Water water everywhere!

Woohoo, our new pump is in! That's right, we had to break down and buy a new well pump. Unfortunately the old pump started giving us problems earlier this summer. It started shutting itself down due to "overload" and was getting harder and harder to get started up. The pump was super efficient and designed for off-grid living, but unfortunately I don't think it was installed correctly in the first place. I did a few calculations when we started having problems and it turns out the installers undersized the wiring pretty significantly so the voltage at the pump was probably too low for the pump's entire life. It lasted 7 years this way; not too bad, but less than I would expect from a $3000 pump. The pump is likely salvageable, but it is produced by a German company and getting local service for it is nearly impossible. Also, the thought of spending $500 on appropriately sized wire and needing to dig a trench for the new cable was enough to make me rethink the options.

The choice of submersible pump for the off-grid home owner should not be taken lightly. There are a number of options out there:

• Low Voltage high capacity pumps like our previous Lorentz or the Grundfos SQFlex are designed to run directly off solar panels or batteries.  They tend to very efficient, but the upfront cost for the pump, heavy wiring, and optional solar panels can be significant.  The other downside is that they tend to be more complex, or at least rarer, and finding someone to service them can be a challenge.  Since we only got 7 years out of our last pump, I wasn't willing to go down this road again.  
• Incorporating a cistern is often times a good option for off-gridders.  Cisterns can be filled using solar slow pump or a large gas pump if the water source is close enough to the surface.  We may get a cistern for summertime watering some day, but since we don't already have one -- and we needed water now -- we didn't really consider this as a viable option.  
• The other main option is more traditional 120V and 240V pumps.  There are a variety of models to choose from, they are available locally, and they are relatively cheap.  But, they use more power.  Off-gridders need to consider not only how much the energy it takes to run the pump, but also the amount of energy it takes to start it up.  

In the end, we went with a 240V, 1/2hp 10gpm Franklin pump.  Our well recharge rate is ~10 gpm and our old pump (at 6-7 gpm) was getting worked  pretty hard when irrigating the wind break, so 10gpm pump is a pretty good match. The new pump uses about 1400watts.  I'm not sure what the startup watts are, but our 3500 watt (6000 watt surge) inverter doesn't seem to have any trouble getting it going.  To reduce number of startups, we got a second pressure tank.  We now have two 45 gallon pressure tanks, set at 25-45psi, so we get about 25 gallons of water per pump cycle.  The pump will cycle quite often in the summer when we're irrigating, but only a few times a day in the winter when we don't have much energy to spare.  

So...are we going to regret the decision not to buy a super-efficient solar pump?  I actually don't think we will. We are most likely to regret the decision in the winter since that's when we have the largest energy deficit.  But in the winter we don't really use a lot of water. On a big day, we might use 100 gallons of water/day. Here is how much energy it takes pump to move 100 gallons :

• Lorentz solar pump: 100 gallons @ 7gpm = 0.238 hours of pumping * 500 watts = 119 watt-hours
• Franklin 0.5hp pump: 100 gallons @ 10gpm = 0.167 hours of pumping * 1400 watts = 233 watt-hours

Based on these numbers, the Franklin will use about twice as much energy, but...120watt-hours is really pretty insignificant in the grand scheme of things. One $300 solar panel would more than make up the difference.  The difference in price between the pumps is on the order of thousands! There was also an additional energy expense associate with the Lorentz pump.  Since we needed a 48v version to match our water needs and our system runs on 24V, we needed to incorporate a 24-48v converter.  This converter consumed 3watts at all times -- ~75watt-hours per day, so the realized difference in energy is actually smaller than the example above. With the new pump, we do need to run a 240V auto tranformer 24 hours a day, but I've been doing that right along anyway for power tools in the shop.   Once we can move the big generator over to the shop, I will likely rewire the transformer to run only during the pump cycles.

To make a long story short...No, I don't think we'll regret the decision.