JWR:
In this entry, the idea of having a hand pump for the water well, and wanting to have at least some redundancy regarding the ability to pump water, is mentioned. Since potable water is a primary concern for me, I have been looking into the alternatives to our municipal water supply (which currently depends on the electrical grid to be operational).
Since I sell solar electric equipment, I naturally thought of having a solar powered water pump as a back up. But what if something knocks out my solar array? I ultimately would like to have a manual water pump. At the same time, I have a limited budget, so the equipment needs to be very cost effective.
Searching for an solution, I found the Simple Pump.
This is the most efficient solar pump that I have found, and it can be powered directly from a single solar panel without using batteries. If the motor fails, then it can easily be replaced with a handle, and even a child could operate the pump manually. I have talked with several of my neighbors about taking advantage of the Simple Pump “Friends and Family Discount”. I really don’t want to be the only one in the neighbor with a working well. Thank you for keeping the discussions going. – P.B.
Mr. Rawles:
As usual many thanks for the time and effort on the prep subject. Just wanted to pass along a note on grid-down well pumping. My wife and I have been off grid for 20 years now. We enjoy the outdoors and just consider it a long adventure. As to pumping the well the best option we have found to date is the Shurflo 9300 series pump. It has the best power to pumping ratio I have found for low volume pumping at an average of 78watts for 1.2 to 1.6gpm @ 150′ total head. We do miss the volume of the conventional 3/4hp pump during fire season but have added 20,000 gallons of storage to help out a bit. One of the tipping factors on the cost/benefit scale is that it can be installed by one average to competent person. – Brent S.
Dear Editor:
Your advice to avoid DC well pumps is out of date. Over 15 years I have installed Shurflo, Solarjack (now Sun Pumps), SunRise (defunct), ETA/Lorentz, SunRotor, Grundfos SQF, and Grundfos SQ (AC only) submersible pumps in my trade as an off-grid PV specialist.
First, the issue has nothing to do with DC versus AC – both have identical voltage drop characteristics. Voltage drop is a function of voltage, current, length, and cable resistance. Older DC pumps tended to be low-voltage; that’s where this idea came from.
However, “inefficiency” is a red herring, in that any traditional brush-type DC motor runs at a speed that is directly related to voltage. As long as the pump is of a positive-displacement design (diaphragm and helical rotor are the most common today) it will maintain full head capacity, but simply pump at lower speed. Thus, as long as the water volume is adequate for the need, the pump speed and the resistance losses in the wire are irrelevant.
For a simple, low-cost example, the common $850 Shurflo 9325 DC submersible diaphragm pump is rated to 230 feet max head, fits only #10 and #12 two-conductor flat jacketed submersible cable, and pumps about 1.5 gpm m/l at 35V (the maximum power voltage of a 24V nominal array). It can be run, however, at 12V, off a single PV module, at about 50% output. Doesn’t hurt the motor at all – in fact, the low speed greatly increases pump life. Six hours/day at 0.75 gpm is 270 gallons — enough to sustain a remote residence.
On a separate note, several PV-direct submersible pumps (Grundfos SQ Flex, Lorentz, and SunRotor) all take the DC from the PV array and electronically invert it to 3-phase “wild” AC. This eliminates motor brushes and thus most maintenance. All three run off of DC, and all can be run off of AC with an optional AC converter. The control circuitry in these pumps varies pump output with available wattage – again making conductor losses relatively unimportant.
Your blanket statement to avoid DC pumps is thus quite misleading and limits options, as in deep wells that limits a homeowner to either a fueled generator or a large inverter-based supply to run a conventional pump. Incidentally, none of the latter pumps were available ten years ago. Pumps suitable for remote applications have advanced tremendously in recent years.