Running a swimming pool offgrid.

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Running a swimming pool offgrid.

Postby offgridQLD » Tue Oct 16, 2012 10:15 pm

Swimming pools are usually put into the same category as v8 engine's, bar heaters and hosing down driveways. I know they can be energy hogs. Am I crazy to think with smart design,north aspect and solar heating along with efficient pumping that running a swimming pool of grid isn't out of the question.

My thinking is some efficient pumps i was looking at in the window of a pool shop today. Reading the poster for a 240v pump that was rated to circulate 50,000lt a day it consumed 400kwh a year (175w when running) Around 1kwh a day. That's about the same as my 500lt fridge freezer uses. If most of the run time was during the day I guess it would be more or less directly from my PV's. not sure how long it would need to run each day though if all its run time could be done between 6am 4pm - 10hrs? ...Actually basing it on there advertised 400kwh a year it works out to be just over 6hrs a day with a 175w pump.

Then there is heating. No point in having a pool if you can only use it 1 month a year. My thinking is the black pipes style systems on a large unused 12m x 5m section of north facing roof I have spare would solve that problem . Not sure if additional pumping is required?

Anyhow we are looking into perhaps a 8m x 4m lap pool.

We are 45km from a very nice beach and we do have the local lake and some creeks. We usually prefer the beach but its a 90km round trip and most of that 90km trip is getting down the range and climbing back up it again . So your looking at consuming 8lt of diesel at $12 and a good 1.5hrs of time to take a dip. I guess some things in life are not adjustable but if you can get away with them a little guilt free then why not.

Anyhow just looking into options for energy efficient way to run a heated pool off grid .I did see some DC pool pumps that had some associated hardware and they could run directly off say 400w of pv.

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Re: Running a swimming pool offgrid.

Postby Gordon-Loomberah » Wed Oct 17, 2012 5:40 am

offgridQLD wrote:. Not sure if additional pumping is required?


If the pipe is above the pool, yes it will be necessary, as you wont have any thermosyphon.
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Re: Running a swimming pool offgrid.

Postby offgridQLD » Wed Oct 17, 2012 9:25 am

Yes though I wasn't thinking thermosyphon.

More if the filtration pump would also circulate the water through the heating pipes or if I would need a second pump for heating circulation. Looking into it some more it looks like a additional separate pump is usually used for heating.Though I found there are many commercially available options for direct drive solar powered DC filtration and heating pumps :D. So having a heating and filtration system that was totally self sufficient.

As for the actual heat exchanger. Perhaps even several vac tube heaters would be more effective than the simple black plastic pipe systems. With a pool you don't need boiling hot water 30 deg C max is the usual temp for leisure pools. So it's not a big jump over ambient water temp over summer though the volume is very large at 30,000 - 40,000ltrs.

Looking into what it will all cost :shock: perhaps convincing the other 1/2 that a electric car is cheaper to build and drive to the beach than the pool :lol:

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Re: Running a swimming pool offgrid.

Postby zzsstt » Wed Oct 17, 2012 11:20 am

For much of the summer you might just find the pool is too hot, even without heating, and the other big (BIG) issue is water usage. Our pool can lose 15mm of water a day in the middle of summer (possibly more), and to stop this you need a cover - which (unless powered) is a nuisance to put on and off, and also causes the pool to warm even more. A hot bath is fine to relax in, but no good if you want to swim for exercise! I have seen (in the US) heat pump COOLERS for swimming pools....

The PV direct pool pumps work on the basis of a constant small flow of water through the filter (I do not know if they require a special filter or work with the normal "sand" units), rather than a high flow for a short time. That creates other issues, like salt cell flow and possible dead spots in the pool where the water never circulates. They are almost certainly incapable of driving a creepy crawly.....

Pool heaters can be fed from the main pump, but for best efficiency they normally have a dedicated pump with temperature controls. However that pump can be fairly small and is probably a better candidate for PV direct, because there's no heat to be gained when the sun isn't shining!

If you have a reasonable PV array and batteries, you are probably better off running a "best of breed" 240V pump and filter for 2 hours in the middle of the day, rather than trying to create a dedicated PV pump system with its own "low flow" complications.
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Re: Running a swimming pool offgrid.

Postby Tracker » Wed Oct 17, 2012 11:42 am

offgridQLD wrote:As for the actual heat exchanger. Perhaps even several vac tube heaters would be more effective than the simple black plastic pipe systems. With a pool you don't need boiling hot water 30 deg C max is the usual temp for leisure pools. So it's not a big jump over ambient water temp over summer though the volume is very large at 30,000 - 40,000ltrs.

The more efficient the actual heating, the lower the actual VOLUME of water needed and hence the lower the amount of electricity needed to circulate that heat.. WIN-WIN..... .. :roll:
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Re: Running a swimming pool offgrid.

Postby offgridQLD » Wed Oct 17, 2012 4:00 pm

If you have a reasonable PV array and batteries, you are probably better off running a "best of breed" 240V pump and filter for 2 hours in the middle of the day, rather than trying to create a dedicated PV pump system with its own "low flow" complications.


Is 2hrs all the pump runs for? What size (wattage) pump would you need to only require 2hrs run time a day? I'm guessing 1000w?

I see your point on keeping it simple with a more common 240v pump. Although for example a 500w pump running for 4hrs is perhaps a nicer load for battery's than a 1000w load for 2hrs. If the average size pool holds 45,000l. The 6 star 175w 240v pump I mentioned earlier claimed it could flow 50,000lt a day running for 6 hrs and just over 1kw a day. Friends just had a pool put in and from what they have told me they have some kind of variable speed pump that's more efficient .

