Following on from the last post, ‘George’ was asking about mass-production and very small wind turbines. The impression was that he was thinking of extremely small ‘mills’, so for the sake of discussion, we’ll assume that something like the Eclectic Energy Stealthgen, or Marlec’s Rutland 903 is what he had in mind. These are 300 watt, lightweight HAWTs designed to mount on small yachts, lamp posts or road signs; I have seen a few used in this way in Oxfordshire, in conjunction with very small solar PV cells. As small turbines go, they are reasonably efficient for their size, and modestly priced (a few hundred pounds/dollars each). Being made of standard materials and of simple design, they are amenable to mass-production and could, in theory, be mounted in groups of fifty or a hundred in relatively small sites. Would this be a good idea?
To help explain why this would be less efficient (in both materials and productivity) than larger systems, a few very important basics of wind power need to be covered. I’ll skip some of the detail, but the principles are well-understood and already factored in to many manufacturing decisions.
The two most critical factors in the amount of power which can be generated from any wind turbine are the strength of the available wind (the wind energy potential) and the amount of wind ‘going through’ a turbine’s blades (the swept area). Other important factors include the ‘quality’ of the wind resource (energy-reducing elements such as shear and turbulence) and the siting of the turbine relative to surface conditions (surface roughness).
The greatest amount of wind energy potential anywhere is relative to height above ground level; the higher you go, the more energy is available. This is able to be calculated using the wind power law or the wind log law. Even a difference of a few inches can increase or decrease the average amount of wind received at the turbine head. And it is the average, or mean wind, which matters here; both in terms of directional stability and long-term unit productivity. This is why large wind turbines want to be sited on tall masts.
The ‘down-side’ of this factor is that effective (by which I mean cost-effective) installations are likely to be, by definition, visible in the landscape. Without going into the arguments here, I’d suggest that almost all of the objections (in the UK at least) to wind installations derive from people believing they will be visually intrusive or ‘ugly’. My simple response is that in many cases a single small or medium-sized turbine has considerably less visual impact than a radio mast or electricity pylon, and that, assuming that the aim of objectors is to preserve the countryside they cherish, the long-term view must be that, without renewable energy, the countryside is likely to be transformed in ways which are more permanent, more damaging, and more ‘ugly’ than almost any alternative.
The relation between swept area and power output is in a squared proportion. A turbine which sweeps 10% more area than an alternative will give perhaps 40% more power (I can’t be bothered to do the sums today) for the same wind energy available. This explains why the manufacturers of large systems, such as the ones used on wind farms, are focussing their production on ever-larger, ever more powerful turbines. In fact, most of the companies which once produced ‘mid-sized’ systems no longer make them at all. This is a matter which I’ll return to later, in discussing ‘affordable’ local solutions.
This does not mean that there is no place for small wind systems; on the contrary, ‘small’ wind could (according to recent estimates) account for a sizeable percentage of the entire UK’s ‘domestic’ energy use. It also does not mean that only large systems are economically viable. This is because, whilst wind farms needs to justify their costs by providing a return on investment and productivity at rates of 2-4 pence per kWh, small systems only need to work out as competitive in relation to end-user energy charges (tariffs), in order to be worthwhile. Having just seen a 13% rise in electricity charges yesterday, anyone who has energy generating capacity to replace that provided on the grid is making a net gain, since energy prices are rising faster than background inflation.
As things stand, with the technology currently available, (and depending on individuals’ current best available tariff), if a small turbine can produce 700-1100 kWh per £100 spent ($200), then it is probably going to both pay for itself and provide a long-term net return on the cost. If domestic users are willing to accept a small penalty in terms of cost in return for making a contribution towards reducing emissions, then the productivity can be even lower. Given the likelihood of ongoing long-term energy price inflation, a canny reader might realise that, so long as the additional cost is less than the sum of the inflation over the turbine’s lifetime, there is a reasonable chance that no cost will be incurred at all.
Rather than a field filled with extremely small turbines, then, I’d suggest that a chain of slightly larger ones (5-25 kW), is a more practical and more economic idea. In the next post or two, I’ll continue with more reasons why it works out this way.
In the meantime, if you have been thinking about putting a wind turbine up but aren’t really sure whether it is for you, or if you have a company which is suffering because of the high cost of energy, be warned that the Old man is now working for an engineering company in the UK which installs these things; get in touch, and I’ll try to help give you some answers (no charge, since it’s you…).
