Why are daily water requirements important to know, and not necessarily flow per hour?
Unlike conventional electric pumps which pump at a constant rate, once switched on, flow rates for solar pumps are variable over the course of the day. Therefore solar direct pumps start pumping slowly in the morning, with peak flow rate over midday, then dropping off in the afternoon.
This variable flow rate is represented in the illustration below, resulting in an average pumped volume per day, which repeats itself on a daily cycle ( sun permitting). In order to optimise solar pump sizing, daily water requirements, and not ( only) hourly flow rates should be known.
It is possible to extend peak hourly flow rates for more hours around the noon period, as illustrated in the graphic below. This may for example be desirable in pressure irrigation applications, where the sprayer or sprinkler nozzles require constant flow and pressure for longer periods per day, to operate effectively.
This is done by adding more solar panels in order to getting maximum power to the pump earlier in the morning and till later in the afternoon. The downside of this is only a marginal increase in overall daily volume, relative to the increase in solar power. This is due to a solar overcapacity at midday which the pump cannot absorb, since the solar pump only draws the power that it requires for the given parameters in which it operates – much the same as a conventional electric pump, which does not draw all the available power which may be available at the plug point.