Solar hot water pump controller
 

Hey guys. I'm getting close to putting up my solar hot water panels. However, I still need a controller for the setup. Can anyone recommend anything? Is it simply a differential temperature controller? Is there any new tech or features I should be looking for in this area? Variable speed pump control?

Have built a few of these controllers over the years, you need a min. of 2 sensors for differential control, plus a setting for the min. pump on differential, usually about 3-4 degrees Celsius, as there is no point in running the pump when the difference is only a few degrees or less.

For water flow through the panel array: needs to be fast enough for turbulent flow in the pipes to get best heat transfer. Pump size depends a lot on length of your pipes to the array and array size; you want enough flow to get approx a 10 degree Celsius temperature rise out of the array; any higher (less water flow) will loose efficiency through heat radiation.

Last controller I built used a Picaxe 8 pin CPU (program in basic) and a couple of 1-wire temperature sensors DS18B20.

Also have one using a couple of Op Amps, will have a look for the schematic.

Edit: found it, I published this in Silicon Chip many years ago https://www.eeweb.com/solar-hot-wate...mp-controller/

Cheers
Mike

Thanks Mike. A DIY controller sounds fun, but I simply don't have the time to put one together at this point.

I use a Resol Deltsol BS Pro. The plus points are that it is easy to use, it has setups to suit a number of equipment configurations, and it has proven reliable. I have been happy with it. The possible downsides are that I have had it some years now so it is an older design and newer controllers may have new/improved features. Also I don't know if it is still made, but if not I am sure Resol make an alternative.

Well, I am running out of time on this. I ended up going with a Steca 0301 U. I basically went with this due to limited availability of other name brand controllers, and my need to have one soon. I was hoping to find something with data logging so I could evaluate how the system is working. Perhaps that'll be something to upgrade to in the future.

I believe my controller is a resol as well.
The one you chose is fine..

The resol has some a few more benes then the less expensive ones but they all basically do the same important things.
Turn the pump on when the collector is hotter then the storage tank water.
Bingo.. you're done. Ha

The one I have runs the pump at high speed for about 5 seconds to help push the water up to the roof and thru the collectors.
The second the water begins retrieving from the roof the pump speed drops down to a slower speed which allows the water going thru the collectors to pick up a little more heat from the collector headers. I'm using evacuated tube collectors. (ONLY WAY TO GO, I love these things)

The simplest method here is to have a small 20w PV panel direct driving a small magnetic drive DC inline circulation pump; soon as the sun is strong enough to drive the pump then there is enough energy to heat your panels. Sun goes in (cloud) or at night then pump turns off.

No fancy controller needed.

Cheers
Mike

Reply to Solar Mike
 

Hi Mike,

What application are you speaking of?
Are you talking about DAOX's project?

Will that DC pump push water up to a roof, thru the collectors and back?
I know it wouldn't work for my application because my EVAC collectors get hot in over cast days..

Mine would be heating up but not enough sun for the DC pump to kick in using the 20W solar collector.. dig?

Thanks

The solar-powered pump might struggle to raise the water to a high roof roof for a drainback system. I don't know if a sealed & presurised system might be easier or harder for the pump.

For my system though it is an interesting option. My panels are on the wall, not the roof. The total head in the system is less than 2 metres with the panels half way up that height. A relatively weak pump might cope with that.

I don't know why I didn't think of it when I installed my system but it might be a worthwhile item to retrofit as a backup in case of power failure on a sunny day. If it worked my mains-powered pump could be configured to kick in at a higher temperature delta so that normal pumping operations would be done by the DC pump and the AC pump would only kick in in extremis. I will give that some thought.