Old man in a cave 
11 comments
Comments feed for this article
January 5, 2008 at 2:48 pm
S2
Increasing the diameter of a turbine by 10% would (all other things being equal) increase it’s output by 21%.
The output of a turbine is proportional to the cube of the wind speed, though – so increasing the average wind speed by 10% (e.g. by increasing the height of the supporting mast) would give about a 33% improvement.
For readers in the UK, the DTI has a database of wind speeds by area which you can access via http://www.bwea.com/noabl/
I don’t know how accurate it is, but at my location (apparently) I have 6.1 m/s at 10 metres above ground level. This increases to 7.8 m/s at 45 metres. That’s an increase of 28%, but that would be enough to double the output of a turbine (not that I think I’d get away with a 45 metre mast).
If this is typical then wouldn’t large arrays of small turbines still need to be mounted on fairly tall (and heavy) masts for optimum efficiency?
January 5, 2008 at 3:01 pm
george
Fergus, you’re thinking much bigger than the possibility I was and am curious about. Your 300 watt “small” turbine example is still designed as a stand alone unit & grouping them only scales down the farm. I’m wondering about scaling down the turbine to a miniscule unit comparable in size to a child’s pinwheel, then packing dozens or hundreds of these tiny units as tightly as feasible into a frame designed to hold, support and orient them to wind direction. The resulting “wind frame” or “wind box” could be flexible in size and shape, but perhaps averaging no larger than, say, the old-style sat TV dishes.
January 5, 2008 at 3:55 pm
fergusbrown
S2: thanks for the proper numbers. The answer is a simple yes; for optimum efficiency, height always pays off. In practical terms, upgrading from a 9m mast to a 15m one adds only about 4-5% to the cost of installation, for a much larger performance improvement. (info. from a manufacturer’s costings).
The trick, as ever, is to balance the complexity factor (to mount a 15m mast, you need 30m of space and 3m2 of concrete foundation), the amenity value/objection ‘problem’ (if there really is one; this is often more real in the imagination than in practice), and the return. This is why even relatively small installations are carefully considered and planned, so that every possible factor can be taken into consideration, and the optimum decision reached; which may sometimes involve accepting a small reduction in performance under some circumstances, if this makes the project ‘work better’ in other ways.
George; it was as I understood it then. The only possible use for pin-wheel-sized units would be to trickle-charge relatively small batteries; their energy output would simply not be large enough. It is important to remember that to produce a charge, you need to have a degree of torque, to drive the generator/stator, however small it is. Such small ‘mills’ could not produce more than a tiny amount of electrical charge, even in groups. The bottom line is that you could only produce pennies-worth of energy, and even if a boxful of mini-micro mills only cost a few bucks, it would be hard to get a return on the cost. I still think you should be thinking bigger; for example, at least a couple of feet high.
Another critical limiting factor is the component costs of the electrical equipment. You have to convert wild AC into DC to charge batteries, or have a flow regulator in the system. In a nutshell, one big generator/inverter/rectifier/regulator is proportionally less expensive than several small ones.
January 5, 2008 at 8:50 pm
Aaron Lewis
The local paper recently carried a front-page photo of a golden eagle that had been killed (along with a pile of other birds) by a local wind farm. That makes me want to go back and rethink the “outside the box” alternatives.
Consider a city where the buildings deflect and channel wind so that in some areas near the buildings, average wind velocity is greater than it would be without the buildings. In this case, a wall of micro-turbines (pinwheels) could be used to absorb the wind energy and make the environment around the buildings less windy and more comfortable. In this case, the entire cost of the turbine system could be charged to “ambiance” and any power would be free.
This brings up the question of, could a “wall” of light weight, low cost turbines with engineered ducting /cowling deflecting and accelerating wind through the wall provide a useful amount of energy?
The connectors and electronics could be essentially printed on the modular support structure, and thereby be very low cost. Think about the “wall” as a modular building material used for a very wide uses where it is desirable to deflect rain, or noise, or livestock, or wind but air flow is allowed. For example, a rancher, instead of putting up a thousand miles of barbed wire fence might use a 3 meter high “wind wall” and sell the power to the Texas grid. In addition, the walls could be used to build large structures intended specifically to capture wind energy. The area swept by such structures could be larger than the area swept by even the largest wind turbines.
