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Many solar pumping systems are of the "Deep Well" type, i.e. made of a submersible pump placed in the bottom of a borehole.

The borehole is usually sunk by specific machines, with a diameter of about 12 to 20 cm. Special submersible pumps are designed for being inserted in such boreholes. They should of course lie below the water level, and are connected to the surface by a pipe for the water, and the feeding/control electrical wires. The water is pumped into a storage tank, according to sun availability.

Remember that the Pressure or Head is mainly related to the difference between the input and output levels. The pump has to provide a total head resulting of several contributions.

In PVsyst we take reference to the ground level, we have (cf fig):

HT  =   HG  +  HS  +  HD  + HF

where:

HG = head due to the height of the outlet pipe above the ground (assuming that outlet pressure is negligible).

HS = static head due to the depth of the water level in the well, in absence of any pumping.

HD = dynamic "drawdown" head: in a borehole well, the effective water level is dynamically lowered by the water flow extraction (see below).

HF = friction losses in the piping circuit, which depend on the flowrate.

 

 

For this system, in the "Pumping Hydraulic definitions" dialog, you will be asked to specify:

-  The static depth. This may be also be given in seasonal or monthly values, in the  "Water Needs" next dialog.

-  The maximum pumping depth, corresponding to the inlet aspiration level. The system will stop the pump when the dynamic level reaches this level, avoiding dry running.

-  The Pump depth, should be below the maximum pumping depth,

-  The borehole diameter (in cm),

-  The specific drawdown, expressed in [m / m3/h]: this is a characteristics of the borehole and the surrounding ground  (see Deep well modelling).

You will also define the Storage Tank  and Hydraulic circuit parameters.

A little graphical tool shows the total head and its contributions, as a function of pump flowrate.