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.
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)
Although solar pump motors and controllers have nominal power ratings, the power at which solar pumps operate are variable. This depends on the solar array size, and time of day ( sun radiation intensity varies over course of the day), and factors such as temperature, pump geometry and dynamic head of the application.
Although the initial capital cost of diesel pumps may be lower than solar, the operating and maintenace cost for diesel accummulate quickly so that the break-even point for solar can be reached after a fairly short time, after which further savings accumulate, making solar a far cheaper option over the solar pump's life time.
To illustrate this, a Solar vs Diesel calculator is available which you can access by clicking on: Solar vs Diesel Calculator