Queries

What about micro-generation? If you plop one of those mini-
turbines on your roof, what energy can you expect it to deliver?

Assuming a windspeed of 6 m/s, which, as I said before, is above the av-
erage for most parts of Britain; and assuming a diameter of 1 m, the power
delivered would be 50 W. That’s 1.3 kWh per day – not very much. And in
reality, in a typical urban location in England, a microturbine delivers just
0.2 kWh per day – see p66.

Perhaps the worst windmills in the world are a set in Tsukuba City,
Japan, which actually consume more power than they generate. Their in-
stallers were so embarrassed by the stationary turbines that they imported
power to make them spin so that they looked like they were working!
[6bkvbn]

Notes and further reading

page no.

264The maximum fraction of the incoming energy that can be extracted by a
disc-like windmill... There is a nice explanation of this on the Danish Wind
Industry Association’s website. [yekdaa].

267Usually, wind turbines are designed to start running at wind speeds around
3 to 5 m/s. [ymfbsn].

–a typical load factor for a good site is 30%. In 2005, the average load factor
of all major UK wind farms was 28% [ypvbvd]. The load factor varied
during the year, with a low of 17% in June and July. The load factor for
the best region in the country – Caithness, Orkney and the Shetlands – was
33%. The load factors of the two offshore wind farms operating in 2005 were
36% for North Hoyle (off North Wales) and 29% for Scroby Sands (off Great
Yarmouth). Average load factors in 2006 for ten regions were: Cornwall 25%;
Mid-Wales 27%; Cambridgeshire and Norfolk 25%; Cumbria 25%; Durham
16%; Southern Scotland 28%; Orkney and Shetlands 35%; Northeast Scotland
26%; Northern Ireland 31%; offshore 29%. [wbd8o]

Watson et al. (2002) say a minimum annual mean wind speed of 7.0 m/s is
currently thought to be necessary for commercial viability of wind power.
About 33% of UK land area has such speeds.

Figure B.9. An Ampair “600 W” micro-turbine. The average power generated by this micro-turbine in Leamington Spa is 0.037 kWh per day (1.5 W).
Figure B.10. A 5.5-m diameter Iskra 5 kW turbine [www.iskrawind.com] having its annual check-up. This turbine, located in Hertfordshire (not the windiest of locations in Britain), mounted at a height of 12 m, has an average output of 11 kWh per day. A wind farm of machines with this performance, one per 30 m × 30 m square, would have a power per unit area of 0.5 W/m2.