Small Wind Turbines
Technological advances in wind turbines have grown rapidly. In the shadow of multi-megawatt wind turbines emerges another growing sector within this industry: residential wind energy. Improving the design of the blades for maximum efficiency at low wind speeds, high efficiency generators with permanent magnet devices, improved control methods, control systems and sophisticated inverters, will now allow home owners to connect in parallel directly with utility companies or proyect a system which will be independent of the grid. These systems have increased energy independence, competing with current energy prices and reducing environmental impacts. Several new small wind turbines that use modern and advanced technologies have been introduced in the market and with the promise of more to come.
Small size wind turbines are defined as any wind turbine with a rated capacity of less than 100 kW. Many small wind turbines and the makers of these turbines have been criticized of poorly manufactured and estimated lifetime.
Slow speed wind industry has been growing in the last couple of years, and with the adventage of modern technologies today, the efficiency and lifetime of slow speed wind turbines has improved dramatically. Now more than ever the focus is on the economic viability of these machines and some manufacturers have taken this opportunity to increase the overall quality and performance. Not many people live in a place with wind high winds, and quite often they lack of quality or amount of wind needed for consistent power production. This scenario has increased efforts directed toward improvement in the efficiency of the turbine for low wind speeds.
An important consideration in designing a wind turbine is the Tip Speed Ratio (TSR) of the blades to the alternator / generator. The TSR is the ratio of the speed of the blades on the wind speed. Although a high TSR may be advantageous to keep the costs of the blades because they can use thinner sheets as well as the need for a smaller alternator due to a higher rotor rpm, this usually results in machines with shorter life cycles and louder blades. Designing wind turbines with low TSR means to increase the width of the blade resulting in an increase in efficiency at low wind speeds and lower rpm resulting in a silent and durable turbine. This helped to maximize the start at low wind speeds and increase energy production at the lowest levels of the power curve. Controlling the output of a wind turbine and the rotor speed can be one of the biggest challenges for designers and manufacturers. Without proper control of wind turbines speed can affect the maximum efficiency, also high winds can damage equipment. Electronic controls load the alternator to keep the rotor at the maximum peak power as the wind speed until the desired maximum power level is reached. Controllers also enable maximum power to be transferred to the batteries, consistent with preservation of battery life time related to your charging system. The power that exceeds the available battery charge is diverted to a heat load, which can be a normal water-heating element that allows end users to use the surplus energy that would otherwise be dissipated as heat. The advanced control enables small wind turbines to couple directly to the utility grid without using the battery bank. Several inverters are now available to communicate with the machine controller and synchronize with the voltage and frequency of the grid with very small conversion losses. These network inverters provide maximum power at high efficiency range on a system without a battery bank, ideal for a remote measurement system. This enables consumers that use the public grid opportunity to sell their excess power to the grid at the same price that they charge their users. Combining several or all of these technological advances in wind turbines could result in the manufacture of quieter more efficient and extended life of small wind turbines. The implementation of these technological advances do not come without its cost. By increasing the size of the alternator and blades also increases its weight. This leads to more expensive manufacturing costs, more robust and higher requirements for the construction of the support towers and higher shipping costs. Sophisticated controllers and inverters also come with a price tag slightly higher than their predecessors.