Quick advert: The results to date for Ampair are that:

• The Ampair 600 appears to be at least as powerful as the Windsave WS 1000 and the Zephyr AirDolphin, i.e. Ampair's 0.6kW turbine is at least as powerful as the so-called 1.0kW turbines of the competitors.
• The Ampair 600 is yielding a much better import:export ratio than the competitors.
• The Ampair 600 has a much wider range of mounting systems than the competitors.
• The Ampair 600 is proving noisy in very high winds (on top of three exposed tower blocks - we are fixing this pretty quickly and already have workarounds in place).

In an Ampair context almost all our building mounted turbines have been included in the WWT, i.e. we're not hiding anything. In fact we've encouraged WWT to deliberately put turbines at very poor locations and it has been Ampairs that have ended up in the bad locations so we are certainly not cherry picking sites. Anyway we regard building mounted or urban microwind as being very much for R+D or for early adopters at present.

Overall the results so far are that at current energy prices there is not an economic case to be made for grid connecting at typical suburban roofline. There may be a rational economic case for grid connecting at tower block roofs. And of course there is always an irrational case (the green statement thing) or the rational case on non-power production grounds (e.g. for education). Already this crucifies many of the new entrants’ original business case but they are adapting and are now trying to persuade their backers that they will be mega rich at 2% of the UK housing stock. There is a prospect of some sites being suitable and I can see some sites yielding 1000kWh over the course of a year (i.e. 25% of a typical on-gas semi's electricity use; or 20 year payback from a £2k turbine not that the current £2k turbines models will last 20 years). Bear in mind that the UK has about 20 million dwellings.

Quickly we should put to bed the CO2 content issue. The BRE assessment FB17 analyses this in conjunction with the Bath Life Cycle Assessment work (we assisted both projects, see my earlier commentary) and the results are that for a wind turbine that has the design choices of an Ampair (think 'right' weight - too much or too little weight are both bad, as bad as weight in the wrong place) and is in a moderately windy location will have CO2 paybacks of less than 5 years. In a poor wind location CO2 payback for an Ampair is more than 10 years. In good wind CO2 payback on the Ampair 600 is less than 1 year. These paybacks are very sensitive to design choices and so the RD Swift and the Windsave are both much worse than the Ampair (which now gives you the three anonymous turbines in the BRE assessment FB17) which is a function of their poor weight ratios. This would be even worse for Windsave if the actual location of the manufacture of the Windsave were taken into account. It would also be bad for Windsave and for RD Swift if the actual performance of their units were taken into account (BRE have assumed the manufacturers' power curves are believable and only adjusted for wind resource: a fair assumption for Ampair but as is becoming evident this is not a good assumption fr everyone). So on CO2 payback turbines can vary from good to bad depending on wind resource and on model chosen.

Then returning again to the 'futility of using wind turbines in urban locations' question I would say that right now for most premises it is futile. But I think it is premature to write off the whole area in the way we were doing 2-3 years ago. As with other small wind turbine markets we will find that there are niches that are viable and slowly we will build successively better performing generations of turbines that compete in those niches. If I was a guessing man I would guess at seaside locations (so they must be marine grade) and high rise buildings (so they must be safe) and right weight designs and 20 year lifetimes for microwind which sounds like a fair description of an Ampair turbine. For small wind (5-15kW) it will mean a different set of clients (those with large plots of land). And the jury is still out on the Darrieus rotor crew (i.e. VAWT designs).

So if we can get 0.01% of the UK habitable stock to take a sub 1kW turbine each year that represents a market of 2000 units/yr which would be a useful contribution to greater volume manufacturing. Can we do that - I don't know. Are we taking it seriously ? Yes we are now which is not what we would have said two years ago. Are we betting the business on it ? No as we see it as just one of the many niches we have to compete in. Will we change our mind ? Probably, we must be rational technical/economic decision makers and we must be guided by the science in all this and as more facts emerge we will rethink things. If we can make a small wind turbine that can be affordabe and be building mounted and meet the criteria then we can progress towards the economies of scale. But we would be doing that in any case so it's not too great a distraction from our other markets which obviously look very different from a user perspective.

