Microwind 3.5 Full Version 376
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In a wind farm, individual turbines are interconnected with a medium voltage (often 34.5 kV) power collection system[32] and communications network. In general, a distance of 7D (7 times the rotor diameter of the wind turbine) is set between each turbine in a fully developed wind farm.[33] At a substation, this medium-voltage electric current is increased in voltage with a transformer for connection to the high voltage electric power transmission system.[34]
Induction generators are not used in current turbines. Instead, most turbines use variable speed generators combined with either a partial or full-scale power converter between the turbine generator and the collector system, which generally have more desirable properties for grid interconnection and have low voltage ride through-capabilities.[35] Modern turbines use either doubly fed electric machines with partial-scale converters or squirrel-cage induction generators or synchronous generators (both permanently and electrically excited) with full-scale converters.[36] Black start is possible[37] and is being further developed for places (such as Iowa) which generate most of their electricity from wind.[38]
When the transmission capacity does not meet the generation capacity, wind farms are forced to produce below their full potential or stop running altogether, in a process known as curtailment. While this leads to potential renewable generation left untapped, it prevents possible grid overload or risk to reliable service.[47]
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. Integrating ever-higher levels of renewables is being successfully demonstrated in the real world.[74]
In 2021, a Lazard study of unsubsidized electricity said that wind power levelized cost of electricity continues to fall but more slowly than before. The study estimated new wind-generated electricity cost from $26 to $50/MWh, compared to new gas power from $45 to $74/MWh. The median cost of fully deprecated existing coal power was $42/MWh, nuclear $29/MWh and gas $24/MWh. The study estimated offshore wind at around $83/MWh. Compound annual growth rate was 4% per year from 2016 to 2021, compared to 10% per year from 2009 to 2021.[1]
Of the papers just cited, only Pourrajabian and Mirzaei (2014) considered structural optimization which is important for large-blade design partly because blade manufacturing cost correlates with blade weight (e.g. Sessarego et al. 2014). Structure is important for small blades in another way: starting depends on the aerodynamic torque generated by the blade shape and is improved by a low blade inertia, J B, which depends on shape, material, and manufacturing technique. It is to be expected that including structure in small-blade optimization will introduce complex interactions between the objective functions. To fully exploit the possibilities of structural optimization, it is necessary to design hollow blades, whose shell thickness can be minimized to reduce J B while remaining sufficiently strong. Examples of hollow composite small turbine blades are given in Clausen et al. (2013).
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