This is an idea proposed by UC Berkeley students. These designs are still in the concept stage and some details need to be worked out. The ideas and innovations are most important.
This box will pump enough water for the farmer using a solar powered electric pump and retractable hoses.
-large all-terrain wheels
-pivoting solar panels for efficiency, safety, protection
-photometer for real-time feedback on efficiency of panels
-flexible output hose to distribute water (think: garden hose)
-embedded compass for direction/navigation
-rechargeable lead-acid battery for storage and discharge
-electric pump, solar panels, and most other components can be purchased off-the-shelf
-vented body for heat dissipation from pump
-After sunrise, the farmer will wheel the box to the well and crank the hose down to water depth. He slides out the solar panels and positions them in the direction of the sun (using the compass and photometer). The solar panels always charge the battery. He turns on the box (completing the circuit) to turn on the pump. Water will soon arrive from the output hose.
-During the day, the farmer can reposition the PV panels to increase efficiency. On a cloudy day, the on-switch will still power the pump, assuming the battery still has charge. If necessary, the battery is removable to recharge or replace.
-At the end of the day, the farmer turns off the pump, slides in the solar panels, and cranks the hose back inside the box. He then can wheel the box back into his home.
-4 all-terrain wheels
-2 flexible 10m hose (for input and output) and cranks. Off-the-shelf. Possible: lay-flat hose for easy storage.
-1 lead-acid battery
-6 sides of the box. Dimensions will be determined by cheapest solar panel size. Made of teflon (high heat resistance, low density).
-1 electric pump (off-the-shelf)
-1-5 solar panels (off-the-shelf, standard size or 60"x40")
-Compass and photometer (off-the-shelf)
-Aluminum for pivot-arms and wheel axles
-Circuit breaker (on-off switch)
-Holes cut out of sides for hose, crank, compass, photometer, and vents.
-Fillets cut out of sides for sliding panels.
-Cut pivot arms to length.
-Assemble box, connect electrical components.
-Attach wheels (aluminum rods as axles).
-Filter for some water purification
-Auto-pivoting PV cells (with microcontroller and photometer)
-Water storage in box or in separate component for easy watering
-Assumed 1 hectare to irrigate = 10 billion mm^2
-Assumed 200mm water/day required of plants on most intensive days
-->2 million liters water required per day
-->0.07m^3/s pumped over 8 hours (1100gpm)
-Assumed 10mm water/day during season
-->100,000 liters water required per day
-->.00035m^3/s pumped over 8 hours (55gpm)