Friday, June 19, 2009
Letter Re: Advice on Deep Water Wells in a Grid-Down Era
James,The original post has numerous embedded links, so if you are interested in more information, click through.
I know that I have seen posts about deep water wells, but when I search I really don't see that many applicable posts. I am looking at a property where water [static level] is about 400 feet down. In a "grid-up" scenario, this isn't really a problem, but I am looking for "grid-down" options for using a well at this depth. Not knowing much about the specifics of wells, I am not having much luck searching with Google, either. Would you be able to cover some deep well basics and some options for grid down/solar/backup pumping, specifically for deep wells? - John C.
JWR Replies: As per your request, here are a few deep well basics:
Solar and wind power are the best solutions for deep wells in a grid-down collapse. If you live in an area with reliable winds, a windmill used in conjunction with a large gravity-fed tank or cistern, is relatively inexpensive and trouble-free. Photovoltaics are getting less expensive with each passing year, but system complexity is an issue, especially with systems that use a battery bank. (To maintain water pressure during hours of darkness, you will either need to store water in a gravity-fed cistern, or you will need a battery bank, so that you can operate your well pump. )
Deep wells can be pumped with submersible AC pumps, but not submersible DC pumps. This is because the "line loss" (voltage drop) in DC cabling is tremendous. Even with fat, heavy gauge DC cables, if you start out with 24 Volts DC (VDC) at your battery bank, you will likely be down to just two or three volts at 400 feet! Given that sad fact, there are two good solutions:
1.) Use a DC-to-AC inverter top-side, and run AC cabling down the well shaft to an AC well pump. (Note: Many of these pumps require 220 VAC, so you will either have to use a much more expensive 220-capable inverter, or replace the pump with a 120 VAC model. (You may be an electrical neophyte, and asking "What type of pump do I have?" Take a quick look at your AC circuit breaker box. If the breaker labeled "Well Pump" is a pair of breakers that are ganged-together with a wire loop so that they'll be actuated simultaneously, then the chances are 99% that you have a 220 VAC pump.)
2.) Install a jack ("cricket") type pump or a windmill to actuate the sucker rod pump cylinder. Traditionally, sucker rods were made from hardwoods such as white ash. More recently they've been made with metal or fiberglass. Even with ash wood, their service life is measured in decades. The pump cylinders are made of brass and will last many decades. However, the pump leathers will eventually wear out, so you should consider buying a couple of spare sets and storing them someplace safe from mice and moisture/mold. Unfortunately changing all of the leathers on a down-hole sucker-rod actuated pump means yanking the entire sucker rod and then the weight of all 400 feet of your service line. That is a lot of weight, requiring a heavy duty hoist and of course all the usual "mind your head, fingers and toes" safety precautions and protective gear. Lifting a 1-1/2" or 2" diameter 400 foot long pipe is no problem for a pump company, but it would be a challenge for a typical rural family working with an improvised hoist. I recommend that you watch your pump company man carefully as he installs the pump in your well for the first time. You will notice that the crucial piece required is the flange that catches the pipe unions on each 20+ foot long section of service line pipe as they are raised or lowered in the well casing.
I've previously owned a jack type pump, and in my experience I found them problematic. I would much rather use an AC submersible pump.
Shallow wells (say, 50 feet or less) can be pumped with a DC submersible pump. I generally advise my consulting clients to "hang" both an AC pump and and a DC pump, one above the other in the same well casing, for the sake of versatility an redundancy.
Just use a windmill. Aermotor or Dempster. Pumpjacks are dependable. A pumpjack can be run by a small gas engine, like a Briggs and Scrapiron. You don't have to use electricity. Pumpjacks just don't pump as fast as as a submersible. Sucker rods have always been steel.
Line loss is always a problem with DC, particularly in a marine environment, even over shorter distances than 400'. For example, older sailboats rarely have adequate wiring to handle new electronic instruments; as you add new equipment (radar, chartplotter, etc.) it is almost always better to rewire the entire circuit with better gauge wiring.
Line loss isn't an AC vs DC problem so much as it is a function of voltage. Specifically, line loss is proportional to the inverse square of voltage. So when you talk 220 VS 20 volt, the line loss is ~84 times greater in the lower-voltage DC system.
This is why transmission lines operate at the level of hundreds of kilovolts.
why aren't these solutions adopted to lessen energy usage; that is, a dual use for your paranoia (no offense intended).
I'm quite serious. Remember driving across Iowa. Every farm had a windmill, which was used to pump water up.