Solar Thermal Power Plants - Renewable Energy: Technology, Economics and Environment - page 214

Without the energy extraction of the turbines a maximum air flow v Air,max of the
flowing air masses m . Air is created. Under these circumstances the entire pressure
difference ∆ p is converted into kinetic energy, i.e. the air flow is accelerated. The
power contained in the air flow P Flow is calculated according to Equation (5.12).

1

P = & m ⋅ v

2

(5.12)

Flow Air Air , max

2

Under the simplifying supposition that temperature profiles inside the tower
and the environment are more or less parallel, the flow speed created at free con-
vection can be expressed by Torricelli's temperature-modified equation (Equation
(5.13)); g stands for gravity acceleration, θ Air for ambient temperature of the air
and ∆θ Air for the temperature rise from the temperature at the collector exit or
tower entry.

∆

v = 2 g h

Air

(5.13)

Air , max T

θ

Air

Based on the discussed correlations, the tower efficiency η Tower can also be de-
termined by Equation (5.14).

g ⋅ h

η =

T

(5.14)

Tower

c ⋅ θ

p , Air Air

Fig. 5.26 Basic relations of a solar updraft tower power plant

The simplified presentation according to Equation (5.14) reveals that the tower
efficiency mainly depends on the tower height. All in all, the power output of the
solar updraft tower power plant is thus proportional to the collector surface and to