I endorse Eric's comments from
experience. My tank is supplied by a small, 24 V submersible (see
http://www.amazon.co.uk/Surgeflo-Solar-Deep-well-bore/dp/B00GZ08R1I). A six zone controller operates solenoid valves from the same line that supplies the tank. The discharge from the pump into the tank is only about 2 m above the irrigation lines. The pump delivers about 250 l/h. If a solenoid valve is open, the irrigation line takes most of the flow if the tank level is down. If the tank level is high, the irrigation lines take the total flow. I also have irrigated areas lower down the hill. These are supplied from the tank.
The pump will operate directly from
solar panels. Controllers are available that extend the operating hours without a battery. I choose to use a low cost 24V supply from mains power because I wanted night time watering. At this stage, I start and stop the pump. My next step is to start and stop the pump using the pump function on either of the two 6 zone controllers or a float switch in the tank. The power draw during watering periods is less than 100 W. I paid less than A$250 for the pump and power supply.