Curt, a benefit of using solar for a water pumping application where a dc motor is used is that the system is voltage tolerant. A battery
should not be required. It's possible to connect a solar panel directly to the pump motor. Of
course, the pump will operate only when the panel is producing. If you size everything right, then you should get the flow required each day without resorting to a battery system. Go with the least expensive panel on a $/watt basis as long as it's UL listed. Astroenergy panels might be a good choice (see wholesalesolar.com). Note that you probably want a fairly large panel as these will provide sufficient voltage to take the pump to a high output. The open voltage on these large panels are generally at least 30 volts. A 250 watt panel at 30 volt open voltage might be a good match. Note that there is no danger of sending 250 watts through the pump motor as the voltage will not be high
enough, but there is enough extra capacity to keep the motor at a high output even when the panel sees low solar flux. I don't know how well the pump can handle continuous duty at the voltage provided by such a panel, but providing long and/or thinner wires might be useful to drop the voltage to a safer level.
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