Wind farm layouts

Wind farm layouts are pretty controversial. The bare fact is that putting turbines in the most lucrative positions which catch the most wind generally means putting them on top of hills. Which makes them visible for miles around.

There’s not really much that can be done about this conflict.

Besides, developers of wind farms don’t, as a general rule, actually buy the land they’re building on. Usually they rent it under contract from the landowner. And although the area of the wind farm is usually large, there’s usually a fair bit of spare ground around the turbines which can continue to be used for livestock or crops. In Scotland, we have laws protecting the right to access land; this means that if you want to go mountain biking at an operational wind farm the law is on your side (up to the point where you do any malicious or criminal damage etc obviously).

Once a contract has been drawn up with the landowner or landowners for a particular wind farm, it’s time to design a layout. This remains a challenging issue.

There are a number of criteria which are likely to restrict your options before the wind can be taken into account. These will include bird and wildlife surveys; land use and availability for roads; waterways and steep valleys which restrict access to heavy plant; planning restrictions on tip height; noise considerations; nearby residents; ground suitability; and local considerations such as archaeology, sites of scientific interest, and so on.

From there, the best practice is to use actual wind measurements to model how the wind flow changes across the site. Because you need at least a year’s worth of data from a met mast before you can really use the data (to cover all seasons), the reality of this part will vary substantially depending on how far into the project we are. If the project has two years’ of measurements at one or more masts on site, then great. Otherwise there are other sources of wind information we can use: bought data from a Met office measurement station; a virtual met mast built from a model; reanalysis data based on satellite measurements; extrapolation based on a combination of measurements. If the worst comes to the very worst the rule of thumb that “higher elevation = windier” would provide at least a guide.

Once you have an idea of the wind flow, you need to decide where to put the turbines. There are a number of things to take into consideration when doing this.

Each individual turbine removes a little of the energy from the wind it encounters, resulting in a slower wind speed for those turbines behind it. It also increases the turbulence, which further reduces the effectiveness of the turbines behind: it’s harder to extract energy from turbulent air. The combination of these is called the “wake” effects in the industry. To reduce the impact, it’s considered best practice to leave between 4 and 7 rotor diameters’ worth of gap between the turbines. Larger spacing is generally left in the predominant wind direction so that the overall wake effect is lower. (Offshore the spacing is larger, because wakes travel further offshore for reasons to do with atmospheric effects. Best practice will also vary from region to region based on the appropriate climate drivers.)

Trees and slopes will have several impacts on your positions. The top of a hill will be the windiest location, but steep slopes can provide huge challenges for accessing the turbines for construction or maintenance. Steep slopes also tilt the wind to an angle, and above 17° or so start to cause real problems for accurate wind flow or turbine performance modelling. Forestry increases turbulence directly above the forest, and can have other effects on the wind flow (increased change in wind speed with height, for instance, and boundary effects at the edge of the forest) which reduce the efficiency of the turbines.

Dwellings should generally be avoided as far as possible. I think the guideline in Scotland is 500m (note: there are experts on these constraints, and I’m not one), but a much larger buffer zone is wise. The issues of noise and shadow flicker are only relevant with regards to nearby homes. The danger of ice throw from blades or of blade throw is not thought to be a risk beyond tip height of the turbine (so if the turbine is 160m tall and you’re more than 500m away the risk to your property from these things is vanishingly small). To be honest I think the main driver here is the good will of the community. Big wind farms are generally built by bespoke developers, and there is much to be lost in appearing to trample over communities.

You want to maximise both the number of turbines and their output. Developers (or the banks who lend to them) take on the financial risk of a project when they sink their money into constructing the wind farm; they get nothing back until they start to produce electricity. If the costs of building and maintaining the wind farm turn out to be more than the wind farm can generate, the project is a failure. So the energy output is actually critical to project success.

Ultimately, then, from an industry perspective, the challenges of layouts are as follows:

• Comply with all planning restrictions
• Keep the local community on-side as far as possible
• Space the turbines 5 by 3 rotor diameters, which for an 82m rotor diameter machine (about average for large wind farms at present) is 410m by 246m
• Keep the turbines away from steep slopes, forestry, and dwellings as far as possible
• Install as many turbines as you can to increase your maximum production
• Put your turbines as high up as you can manage

I’ve often seen the accusation “poorly sited” levied at wind farms in newspaper letters. Reading between the lines, I suspect that this is because the writer objects to wind farms on hills where they can be seen, rather than that they know a secret way of establishing the best place to put wind farms that the industry hasn’t stumbled on yet.

Read Full Post »

Are we serious about climate change?

Imagine we lived in a world where climate change was an established fact, politically as well as scientifically. Governments believed it was a serious mid-term threat to our climate and our world, and that action must be taken, without violating civil liberties, to minimise the risk of global catastrophe.

What would we do? What could we do that we aren’t doing now?

Actually we could do a lot that we’re barely even looking at. A lot of it would have social benefits at the same time. The following are just my suggestions of what a government which truly believed in a green future would do.

