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Small Wind Turbines – An Irish User’s Guide

Nov 5, 12 • Energy, FeaturedNo CommentsRead More »

In the last few years, more and more small wind turbines are popping up around Ireland. This is testament to the ‘wind bug’ that enthusiasts get when they start looking into the technology.

Wind energy is clean and infinite and the fuel is free! However, the situation in the Republic of Ireland is still such that there is no support for small wind turbines, either financial or educational, and it is left to individuals and small companies to provide help to those with the foresight to see beyond the current fossil fuel-fired economic boom.
So, despite the very good wind resource here, the excellent technology available and the fact that wind energy is completely clean and renewable, small wind electric systems have difficulty competing on price alone. This is a pity, because they could make a significant contribution to this island’s energy needs – and save the country a lot of money and pollution – by providing energy at the point where it is consumed, rather than transporting it long distances, at high voltages and overhead on large transmission lines.

Grid-Connected Systems
For anyone with a mains electricity supply at their home or business, a grid-connected system is the most economical, efficient and environmentally friendly. The simple reason for this is that no batteries are required for grid-connected small wind turbines. Batteries are bulky and expensive, they require maintenance and have short lives, and there is an environmental (and social) cost when lead-acid batteries are disposed.
Westwind was the first company in the Republic of Ireland to install a grid-connected small wind turbine, after over two years of lobbying and making the case for the technical and safety aspects of such systems.
Grid-connected turbines are simple systems that connect into an existing fuse board (distribution panel). They synchronise with the grid and shut-down when the grid goes down, ensuring safety for linesmen that may be working in the vicinity. Unfortunately though, the current situation is that power generated in excess of the consumption of the house or business is (in most cases) ‘dumped’ when back-fed into the grid. This is because there is no provision in Ireland to pay the small turbine owner for excess energy generation.

Off-Grid Systems
A power supply based on a wind turbine, a suitably sized battery storage and in some cases a back-up diesel generator, will produce electricity much cheaper than the costs of bringing in power lines long distances or transporting costly diesel for running generators full-time.
For remote locations ‘off the grid’ (such as islands or remote homes) there is no other system in Ireland which can provide cheaper power. These systems will pay themselves off in a matter of years, if displacing diesel generation. Savings from having free fuel after this period will be substantial and would literally be an income stream.

Siting & System Design

Will Wind Energy Work For Me? 
Wind turbines large enough to provide a significant portion of the energy needs of the average household generally require a half to one acre or more of property. Ireland, with its largely rural-based population, has the space for literally thousands of wind turbines.
A small wind turbine will be suitable for your home or business if:
• There is enough wind where you live
• Local planning regulations allow small wind turbines
• You have enough space
• You can determine how much electricity you need or want to produce
• It works for you economically

What Size Wind Turbine Would Be Suitable for Me? 
Before you choose a wind turbine, it is wise to reduce your energy consumption by making your home or business more energy efficient. In many cases, installation of energy efficient bulbs, appliances and proper insulation can result in very large reductions in energy use. Depending on how much electricity you want or need to produce, an appropriately sized small wind turbine system can then be chosen.
Cost effective turbines that will generate a significant annual energy output (in kilowatt-hours, kWh, or “units”) for domestic applications range in size from about 1 kilowatt (1kW = 1000W) up to 10kW. Larger models are available and are suitable for small business or light-industrial applications. Smaller, or ‘micro’, turbines under 600W tend to be not as cost-effective, but are ideal for small spaces such as yachts or mobile homes, or for specialist battery-charging applications. Generally, the larger the turbine, the more economical it is at generating power.
Despite the fact that the island of Ireland is known for its excellent wind resources, the annual average wind speed – that which will determine a wind electric system’s output – can vary dramatically from one site to the next (see below). However, some indicative figures can be used to show what sort of outputs can be expected from small wind turbines:
A typical home in Ireland consumes about 5,000 – 7,000 kWh of electricity per year. 2.5 – 6kW models will usually cover part or most household consumption in a typical Irish household, depending on the wind regime.

Do I Have Enough Wind Speed? 
A lot of people in Ireland would say they have a lot of wind (!), mainly because of the awesome nature of the storms that are regularly thrown up from the Atlantic and pass over the island. Unfortunately though, many places do not have sufficient wind all year round or would be unsuitable for wind turbines because of trees, buildings and other obstacles.
Wind speeds up as it goes up a hill, so that the windward side and crests of hills generally have higher average wind speeds. The lee of a hill (i.e. in the wind ‘shadow’) will have a lower wind speed than the windward side.
The ‘roughness’ of an area also affects the average wind speed at a particular height. Higher wind speeds are experienced over smooth surfaces such as water and open bog-land compared to ‘rough’ landscapes such as forests.
Wind speed increases with height as you go up, so that generally, the taller the mast, the better will be the energy output of a turbine. The ‘quality’ of the wind also gets better with height, wind being more turbulent close to the ground. Turbulence results in decreased performance from a wind turbine and shorter life. Putting a wind turbine on too short a tower is like putting a solar panel in the shade!
The output of any given wind turbine is determined almost exclusively by the wind speed, as the power in the wind is proportional to the cube of the wind speed. Another way to say this is that if you double the wind speed you increase the power in the wind by a factor of eight.
In Ireland, small wind turbines will be most useful and economically beneficial where the annual average wind speed is greater than about 5 metres/sec (11 mph).
Average wind speeds can be determined a number of ways:
- By a year-long program of monitoring with an “anemometer” (wind speed measuring instrument, usually mounted on a tall mast). Westwind undertakes these measurement programs for designing large wind farms, but it really isn’t usually an option for small wind turbine installations, as the cost of monitoring the wind and the subsequent wind analysis required can in some cases be a substantial proportion of the wind turbine system cost.
- There is public wind data available (e.g. Irish Wind Atlas from www.sei.ie; or the Northern Ireland Wind Atlas from www.actionrenewables.org). These data must be treated with caution, as they are calculated by interpolation between widely spaced wind monitoring sites and gross assumptions of surface ‘roughness’ etc. They will also require logarithmic extrapolation down to a typical small wind turbine height.
- Companies such as Westwind offer a full system design service, which includes a site visit, wind speed research and calculations, and detailed design (the cost is refunded if a system is then purchased).