The initial results from WWT have triggered a substantial series of articles in Powerhouse News under the headline "Micro-wind manufacturers cry foul at trial humiliation” which I can't post for obvious copyright reasons. Well at Ampair we are not crying foul and nor do we feel humiliated. We have plenty of problems but we will fix the issues we are seeing because they are learning experience. I would encourage any other manufacturer or importer to step forwards, volunteer more sites for datalogging, and get on with learning. Ideally that could include small wind manufacturers in the 5-15kW bracket out in open terrain because now that WWT have a decent instrumentation package and data analysis process they can start to cost effectively deliver results to the public.

So to summarise the Warwick Wind Trial is a huge step forwards and the team behind it are to be congratulated. They are simply putting the data out and are letting it speak for itself. As ever more data is welcome and inevitably there will be comparisons made, some valid and some not but that’s life.

Small wind turbine power curves - Ampair historic practice

I thought it worth writing down how Ampair has been doing its power curve testing over the years. This is not intended to show ourselves as some sort of gold standard for technique but simply to say what we are doing in the spirit of full disclosure. Anyway historically Ampair has measured and reported its power curves:

1. Using real turbines, regulators, batteries, etc.
2. In open air.
3. Either on short poles or on vehicles.
4. With manual data logging of cup type anemometers at approximately hub height, and with manual data logging of voltmeters and ammeters.
5. Noting power into battery at typical battery voltages, and more recently of power into grid for grid connected (G83) inverters.
6. Publishing the results in our manuals and marketing literature.

Our underlying intent has always been to try and report a power curve that a client could reasonably expect to reproduce if they had commonly available instrumentation and patience. Taking the points in turn shows how things can be done differently.

1. Real systems have not been tuned for abnormally high performance, and include all the components that should be in a client's system.
2. An important part of the way Ampair tests turbines is that it is in the open air. The open air has a lot of variation in it and this causes turbines a lot of problems trying to respond. If you test in unreal conditions such as the smooth and stable flow of a wind tunnel it is easy to get much more power out of a wind turbine system than of the same system in real wind. This is because the mechanical and electrical system responses don't have any tracking error in steady flows and doubling of system power can be achieved in wind tunnels like this (assuming the wind tunnel is large enough, if it is smaller then the power out is even higher in a wind tunnel). By the way there is a role for wind tunnels and small wind turbines - but only for R&D work, not for published power curves.
3. Historically we've tested on short poles, or on vehicles. Both ways give similar results if you avoid too ideal a set up, or distortions induced by putting instrumentation in the wrong place. We typically do our vehicle testing in cluttered environments so we get very unclean wind on to the turbine, similarly our poles are ordinarily very low down and again we get foul wind. This is exactly how our clients tend to use our turbines.
4. We have used manual recording of the data from standard instrumentation. We do not use high precision instrumentation (we keep an eye out for calibration errors, but do no more than this) and we manually record what is best thought of as the visual average of the data we see. This visual filtering is important as it means we watch the three meters (volts, amps, knots) and look for the periods when they are steady enough that we can write down all three quickly. We could try and be very optimistic and write down only the peaks but that wouldn't be helpful, and if we were pessimistic and wrote down only the troughs we would be out of business as nobody would ever buy our turbines (this is what Hugh Piggott refers to as "marketing suicide"). We use cup type anemometers so that we are always recording the maximum wind available irrespective of direction and we set the anemometer at a height that gives it representative wind on to the turbine. A feature of using pretty basic instrumentation is that our results can be reproduced by clients (so in the olden days we used Avometers, these days we use Flukes) who aren't able to buy fancy kit. Until recently dataloggers were barely affordable for the smallwind manufacturers (such as Bergey and Proven) and not affordable for microwind manufacturers (such as Ampair).
5. We are interested in 'useful power for the client' so we are logging power into the battery or power into the grid. This is important as some people measure power out of the turbine which is often much higher than power into battery or grid because regulator and inverter inefficiencies can be much higher than people think.
6. It may seem obvious but we publish our results in our manuals and our marketing literature. Not all manufacturers are quite this transparent.

What I have just described above is a low tech equivalent of what is done in large wind turbines. The real issue is the genuineness of the good intent of the people writing the power curve. No amount of fancy instrumentation makes up for a person who is trying to push the data to mis-represent reality. In fact high tech instrumentation can make it easier to artificially over report a power curve. So when we read a test report (such as the yachting magazines produce every few years, or we have a conscientious client write in, or folk like Piggott and Gipe do tests) we pay attention if our turbines are behaving differently than we think they should be. And when people like Piggott say nice things like "It has never (except with Ampair) been my experience that the outputs I measure match manufacturer's predictions" then we think we are getting it about right.

