Thinking of a solar back up for well pump

handirifle · May 8, 2017

We are in the process of getting solar on our house, with a 14KW Lithium Ion (Tesla) battery backup, for power outages, mainly. The solar will provide 96% of our annual usage, compared to past electric bills. The battery is a iffy right now, the engineers are deciding if and how they can connect it to my main panel, since the panel is not connected (other than wiring) to the house. Plus the solar panels will be on the roof of my shop, that is currently neither electrically or physically attached to the house.

I originally priced out a system for the submersible and pressure pumps, with the battery, but it was way too expensive. There are some excellent federal tax credits and rebates available, making the house system affordable.

The company does not do less than 6 panel installs and that is way too much for the well system, so I was thinking of doing my own. Power outages here are not super frequent, but often enough, and in fire conditions, it can be out for days.

What I had in mind, is 2-3 100w panels with about 150ah of battery backup and a 220v inverter, since all my pumps are 220v. It would be a manual switch over system, that will lock out any possibility of grid back feed.

Has anyone ever done a similar project? I will do some more research, but the pressure pump will be the most common draw, and it cycles with the pressure switch, as need requires. It would only be for necessities, shower, toilets and kitchen use, showers being the largest use. We could take navy showers then, if need be.

I don't think 300w would fully charge the batteries if drained, but might keep them topped off. I would like to avoid a generator, if possible. Cost would be similar, (am hoping to keep it under 1K) but no fuel to maintain, (and a lot quieter) and once switched, I would not have to turn it on every time I needed water.

Thoughts?

handirifle · May 8, 2017

I might add, both pumps are 220v, 1hp each.

TnAndy · May 8, 2017

Can't tell from your description....is this too be a backup system for the well pumps, or do you intend it to run them full time with no grid tie ?

Why do you have two pumps ? Is there a reservoir that one pumps into and the other draws from ?

You'll need to get a good figure on the amount of time per day/etc that your pumps run to get a decent idea if the amount of panel/battery will handle it over a given period of time.

jenkinsph · May 8, 2017

TnAndy said:
Can't tell from your description....is this too be a backup system for the well pumps, or do you intend it to run them full time with no grid tie ?

Why do you have two pumps ? Is there a reservoir that one pumps into and the other draws from ?

You'll need to get a good figure on the amount of time per day/etc that your pumps run to get a decent idea if the amount of panel/battery will handle it over a given period of time.

Good questions that need to be answered to give meaningful advice. ^^^

Just off the top of my head I would think you need more than 150 amp hours of battery to run two pumps. Also remember that to get optimum use of the reserve capacity that a slow draw down over a 20 hour period is what most batteries are designed for. Drawing the power out of the batteries at a rapid rate will provide much less run time with reduced capacity. I would suspect the batteries will blow your budget and then some.

handirifle · May 8, 2017

Sorry, thought I mentioned it. This is for power outages only. Those can range from a few hours to a few days. Definitely NOT full time or off grid, unless there was no grid.

We have 2 pumps because when we built (2010) we were required by fire dept to have emergency fire storage. In our case 5400 gallons, based on sq footage of house. We have the submersible pump that is 360 ft down in a 400ft well, and is located 560ft from the storage tank. The second pump is sized to provide 35 gpm constant at 50 psi constant, for the fire sprinkler system, we also were required to install ($5000). The pump itself is also a jet pump just like the submersible, to meet those specs. That was $1150 just for that pump.

The house pressure pump is my main concern, since we have the storage tank that the pressure pump draws from. The well pump only comes on when tank level demands it. In my case, when on back up, I would turn that pumps breaker off and only supply one at a time. If the outage lasted long enough to need the tank filled, I could turn off the pressure pump and run only the well pump till the inverter shut off due to low voltage.

All electrical controls and panels are located by my storage tank, so that will be easy enough. All are housed (now) in the shed I made from pallets, that I have a thread on somewhere on this site.

I am thinking 5 batteries at 35ah each would give me what I needed and that would stay in the budget easily. I am figuring a 4000w 220v inverter, and THAT is the big ticket item. Still have to shop around for that. The $1K might be on the low side, but I have other design ideas if this becomes too pricey.

Another thought was suitable batteries, an inverter, and a 110v battery charger. I could charge them up with my 2000w generators when the time came. In that case, I would eventually go solar and the transition would be easy. I do not want to have to rely on having gas or some other fuel, for worst case scenario. Out here that would be extended fire fighting. Those have taken power for a week or two at some locations. The fires take out transformers and short part of the grid, so it is shut down till repaired. That doesn't happen till the fire is out.

The home system is designed to provide power to the house automatically, so if on extended RV trips the fridge and freezer will be fine, and although the water system wouldn't work, that would have to be OK.

The pressure pump is intermittent, and I know the startup is the hardest. Running amps should be around 8 with a short surge to 15-20 on start. I have clamp on ammeters that I could easily test that with. Those are left over from my Air Conditioning repairman days.

Am I missing something?

buickanddeere · May 8, 2017

Not enough battery or pv panel. 2-1/2 hr run time at best .

handirifle · May 8, 2017

Actually that would be enough run time for my needs. The pressure pump would be "as needed" which would be self restricted since we were on back up power. The longest run time of the pressure pump is during showers, or currently sprinklers (summer time only). In this case, the sprinklers would be turned off until back on the grid. The submersible, if I ran it for 2hrs would add about 1000 gallons to the storage tank. I'm not sure how much drop in tank volume it takes to kick on the well pump to refill. If the tank was low, I would turn off the pressure pump for the one day and let the tank refill.

There is only 2 of us living in the house, and showers would be 10 min each. I can take longer showers but in these cases I would shorten them, similar to when we RV.

Even during, say a 10 min shower, the pump runs about half that to pressure up the tank then shuts off. The cycling would draw power faster than constant running, but it is what it is.

Also, if I do add solar panels to this, they will be in constant state of charge during the day. The ones I looked at were $99 for one 100w panel. That is about an 8 amp per panel (at 12v, if I figured it right) charge so I figured about 3 panels ought to do it, with a good charge controller. The pump house is only 12ft long so I doubt I could fit much more on it.

Am I missing something?

handirifle · May 8, 2017

In this scenario we would also be sure to shower early in the day, to allow a full day to recharge the system. I wished we could tie into the house circuit, then none of this would be necessary, with a 14KW battery, but I sure don't know of any safe way to do that, since they are each on separate meters.

TheGoose · May 8, 2017

No way a 400w inverter will start and run a 1-hp pump. 1-hp is exactly 746 watts but by the time you add in losses etc you're really looking at 1200-1500 watts and 7x that for starting. I can tell you from experience that it requires a 3500-5500 watt generator to start a submersible pump ( quality matters).

I'm sure the company tried to sell you a grunfos sq flex? That is the system you want. It will run on 90-230 vac or 30-300 VDC. Lots of options for batteries etc.