Basics of Renewable Energy Supply - Renewable Energy: Technology, Economics and Environment - page 72

P = ρ g q h

(2.25)

Wa Wa Wa util

By integrating Equation (2.25) over time, the corresponding work capacity of
water power is obtained. It is thus calculated on the basis of the water density, the
gravitational acceleration, the flow rate related to a defined time period and the
utilisable head.
A certain water volume V Reservoir can be held back in times of high precipitation.
Also for that type of storage, the water resources equation (Equation (2.21)), in-
cluding inflow, outflow, and occurring leakage and evaporation losses, applies.
Additionally the discussed conditions apply to the power and work that can be
provided by the reservoir. The power depends on the time period required for
emptying the reservoir. The stored energy E Wa is defined by the size of the reser-
voir and thus by the stored water volume and the utilisable head. Equation (2.26)
applies.

E = ρ g h V

(2.26)

Wa Wa util Reservoir

2.4.2 Supply characteristics

Measuring water-technical parameters. The utilisation options for hydro power
can only be reliably estimated on the basis of measured values. Therefore, meas-
uring precipitation, runoff, or flow is of great importance. The individual tech-
niques will be briefly explained in the following (see /2-23/).

Measuring precipitation. Currently, common precipitation measuring instruments
represent tiny catchment areas for which the water balance is drawn. These are
relatively simple collecting basins designed as a rain gauge (pluviometer) or as a
recording rain gauge (pluviograph).
The simplest standard model of a pluviometer measures the precipitation
caught within a certain time period. This is done by a cylindrical gauging vessel,
where every increase of the level equals a certain precipitation height.
Pluviographs continuously record the retention. This can for example be done
by a float gauge inside the collecting basin or by permanent weighing of this ba-
sin.
Of the solid precipitation deposit (e.g. snow precipitation), a vertical column
with a specific volume is withdrawn from the fallen snow blanket using a so-
called snow core cylinder. This amount of snow is melted and subsequently ex-
pressed as precipitation level.

Runoff measurement. In order to measure the flow of running waters, currently
primarily three fundamentally different methods are applied.