January 6, 2008 at 1:28 am
fergusbrown
Birds are occasionally killed at wind farms. The average rate appears to be around 2 birds per turbine per year. By comparison, around 100,000 birds are killed from hitting/being hit by cars, in the UK alone. Perhaps we should rethink our transport policy? Whilst no bird deaths at all would be ideal, as a cause of mortality, wind farms rank a very long way down the list of problems. Further evidence of the relative safety of wind systems, even small ones, should be clear from the fact that several bird sanctuaries have them installed, and they are approved by the RSPB in principle. The idea that birdkill is a windfarm problem is a myth fabricated by NIMBY groups seeking to block their progress in the planning stages. basically, birds can see turbines, feel the wind flow, and either fly through them or around them.
Unfortunately, your assumption about average wind speeds in cities is not quite right. Yes, there is a funnelling effect around high-rise buildings, especially in some places such as New York or Chicago, but there is also a very large level of turbulence, cross-directional flow and shear; generally speaking, the ‘quality’ of the wind resource in cities is considerably lower than in open spaces; this is one of the reasons why Urban Wind Turbines (UWTs) have not been very effective so far. There are some interesting innovations around, such as the Quiet Revolution and the WindWall, but these are less productive on average than a standard HAWT, well-sited.
On the installation of wind into the fabric of buildings; this is being tried at the moment, but on a different scale. Back to the pin-wheels, you have to consider that a modular supporting structure would have to have thousands of electrical connectors, miles of wire, and some device to hold the pin-wheel in place when the wind hits 50 mph plus. To ensure they are not smashed apart the first time there is a storm, they’d have to be overbuilt. adding considerably to costs. Each pin-wheel would have to have its own generator/stator, which would probably cost more than the wheel itself. Then you’d have to link them to inverters, and probably bridge rectifiers, flow regulators and meters. All of this then has to be connected to the grid, or to a battery system.
I’d be surprised if a pin-wheel could generate even so much as a watt of energy at peak output, and a proportion of this would be lost through normal system losses in electrical power. Given that you’d need to space them so they don’t ‘shadow’ each other and stop the flow from reaching nearby wheels, you might be able to fit them 50 cms apart. On a 3m high ‘wall’, you might have them four or five ‘deep’; if each produced half a watt on average, to produce one megawatt of power, you’d need a ‘wall’ 200 kilometres long. How much would a 200 kilometre wall cost, and how much material would be used in its construction, compared to one not-so big turbine on a 65m tower, or say 4 x 250kW turbines on 30m masts? Would the visual/environmental impact of such walls be less than the alternatives? If the rancher put up ten 100kW turbines, one every few miles, along his fence line, it would almost certainly cost less, be less intrusive, and be much more reliable.
In your ‘fence’ suggestion, you’d also need to show that such a structure could survive ice, snow and hurricanes; something that even a reasonably small standard turbine can do (a Proven 6kW continued operating throughout a super-typhoon in Kobe last year, and is still working fine afterwards). A similar turbine is being taken to the Antarctic (not for the first time) by the BAS. Windside VAWTs are purpose-designed for extreme weather and are frequently used in the Arctic circle, for example at mountain lodges or military patrol stations.
Finally, the cost; To produce 1mW of output, you want to be spending what? Big wind does it at around £700/mW, or around 3 pence per kWh produced (this is expected to go down to around 2.2-2.4 pence in the next ten years). Medium sized turbines, around 250kW, cost in the range of £1600/mW, or 4-5 pence/kWh. If your wall produced effectively for its size, you might get 20,000kwH/year from its entire length, if you were lucky, and if the site was reasonable windy. If the value per unit was 13p, a 200 kilometre wall would produce around £2600 worth of electricity in a year. If the wall cost £10 per metre installed – an extremely optimistic suggestion, that would be 2 million pounds/mW installed. That’s two thousand times more expensive than a single medium-large turbine.