In the future it is likely that we will start using higher tech instrumentation but we will do so in the context of a very tightly defined standard that will lay out exactly how to report power curves, which we are almost at with the BWEA small wind standard (and the related parallel AWEA one). We've been upgrading our long term test site at Misty View Farm in Cornwall with that in mind and we continue to install more and more kit as we search for a better way to do it. Until we are happy with that methodology we'll carry on doing it the way we always have. Amazingly very few people have ever done any serious work on comparative testing of small wind turbines and manufacturers' power curve claims and to this day the best work has been done by Paul Gipe (see Windworks ) who comes up with some alarming reports about almost all manufacturers' power curves. Fortunately Ampair come out well with the quote from Gipe of ".. the Ampair 100 were the only machines to exceed their power curves at any time". The other independent person who has looked seriously at this topic is Hugh Piggot of Scoraig Wind who has been turned down by the UK government when he has proposed to do independent testing on small wind turbines in the past which is a shame and which has limited his ability to do work in this area.

Why does all this matter ? Simple: clients make purchasing decisions on the basis of power curves and governments give grants on the basis of power curves. So if one manufacturer gives a power curve that is over-optimistic they attract a lot more (taxpayer funded) government grant and a lot more eager customers than another manufacturer that is more cautious. I would like to say that honesty is always rewarded in the long term, but unfortunately in the short term history reports that manufacturers can quickly be out of business.

Over the last two years Ampair have put a lot of effort in to move the standards agenda forwards and we've left it for others to do comparative testing of modern grid-connected microwind turbines. Now results are starting to come from public testing in but that's a topic for another post.

BRE report FB17: Ampair comments part 2

(continued from previous post on the BRE urban micro wind turbine assessment)

In calculating electricity generation BRE make the careful statement “the conditions under which the the [manufacturers’] power curves were obtained is, in most cases, uncertain, it is expected that they were obtained in wind tunnels or using free standing mast-mounted turbines”. Herein lies my biggest quibble with the FB17 methodology as BRE should have put this in much bigger letters and written an additional caution, namely:

WIND TUNNEL POWER CURVES ARE NOT COMPARABLE WITH OPEN FIELD POWER CURVES.

At the moment to use all wind turbine manufacturers’ power curves to predict electricity generation as if they were equal in quality is to introduce a large error especially as (to the best of my knowledge) of the three systems analysed only the Ampair 600 is an open field power curve. The reason for the difference is that in a wind tunnel one can hold the wind speed absolutely constant for the measurement period, and the wind direction is necessarily constant, and the turulence can be reduced to a minimum. This means that the turbine system performance is not degraded by a variety of tracking errors irrespective of whether they are mechanical in nature or electrical in nature. (This unfortunate situation will change as very rigorous standards for generating power curves are being introduced, but it is so important a quibble that we are disappointed with BRE for not emphasising their predicament).

Once this quibble is out of the way the actual values for electricity production in an urban environment are of approximately the right order of magnitude (at least for the Ampair). But the net electricity generation is different than the gross electricity production. This is because BRE have assumed (or not even stated the assumption) that the turbines are not importing electricity. Again for some systems this is an unwise assumption as the annual standby power consumption can be of the same order of magnitude as the annual production leading to a net generation of approximately zero, or even negative. For an Ampair system the extra money we put in to a high quality inverter pays off in very low standby powers so for Ampair the BRE assumption is valid.

The energy production figures are not corrected for any wind quality issues. As BRE themselves state this is a known issue and it is too early to try and make such adjustments.

The CO2 payback results appear sound. From an Ampair perspective it is pleasing that the Ampair pays back CO2 more quickly than the other turbines. We believe that this would be even more noticeable if the power curves were put on a level playing field and if the electricity import issue was accurately modelled.

The lifecycle costings contain an important error regarding the actual cost of System 3 (RD Swift). Obtaining pricing for this system has been notoriously difficult for the last two years and so it is unsuprising that BRE have used the only public domain data they could locate, that of £3.5k as provided by bettergeneration.co.uk who are not an RD Swift distributor and who are themselves misled. Unfortunately it is very misleading and a more accurate cost would have been about £7k. Whilst RD Swift are working hard to reduce both price and cost and certainly aspire to much lower than £7k the other two systems are being evaluated on their costs in the market today and once again a level playing field should have been applied.

