Automatic solar dump

[waterdog]

6 hours ago, blackrose said:

 

So you're using a solar dump to run a mains immersion, is that right? I didn't think that was possible? It sounds easier than having to drain my calorifier and fit a 12v immersion.

 

Sorry I'm not on Facebook so I don't know how the Facebook 12v group do it.

 

Which solar dump kit are you using?

Hi Blackrose, yes a mains immersion.

 

I added a digital timer to the 12v control circuit(see above post) otherwise its wired as the link below.

 

edited to add - I didn't bother with the additional temp displays and circulation pump.

Implementing the Solar Dump Arrangement (1).pdf

Edited May 6, 2023 by waterdog
more info

[DarrenG]

On 03/05/2023 at 10:46, cheesegas said:

I have set up a couple, my favoured way at the moment is a bit of NodeRED flow I wrote which waits for the batteries to get to 100%, and then switches the immersion on and off with a very long duty cycle of between 10-60 seconds, like a PWM controller. When the immersion heater is on, it monitors the solar wattage and gets an average. This value then changes the duty cycle of the immersion heater being on, so the wattage of the solar input is roughly equal to the wattage of the immersion heater.

 

@cheesegas could you share the flow? I really like power monitoring and cycle approach, it's a clever way to adjust consumption to match the available solar.

 

Thanks

[blackrose]

I was put off changing over to a 300w 12v immersion and using a dump load from the solar controller because of the risk of damaging the calorifier trying to get my existing mains immersion out. The guy selling the 12v immersion heaters was kind enough to warn me about the possibility of that rather than just selling me stuff.

 

If there was an easy way of automatically switching my existing 1kW mains immersion heater on/off controlled by the battery voltage then I'd definitely do it, but it seems too complicated to me. I think someone posted a bit of equipment that could do this on another thread but then another member said they weren't reliable or something, I can't really remember.

 

Anyway, my inverter is on all the time to run the fridge and I have an immersion heater timer, so I suppose I could just set the immersion to come on for an hour a day when the forecast looks sunny n summer? I have 910w of panels.

Edited December 5, 2023 by blackrose

[magnetman]

 

I had a play with relays and very small solar panels once as a way to operate a DIY motorised satellite dish solar tracker. 

 

I discovered that if you have a very small solar panel (it was about 6 x 3 inches) and wire the output leads straight to the a relay then the relay will close when the sun shines on it and open when it is not in the sun anymore. So by putting this at right angles to the panel on the tracker it would switch the actuator on and track the sun until shaded. Worked really well actually. 

 

Maybe something like this could be adapted to switch on an immersion heater according to the sunshine. 

 

 

 

Another way to do it might be to fit one of these hall effect current sensors on a wire between the mppt and the batteries.  Wire the relay to the immersion heater. The device can be set to switch at a preset current. 

 

 

 

 

 

DC current sensing switch (hall effect sensor no wire needs cutting). 

 

https://www.ebay.co.uk/itm/284803877139

 

These ones have a display and are programmable

 

https://www.ebay.co.uk/itm/193930979670

 

 

 

DC to AC solid state relay for the immersion ? 

 

https://www.ebay.co.uk/itm/175793943517

[Chewbacka]

On 05/12/2023 at 07:15, magnetman said:

 

I had a play with relays and very small solar panels once as a way to operate a DIY motorised satellite dish solar tracker. 

 

I discovered that if you have a very small solar panel (it was about 6 x 3 inches) and wire the output leads straight to the a relay then the relay will close when the sun shines on it and open when it is not in the sun anymore. So by putting this at right angles to the panel on the tracker it would switch the actuator on and track the sun until shaded. Worked really well actually. 

 

Maybe something like this could be adapted to switch on an immersion heater according to the sunshine. 

 

 

 

Another way to do it might be to fit one of these hall effect current sensors on a wire between the mppt and the batteries.  Wire the relay to the immersion heater. The device can be set to switch at a preset current. 

 

 

 

 

 

DC current sensing switch (hall effect sensor no wire needs cutting). 

 

https://www.ebay.co.uk/itm/284803877139

 

These ones have a display and are programmable

 

https://www.ebay.co.uk/itm/193930979670

 

 

 

DC to AC solid state relay for the immersion ? 

 

https://www.ebay.co.uk/itm/175793943517

You would still need to sense battery voltage as well.  My thinking being that if there is lots of sun and the charging current is high then you don’t want it to switch on the immersion heater as the batteries are charging, however as the batteries become charged the current will fall and that’s when you want the immersion heater on.  BUT the current would also fall even if the batteries are nowhere near charged if the sun stops shining - clouds, night etc.  and you wouldn’t want the immersion heater on.  So you need a high battery voltage AND low charging current.

[IanD]

41 minutes ago, Chewbacka said:

You would still need to sense battery voltage as well.  My thinking being that if there is lots of sun and the charging current is high then you don’t want it to switch on the immersion heater as the batteries are charging, however as the batteries become charged the current will fall and that’s when you want the immersion heater on.  BUT the current would also fall even if the batteries are nowhere near charged if the sun stops shining - clouds, night etc.  and you wouldn’t want the immersion heater on.  So you need a high battery voltage AND low charging current.

