Automatic solar dump

[pollip]

I’ve got 1170w solar 2 panels running through an epever and 2 through a victron 100/50 smartsolar.. epever will eventually be replaced for another 100/50. I’m wanting to dump the excess solar to a 1kw 230v immersion heater. I’m running a multiplus 3000/12/120 16 amp, victron smart shunt, cerbo gx and touch 50. I’ve seen the usual way to do it on 12v boating group but I’m wanting a fit and forget auto solar dump where I don’t have to touch anything at all it just does it’s thing. I’ve heard of running it off l2 on the multiplus but that apparently can run off batts and I don’t want that (5 x 105ah lead carbon agms). Does anybody have any pointers ??

[pearley]

I was looking at same thing as fitting a dual voltage immersion would be a bit of a pain. So found this on Victron Community Forum.

 

https://community.victronenergy.com/questions/57414/help-with-assistants-to-use-ac2-as-dumload.html

 

If it works let me know then I can try it 

[pollip]

5 minutes ago, pearley said:

I was looking at same thing as fitting a dual voltage immersion would be a bit of a pain. So found this on Victron Community Forum.

 

https://community.victronenergy.com/questions/57414/help-with-assistants-to-use-ac2-as-dumload.html

 

If it works let me know then I can try it 

 

5 minutes ago, pearley said:

I was looking at same thing as fitting a dual voltage immersion would be a bit of a pain. So found this on Victron Community Forum.

 

https://community.victronenergy.com/questions/57414/help-with-assistants-to-use-ac2-as-dumload.html

 

If it works let me know then I can try it 

 

 

 

 

 

 

 

6 minutes ago, pearley said:

I don’t really know how to work this forum so you’ll have t bare with me… I asked on the victron pages before and that what a lot of people said, all using lifepo4 though which the load really wouldn’t bother. I think my solution is a 12v Immersion tbh but I really don’t want to have to change the element out but then I also don’t want to have to run the inverter to get the solar dump lol. All the 230v/12v dual elements I’ve found are suited to horizontal tanks and mines vertical 🤷🏻‍♂️

[peterboat]

I did it the easy way, I have 5kw of solar 3kw is for drive [electric drive] and 2 is for domestic, the drive solar I switch to my 3kw immersion heater as it leaves the MCB. Like today not much sun but water hot, equally batteries fully charged. Sometimes simple is the best way

[PeterF]

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.

[pollip]

2 hours ago, 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.

That is one of the things that put me off in the first place, it probably takes 2 hours to heat my tank with a 1kw and I wouldn’t say that was red hot. 300w would take an age.  Now my theory is though that in the summer water doesn’t need to be as hot as it’s hot out and the waters warmer to begin with so takes less heating. Even slightly warm water is a bonus. That’s pretty much what was said on the victron Forum, I think part of my problem is I want it to do it’s thing when I’m not there and don’t want to leave the inverter on if I’m not incase something happens fire loose sun and run the batts down yada yada. That is a really simple easy solution to my problem but I’ll be less bothered about leaving it on if I wasn’t leaving the dogs in there aswell. That’s the reason I want an auto system so I can get home and have a shower when needed rather than thinking I’ll just sit and wait a few hours for the water to heat up

[DandV]

It certainly can be achieved with late model Victron multiplus's

We stayed for nearly a fortnight of particularily gloomy weather in my sister's off grid holiday home that has this arrangement.

Presumably the Inverter had at least 2 AC outlets. 

 

With near no sunshine it took till after  mid day for the system to replenish the batteries after overnight draw down, very largely the refrigerator.

Then the fan would start on the Inverter signaling that the 1500W hot water element was connected for a relitively brief run before dropping out again to repeat perhaps in about an hours time. Only enough time to take some chill out of the water. We had to light the water jacketed stove to get the water to shower temperature.

However on sunny days, the fan would kick in about an hour after sun strike on the panels, and run until the water either the water was fully heated, or the sun disappeared. 

 

A big advantage was if you were away you would come to a full cylinder of hot water. 

Edited May 2, 2023 by DandV

[pollip]

3 hours ago, peterboat said:

I did it the easy way, I have 5kw of solar 3kw is for drive [electric drive] and 2 is for domestic, the drive solar I switch to my 3kw immersion heater as it leaves the MCB. Like today not much sun but water hot, equally batteries fully charged. Sometimes simple is the best way

That does sound pretty simple tbf but does require being around to press switches which I’m trying to avoid.. don’t get me wrong if that’s the way I’ve got to do it pressing switches then that’s the way but It won’t fully help because I’m not always going to be there to flick switches and there will be times I’ll have to come back and wait hours for hot water to heat when it could of been heating all day because I’m not there so not using power but I’m not there so I cor flick the switches 

5 minutes ago, DandV said:

It certainly can be achieved with late model Victron multiplus's

We stayed for nearly a fortnight of particularily gloomy weather in my sister's off grid holiday home that has this arrangement.

Presumably the Inverter had at least 2 AC outlets. 

 

With near no sunshine it took till after  mid day for the system to replenish the batteries after overnight draw down, very largely the refrigerator.

Then the fan would start on the Inverter signaling that the 1500W hot water element was connected for a relitively brief run before dropping out again to repeat perhaps in about an hours time. Only enough time to take some chill out of the water. We had to light the water jacketed stove to get the water to shower temperature.