The other issue with lifecycle costings is the maintenance and longevity one discussed earlier. We think that a quality turbine should aim to last on average 15 years with perhaps a five yearly on demand maintenance visit (i.e. four visits: once to install; two for maintenance; and one to remove), and a lower quality turbine should aim to last on average 10 years with four visits in total (at reduced intervals). We don’t mean lower quality in a pejorative sense: it may be more cost effective to make a cheaper turbine with a shorter life.

These two costing problems contaminate the finncial payback calculations sufficiently that one cannot make any further comments.

Further research is of course required and the proposed list is a sensible one. Overall I think this FB17 report from BRE is a pretty good assessment of the aspects of urban microwind and look forward to more pieces of the puzzle being slotted into the jigsaw in due course. Whether one thinks urban microwind is a good idea is a different thing and one we'll comment on separately.

(concluded)

BRE report FB17: Ampair comments part 1

These notes on the BRE microwind assessment are not intended to be a comprehensive scientific critique, just an informal and necessarily limited set of comments. We are a manufacturer not an academic institution.

This area is short of good quality work so anything as sound as this is to be welcomed. To ask for perfection at this stage would be mind numbingly boring and so any niggles must be put in that context.

Our most important criticisms are:

1. The cost of the System 3 is completely inaccurate. Our sources tell us that the true cost of this system is typically £5k-10k installed not the £3.5k assumed in the report which came from a very dated website which was quoting a 'target' price.
2. The manufacturer’s power curves have been used. The three systems have very different ‘quality’ power curves only one of which is measured in real wind conditions.

System 1 is an Ampair 600-230 EU2. We assisted Bath University in their Life Cycle Analysis (LCA) in the data gathering phase of their work, and put them in touch with BRE when we were approached by BRE to conduct another LCA. We thought another LCA would be repetitious and instead we asked BRE to invest their resources in a complementary piece of work which has become the resource piece of this BRE assessment. So in a sense we were the matchmaker but beyond that both Bath and BRE are autonomous and independent organisations and Ampair has not had any influence over either beyond commenting on an early BRE draft with respect to references to the Ampair product. In due course we look forwards to seing the full analysis that Bath have been conducting.

System 3 is the Renewable Devices Swift. This can be seen at a glance since it is the only 1.5kW turbine in production. More academically rigorous is the fact that ref 5 (Rankine, Chick, Harrison) has been quoted by RD Swift in the Swift marketing literature of 2006/2007.

System 2 must be the Windsave WS 1000 system complete with the Plug’n’Save inverter. This can be deduced because there are only two systems that meet the basic specification on p10 (albeit with some errors) and the price of £1798 on p40 narrows it down to the Windsave.

I’m writing the above paragraphs because it will assist researchers who need an independent reference for identifying the three systems which are being examined as exemplars of the microwind industry. They are also the only three systems currently on the market which pass the basic adequacy tests for grid connected urban microwind products so they are truly typical.

The inventory analysis is pretty sound. The WS 1000 is largely imported from Asian sources and so I think the impact would be higher than is predicted. The RD Swift data is for the Mk1 Swift and they have changed inverter for the Mk2 so it may no longer be representative, also I’m not sure that the impact data for the carbon fibre blades truly represents end of lifecycle costs (but that’s just a suspicion of mine re the HSE costs). The Ampair data is for the EU2 version and so is up to date. The most important issue I have with the inventory section is the assumption regarding maintenance. The authors seem to disregard visual observation as a good way of initiating condition-based maintenance which is a pity. Our experience is that the combination of visual observation and a passable ear is appropriate. Maintenance issues don’t come on neatly in annual cycles – they arise much faster – so an annual inspection is very costly (economically and environmentally) and ultimately futile. Instead it is better to either assume condition-based maintenance or a range of lifetimes. In this respect I would be extremely suprised to see all these turbines lasting very long in a coastal environment as the only one that appears to be marine grade is the Ampair although again I am happy to be corrected. Constructing a marine grade turbine is an expensive business and is directly reflected in the purchase price of the units.

