I’ve moved into a house that is completely off-grid with water and we only use borehole water, while this is great the electricity consumption is quite wild particularly in summer when I’m having to run irrigation, fill the pool etc… at a guess its easily over R10K-15K per year.
I have 3 pumps in my setup…
Borehole pump to main storage tank ±2500l
Pump from main storage tank to smaller ±1000l tank for house consumption, this pump also runs the irrigation and is a 1.5kw pump
Pump from smaller house tank which is a DAB VSP pump and pretty efficient.
My problem is electrcity consumption, when 2 of these guys are on when running irrigation or filling pool I’m at 3400W which is pretty hefty, I’m thinking of changing out the 1.5kw pump with a VSP pump as these seem to use considerably less power but wanting to find out from the clever folk in the community if this is a worthwile excercise?
A further caveat is that this 1.5kw pump has been a little bit of a pain in the arse, I had a pipe pop off the outlet (mains house supply) and emptied the tank, fixed this but then had an issue of it running all the time even if I closed the shut off valve, this eventualy corrected itself, then…
Had a second pipe pop off (rusted hose clamp) and now having the same issue but not correcting itself over a week later so suspect the regulator may be faulty and if I’m going to have to replace this may as well spend some extra money and get the varial speed pump if there is a pontential long term saving…
I run my house (but everybody’s water needs differ) off a 800W pump with an in-like pressure tank. It works decently and cost me very little (was on a sale at Builders for less than R1k, normal price was R2.5k iirc). At the time I looked at VSD as well, but price was just too steep to justify in my case, as I only use mine during winter, or as backup water the rest of the year.
Depending on your situation, a water tower might be a more practical solution?
Perhaps these can be controlled to only switch on when excess power is available.
Battery inverters often have a relay for Excess Energy in Off-Grid Systems.
This basically indicates that the batteries are fully charged and the PV power is being throttled…
I’m on a farm, I have a borehole filling 2x 5 kl tanks and then a pressure pump to supply the water for the houses, irrigation etc.
When we bought the place it came with a 1.5 kW centrifugal pump which packed up around 6 months ago, I then replaced it with a similar centrifugal pump, but a 1.1 kW PASCALI PUMP CENTRIFUGAL 1.1KW 230V
At the time, I also considered going VSD, but it wasn’t worth the additional cost in my opinion, it would have costed R10k more than the centrifugal pump.
I can’t tell you exactly how much electricity my pump use on a daily basis and whether it’s excessive, but yes I can definitely see it on the electricity bill when we irrigate a lot.
I took a chance by going from a 1.5 kW to a 1.1 kW pump because I figured our pressure was more than good enough and it worked out fine, there was almost no noticable change in pressure in terms of daily use in the house, shower etc. This will largely depend on your pipe sizes as well, almost all my pipes are 40mm HDPE and I have a 32mm HDPE run to one building as well.
As suggested since you already have a VSD pump experriment, use it as your main pump for a while and see if it makes a difference in your electricity usage.
I have no first hand experience with them, but how I understand is that it won’t run at full power if you open a tap for a glass of water or to wash your hands, but if you irrigate or fill the pool, it will anyway run at full power which is what uses the most electricity.
Last I checked around 2 years ago, a proper 9m high tank stand for two 5 kl tanks worked out to around R50k.
This will only give you about a bar of pressure.
I’m fortunate to have my tanks on a stand around 7m high, this helps when the electricity is down, but there’s no way I will be able to live without a pressure pump.
Thats a pretty good suggestion, I actually thought about it last night and wondered if I couldn’t just take the 1.5kw out and use the house pump to fill the 1000l tank.
They’re not too far away so plumbing won’t be terribly complicated so might just give it a try.
The only issue I can think of and is perhaps why there are 3 pumps is if for example someone is showering and at the same time the float switch in the tank kicks in and the pump then also needs to fill the tank, there will be quite a sharp drop off in water pressure.
They do… a LITTLE. A lot of the energy expended during the starting of an induction motor doesn’t do any meaningful work, and it does have a really big starting peak that is hard on an inverter.
If the motor is just constantly running, at least for long periods, then yes, the overall energy and power use will probably be proportional to the water use, regardless of the type of pump, but for the typical start/stop nature of a residential setting, I will put this in the same box as inverter air conditioners: A really nice thing to have.
What I tried to say above which probably didn’t come across so clearly.
For constant running like irrigation it will anyway run at full power so stick to less expensive centrifugal.
For use on your house with multiple stop starts all day every day there might be an advantage to VSD.
That is an exceptionally brilliant idea, they are literally next to each other, that would elimiate the need for the pump to fill the small tank dedicated to the house and it would then only be used for irrigation and I could perhaps look at a smaller 1.1kw pump.
I’m just not sure if there is a filter between this pump and the tank for the house, that would be the only caveat.
Yeah that might be an issue, if its irrigating its probably going to be running flat out anyway so there won’t be any saving and the better option then may be to put a smaller pump in.
A suggestion to consider, what I would probably do if it was me.
Buy yourself a 5 kl tank to be used as your main tank feeding the house, place it next to the 2 kl tank.
Connect your borehole to pump in to the 5 kl tank and its overflow to go in to the 2 kl tank, but put the float valve which starts and stops the borehole pump in to the smaller 2 kl tank.
Connect your VSD pump on the outlet of the 5 kl tank for feeding the house, depending on your water quality you can also put filters in line.
Then put the 1.5 kW pump on the outlet of the 2 kl tank for the irrigation.
I don’t know how you’re doing this control but these are typically big loads. When installing my system I decided to have water heating on it’s own setup.
There’s no need to hammer your inverter with water heating given that it has inherent storage capacity so is less demanding.
These solar PV water systems can use old PV panels which really are cost effective if you have the roof space.
Thank you, this is essentially exactly my setup apart from the fact that the tank sizes are switched around and there is no overflow between them.
I do have inline fltration and just need to check if the 1 filter on the house tank is between the borehole tank and house tank (I don’t want to baypass any filtration), if not I can just get the overflow put in place between the two tanks and this should drop power draw quite a bit, I’ll then look at replacing the 1.5kw with a smaller say 1.1kw pump.