Author Topic: Low voltage DC solar heating pump from europe?  (Read 481 times)

Offline PekkaNF

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Low voltage DC solar heating pump from europe?
« on: July 17, 2022, 09:09:31 AM »
I am thinking of building a small off-grid solar heating system for warm water. Solar heating will not provide 100% all year, but should do about 6 months without any external energy. Middle of winter would need 100% of external energy. Space heating is different system altogether, but there low voltage heat circulation pump would be really useful too.

Therefore:

1: Circulation pump for solar panel circuit.

2: Circulation pump for space heating system.

Ideally these pumps would be then same model, if dimensioning and chemical resistance etc. works out. I am looking for a decent quality residental type pump, not all plastic caravan type pump.

There seems to be plenty of solar heating and PV panes, controllers and other hardware, which most of it normal domestic heating.

It is easy to locate 230 VAC mains operated circulation pumps, but low voltage (12/24/48VDC) circulation pumps seem to be rare.

Saw this one on YT:


This is not exactly, what I need, but othervise looks pretty good:
https://shop.solardirect.com/product_info.php?products_id=880

There is possibility to use DC/AC sinewave inverter, but this is of additional complexity and losses.

Ideas or good pointers?

Offline ZebraDriver

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Re: Low voltage DC solar heating pump from europe?
« Reply #1 on: July 17, 2022, 10:29:30 AM »
A quick look at ebay shows lots of solar hot water brushless 12 volt pumps, Ok they look to be plastic but at the price of them (under 20 euros) they might  do your job and be replaceable as they possibly wear out.

Martin
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Offline vtsteam

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Re: Low voltage DC solar heating pump from europe?
« Reply #2 on: July 17, 2022, 03:18:35 PM »
So Pekka, the reason for low voltage is that you also want to power the pumps from a photovoltaic source?
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline PekkaNF

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Re: Low voltage DC solar heating pump from europe?
« Reply #3 on: July 18, 2022, 03:47:14 AM »
So Pekka, the reason for low voltage is that you also want to power the pumps from a photovoltaic source?

Correct. Sort of UPS for power breaks and other exeptional (and hopefully rare situations). Small DC PV system is simple to work with.

I do have 3 phase mains, but there are ocassional power breaks and world is a bit grazy....therefore I am looking for a little redundancy, back-up and maybe a little energy bill savings.

My logic goes for a separate discrete systems that are easily replaced or upgraded. Solar thermal system needs very little external electricity to work. However, most controllers and pumps are build for mains use. No problem, if the solar energy is used only when main energy is available....but I want it also when it is not. I do know that energy demand is low and I could use an inverter, but that is added loss, reliability and complexity. Ofcourse this is no problem in a bigger PV system, but that would need to have all island use hardware.

I was looking a little thermosolar system, because it is proven and simple. Also storing enough energy for 2-4 days use for hot water in a insulated "boiler" inside of the house is standard technology and very reliable. There are pretty much all system components available, even packaged, but the low voltage pump part could be a show stopper.

My other alternative for thermosolar panels and pumps would be to use PV panels to produce high DC (equivalent of AC) to heat water in a standard boiler. Here it would be 8 x 375W panes (each nominally 40v open circuit voltage and 12A short circuit current) in series, mounting hardware, isolation switch, wiring and overheating disconnect....and very little anything more. Feels a little daft to use PV electricity to waste it into a restor (heating coil/immersion heater ) to heat water, but it looks like most cost effective way (no inverters, just a relay to disconnect it in a unlikely event of thank overheating). But Solar panels would take more space and in future I could use that space for PV panes that produce usable electricity...

That is my though process and now I am stuck of not finding a low voltage solar heater circulation pump and that might lead to scope creep....and that probably would render simple system unfeasible. Just doing a little feasibility study study before comitting.

Offline JamesC

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Re: Low voltage DC solar heating pump from europe?
« Reply #4 on: July 18, 2022, 07:52:06 AM »
A thought, do you need a pump at all?

With the right design you could have a gravity system which required no pump.

James


Offline PekkaNF

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Re: Low voltage DC solar heating pump from europe?
« Reply #5 on: July 18, 2022, 10:48:42 AM »
At this latitude tank is inside, panels are at the roof there is least 300 mm of insulation against the winter cold and heat transfer fluid must withstand closer to -40C.....so...no thermosiphon...actually shut of valves are needed to prevent unwanted thermosiphon during the coldest winter months....but yes...it will work least 6 months a year.

