For solar pump applications with solar generator sizes of up to about 7kW DC brushless motors provide by far the most efficient solution.
In such solar pump systems the motor sizes that are used are typically not larger then 4kW (5.5HP) since a 6-7kW solar array would only produce around 4kW for most parts of the day. (deduct 25% for temp, dirt & cable losses losses and for most of the day you will not have full sun = 4kW (5.5HP) motor is large enough)
LORENTZ ECDRIVE brushless DC motors are over 90% efficient in this power range of 1-4kW (0.7 to 5.5HP). This would compare with AC motors that are in the 50-70% range for the same size.
Depending on the system size you would need a solar array that is 30% to 100% larger to pump the same amount of water when using AC motor operated solar pump systems!
The graph below demonstrates efficiency of the ECDRIVE (DC brushless motor) compared to AC motors. The important point to note is that the DC brushless motor is efficient across a very wide load range whereas the AC motor only reaches peak (but much lower) efficiency at 100% load. This is a very important consideration for solar pumps as the available power varies through the day with a considerable ramp up and ramp down at the start and end of the day. In many parts of the world the peak power will only be available for 2-3 hours.
Unlike AC motors, LORENTZ brushless DC motors have an extremely high efficiency from low loads upwards. This gives brushless DC motors a further considerable advantage especially during periods of low radiation (start and end of the day, cloudy periods or the winter season).
LORENTZ recommends only to use AC motors on solar pump system of 7kW or larger. A solar pump system with an array size of 6kW can still be by as much as 20% more efficient with a LORENTZ brushless DC motor then the same size AC pump system.
Efficiency is critical with solar pumping as the solar generator is typically the main cost component of a solution. Any cost disadvantage of using a good quality, efficient DC brushless motor over a cheaper, inferior AC model will be immediately compensated for by the significantly smaller PV array that is required.
Or for the same array wattage you will get significantly more water by using modern brushless DC motor technology from LORENTZ