Sorry to be such a negative-nanny, but the numbers are simply not adding up. For a measly million or so, I could let you have three 250kW turbines on 30 metre masts (less than half the dimensions of a wind-farm large turbine, and smaller than the average pylon or radio mast) , which would produce, at a reasonably good site, around £200-250,000 worth of electricity at current rates offered by energy companies for green sell-back, and you’d get an ROI in the double figures after full pay-back in four or five years. For £25000, not including grants and allowances, you could have a small, domestic sized unit which should pay for itself in 11-18 years, depending on the available wind and the site. At a push, and with maximum grants, in a good wind area, like Scotland, a 2.5kW turbine will cover its costs, whilst offsetting tons of carbon in its lifetime, at around £13-14000.
As things stand, any smaller alternative, however it is constructed, is unlikely ever to pay back the cost of installation and maintenance. This could change in the next few years, as innovative designs and higher standard energy tariffs change the scene once again. If my own ‘clever idea’ comes to fruition, there might be a small turbine suitable for domestic use available for a few hundred pounds, which would cover its costs in production over a lifetime of energy production, but this is at the drawing-board stage at the moment. Such a machine is possible, with mass-production. When a million of these are up and running, you could see more than 200,000 tonnes of carbon offset in a year.
Please keep bringing on the ideas; somewhere, someone will hit on the winner. I still don’t think the ‘pin-wheel wall’ is it. 😦
Good night.
January 8, 2008 at 1:41 am
Aaron Lewis
You are thinking like an engineer, and you do a very good job of thinking like that. Nevertheless, sometimes the solution is in the accounting, rather than in the engineering. Sometimes the solution is the design. Sometimes the solution is in the marketing. I think engineers and sailors have dominated the work on wind turbines.
I would say that the number one cause of bird deaths is birds flying into glass windows, being stunned, and thereby subject to predation (by cats). However, there is the rather high take of raptors by the Altamont Pass wind farm. Therefore, bird take by wind turbines demands hitting the Google button at least once. We find http://www.biologicaldiversity.org/swcbd/Programs/bdes/altamont/altamont.html, http://www.aviary.org/csrv/WindEnergyRaptorsWhitePaper.pdf, and http://www.enn.com/top_stories/article/21370. It is worth quoting the last item because it offers numbers relating to raptors:
“Last year a wind turbine project off the coast of Norway was particularly fatal to immature sea eagles. The poorly sited project all but eradicated the resident population of white-tailed eagles, killing nine eagles in 10 months, including all the region’s first-year birds, and apparently causing the decline of breeding pairs in the vicinity from 19 to one pair.”
Unfortunately, I live near Altamont Pass, so it is my back yard. The high raptor mortality at Altamont Pass was the result of a convergence of factors, some of which were due to the bad siting in the local ecosystem while others were due to the wind turbine and tower technology used at the time. Wind turbines at Altamont Pass kill an estimated 880 to 1,300 birds of prey each year, including up to 116 golden eagles, 300 red-tailed hawks, 380 burrowing owls, and additional hundreds of other raptors including kestrels, falcons, vultures, and other owl species. The Altamont Pass is an ecological sink for golden eagles and other raptor species and may be having significant impacts on populations of birds that are rare and reproduce infrequently. These two examples show that wind farms are not inherently bird safe. We can not rule out the possibility that the reason there are relatively few birds killed by wind turbines is that there are relatively few wind turbine sites. More birds are killed by flying into glass walls, but there are many more glass walls than turbines, so fewer birds are killed per glass wall. If we had as many wind turbines as we have glass walls, then we would likely have horrendous bird mortality. (There may also be a sampling problem where owners of wind turbine sites fail to report bird strikes.) In the US, killing migratory birds or almost any raptor without a permit means talking to Fish and Game, and that results in things like “Settling Parties Avian Wildlife Protection Program” (http://www.biologicaldiversity.org/swcbd/Programs/bdes/altamont/Updated-blackline-Exhibit-G-for-Settlement.pdf). Any kind of a serious talk with F&G is expensive.
So my question for anybody that talks like an engineer and understands wind turbines is,” Why are wind turbines not inherently bird safe?” I am not being rude. I am talking like a hardnosed consumer. Killing birds is expensive. Why don’t we just design turbines that avoid that cost? I want to write bigger checks to the engineers and smaller checks to the lawyers and F&G.
