As you may have read here before, wind energy can be captured very efficiently by large, offshore wind turbines. In fact, the larger the better.

Despite this, there is still a place for smaller wind turbines – just so long as it’s the right place. So what is the right place to site a small scale wind turbine? Here a few simple guidelines:

1. Somewhere windy

Stating the obvious here. To be more precise, if you want a small wind turbine but your site doesn’t receive an average annual wind speed of 5 or 6 m/s then it would be wise to think again. You may think you live somewhere windy, but it is advisable to find out what your average wind speed is using an anemometer. Better Generation make the Power Predictor which you can put up on a pole to measure your wind speed. Far better shell out a few pounds now that to find that the wind turbine you bought is just an expensive weather vane. What’s more, you can pass it along to someone else once you know what winds you can expect.

2. The higher you can site the turbine, the better

Wind speed is higher, the higher you go. This means that if you have a taller mast to site your turbine, you will get a better energy return. Much better. As the speed of the wind doubles, the amount of ‘potential’ power contained in the wind does not double – it cubes. If the wind speed doubles, the power increases eight-fold (this also means if the wind speed halves, the power decreases by a factor of eight – bad news for slow wind speeds!).

If you can site your turbine high up at the top of a hill you can also exploit the aerodynamic effect which makes wind speed up as it passes over an obstruction. This is the same effect that gives an aeroplane wing its “lift”.

3. Stay well clear of buildings and trees

Wind turbines hate turbulent wind conditions. Even if you have decent average wind speed, if that wind is gusty and turbulent your turbine will not be able to consistently generate power. Manufacturers of vertical axis turbines (the ones that look like whisks) will say that their turbines perform better in turbulent conditions than a horizontal axis turbine will. This may be true (many are sceptical) but it is unlikely to make an non-viable site viable.

Guidance is that the distance to the obstruction should be at least 10 times the height of the obstruction. A higher mast can also help and a rule of thumb is that the turbine hub should be twice as high as any nearby obstruction.

4. Push the boundaries of small!

Bigger is better with wind turbines. This is a simple way of stating that the power of a turbine increase with the square of the rotor diameter. The longer the turbine blades, the greater the diameter of the rotor and therefore the more wind can be “captured”.

These four simple guidelines should help you to decide if a small wind turbine is right for you, and if it is, where the best place is to site it. If you’re hungry for further information, keep your eyes peeled for Small Scale Wind Power Generation by myself and Gavin Harper, forthcoming from Crowood Press and soon to be found in all good bookshops.

Jamie Bull |

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11 Comments on “The EROEI of energy balancing”

  • Dave says:

    Interesting. We’re looking at this topic this year and possibly next too. I’m not entirely sure that I agree that energy storage will be the most important way of matching supply and demand – there will be a kaleidoscope of alternatives including demand-side management (of course load-shifting might be seen as another form of energy storage in some respects!), but the broad thrust is spot on. Some Danish Universities are also looking at this sort of challenge. DTU Risoe and Aalborg from memory…I may have some useful contacts for you if you’re involved in the UK consultancy arena. Send me an email if you’d like to correspond.

  • Jamie Bull says:

    I totally agree on the demand shifting point – and have slightly edited the post to reflect that. It is a point well made in Mark Barrett’s work that I linked to. He particularly looks at the shifting of heat demand.

    However it’s not a strategy been studied with respect to EROEI that I know of, although there’s no reason why it shouldn’t be – I’m thinking of PCM-enhanced hot water tanks for example, which are certainly a form of storage.

