Environmental Engineering Reference
In-Depth Information
free-running wind energy converters (see Chapter 7.1). They are pressure-staged
as cased wind turbo generator sets, and extract static pressure similar to a hydro-
electric power plant. Achievable efficiencies are thus higher than for free-running
wind turbines.
Air speed in front and behind the turbine is almost the same. The extracted
power is proportional to the product of volume flow and pressure drop at the tur-
bine. Turbine control aims at maximising this product for all possible operation
conditions.
The pressure drop and thus the flow speed and air flow inside the plant are con-
trolled by the blade adjustment mechanism of the turbine. If, in an extreme case,
the blades are at a right angle to the air flow, the power generation is zero. If, for
the other extreme position, the air flow passes the rotor unhindered, then the pres-
sure drop at the turbine equals zero; also under these circumstances no power is
generated by the rotor. The optimum blade position is between these two posi-
tions.
For turbine design, we can revert to the experience gathered with hydroelectric
power plants, wind energy converters, cooling tower technology and wind tunnel
fans. In this respect, the vertical-axis turbine seems to be the most evident solu-
tion. As an alternative, also a larger number of horizontal-axis turbines can be
used, placed concentrically in between the collector and the tower, so that cost-
effective turbines of common dimensions can be applied.
5.5.1.2
Plant concepts
For research purposes, to date, several very small solar updraft tower power ex-
perimental facilities of heights of a few metres have been built (e.g. in the USA,
South Africa, Iran and China). However, only one single plant of larger dimen-
sions in Spain has been built and operated for power generation during several
years in the 1980s.
Prototype located in the vicinity of Manzanares, Spain.
In the years 1981/82, a
pilot solar updraft tower power plant of a peak capacity 50 kW was built in Man-
zanares/Spain (about 150 km south of Madrid/Spain) /5-27/, /5-31/, /5-32/.
This research project was aimed at verifying the theoretical approaches and as-
sessing the impact of the individual components on the capacity and the efficiency
of the power plant under realistic technical and meteorological conditions. For this
purpose a tower (chimney) of a height of 195 m and a diameter of 10 m sur-
rounded by a collector of a diameter of 240 m was built (Table 5.13).
The chimney comprises a guyed tube of trapezoidal sheets (gauge 1.25 mm,
knuckle depth 150 mm). The tube stands on a supporting ring 10 m above ground;
this ring was carried by 8 thin tubular columns, so that the warm air can flow in
practically unhindered at the base of the chimney. A pre-stressed membrane of
plastic-coated fabric, with good flow characteristics, forms the transition between
the roof and the chimney.
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