Wind is a costless, inexhaustible but intermittent energy source. Early twentieth century wind turbines were domestic multibladed fixed-pitch metal machines. Though aviation developments during World War I led to higher efficiency two — and three-bladed rotors [28], output powers before 1945 were generally no greater than 5 KW. A notable exception was the 1.25 MW variable-pitch machine on Grandpa’s Knob (Vermont, US), but after just 6 years in service one of its 8 ton metal blades fractured. Now lighter composite blades, power electronics and control schemes [29] result in mechanically reliable 2 to 3 MW rated machines with 20 to 30 year life expectancies. These are frequently deployed for individual factories or in “farms” of as many as 100 units to enable a cost-effective Grid network connection [30,31]. Powerful motivation for the present commercial developments of wind power emanates from the escalating costs of fossil fuels and the strident pandemic voices urging less global pollution.

An idealized fluid dynamic model [28] for the steady-state output power P of an isolated wind turbine reveals the engineering features necessary for materially sized power generation

P = CppAV 3 (1.5)

where

Cp — power coefficient; p — density of air, which at STP =1.29 kg/m3

A — area swept by blades; V1 — steady incident upstream windspeed

Because the density of air is so small[7] commercially sized power generation requires very large diameter blades. Contemporary 3 MW rated machines have 60 m diameter blades elevated to a total height of 115 m, and so are particularly visually intrusive [324]. Furthermore the 100 units of the Isle of Thanet 300 MW wind offshore wind farm [30,31] occupy 3500 hactares or about 3500 football pitches. Land shortages and therefore prices [20] in the United Kingdom dictate the construction of mainly offshore farms. In contrast, the complete nuclear reactor site at Winfrith occupied [32] about 31/2 hactares and reliably[8] generated its rated 100 MW for around 25 years. Moreover, its structure was designed to be compact, and apart from a water vapor plume all was invisible[9] from the main A352 road about 1 km away.

Equation (1.5) also shows that accessible power is proportional to the cube of the incident wind speed, so the geographical location of a wind farm is very important. As early as 1948 a UK government committee organized a survey of national onshore windspeeds [28]. Since then many countries have produced their own contour maps of annual mean wind speeds (Isovents) with coastal and offshore regions appearing to be the most economically favorable. Though Grid connections using synchronous or induction generators [35] have not encountered insurmountable difficulties [28], UK offshore wind farms now generate three-phase rectified dc current with onshore Grid-tied inverters [33,34] so as to effect an efficient and more economic Grid connection. Specifically, cable costs are determined by both the peak transmitted voltage and current, as heating by the latter reduces the breakdown voltage of its insulation. For a given cable, the ac and dc powers transmitted are

Pac = %VI cos f and Pdc = VI (1.6)

where

V, I — peak transmitted voltage and current respectively, cos f — power factor of the Grid network

(‘ 0.8 lagging for the United Kingdom)

It is seen that a wind farm with a dc cable link carries twice the power for the same installation cost.[10]

Table 1.4

Annual Wind-Power Data 2005-07

United Kingdom United States

Country Spain Denmark Germany

Capacity factor (%) 24.6 24 16 28 16-20

MCR wind power 41 4 81 5“ 105

(GW)

and the Netherlands.[11] However, if a shortfall in UK power is drawn from a continental connector, it would be at a premium price: especially in mid-winter. Furthermore, though Norway has an installed hydro­capacity [43] of about 30 GW, its peak demand in winter is around 22 GW, so this country could not offset [44] a major meteorologically induced disruption to the projected UK’s wind power generation. On the other hand, because reliable predictions of high barometric pressure zones can now be made several days in advance, UK-sited fossil and nuclear stations would be able to increase their outputs at demanded rates well within operational constraint limits.[12] Because nuclear power plants are capital-cost dominant and fossil stations are fuel-cost domi­nant, it is cost-effective for nuclear stations to supply the largely predictable daily base load, and for fossil stations to supply the more rapidly varying load excursions. For this latter purpose a number of fossil stations operate at around 80% of nameplate ratings (MCR) to provide a so-called “spinning reserve.” Sudden very rapid demands such as the unexpected disconnection of a large generating unit or a pause in a very popular TV program are also buffered by the pumped storage schemes at Dinorwic [40] (1.8 GW), Ffestiniog (0.36 GW) and Ben Cruachan (0.44 GW) but due to the very special topography required it is unlikely that other such suitable UK sites can be found. It is to be concluded that a “mix” of wind, fossil and nuclear stations has become necessary for a flexible, secure and economical UK power supply.

Total capitalization of the Isle of Thanet wind farm [31] is $1353 M or $4.5 M per installed MW. However, in addition to the loss of revenue from an inevitable shortfall of delivered power, there are the presently uncertain capital and operational costs of the necessary backup systems [52]. These depend on the future chosen “mix” of fossil and nuclear plants together with charges levied for power dispatched over the as yet unbuilt European Supergrid. Currently quoted costs for wind generation are therefore subject to considerable uncertainty, which perhaps led the Royal Dutch Shell Company to withdraw its support from renewable energy schemes [45]. On the other hand the UK Sustainable Develop­ment Commission [46] reports that “the economics of nuclear new — build are uncertain,” but this statement is contradicted by decades of worldwide practical experience—especially in the Far East. It is possibly of note that the UK’s coalition government disbanded [47] this Commission in July 2010.

Finally, the capacity factor of UK wind turbines in Table 1.4 appears heavily biased: possibly toward offshore systems. According to the UK regulator OFGEM that for the nominal 2 MW Reading city installation was just 15.4% during 2010. Even more significantly the market value of its electricity production was £0.1M, but thanks to a government subsidy, its owner Ecoelectricity received £0.13M. Under these conditions, large-scale wind power is an excellent investment for UK utility companies! Clearly, the true cost per actual MW generated, as well as environmental impacts [324] and Grid compatibility should be properly considered when deciding the future “mix” of UK generat­ing plant.