Why is the borehole depth, and pump depth, of minor importance in solar submersible pump selection and sizing?
The important parameter is vertical lift which is NOT determined by the depth of the borehole, or the depth of the pump setting. It is determined by the depth of the water level in the borehole, plus lift ( height or elevation) above ground to the water delivery point.(see diagram)
Please note that the water level depth refers to the so called dynamic water level. This is the level the water drops to when the pump is in operation, that is the static level ( pump not operating), plus the draw-down when water is being pumped. In weaker boreholes with low yields the draw down can be significant, where as in strong boreholes the water may hardly drop from the static level, especially if the pumping rate is well below the maximum yield of the borehole.
The borehole depth and pump installation depth would determine only the pump cable length and perhaps a worst case scenario. However if system sizing is done on borehole depth this may lead to a wrong pump selection and /or major over design and unnecessary cost. For example say a borehole is 100m deep, but the water level is at 50m: if we design for a 100m ( at a given volume per day) we would end up with a wrong pump selection, and at twice the system cost than required.