Wind as energy source
Wind turbines / wind generators come in all shapes and sizes, but you will most likely recognise them in their industrial form, huge white propellers on giant white stems towering up to 80m high above ground. It is very unlikely your OffGrid project needs such a 150Kw monster. However in most areas a smaller wind turbine around the size of 400watt-3kw can be a worthwhile investment. The wingspan of these are 1m to 3m and will still fit into the landscape without standing out or producing too much noise. Simply put, the wind turns propeller / blades around a rotor, which spins a shaft, which connects to a generator to create electricity. A wind turbine will typically generate 30% of its theoretical maximum output on a slightly windy day.
Having at least one wind generator in OffGrid projects is recommended, even when your location is not particularly windy on normal conditions. During bad weather phases especially Autumn wind can be a very good source of energy to keep your batteries happy over longer periods of little to no solar. It also helps on battery lifetime to have the occasional charge in the night, even if it may only be 20 minutes. Big difference to solar is, do not size wind generators to big! A wind turbine will need to “get rid” of produced energy, if your battery is full and you did not install a resistor to burn off the excessive power you risk damaging your equipment. to give a rough idea, some 500w input for every 300ah of battery should be considered maximum.
Small wind turbines
Small wind turbines, also known as micro wind turbines, are used for microgeneration of electricity, as opposed to large commercial wind turbines, such as those found in wind farms. Small wind turbines often have passive yaw systems as opposed to active ones. They use a direct drive generator and use a tail fin to point into the wind, whereas larger turbines have geared powertrains that are actively pointed into the wind.
Small wind turbines typically produce between 500 W and 10 kW of power, although the smaller turbines may be as small as a 50 Watt auxiliary power generator for a boat, caravan, or miniature refrigeration unit
The generators for small wind turbines are usually three-phase alternating current generators and the trend is to use the induction type, although some models utilize single-phase generators or direct current output.
After running the three phase AC wire through a slip ring and down to the receiving end, a three-phase rectifier is used to convert the AC to rectified DC for battery charging, especially in solar hybrid power systems. The rectifier should be mounted to a heat sink for cooling, with the option of adding a computer fan that is activated by a bimetal thermal switch for active cooling.
A three phase rectifier being used on a rooftop mounted urban wind turbine.
The DC end of the rectifier is then connected to the batteries. This connection should be as short as possible to avoid power losses, typically with a shunted digital wattmeter in between for monitoring. The batteries are then connected to a power inverter, which converts the power back to AC at a constant frequency for grid connectivity and end use.
Types of windgenerators
Horizontal wind generators
These are the design you are probably most used to.
For best results they need to be put on a pole and above roof level, or in reasonable distance to any objects that influence wind flow. They provide very little to no power during slow air movement times, but will produce reasonable power during medium and high winds. Horizontal wind generators do create a certain level of noise. Although not loud, you can certainly hear it when the blades are spinning. Installing one right above your sleeping room might not be the smartest thing to do. Generally they are a bit cheaper than vertical ones.
Vertical wind generators
These provide power even with the smallest movement of air. Vertical wind generators are a lot less influenced by turbulence, as there is no nose that needs to point towards the wind, but instead they can utilise wind from all directions at the same time. If you plan on installing only a single wind generator for your project, a vertical one will provide more reliable power. These can be installed directly on the roof or such, there is no requirement to put them on a pole.
Wind power is variable, and during low wind periods, it must be replaced by other power sources. Transmission networks presently cope with outages of other generation plants and daily changes in electrical demand, but the variability of intermittent power sources such as wind power is more frequent than those of conventional power generation plants which, when scheduled to be operating, may be able to deliver their nameplate capacity around 95% of the time.
Electric power generated from wind power can be highly variable at several different timescales: hourly, daily, or seasonally. Annual variation also exists but is not as significant. Because instantaneous electrical generation and consumption must remain in balance to maintain grid stability, this variability can present substantial challenges to incorporating large amounts of wind power into a grid system. The combination of diversifying variable renewables by type and location, forecasting their variation, and integrating them with dispatchable renewables, flexible fueled generators, and demand response can create a power system that has the potential to meet power supply needs reliably
Solar power tends to be complementary to wind. On daily to weekly timescales, high-pressure areas tend to bring clear skies and low surface winds, whereas low-pressure areas tend to be windier and cloudier. On seasonal timescales, solar energy peaks in summer, whereas in many areas wind energy is lower in summer and higher in winter. Thus the seasonal variation of wind and solar power tend to cancel each other somewhat. Wind hybrid power systems are becoming more popular.