The urban wind resource estimation is as good as it gets at the moment in the public domain from a theoretical perspective. To a certain extent theoretical work can only go so far and practical work can only go so far and the final picture will only become clear when all the pieces of the jigsaw are fitted together (several times). The experimental wind tunnel data re flows over building roofs look fairly similar to results from CFD modelling work carried out by the Loughborough University Centre for Renewable Energy Technologies (CREST) team led by Simon Watson and are not unsuprising, i.e. higher = better, and ends = better, and ridges = better, and best of all is of course to be as far away from buildings and trees and other obstructions as possible.

The BRE comparison of Met Office windspeeds, NOABL windspeeds and predicted actual windspeeds is very interesting. In Appendix B they show the relative location of the Met Office instrumentation and the five sites for which they have predicted wind speeds. The first thing is that the shape of the wind speed distribution is very important in assessing the energy yield and that can be observed in the Fig 5 on p15 and Fig 7 on p16 where the more ‘marine’ a wind is the more energy it contains. This change in a wind’s character is of course not described by the NOABL database. Then the correction factor that BRE calculate using their BREVe tool (based on BS 6399-2) to produce a prediction is as yet not tested against reality (from the perspective of small scale wind) and so for now is a harmless exercise. Soon they will no doubt be cranking the same BREVe tool for comparison with actual winds measured from various trials and then we will get closer to the holy grail of accurate site specific prediction. Ideally such a tool will be predicting mean wind speed, distribution, and turbulence but that is of course an ideal which will have a rather large error bar on it.

(to be continued)

BRE report FB17 available "Microwind turbines in urban environments"

The Building Research Establishment (BRE) have issued a new report titled "Microwind turbines in urban environments - an assessment" which goes by a unique publication number FB17. Since one of the turbines considered as being representative is the Ampair 600 I'll comment on it in another post but for now here is the contents:
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It can be purchased from the BRE online shop
http://www.brebookshop.com/details.jsp?id=287572
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Title: Micro-wind turbines in urban environments - an assessment

Author: R Phillips, P Blackmore, J Anderson, M Clift, A Aguilo-Rullan and S Pester

Date: Nov 30, 2007

Price: £42.30

Stock Code: 287572

ISBN: 978-1-84806-021-0

Abstract:
There is little experience of the operation of small wind turbines mounted on domestic buildings in urban environments and little data on their performance in terms of power generation, service life and maintenance.This BRE Trust-finded study shows that, in addition to the initial embodied carbon and efficiency of the turbine, the payback period is highly sensitive to local wind conditions, transport costs, maintenance requirements and the life of the turbine. It reveals large variations in output of micro-wind turbines in a city such as Manchester and a windy location such as Wick in Scotland, and between the outskirts and town centres in windy locations.In windy locations, micro-wind turbines can generate enough energy to pay back their carbon emissions within a few months or years but in large urban areas, micro-wind turbines may never pay back their carbon emissions. Life cycle costing suggests that, even in favourable urban locations, financial payback is unlikely for all but the most durable, efficient and low maintenance turbines.This work confirms the need for a more rigorous method for estimating the electricity generated from building-mounted micro-wind turbines and for research and innovation in technology, planning and urban design to maximise the effectiveness of the turbine installations. 47 pages.

Benefits:

• Provides a rigorous analysis of all the factors that influence the power that small wind turbines can generate in urban areas
• Studies the whole life costs and carbon emission costs of micro-wind turbines
• Case studies for three locations - Manchester, Wick and Portsmouth

Contents:
Executive summary
1 Introduction
2 Inventory analysis of micro-wind turbine systems
Introduction
University of Bath LCA data
System boundaries
Recycling
Results
Comparison with LCA data for other turbines
Installation, maintenance and operation of the micro-wind systems
3 Estimation of typical urban wind resource
Introduction
Wind resource - adjustment factors for urban environments
4 Electricity generation by building-mounted wind turbines in typical urban scenarios
Introduction
Methodology for the electricity calculation
Results
Conclusions
5 CO2 payback for domestic micro-wind turbines in urban environments
6 Life cycle costs and financial payback for micro-wind turbines
Introduction to life cycle costing
What costs are taken into account when undertaking LCC for a wind turbine?
7 Discussion and conclusions
8 Further work
9 References

Subject/Keywords:
FB17, wind power, renewable energy, microturbines, costs, life cycle analysis, LCA.