Solar water pump system advice needed

Re: Solar water pump system advice needed

Machineman,

Solar water pumping ain’t my forte. However, the following information may help you get headed in the right direction.

The combination the 8 ft siphon, the friction loss in 250 ft of pipe, the 125 ft of lift and, most likely, the friction loss in the 8 ft siphon pipe and the 125 ft of lift pipe will add up to a substantial total dynamic head. The 125 ft of lift alone is +4 bar (~ +58 psi), and low-flow-rate friction losses will likely add another bar or two, for a total of ~87 psi.

You didn’t indicate your projected daily watering requirement. Assuming it’s ~250 gallons per day, and that you average ~four full hours of daily insolation, you’ll need a pump that can deliver one gallon/minute from the pond, through all of the pipe, and up to the tank. The specs for the Shurflo Model 8000-543-138 12 V pump suggest that it could handle that rate and the (gu)estimated total dynamic head pressure.

See: http://www.shurflo.com/pages/new_industrial/Industrial/gen_industrial/genind_doc_sum/8000-543-138.html

Kyocera’s old solar water pumping guide looks like it might be useful in addressing these issues. You can download the pdf file from here: http://www.solar-electric.com/PDF_files/Solar_Pump_Guide.pdf

I’d estimate that you’ll need at least a 130 W (STC) PV module, and probably a 170 W (STC) module, to power the pump for ~one GPM. Examples include the Kyocera 130 or a pair of Kyocera 85’s wired in parallel. The twin 85's might be a better overall choice, as they could be wired in parallel for 12 V nominal or in series for 24 V nominal. The latter would allow you to consider a 24 V pump.

See: http://store.solar-electric.com/kc-120.html
And: http://store.solar-electric.com/kysokc85wa12.html

You’ll likely need a current booster between the PV module(s) and the pump. Something like this might work: http://www.solarconverters.com/ppt15.htm

Unirac makes top-of-pole mounts for PV modules: http://store.solar-electric.com/pountopofpos.html

You’ll also need wire and fuses. Adding a battery may increase system flexibility, but it also increase system complexity, cost and maintenance. You’ll need to consider the best balance for your needs.

HTH, and HNY!
Jim / crewzer

Re: Solar water pump system advice needed

If the pump is a significant distance from the PV array and controller, the power loss in the wiring to a 12 V pump would be 4X that in the wiring to an otherwise equivalent 24 V pump. You'll have to crunch the numbers for various combinations of wire- and pump costs. Here's a link to a 24 V pump: http://www.shurflo.com/pages/new_industrial/Industrial/gen_industrial/genind_doc_sum/8000-853-238.html

This link for another pump seems to suggest that a 130 W module is the minimum for 180 ft lift (~5.5 bar) and ~1.5 GPM (~87 GPH): http://www.shurflo.com/pages/new_industrial/industrial/solar/doc_sum/9325-043-101.html

I think we're in the right ball park w/r/t PV size...

You'll need to check on pressure specs for the tubing you plan to use. This one I found on the 'Net is rated at only 60 psi: http://www.dripirrigation.com/drip_irrigation_info.php?cPath=36_136&products_id=1005 However, the friction loss in 3/4" poly should be lower than that in the 1/2" Schedule 40 I sort-of-assumed in my earlier post.

Good Luck!
Jim / crewzer

Re: Solar water pump system advice needed

MM,

The pump is 24 V "nominal". I'm not able to open the product spec files, but I suspect the operating voltage is probably something in the 21 V to 35 V range. The PV module's Vmp may be 17.4 V, but that's under STC lab conditions. You'll probably see the series pair of modules operating in the ~30 V range once they heat up in the Sun.

HTH,
Jim / crewzer

Re: Solar water pump system advice needed

I think I've got this right: You'll need to choose between powering the pump directly from the PV module or using a pump controller ("linear current booster") between the PV module and the pump.

If you power the pump directly from PV module, you'll need a module rated to supply all of the current required by the pump. The panel will operate at a voltage basically defined by the module's output current and the resistance of the pump motor and the associated wiring (V=IR).

If you use a controller between the PV module and the pump, you should be able to use a smaller module as the controller will convert "extra" voltage from the module into additional current -- sort of like an MPPT charge controller. This is apparently very helpful on cloudy days, when the PV voltage can be high because the module isn't heated up by the Sun, and the PV module current is low due to low insolation.

HTH,
Jim / crewzer