  • Tom says:

    A couple major energy storage technologies you omitted are some of the most effective: thermal storage. Combined with CSP, this is, in effect, a form of fuel storage. In combination with a parabolic trough CSP plant, the RTE is around 85%, due to losses from heat exchange between the mineral oil working fluid and the molten salt storage medium. In contrast, Power tower CSP plants use molten salt as the working fluid, and so do not suffer from heat exchange losses, and hence have a RTE of 95%+

    The other thermal storage technology (which can also be considered a Demand Response Technology) that’s worth considering often has no embodies energy at all: Ice based thermal storage in conjunction with A/C. The reason for the no embodied energy is that the A/C operates at night when it is more efficiency, and can often be downsized in conjunction with adding thermal storage. During the day, the system only uses fans to melt the ice formed at night. The effective RTE can reach 100% or higher depending on the day/night temperature differential, because the ice is created at night when the A/C heat pump operates more efficiently.

    These technologies are probably a lot more important in the United States than the UK, because both work best in hot or sunny regions.

    • Jamie Bull says:

      Some good options there. But as you say, not really much use in the UK or much of Europe (with Spain a notable exception on the CSP front – I got some nice pics of one near Seville recently). Do you have refs for the RTEs?

      Interesting point on the heat pump working better when charging up the “coolth” store at night. I wonder whether that applies to charging up a heat store during the day for heat in the evening.

      • Tom says:

        The calcs for RTE were based on interviews for an article on CSP I did last year:

        The thermal tanks lose about 1%/day, and here’s a quote from the article: “According to Gould [of Solar Reserve] and Glatzmaier [of Sandia National Labs], the thermal storage systems systems at the Andesol [parabolic trough] plants suffer 7%-10% round-trip energy losses in heat exchange.” I’m afraid I had a computer crash a couple months ago and lost the original notes.

        Storing thermal heat during the day would produce higher efficiency electricity generation IF the plant is air-cooled. If it is water cooled, there would probably not be much difference. However, this would probably not make much difference in practice, even for the (rare) air-cooled plant, since the main current use of thermal storage on CSP plants is to shift production just a couple hours into the evening when demand is still high (and it’s still hot.)

        Ice based thermal storage would probably be applicable to most of Southern Europe: anywhere they use air conditioning in commercial buildings.

  • Richard says:

    I’m interested to hear your thoughts on the EROEI as applied to the use of hydrogen for energy storage and energy balancing. Similarly there is an increased interest in the use of the various advanced batteries designed for Electric Vehicle use as plug-in storage and local distribution system support services. I agree with your overall direction of getting the big picture parameters for all the options on the table – perhaps balanced with other more operational matters such as, how can these storage / balancing facilities be most easily evolved / introduced into the existing energy system. Sometimes the solution with the best ultimate macro-credentials don’t make it through these market evolutionary stages / barriers.

    • Tom says:

      The Hydrogen electrolysis/fuel cell cycle has horrible round trip efficiency of about 40-50%… it should not be seriously considered for grid based storage.

      Plug in vehicles can make more sense because the embodied energy of the batteries can be attributed mostly to the vehicle, which makes the overall EROEI picture look better. However, this assumes that the EREOI of plug-in vehicles makes sense. I have not seen an analysis of electric vehicles or PHEVs that takes into account the embodied energy of the batteries, so there is some doubt in my mind that EVs are actually better on an EROEI basis than petroleum fueled HEVs.

    • Jamie Bull says:

      I haven’t seen any study of the EROEI of hydrogen storage. The RTEs don’t look great though and it doesn’t gel too well with existing distribution methods. On the other hand I like the idea of hydrogen stores at the foot of offshore turbines, or alternatively at landfall, with fuel cells to allow power onto the grid when required.

      I note that German researchers have begun making natural gas using excess wind energy. Now if that’s not perfectly placed to tap into existing infrastructure (at least in the UK), I don’t know what is. There, though it will be important to avoid any methane leakage given its high CO2e.

      On the question of EV batteries and V2G storage/balancing services, that is definitely a promising area of the research for the future. I remember seeing some figures claiming the resource is nothing like the size it is sometimes made out to be but I can’t seem to find them. My back of an envelope calculations just now seem to suggest otherwise so I’ll take a closer look. If you’re in the UK there’s a conference on V2G coming up at the end of June in London.

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