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187 The total output of the wind fleet of the Republic of Ireland. Data from eirgrid.com [2hxf6c].

- "Loss of wind causes Texas power grid emergency". [2l99ht] Actually, my reading of this news article is that this event, albeit unusual, was an example of normal power grid operation. The grid has industrial customers whose supply is interruptible, in the event of a mismatch between supply and demand. Wind output dropped by 1.4 GW at the same time that Texans' demand increased by 4.4 GW, causing exactly such a mismatch between supply and demand. The interruptible supplies were interrupted. Everything worked as intended.

Here is another example, where better power-system planning would have helped: "Spain wind power hits record, cut ordered." [3x2kvv] Spain's average electricity consumption is 31 GW. On Tuesday 4th March 2008, its wind generators were delivering 10 GW. "Spain's power market has become particularly sensitive to fluctuations in wind."

- Supporters of wind energy play down this problem: "Don't worry - individual wind farms may be intermittent, but taken together, the sum of all wind farms is much less intermittent." For an example, see the website yes2wind.com, which, on its page "debunking the myth that wind power isn't reliable" asserts that "the variation in output from wind farms distributed around the country is scarcely noticeable." www.yes2wind.com/ intermittency_debunk.html

- ... wind is intermittent, even if we add up lots of turbines covering a whole country. The UKis a bit larger than Ireland, but the same problem holds there too. Source: Oswald et al. (2008).

191 Dinorwig's pumped-storage efficiency is 75%. Figure 26.17 shows data. Further information about Dinorwig and the alternate sites for pumped storage: Baines et al. (1983, 1986).

192 Table 26.7. The working volume required, V, is computed from the height drop h as follows. If e is the efficiency of potential energy to electricity conversion,

V = 100 GWh/ (pghe), where p is the density of water and g is the acceleration of gravity. I assumed the generators have an efficiency of e = 0.9.

power invested

powe

1960 1970 1980 1990 2000

90 80 70 60 50

1960 1970 1980 1990 2000

Figure 26.17. Efficiency of the four pumped storage systems of Britain.

192 Table 26.8, Alternative sites for pumped storage facilities. The proposed upper reservoir for Bowydd was Llyn Newydd, grid reference SH 722 470; for Croesor: Llyn Cwm-y-Foel, SH 653 466.

193 If ten Scottish pumped storage facilities had the same potential as Loch Sloy, then we could store 400GWh. This rough estimate is backed up by a study by Strathclyde University [5o2xgu] which lists 14 sites having an estimated storage capacity of 514 GWh.

196 Fridges can be modified to nudge their internal thermostats up and down ... in response to the mains frequency. [2n3pmb] Further links: Dynamic Demand www.dynamicdemand.co.uk; www.rltec.com; www.responsiveload.com

197 In South Africa ... demand-management systems are being installed. Source: [2k8h4o]

- Almost all of Denmark's wind power is exported to its European neighbours. Source: Sharman (2005).

198 For over 25 years (since 1982), Fair Isle has had two electricity networks. www.fairisle.org.uk/FIECo/

Wind speeds are between 3m/s and 16m/s most of the time; 7m/s is the most probable speed.

199 Figure 26.13. Storage efficiencies. Lithium-ion batteries: 88% efficient. Source: www.national.com/appinfo/power/files/swcap_eet.pdf Lead-acid batteries: 85-95%.

Source: www.windsun.com/Batteries/Battery_FAQ.htm Compressed air storage: 18% efficient. Source: Lemofouet-Gatsi and Rufer (2005); Lemofouet-Gatsi (2006). See also Denholm et al. (2005).

Air/oil: hydraulic accumulators, as used for regenerative braking in trucks, are compressed-air storage devices that can be 90%-efficient round-trip and allow 70% of kinetic energy to be captured. Sources: Lemofouet-Gatsi (2006), [5cp27j].

- Table 26.14. Sources: Xtronicsxtronics.com/reference/energy_density.htm; Battery University [2sxlyj]; flywheel information from Ruddell (2003).

The latest batteries with highest energy density are lithium-sulphur and lithium-sulphide batteries, which have an energy density of 300 Wh/kg.

Some disillusioned hydrogen-enthusiasts seem to be making their way up the periodic table and becoming boron-enthusiasts. Boron (assuming you will burn it to B2O3) has an energy density of 15000 Wh per kg, which is nice and high. But I imagine that my main concern about hydrogen will apply to boron too: that the production of the fuel (here, boron from boron oxide) will be inefficient in energy terms, and so will the combustion process.

200 Vanadium flow batteries. Sources: www.vrbpower.com; Ireland wind farm [ktd7a]; charging rate [627ced]; worldwide production [5fasl7].

201 ... summer heat from roads is stored in aquifers... [2wmuw7].

Dinorwig Croesor0

Figure 26.18. A possible site for another 7 GWh pumped storage facility. Croesor valley is in the centre-left, between the sharp peak (Cnicht) on the left and the broader peaks (the Moelwyns) on the right.

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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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