Solar Thermal Power Plants - Renewable Energy: Technology, Economics and Environment - page 212

the efficiency of the components collector η Coll , chimney tube η Tower and turbine(s)
η Turbine (see /5-29/, /5-30/).

& &

PG = ⋅ η = G ⋅ η η ⋅ ⋅ η

(5.6)

el g ,abs PP g ,abs Coll Tower Turbine

The solar radiation supplied to the plant G . g,abs is calculated according to Equa-
tion (5.7) on the basis of the meteorological global radiation incident on the hori-

zontal collector surface G . g and the horizontal collector surface S abs .

& &

GGS =⋅

(5.7)

g ,abs g abs

The impinging global radiation is characterised by a clear diurnal course which
also has an effect on the capacity cycle of the solar updraft tower power plant. A
balancing of the electric power output of such a power plant - which might be
necessary to allow for a more easy integration within an electricity provision sys-
tem - is possible by an intermediate storage of the solar energy. This is technically
possible by black hoses or bags filled with water, which, placed at the bottom of a
solar updraft tower power plant, serve as an intermediate storage. During the day
the water is heated up inside these storage elements and the stored energy is again
released during the night (Fig. 5.25). This measure allows a continuous updraft
inside the tower in spite of the fluctuating solar radiation throughout the day, and
thus guarantees a continuous power supply (also refer to /5-27/, /5-28/).

Global radiation Global radiation

Glass roof Glass roof Glass roof Glass roof

Day Day

Night Night

To the floor
and the hoses

To the floor
and the hoses

in den Boden
u. die Schläuche

in den Boden
u. die Schläuche

To the air To the air To the air To the air

in die Luft in die Luft in die Luft in die Luft

Ground Ground Water-filled hoses Water-filled hoses Ground Ground

Fig. 5.25 Heat storage by means of water-filled hoses (left: situation during the day; right:
situation during the night)

The collector efficiency η Coll is primarily determined by the radiation absorp-
tion by the collector and the thermal losses (see Chapter 4.1).
The turbine efficiency η Turbine is determined among other parameters by the de-
sign of the turbine blades as well as their speed. Profile and tip losses should be
minimized. Using multi-bladed turbines with inlet guide vanes (total-to-static
pressure) efficiencies of about 80 % can be reached.