3.2.2 SMALL WIND
The small wind turbines are normally up to 100 kW. The homeowner's turbines can be directly connected to the distribution network. In this case there is no need of batteries. The produced electricity in excess of the homeowners' need is transferred to the distribution network. The interconnection with the network requires adherence to the technical standards and installation of a metering point.
Most small wind turbines generate direct current (DC) electricity. Systems that are not connected to the national grid require battery storage and an inverter to convert DC electricity to AC (alternating current - mains electricity)..
Wind systems can also be connected to the national electricity grid. A special inverter and controller converts DC electricity to AC at a quality and standard acceptable to the grid. No battery storage is required. Any unused or excess electricity may be able to be exported to the grid and sold to the local electricity supply company.
There are two types of wind turbines:
- Mast mounted - which are free standing and located near the building(s) that will be using the electricity.
- Roof mounted - which can be installed on house roofs and other buildings.
Individual turbines vary in size and power output from a few hundred watts to two or three megawatts (as a guide, a typical residential system would be from 500 W up to 100 kW).
The following issues should be considered about small-scale wind.
- Wind speed increases with height so it's best to have the turbine high on a mast or tower.
- Generally speaking the ideal site is a smooth top hill with a flat, clear exposure, free from excessive turbulence and obstructions such as large trees, houses or other buildings.
- Small scale wind power is particularly suitable for remote off grid locations where conventional methods of supply are expensive or impractical.
It should be noted that the electricity generated at any one time by a wind turbine is highly dependent on the speed and direction of the wind. The wind speed itself is dependent on a number of factors, such as location, height of the turbine above ground level and nearby obstructions. Ideally, you should undertake a professional assessment of the local wind speed for a full year at the exact location where you plan to install a turbine before proceeding. In practice, this may be difficult, expensive and time consuming to undertake. Therefore we recommend that, if you are considering a domestic building mounted installation and electricity generation is your main motivation, then you only consider a wind turbine under the following circumstances:
- The local annual average wind speed is 6 m/s or more.
- There are no significant nearby obstacles such as buildings, trees or hills that are likely to reduce the wind speed or increase turbulence.
Homes use approximately 10,000 kilowatt-hours (kWh) of electricity per year (about 830 kWh per month) though this amount can vary considerably. Depending upon the average wind speed in the area, a wind turbine rated in the range of 5 to 10 kilowatts would be required to make a significant contribution to meet this demand.
Small wind energy systems cost from € 3,000 to € 5,000 for every kilowatt of generating capacity, or about € 40,000 for a 10-kW system (installed). This is much cheaper than solar systems, but the payback period can still be lengthy – as little as 6 but up to 30 years. That's why it's important to take advantage of rebates or tax credits available for small wind system installations. Well-sited small wind turbines can usually pay for themselves within 15 years, about half their serviceable lifetimes, if the right incentives are applied.
Regarding the maintenance, it should be noted that most small wind turbines have only 2-3 moving parts and do not require any regular maintenance. They are designed for a long life (20-30 years) and operate completely automatically.
Regarding the connection of small wind generator to the distribution electricity systems it should be noted that in most countries the utilities are obliged to interconnect them and to purchase the power from the small wind generators.
Planning issues such as visual impact, noise and conservation issues also have to be considered. System installation normally requires permission from the local authority, so it's important to always check with your local authority about planning issues before you have a system installed.
How do small wind turbines compare with other renewable energy technologies
Small wind turbines (ranging in size from 250 watts to 100 kW) are often the least expensive power for remote sites that are not connected to the utility system.
A study by the Congressional Office of Technology Assessment found wind to be cheaper for meeting remote loads (loads not connected to a utility system) than diesel generators, solar photovoltaics or utility transmission line extensions. (Micro-hydro also was found to be less expensive in many locations).
Hybrid systems of wind/photovoltaic, wind/diesel, and other combinations can often provide the most efficient and cost-effective option for rural electrification. Solar Photovoltaic (PV) cells are often used to supplement wind power since PV tends to operate best in seasons when the wind is more calm. Diesel generators or batteries can be used for backup power and to maintain power production during low wind seasons.
Market status and government policy
The price of the micro wind turbines vary significantly in the different countries. The amount of energy and carbon that roof top micro wind turbines save depends on several things including size, location, wind speed, nearby buildings and the local landscape. At the moment there is not enough data from existing wind turbine installations to provide a figure of how much energy and carbon could typically be saved. Larger systems of 2.5 kW to 6 kW are normally mast mounted.
Turbines can have a life of up to 22.5 years but require service checks every few years to ensure they work efficiently. For battery storage systems, typical battery life is around 6-10 years, depending on the type, so batteries may have to be replaced at some point in the system's life.
The state financial support for the different countries is in different forms. In Bulgaria for example the subsidizing is in the form of obligatory purchase of the electricity produced from wind turbines at preferential prices. In most countries, however, the construction of the installation is subsidized.
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