Solar water pumping and 48volts

System · May 2008

here is the basics:

I want to install a solar water pump (A Sun Pump SDS-128 meets all my requirements).

I don't want to run off the batteries unless absolutely necessary.

I have pair of 48 volt arrays and a MX60 charge controller charging a 12 volt battery bank.

I have 6000 gallons of water storage and can go months without pumping water if needed. If Iam pumped full in the fall I'm good for the winter.

So.... How might I power my pump by tapping off my 48 volt solar arrays? Is there a transformer I can use to deliver 24 volts from 48? Is that an accepted practice?

Oh yeah...my 220 volt pump (or generator) died last night and I have 4500 gallons left till I need water!

thanks

mike

BB. · May 2008

Re: Solar water pumping and 48volts

You cannot "transform" DC with a transformer... They need AC to work.

If you have your heart set on that pump, you would have to find a DC to DC converter to up convert your 12 volts to 24 volts DC.

I am not sure you will be able to find any DC to DC converter that will do what you want for 48 volt solar panel to 24 volt pump.

I don't know anything about sun pumps, but the run from 12 to 30 volts... Either run it from 12 volts (1/3 to 1/2 the GPM rating--but still roughly the same energy used per gallon) and run it during the day time only (so you don't cycle your batteries unnecessarily).

You could also do something to temporarily rewire/switch your solar panels from your MX 60 to your pump as 24 volt setup--but I am not sure that would be any better--except for higher pump flow.

-Bill

I guess I should add, if you are going to be purchasing a pump controller anyway, then look at the Model PVA 30-M1. It does the 12 to 24 volt boost for you (more volume, longer wires supported). Yea, you might only be 80% or so efficient with the voltage doubler--but all things being equal, it is probably not a bad solution.

System2 · May 2008

Re: Solar water pumping and 48volts

Transformer!?!?!?!?!? Arghhhhh! Never mind... my brain dump of the day.

Not wanting to do a bunch of wiring and rewiring (a great way to REALLY screw things up!!) I guess I'll bite the bullet and spring for the two 80 watt panels to power the pump.

The 2 way wiring run is 250 feet, so 24 volts is a must. There is existing AWG 6 wiring in place that I can re-purpose. By adding the panels, I can reduce the wire run by 1/3 AND double the voltage. I can get used 80 watt 12/24 volt Solecs for $299 each right now, so...... c'est la vie!

Thanks Bill

Mike

BB. · May 2008

Re: Solar water pumping and 48volts

This is where a little pencil work may really help...

A new pump controller/voltage doubler costs $360 (plus or minus).

2x 80 watt panels new cost around $800...

You say that you don't use the water pump that much--will those $800 panels just sit around 48 weeks of the year doing nothing?

Then the voltage doubler will cost less to install and use (assuming you have sufficient energy in your current MX 60 system during sunny weather).

If you don't have enough energy--what about adding $xxx worth of solar panels to your existing MX 60 along with the new pump controller? You still spent the $xxx for the new 48 volt solar panels and they will still "be used for 4 weeks out of the year to pump water", but for the rest of the year, you can use the "extra solar panels" to power the rest of your home (at the expense of a $360 pump controller).

I would tend to avoid using dedicated solar panels in an application where the site idle for most of the year. Very expensive solution. If you can find a use for those panels 52 weeks a year--you are getting your best value.

-Bill

Windsun · May 2008

Re: Solar water pumping and 48volts

http://store.solar-electric.com/24voldcaut10.html

Something like that you could run 48V to it and convert down at the pump.

BB. · May 2008

Re: Solar water pumping and 48volts

Cool looking device...

One would have to look very closely at the "48 VDC panels" (between Voc at cold temperatures and Vmppt at high temp)--You can get a very wide "input" voltage range. Since output voltage is just 1/2 the input voltage--your output voltage will vary quite a bit.

What is the input range of the Solar Converter? And what is its standby load (should it be disconnected when not needed?).

Given that this would be in parallel with the input of the MX 60--will they "play" together well?

-Bill

System2 · May 2008

Re: Solar water pumping and 48volts

Bill

I'm kinda overpowered already. I am totaling about .3 to .5 kw of production per day to charge my battery bank to "float". I have 960 watts of 12 volt panels installed in two 48 volt arrays. I haven't run my little DC genny set since January. In fact, I've recently added several electrical appliances to use more power. I have anything BUT a shortage of electricity.

The PVA30-M1 seems like the best option and running it direct direct off the battery bank. I can then cut it off as need be. I pump about 800 gallons a week total for all sources since I am supplying water for my neighbors for a while. My usual consumption is a lot less!

The difference between the PCA and PVA's is PCA is a current boost controller and the PVA is an MPPT type, right? Kickin the electrons out at 30 volts enables me to transit the long wire run with minimal loss (looks like 2.8 %).

I can see plenty of reason to NOT add panels now! Thanks!

Mike

mike95490 · May 2008

Re: Solar water pumping and 48volts

What about an inverter from DC to 120V run a power cord to pumphouse, and use a sturdy 120V- 24V DC powersupply (linear or switcher) ?
Omron S8VS-48024
http://www.omron247.com/doc/pdfcatal.nsf/7C37217B29EC86D286257347004FF7E9/$FILE/D17S8VS0807.pdf

What's the duty cycle on the pump, on for 5 minutes/hr ? you could get by with that new small 300w/600w sure sine inverter, depending on the start-up surge, if the dc supply could handle it.
http://www.morningstarcorp.com/products/SureSine/index.shtml

icarus · May 2008

Re: Solar water pumping and 48volts

Windsun wrote: »

http://store.solar-electric.com/24voldcaut10.html

Something like that you could run 48V to it and convert down at the pump.

I use this exact hardware to run a 24 volt shurflo submersible off of 12 vdc. It doubles my pump speed so that I never have to worry about running out of water. 50 gph so the shower could run down, but @ 24 vdc it pumps ~ 120gpr so the shower is safe.

As Bill suggests, a little loss of efficiency is more than made up for in having the pump run for ~ 5 minutes to pump the tank to 60 psi vs 12-15 minutes. I usually turn off the pump after evening showers (at the breaker) so that incidental water use doesn't make the pump trip on and pump up at night when I don't need it to. I then switch it on in the morning under full sun so that it doesn't drag the batteries down. (More efficient that way I think)

All things considered, I am very happy with the system. My biggest problem is freeze protection since I pump out of a frozen lake 6 months a year. ( Our ice just went out yesterday,,, May 14th. Still big chunks floating around the lake though)!

icarus · May 2008

Re: Solar water pumping and 48volts

One more thought. You didn't say how deep you are pumping from, but if you can pump as much as 6000 gallons at a time, what about using a high volume gasoline pump. Won't work in a deep well, but it may be way cheaper on a volume basis,,, Just a thought

Icarus

Solar water pumping and 48volts

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