 

Ideally you need to sense battery SoC and solar panel output, and if SoC gets to 100% (with LFP batteries) because of solar charging turn the immersion heater on -- then turn it off when SoC has dropped back a bit (e.g. to 95%) if the immersion takes more power than the solar is putting in, which is what you want to stop solar power being wasted. That's what mine's programmed to do (2kWp solar, 2.7kW immersion IIRC), but until next summer I won't know how well it works... 🙂

 

Much more difficult to do with LA batteries because the charge current drops off at high SoC... 😞

Edited December 8, 2023 by IanD

[DShK]

On 02/05/2023 at 18:50, PeterF said:

The problem with the dual elements is that they are limited to around 300W so it takes time for heating the water, but on the plus side if you lose the sun you are not dragging 1 kW from your batteries. It is harder to do for lead acid because of the desire to fully charge them and then not deplete them. A fully automatic system could be developed on the Cerbo GX if you used AC Out2 and the node red programming option.

You coyld use AC2 out and as mentioned above use assistants to control this and stop AC2 out if the batteries fell below say 95% SOC.

This is what I looked into doing. I decided that it wasn't worth it and I'd just put the immersion element on manually (with a timer) if my batteries were fully charged in the morning with the look of plenty more sunshine. Computers don't need to do all the thinking! I do have lithium though.

 

I am fairly sure that automatic dump loads are misunderstood and don't work the way people think. The way they work seems like a good way to kill lead acid batteries.

[magnetman]

3 hours ago, Chewbacka said:

You would still need to sense battery voltage as well.  My thinking being that if there is lots of sun and the charging current is high then you don’t want it to switch on the immersion heater as the batteries are charging, however as the batteries become charged the current will fall and that’s when you want the immersion heater on.  BUT the current would also fall even if the batteries are nowhere near charged if the sun stops shining - clouds, night etc.  and you wouldn’t want the immersion heater on.  So you need a high battery voltage AND low charging current.

Yes I admit I was assuming that the batteries would be charged fairly quickly after daybreak. 

If the current never reached the cut-in level this would indicate that its not a good day for charging so power would not be stolen to divert to the immersion. 

 

I don't have a use for hot water for washing as have worked out alternatives. Also have small batteries. 

 

 

 

 

[IanD]

2 hours ago, DShK said:

This is what I looked into doing. I decided that it wasn't worth it and I'd just put the immersion element on manually (with a timer) if my batteries were fully charged in the morning with the look of plenty more sunshine. Computers don't need to do all the thinking! I do have lithium though.

 

I am fairly sure that automatic dump loads are misunderstood and don't work the way people think. The way they work seems like a good way to kill lead acid batteries.

You don't need Node Red, mine is connected to AC2 out and uses an assistant to turn it on and off. Doing it manually or with a timer is fine if you're on the boat (and you remember, and watch the weather/solar yield), but automating it is easy (if you have the hardware, like a Cerbo) so why not do it?

 

Fine with LFP but don't do it with LA batteries, as noted...

[rusty69]

2 hours ago, DShK said:

This is what I looked into doing. I decided that it wasn't worth it and I'd just put the immersion element on manually (with a timer) if my batteries were fully charged in the morning with the look of plenty more sunshine. Computers don't need to do all the thinking! I do have lithium though.

 

I am fairly sure that automatic dump loads are misunderstood and don't work the way people think. The way they work seems like a good way to kill lead acid batteries.

Thats what I have been doing too. Just use a smart plug to turn it on/off remotely.

 

2 hours ago, magnetman said:

 

 

I don't have a use for hot water for washing as have worked out alternatives. Also have small batteries. 

 

 

 

 

 

 

Is that alternative 1)Not to wash at all. 2)Occasionally fall in the river

 

 

Edited December 8, 2023 by rusty69

[magnetman]

Navy shower with cold water. 

[DShK]

13 minutes ago, IanD said:

You don't need Node Red, mine is connected to AC2 out and uses an assistant to turn it on and off. Doing it manually or with a timer is fine if you're on the boat (and you remember, and watch the weather/solar yield), but automating it is easy (if you have the hardware, like a Cerbo) so why not do it?

 

Fine with LFP but don't do it with LA batteries, as noted...

I'll be honest the biggest put off for me was running a new AC line to the immersion 😄 I'll probably have a crack at doing it one day, I've got enough other bits to do at the moment!

[magnetman]

Install the batteries near the calorifier? 

[blackrose]

8 hours ago, DShK said:

I am fairly sure that automatic dump loads are misunderstood and don't work the way people think. The way they work seems like a good way to kill lead acid batteries.

 

Some people understand how they work, some don't. The one I looked at from Bimble seemed fairly straightforward but there may be different systems out there.

 

I have manually switched on my 1kW mains immersion heater on sunny days for over 2 hours with the (450ah) LA battery bank starting from 100% SoC and about 55-60 amps coming into the batteries from the (910w) panels. When I switched the immersion off the batteries were down to about 70% SOC and during the rest of day were charged back to 100% with no ill effects. If a solar dump load system does a similar thing automatically with a smaller 300w/12v heater I don't see why it should kill LA batteries.

 

The one thing it can't do of course is know the weather forecast. When I manually switched my immersion off I knew that there was going to be plenty of sunshine left that day to fully charge the batteries. 

Edited December 8, 2023 by blackrose