help on transformer size

[Justloadit]

Which ever way you are going to take, it is no simple walk in the park.
You have to do the maths for each method that can be used to achieve your requirements.

Careful consideration has to be taken into account for each method including external factors which may influence the cost of the installation.
You have to almost walk the terrain, and look for possible points which may influence the installation which may bring in added cost.

If you are going overhead supply, you have to almost feel the ground where you are going to dig the holes to plant the poles.
You have to visualize where the cable will be fed from pole to pole, and see if there are any obstructions.
Maybe look for an contractor who does this kind of work on a regular basis, and has the experience to give you a quote.

Another option is to approach ESKOM to install a 400V point where you require it, and from there feed the motors.

Maybe solar may be a solution.
Just remember the most cost effective solar solution would only pump water when there is sunshine.
For 7.5KW you would need around 42 (250W) solar panels. Brochures tend to under spec the number of panels required. You have to add approximately 40% to the panel capacity for winter water pumping, and to allow pumping from earlier/later in the day.