I have no experience with large-scale applications like this, but perhaps my own experience with moving water in a solar greenhouse is germane. (This may get complicated... I learned a lot of lessons along the way.) 12 volt pumps (designed for solar) are remarkably efficient in terms of the amount of water they can move with only relatively small inputs of energy from a P-V panel. (My little setup will easily pump 10 l/min, using just a 90Watt P-V panel, which cost me $150). You will have to do your own arithmetic to determine how much water you need to move, and hence how big a pump and how big a panel you need, but on the whole, I think it is entirely economically feasible to pump water from A to B using a solar panel. What is
not nearly so feasible is seeking to run the system continuously, rather than only when the sun shines, (or more accurately, only when there is an adequate amount of light - it will work even in cloudy-bright weather). This requires battery storage, and that costs easily twice as much as the P-V panel itself. Personally, the way I would approach this would be to install a storage tank at a high point in the orchard, and plan on pumping the total amount of water you need, during sunny periods, and allowing gravity trickle irrigation to distribute the water over time. (ie. forget about trying to store solar energy in battery banks - store the energy in the pumped water itself).
There were some wrinkles I learned in the course of my own installation. My panel was labelled "12 Volt, 90 Watt". Seems pretty straight-forward. Except that a "12 Volt" panel does not actually put out 12 Volts - it puts out as much as 22.5 volts in full sun. The "12 Volt" rating means it will
charge a bank of 12 Volt batteries, (which actually requires a minimum of 14.2 volts). If you connect something designed simply to run on 12 volts, you will fry it. (Took less than 60 seconds in my case). This caveat does not extend to appliances specifically designed for direct connection to solar panels, (which may actually tolerate as high as 24 volts without complaint, but will still operate down to below 12 volts). Or, the alternative is to insert a "voltage regulator" into the circuit - a simple black box, available on eBay for very small amounts of money, which will adjust the input to put out a standard 12 volts., (and actually cut off the load if the voltage falls too low).
It is probably important to note that I was not assembling my system from "official" components purchased from fancy solar equipment vendors. Most of the bits came form China, purchased over eBay, mostly at prices less than $20 apiece. But once I cottoned on to the points where things could go wrong, my cheap kludged system works entirely satisfactorily.
Broomholm OrchardZone 5b in Nova Scotia