• Seriously invest in public transport.
  I’ve been to Europe, and every country I’ve visited has better public transport than Glasgow does. They might have an extensive tram system, buses that give change, an extensive underground system, websites which actually mention where buses actually stop with reference to some map. German buses run to the minute on timetables; in Poland you can buy handfuls of bus tickets at newsagents.
  Compare this to Glasgow where the leading bus company provides maps with no street names, timetables that say “every twenty minutes” for much of the day, no information on fares, no change given, and buses that start and end in locations so far from Glasgow that nine times out of ten their stated destinations give no clue as to the route. (Campaign to change this: Better Buses.)

  Bus companies are private, but if a government really wanted to see improvement there’s loads of things they could do, up to and including renationalising. They could have some sort of legal minimum standards to protect rural areas and vulnerable passengers. They could require frequent independent assessments of any bus service. They could provide funds to councils to maintain several bus stations of a reasonable size to negate the problem that you can only change from one route to the other in the city centre. And that’s just my ideas. On the trains there are problems of overcrowding, overpricing and underinvestment. When was the last time you saw a new housing estate which merited a new station? Or a new station for that matter? Glasgow’s underground is pretty reliable most of the time, from past experience, but it runs in a circle which is only of use if both origin and destination are on that circle.

• Sanctions on new home energy efficiency.
  New homes would have to meet minimum standards for insulation, double glazing and energy efficiency. Any appliances provided would have to meet a minimum criteria. It’s far easier insulating properly as you build rather than re-doing it later, especially if it’s been decorated for you and you don’t want to do it again. Refurbishments for letting or that require planning could have similar standards applied.

  Sanctions applied on new builds now mean that 10 years down the line all homes up to ten years old meet reasonable modern standards. If we hesitate that’s even longer with valuable heat leaking out unnecessarily. Bonus is of course that the people who live in the house are warmer in winter, cooler in summer and spend less on fuel: everybody wins (except the big six, apparently).

• Reduction of cheap short-haul air travel.
  Want to go to London from Glasgow? Considered taking the train? Well you’ll find it can be twice the cost of a flight. You need to be really serious about your eco footprint to pay double for the sake of the environment. Ferry trips to Ireland or the continent are similarly enormously expensive compared to flights.

  A serious government would put systems in place to allow the same sort of cheap rates to apply to rail and ferry travel as apply to air travel. Or would put sanctions on cheap flights. I know that forcing things to be more expensive means the rich get as much as they like and the poor get squat. Sadly I haven’t come up with a better alternative to capitalism that will sell. The rich always get what they like in a capitalist system.

• Help to people making their home more efficient.
  There is some of this about. It’s restricted to cavity wall and loft insulation, though, there’s no “of equivalent value” for alternatives where necessary. I’ve not heard of any government schemes to install double glazing in rented accomondation, nor relaxing of planning consent requirements for energy-efficiency options. Listed buildings still need to put the look of any planned improvements ahead of their functional use.

  Free energy-efficient light bulbs just doesn’t cut the mustard in my book though.

• Recycling facilities.
  There are some recycling facilities. It’s fairly common to have doorstop recycling and landfill collections. This is a step forward: five years ago I could only drop off my recycling by driving to an obscure supermarket about fifteen miles away which seemed daft. However most bins in public spaces are simple rubbish bins with no option for recycling. But other reuse schemes seem to have mostly stopped. Remember the 20p collection for glass bottles? They still exist but it’s far harder to find them, or a shop that will exchange them, and far easier to find plastic bottles. Not to mention that 20p buys far less these days. Or morning milk deliveries that collected your glass bottles to refill them?

  I think we could do better on this, and I don’t think it’d take much effort. (I also fully expect that at some point in the future people will mine our landfill sites for rare earth metals. Not sure if it’ll happen in my lifetime… unless the recession gets really bad.)

• International negotiating.
  There are global resources that we all benefit from preserving. But I’ve yet to see a rich nation voluntarily paying rent to a poorer nation for a share of their resources. We condemn Brazil for chopping down the rainforest, but will we suggest or pay for other ways to feed their population than farming on previously rainforest land?

I’ve not mentioned renewable energy in here much. Although we could do more, our installed capacity of renewable energy has been growing at a huge rate, so that of the three main carbon producers in public life — electricity, heat, and transport — we’re doing far better on electricity than on heat or transport. Part of me wonders if that’s because you can wear renewable energy like a badge: Look at me, I’m eco-conscious, look how many wind farms I have! Harder to do with an inexpensive, fast and efficient railway system.

The evidence is that we in the UK are not living in a world which accepts climate change. We might say we want to reduce energy bills for vulnerable customers, but we want to do it by reducing profits of utility companies rather than by ensuring homes are as warm as possible. None of these suggestions are particularly risky, and most offer benefits to the poorest even if you don’t consider climate change a problem.

In a very real sense, we are not serious about climate change.

Perhaps we do need a true, personal catastrophe before we can take even these small steps. If so, what does that say about us?

Read Full Post »