The covers sounds like a good idea to hold some heat in and help with the odd leaf getting in. Evaporation over summer is when we usually get more rain than we know what to do with. Annual rainfall of 2500 - 3000mm most of it is dumped in summer. In fact I could dedicate the rainwater 120m catchment from my shed just for pool top up purpose rather than just dumping it into a dam. Or is there another issue around this evaporation other than just water replacement?

All this said I have no experience with a pool or what the usual pump run times and pump programing over the year.
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Re: Running a swimming pool offgrid.

Postby zzsstt » Wed Oct 17, 2012 5:34 pm

Much of this varies with the type of pool. I like saltwater pools, where the water passed through the filter and then through a salt cell where NaCl is broken down to release chlorine which is the sanitiser. The salt then reforms so the concentration of salt remains constant. However in a heavy rain event, where the pool overflows, salt is lost and must be replaced. The overflow (and filter backwash) water is useless because it has salt and various other chemicals in it, but the chemical levels in the pool mus be maintained with top-ups. This applies whether you have a saltwater pool, or one to which you make regular doses of chlorine. Under those circumstances, and obviously budget dependent, a better option might be either a perspex "carport" over the pool, or some other mechansim to catch the rain before it enters the pool - that way the rainwater is still usable (no salt, chlorine, copper algaecides, stabiliser etc.) and the pool chemicals stay put!

The pool pump, obviously, pushes water through a sand filter and then a salt cell and back to the pool. It needs to develop enough pressure to force water through the filter, and this gets harder as the filter build up a load of dirt - at which time it is backwashed, i.e. an amount of water is pumped backwards through the sand thus flushing the "dirt" to waste. The salt cell offers no resistance to flow, but rate of flow must be sufficient. The returning water needs to enter the pool with enough velocity to mix the chlorine throughout the entire volume of water. A very small pump may not create enough turbulence in the pool to do this, which could (?) result in areas of the pool where the water never gets sanitised. Then, potentially, algae and bacteria start to multiply. So there are clear advantages to using a reasonably sized pump for a shorter time, rather than a very small pump for a very long time!

The thing to remember is that just because a pump is able to move 50,000L a day doesn't mean that EVERY litre of water will be filtered! A slow pump might simply create a small stream of water up the middle of the pool, filtering largely the same water 10 times and leaving the edges and depths of the pool untouched. This is also why pools with built-in cleaners (basically revolving water jets in the floor of the pool) can have reduced sanitising times, because the entire pool is "stirred" and the chlorine is mixed more efficiently.

The variable speed pumps are simply a manual over-ride, where the pump is slowed for everyday filtering but then can be increased for backwashing or when a creepy crawly is used. That's fine, as long as the "just filtering" speed is sufficient to fully circulate the water from both a total volume and "stirring" viewpoint.

There are also differing approaches to pool sanitising. Some pool companies recommend running the pump almost continuously on the basis that stationary water (when the pump is off) can allow bacteria/algae to breed. Some recommend short and vigorous treament! Obviously running a 1000W pump for an hour costs the same as running a 500W pump for two hours. As long as all the water is sanitised, either will do!

I have always used stabilsier to "protect" the chlorine from sunlight, together with copper sulphate as an algaecide, and (as long as I haven't forgotten to check the chemical levels weekly, especially after heavy rain) have never seen a problem using 2 hours of filtration per day. I do vary this, increasing it slightly in the summer when the pool is used heavily, and decreasing it in the cool of winter when the pool is covered an unused.

The only exception to the above was when I ran a pool on borewater, with very high TDS. that water required far more effort to stop alage growing.
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Re: Running a swimming pool offgrid.

Postby offgridQLD » Wed Oct 17, 2012 6:24 pm

All interesting considerations, thanks for taking the time to share. Very large down pores of rain unfortunately are very common in my area . So overflowing sounds like it would be a common thing. The deck roof could potentially be continued over the area we are considering having a pool.

Though with the amount of potential issues and maintenance that has just been listed. Riding our Ebikes to the local river and waterfall sounds tempting. :lol:

I will look into all the options a little more.

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Re: Running a swimming pool offgrid.

Postby akkk » Mon May 06, 2013 11:58 am

bringing up an old post. I looked into these dc pumps and found the internals are made from 304 s/s. I dont think they will last for 6 months. There are a few pumps that use plastic internals so weather or not its strong enough to pump enough water is the issue. Would be keen to hear real life stories
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Re: Running a swimming pool offgrid.

Postby davidg » Tue May 07, 2013 12:06 am

offgridQLD wrote:The deck roof could potentially be continued over the area we are considering having a pool. Riding our Ebikes to the local river and waterfall sounds tempting. :lol:


Because you are off grid, use the bigger pump and pump for a shorter time, of course pick the time when the sun at its best, as you are more than aware thats when you have the "power" to run it.

When I was kid, my parents had a pool, I had to look after it, I got really good at it, no matter whether it's salt or chlorine direct, it gets lost into the atmosphere regardless direct sun leaches it.

If you are going to put a pool in, no matter what anyone says make the surround slope AWAY from the pool, NEVER towards it. If it's sloped towards it, all the crap gets washed in, I seen them done that way it's just a disaster and a never ending cleaning heartache.

Catch some extra in tank if necessary, if using tank, dam or bore water the solution to minimize algae is use UV light sterilizer in the filtering system and only run it when the pump is running, that will fix algae, it makes it sterile and it cannot breed end result algae problem will be minimal, make sure the water is kept "neutral", if there is a chance of over flow don't use a salt system that causes a salt issue with the surrounding ground, chlorine is not a problem on ground the sun leaches it out pretty quickly.

The only issue will be some heat to add when sun is very bad don't use the pool, or run the generator if really required for the two hours of filtering / heating.

If closing it down for a period use one of those shutdown pool covers that block out the light completely you will not even have to run the filter when covered as it acts like a tank.
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