Offline vtsteam

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Re: Low voltage DC solar heating pump from europe?
« Reply #6 on: July 19, 2022, 12:17:27 PM »
I don't know why photovoltaic panels aren't fitted with backside heat exchangers and insulation since most of the energy hitting a them is wasted as heat..... estimated at 80%+ or 1kW/sq M in direct sun. Cogeneration is a big topic for DIY engine driven generators, why not photocells? Why should one have to install both types as separate panels taking up additional space and materials?

Well as long as we're going outside the box, add thermoelectric modules between the cells and the heat exchanger since they work on a delta T for maybe another 3% sunlight/electrical conversion efficiency. and use a liquid Stirling engine pump for circulation if thermosiphoning isn't possible.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline WeldingRod

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Re: Low voltage DC solar heating pump from europe?
« Reply #7 on: July 19, 2022, 04:54:55 PM »
Note that a regular relay will not survive switching 200+ Volts DC..

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Offline vtsteam

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Re: Low voltage DC solar heating pump from europe?
« Reply #8 on: July 19, 2022, 05:51:12 PM »
Pekka,
March brand pumps are available in Germany:
https://www.marchpump.com/en-de/pumps/

The 809 and 815 pumps come in bronze and 12v and 24V, example:
https://pumpbiz.com/march-bronze-circ-pump-809-br-24v-dc-brush#

They have less expensive pumps using plastic, but seemingly high quality.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline PekkaNF

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Re: Low voltage DC solar heating pump from europe?
« Reply #9 on: July 20, 2022, 03:30:52 PM »
Thank you all!

I don't know why photovoltaic panels aren't fitted with backside heat exchangers and insulation since most of the energy hitting a them is wasted as heat..... estimated at 80%+ or 1kW/sq M in direct sun. Cogeneration is a big topic for DIY engine driven generators, why not photocells? Why should one have to install both types as separate panels taking up additional space and materials?

Well as long as we're going outside the box, add thermoelectric modules between the cells and the heat exchanger since they work on a delta T for maybe another 3% sunlight/electrical conversion efficiency. and use a liquid Stirling engine pump for circulation if thermosiphoning isn't possible.

I have seen some studies of cooling the PV panel and also using the cooling energy for heating. I went two years ago to Biosphere II, AZ ant they had outside few PV panels elevated little off from the ground. The shade was used grow some plants who in turn kept panels cooler.  I heard that some panel plantations in very arid climate attracted plant undergrow due to more favorable microclimate. Apparently panels here produce pretty well early on spring when ambient temperature is cold but sun shines from clear sky.

I saw one study about liquid cooling of the PV panel back, there was some complications on chemistry and physical structure....nothing show stopper, but needed some special encapsulation to keep the coolant of the traditional PV-parts...voltages get easily few hundred volts across the panel string, there is another consideration.

Note that a regular relay will not survive switching 200+ Volts DC..

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Noted. AC and DC is ibit different when it comes to contactors. Here the current would be pretty low (10-16A absolute max) and resistive load is pretty well behaved. Most likely electronic solution would be eventually better choice, because PV panels are not a linear power supply and something should change (like load) to get best out of them. Here it pays off to use excessive energy for heating instead of pushing back to network. One solution would be "diverter".
https://www.solarpanelprices.co.uk/articles/solar-panels/solar-pv-diverter-explained/


Pekka,
March brand pumps are available in Germany:
https://www.marchpump.com/en-de/pumps/

The 809 and 815 pumps come in bronze and 12v and 24V, example:
https://pumpbiz.com/march-bronze-circ-pump-809-br-24v-dc-brush#

They have less expensive pumps using plastic, but seemingly high quality.

That looks pretty good. I'll follow that lead and see what cost structure it would produce.

Thank you,
Pekka

Offline hanermo

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Re: Low voltage DC solar heating pump from europe?
« Reply #10 on: August 04, 2022, 01:09:31 PM »
Em..
the dc direct voltages get high.
We just installed our latest 10 kW system, 3-phase, and the open circuit voltage is rated at 1000 V.
With isolation relays and all paperwork and certs.

The more serials you get in a string, the higher the voltage can go.
And it varies a lot, during the day.
20 panels in 2 strings with a huawei 3-phase mppt inverter.

Connecting the pump behind the inverter is likely to be much more durable, and easy, and cheap.
Things like 220V well pumps are meant for "harsh service" aka industrial use, and are really cheap.
Optionally 220V airco circulation pumps, or shower booster pumps.