Help Selecting a Solar Water Pump Solution

5 Posts
Sep 9, 2008 12:21 pm
Help Selecting a Solar Water Pump Solution

Seeking suggested configurations, concerns & mitigations regarding the below solar water pump application.

Need to pump ~1,200 gallons of salt water to a non-pressurized holding tank 30' above and 300' distant from the source once per month.  Pumping desireably should take two hours or less suggesting 10GPM or better.  Source is salt water lagoon.  Location worst case is 4.5 solar energy hours / day according to NREL. Off grid, no mains available. Site exposed to occasional high winds.  Possibility of scaling fourfold over time.  Possibility of additional electrical demand (e.g. appliances, PCs).  Water needs to remain as pure as at source.

Concerns: caustic nature of salt water and environment, wind risk to PV array, weed / debris at intake, remote location makes reliability very important

Thanks in advance for your counsel.

Sep 12, 2008 11:38 am
Re: Help Selecting a Solar Water Pump Solution

Thats really a "tall" order when think about it. Sounds to me like you need the help of a professional, not a community forum.
That 1200 gallons in 2 hours could easily be accomplished by a gasoline engine powered pump. it would take less than a gallon of gasoline. Even at todays high gasoline prices your looking at an operational cost of less than $50 US a year. But of course thats not the bottom line, is it? We are, after all, trying to save the planet Earth from ourselves and burning gasoline doesn't help. So...
Scroll to the bottom of the above page.
It might take a while and a little persistence but, if use the search at, sourcegudies, your might find just what your looking for. Good luck!
I could help, but it would help me if you could narrow this down to a region. East coast, west coast, of a continent, that sort of thing.
5 Posts
Sep 12, 2008 12:58 pm
Re: Help Selecting a Solar Water Pump Solution

Thank you for your interest.  I'm just trying to cost an idea so please don't invest too much energy in a response.  Directionally accurate solutions and costs are all that is required at this point.

The location is an island off Belize.

As you note a gas pump is more economical, easier to repair et cetera so it wins on the practical front.
Sep 13, 2008 07:16 am
Re: Help Selecting a Solar Water Pump Solution

Oh please, its just photovoltaics and electricity. Its not like stellar cartography and quantum physics or anything like that.

I could go through all the math and give you an example PV array size, but whats really killing you here is that it will only be used once a month for two hours!

But, here it goes...
An electric motor powered pump that can perform this task might take as much as 10 amps at 120 vac, or put simply - 10 X 120 = 12000 watts
12000 X 2 hrs. = 24000 watts
I am not sure what the total number of hours of equivalent full rated power for a PV module would be in Belize, but it should be a lot, being so close to the equator and all. So I am going to guess at 7 hours.

The power would come from a battery bank...
24000 / 48 = 500
500 X 2 = 1000 amp hours capacity @ 48volts
I doubled it so that the battery would discharge by 50%
This helps to keep the voltage higher under load as well.

So, to recharge that battery bank over the coarse of the month...
30 days X 7Hrs. / 66% = *138 hours equivalent full rated power per month.
(* this number will vary from month to month depending on weather conditions)

24000 / 138 = a 200 watt PV array at 48 volts nominal. $1,000.00 not installed.
But the battery bank could cost $11,400.00 not installed.

Keep in mind that these are just rough figures. Your looking at spending about $20,000.00 with inverter(s) and  installation and shipping and all.

Yikes! Somebody, prove me wrong, please! Thats to much.
« Last Edit: Sep 13, 2008 07:20 am by Thomas Allen Schmidt »
220 Posts
Sep 13, 2008 11:15 am
Re: Help Selecting a Solar Water Pump Solution


  somehow we picked up an extra zero in our watts calculation. thats something i do all too often when doing the numbers in my head. so that 1.5 hp pump sounds about  right 10a @ 120 = 1200watts x 2 = 2400watts. that brings our battery bank down to a reasonable 500ah (12v) at 50% soc. we may want to only go to an 80% soc with the bank so lets say 1000ah at 12vdc. now we still don't want to get too small with our pv input. perhaps bring our bank back up to full in two or three days (batteries don't like to sit for long partially discharged) and then float there till next month. somewhere between 100 and 200watts should be fine. that brings our ballpark cost to a reasonable? three grand (without the plumbing).

good luck on your project.
351 Posts
Sep 13, 2008 01:17 pm
Re: Help Selecting a Solar Water Pump Solution

The "requirements" of pumping once a month and doing it in 2 hours or less, are driving the system costs.
Your 1200 gallons a month is about 40 gallons a day.  Why not pump daily Huh
The task could be accomplished with a small panel driving a small pump. NO batteries.
5 Posts
Sep 13, 2008 03:27 pm
Re: Help Selecting a Solar Water Pump Solution

The 1,200 in two hours every month is driven by the production cycle although the two hours was best case and can flex to say 24 hours (12x) if that drives cost reductions.

I take your point about using the whole month and lowering the requirements by 2 orders of magnitude.  I suppose I could add another stage to production at the front end if the improvement is material on cost and reliability.

Thanks to all for the feedback.
5 Posts
Sep 13, 2008 03:31 pm
Re: Help Selecting a Solar Water Pump Solution

$3,000 w/out the plumbing is more in the ballpark and the extra PV capacity post recharge can be gainfully used for a circulating pump.

5 Posts
Sep 13, 2008 03:33 pm
Re: Help Selecting a Solar Water Pump Solution

Any concerns or history with using these solar pumps in salt water?  The only applications I've seen are fresh.
351 Posts
Sep 13, 2008 05:02 pm
Re: Help Selecting a Solar Water Pump Solution

I haven't used one in saltwater. But the Shurflow pumps are fairly chemical resistant.  I would contact them about how saltwater safe the pump is, and which one they feel would be best for your application.
Another idea would be to contact bilge pump manufacturers (Attwood, Lovett, or Rule, are three that come to mind).  Their products are definitely saltwater resistant.  The question with them would be whether they make one that would operate under continuous duty for 4-6 hours a day at the 30 foot lift requirement.

Before I contacted them, I would think about water storage.  A tank, “pool”,  pond, etc.. If you place the storage above your production process, you could gravity flow or siphon it to meet your once a month production schedule.   Where the storage is placed could add a few feet to your lift requirement.
462 Posts
Sep 15, 2008 10:30 am
Re: Help Selecting a Solar Water Pump Solution

Matt, something to consider for both cost reduction and increased reliability is to use several pumps in parallel. Pumps in parallel share the load so there is less stress on each pump contributing to longer life. If one pump fails then at least there are others to continue doing the job. Smaller, more efficient and even DC pumps could then be considered.

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