How Do I Choose the Best Site for My Wind Turbine? 
Any site will have different average wind speeds at different locations within the property. A first consideration will be height – are there any hills or raised portions of the property not too distant from the load (house, batteries, water pump etc)? These will be more suitable than gullies or in the lee of hills.
The site must also have a good ‘aspect’ to the prevailing wind. In Ireland, the most energetic winds come from the southwest and west, so that wherever a turbine is located, there must be few (if any) obstacles in these directions. The turbine should be ideally sited upwind of any buildings or trees and needs to be at least 10m above anything within 100m. You need to plan for new buildings and trees which have not reached their full height as well.
There must also be enough room for guy wires on a guyed tower, room to lower the tower for maintenance and safety margins for proximity to power lines and dwellings. For guyed towers, the size of the ‘footprint’ increases with height. ‘Free-standing’ towers do not require guys and can be fit into smaller spaces, however, they are more costly.
The wire run from turbine to load (batteries, house, water pump etc.) must be considered at this stage too. A substantial amount of electricity can be lost as a result of wire resistance, so that the longer the wire run, the higher the losses. Thicker wire will reduce the losses, but this comes at a greater expense.

Types of Systems
There is a range of small wind turbines to suit all consumption patterns, be they remote, unattended sites, domestic, business or farm use. Models are available for direct grid connection, direct-heating or ‘traditional’ battery-charging.
‘Grid connect’ is new in Ireland, and is recommended where there is an exisiting mains supply, as these are the most simple and economical systems.
Heating-only turbines are also efficient, and where there is a good wind resource these can substantially reduce existing heating-oil consumption.

‘Balance-of-System’ Components
Other system components include controllers, inverters, isolators, meters etc, and batteries in ‘stand-alone’ systems.
Inverters in battery-charging systems are sized by adding up all the watt or kW ratings of appliances and equipment you want to run simultaneously to give the maximum power needed (and adding in a safety factor, for equipment with high in-rush currents). Good inverters for battery-charging systems will have the ability to surge for short periods of time, usually 2 or more times their nominal rated power.
It is not necessary to size inverters for grid connect systems in this manner, as a grid-connect inverter is sized only to the generator output.
Battery bank sizing will depend on the application, the average daily consumption, the wind (and/or solar) regime and the maximum expected length of time for which no charging source will be available. Battery bank sizes can be reduced with the addition of solar PV modules to provide a charging source during calm days. Anything to reduce or remove batteries from small wind systems is ultimately smart, both economically and environmentally.

Planning Applications
In March 2007, the Department of Environment, Heritage and Local Government (DoEHLG) published draft exemptions for small wind turbines and other ‘Micro Renewable Technology’. Wind turbines must be ‘within the curtilage of a house’, and will be exempt from planning permission requirements if the tower does not exceed 10m in height and the rotor diameter does not exceed 6m (this corresponds to a turbine with ~6kW maximum output). There are also other requirements and these can be viewed at the DoEHLG website, www.environ.ie.
For wind turbines or locations not meeting these exemptions, planning application will be required, but this is generally not problematic, and most Planning Authorities are positive towards small domestic wind power.

Maintenance
Beware light and cheap turbines! Heavy, sturdier machines with strong towers are the most suitable for the Irish climate. They still require maintenance, but this is minimal with a sturdy machine, usually amounting to greasing bearings and polishing a slip-ring assembly annually. Guyed towers would require additional maintenance, to ensure guys are tensioned and fixings are secure.
With proper installation and basic annual maintenance, the turbines are designed for lifetimes of over 20 years.

The future for small wind systems in Ireland

The Way Forward
Ireland needs a system where a consumer can connect a small wind turbine to the grid (at their existing fuse board) and be paid the full retail rate for all power excess to their needs that is back-fed into the grid. This system is called ‘net billing’ and would allow turbines sized to enable full offset of the consumption of a household or business.
At the moment, a small wind turbine can be directly connected to the grid. However, any excess generated is not paid for by the supplier (e.g. ESB). Full net billing would make it economically viable for a larger-sized small wind turbine to be installed. The straight forward economics of net billing for small turbines would then result in benefits to the environment, the turbine owner’s finances and energy-use, and ultimately Ireland’s economy.
Another means of supporting the technology could be through capital grants and tax credits, such as in California and the UK, which would incentivize businesses and individuals even more than net billing.
In the UK, a payment is also made to the turbine owner for the environmental (i.e. CO2) benefit of on-site renewable generation. This is called a Renewable Obligation Certificate (ROC). Three different ways of assisting the small wind turbine owner are therefore available (none of which unfortunately yet exist in Ireland): A capital grant, payment for excess generation, and an environmental payment for all generation.
A zero rate of VAT on small wind (and other renewable energy) systems is also necessary. This would be the simplest, most direct way of supporting renewable energy and may even foster indigenous manufacturing, creating more jobs in the process.

For more information, visit www.westwind.ie

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