January 11, 2008 at 8:05 am
fergusbrown
Lots to mull over her, Aaron. Am I thinking too much like an engineer? Can’t answer that one. Like all developing industries, wind turbine discussion has been the domain of engineers, whilst they continue to look for the best solutions to the problem from the point of view of sustainable productivity. It’s been of interest to sailors because, for them, it works; when you’re crossing oceans, a source of battery recharging power which pretty much works all the time (so long as the boats move) is extremely useful, if not a lifesaver. But right from the start, it has also been the domain of environmentalists and conservationists.
There is no question that birds do die at wind farms, and that this is not what we want to happen; it is actually bad news for everyone. Since at least some of me is an environmental ethicist, perhaps you can permit that I, too, would like to see the impact of these things reduced to zero, or at least as near zero as possible.
The two examples you cite are well known. They demonstrate that poorly planned developments can have a negative impact on aspects of the environment. (This is why EIAs are carried out routinely on most projects). However, even these are not uncontroversial results. Some doubt has been cast on the Altamont numbers, though nobody argues that it didn’t turn out to be an ideal site for a very large wind farm. Apparently, there are suggestions that some of the casualties might have been ‘plants’.
Leaving aside the question of how many and how bad – and this really is not as cut and dried as either the developers or the NIMBYs would like – let’s address your end question: why aren’t turbines ‘bird safe’? My first question to you would be; are they not ‘bird safe’? Just about everything we do has an impact on birds in some way or another. The only place they are safe from human influence is in large wilderness areas. And these are at risk because of climate change. Ecosystem loss is a much greater, more meaningful risk to bird population than wind turbines. The RSPB estimates that 50% of bird species in the UK may be lost by the end of the century. In the face of this long-term risk, which is undoubtedly more to be avoided than the coincidental deaths of individual birds, however unfortunate these are, we need to respond.
Having spent some time researching this issue, I reached the conclusion that, other things being equal, and risks taken into consideration, wind power remains the cleanest, most environmentally-friendly, potential energy resource (avoiding the nuclear option, at the moment). The current designs appear to represent no more risk than any human structure, so long as they aren’t put in stupid places. We have to balance the relative expense of occasional bird loss against the relative expense of massive species loss, ecosystem damage, and (somewhat reluctantly) human needs, which currently include electricity. Though the case can be argued, it has been stated for some years now that the notion that wind farms represent an enhanced risk to bird populations is a myth.
On the question of design, two thoughts; first, one or two designers of VAWTs have claimed that these are inherently safer than HAWTs, but there is little evidence to support this claim. Second, there is the issue of cost. As things stand, nobody would be investing in wind if it was not relatively good value as an energy source. Alternatives to the standard design are generally expensive, less efficient, and not clearly beneficial. No matter what you build, it seems that some birds will fly into it. The answer, at the moment, is in the location and siting of facilities: in other words, careful planning and proper accounting of damage relative to returns.
For an environmentalist, an ideal world would contain few if any humans; that way, ecosystems and species would develop and fall away ‘naturally’. For a conservationist, an ideal world would contain no new building at all. Since neither option is practical, we have to evaluate what we do, balance environmental costs and returns in the same way we evaluate financial ones, and make sure that all environmental issues are given their due weight in decision-making. What bugs me is the almost certain knowledge that the environment in all its forms is still undervalued against other considerations when the decisions get made.
So, we can be critical of wind, of nuclear, of renewables and of fossil fuels. We can see costs to anything we do, but how do these stack up against the bigger, longer-term, global risks? Of all the things we can do to mitigate against climate change, I contend that developing wind power is the best, all things considered. Of all the things which have a negative impact on the environment, I suggest that wind is a long way ahead of almost every alternative in its ‘friendliness’.
January 23, 2008 at 12:02 pm
Rencontre
Well I find it terrible for the birds to get killed by wind farms. On the other hand we live in an industrial world with lots of energy needs and I guess that wind farms are at least delivering clean energy.
January 31, 2008 at 9:39 pm
Connecting News, Commentaries and Blogs at NineReports.com -
[…] … national wind watch: news – Last Updated – Sunday January 20 Request a Trackback Wind energy; how small is practical? Following on from the last post, ‘George’ was asking about mass-production and very […]
February 18, 2008 at 9:59 am
SCM
Its awful quiet in here.
Where are you Fergus?
August 28, 2009 at 1:01 am
slingword
My take:
http://slingword.wordpress.com/2009/08/27/obamo-blew-it-or-how-your-government-let-you-down/