However on sunny days, the fan would kick in about an hour after sun strike on the panels, and run until the water either the water was fully heated, or the sun disappeared. 

 

A big advantage was if you were away you would come to a full cylinder of hot water. 

That’s about the way I want it to go tbh, if there’s no sun there’s no sun you just heat it up yourself but having the opportunity and not taking it is just wasteful when it could be rather beneficial.. I have heard still though you are better to run it through a separate relay rather than keep flicking the inverter relay on and off like you say sometimes every hours.. the only thing I can think about there is one’s a lot more to replace than the other

[DandV]

In the time we were there the most starts on the hot water system in a day was three. 

On days with sunshine only the one.

Mind you that was with a fairly substantial lithium battery bank 

[PeterF]

I think the doing it automatically with lithium is much easier because they do not need to be fully charged like lead acid batteries. I looked into doing on my boat, big enough bank and solar but the batteries are AGM so I have not gone any further because you only want to use excess solar and not pull the batteries back down.

[pollip]

3 minutes ago, DandV said:

In the time we were there the most starts on the hot water system in a day was three. 

On days with sunshine only the one.

Mind you that was with a fairly substantial lithium battery bank 

That’s not bad actually, I’m curious at what point during the day say the waters piping hot how would the system no to stop heating it 🤔🤷🏻‍♂️. I’ve just been looking at 12v elements but have had a thought that at least with 230v I have the option to remotely turn it off, 12v I’m stuffed and it will have to wait until I’m home

[PeterF]

There will still be a thermostat switch to switch the element off just like normal.

[pollip]

2 minutes ago, PeterF said:

I think the doing it automatically with lithium is much easier because they do not need to be fully charged like lead acid batteries. I looked into doing on my boat, big enough bank and solar but the batteries are AGM so I have not gone any further because you only want to use excess solar and not pull the batteries back down.

That was my issue with using the ac2 on the multiplus, everyone that was saying it was using lithium, they were saying something along the lines of setting the assistant to 80% of battery capacity to prevent it cutting in and out all the time but like you say that doesn’t really work without lithium. If I put a 1000w draw on my batts they would kick up a right fuss. Maybe I leave this one until I have lifepo4 🤔. I’m assuming it would be similar issues doing and auto system using 12v ?

[PeterF]

If the system is 12V limited to 300W then there is less load so it is more likely solar will keep up and not draw down the batteries, but you would still need some over rides on low SOC.

[pollip]

2 minutes ago, PeterF said:

If the system is 12V limited to 300W then there is less load so it is more likely solar will keep up and not draw down the batteries, but you would still need some over rides on low SOC.

Just pop a relay in that cuts in at a certain voltage and out at a certainly voltage ?. Kind of like a split charge relay ?. Is it worth doing considering the cost of a 12/230v element and those aren’t suitable anyway so I’ll have to look further afield 

[peterboat]

52 minutes ago, pollip said:

That does sound pretty simple tbf but does require being around to press switches which I’m trying to avoid.. don’t get me wrong if that’s the way I’ve got to do it pressing switches then that’s the way but It won’t fully help because I’m not always going to be there to flick switches and there will be times I’ll have to come back and wait hours for hot water to heat when it could of been heating all day because I’m not there so not using power but I’m not there so I cor flick the switches 

That’s about the way I want it to go tbh, if there’s no sun there’s no sun you just heat it up yourself but having the opportunity and not taking it is just wasteful when it could be rather beneficial.. I have heard still though you are better to run it through a separate relay rather than keep flicking the inverter relay on and off like you say sometimes every hours.. the only thing I can think about there is one’s a lot more to replace than the other

I am not around to flick switches most of the time, I have sufficient solar to charge my Lifepo4s so unless cruising its left on all the time. Its easier that way, I have a 3kw immersion running on 200 volts of DC straight from the solar. Its very effective and produces hot water fro April to October. Whilst cruising I use the generator to create some hot water as well as charging batteries and maybe the washing machine and dishwasher 

[PeterF]

11 hours ago, pollip said:

Just pop a relay in that cuts in at a certain voltage and out at a certainly voltage ?. Kind of like a split charge relay ?. Is it worth doing considering the cost of a 12/230v element and those aren’t suitable anyway so I’ll have to look further afield 

A simple voltage sensing relay will not be ideal. Consider the case where you have 250W solar available, the batteries are taking 100W and the heating element is 300W. Batteries are taking 100W so voltage is at 14.4V, the VSR closes, 300W goes to the heater, 50W is drawn from the battery, the voltage drops to 12.7V, the VSR opens, 100W solar goes to batteries, voltage goes to 14.4V and the cycle repeats every few seconds. That is why with lithium you use the battery monitor and SOC to control it to avoid the rapid cycling when not enough excess is available.

[cheesegas]

As you have a Cerbo, it can be done in software but it does need some coding knowhow. Install Venus OS Large and activate NodeRED on the Cerbo, and then connect a heavy duty solid state relay capable of switching mains to the relay output of the Cerbo with a 12v trigger. Wire this relay to switch the immersion on and off.

 

(I've assumed that you have a Multiplus rather than a Multiplus II; these have a second output which can be switched via the Aux and an appropriately configured Assistant. Some later firmware versions will allow it to be controlled via ve.bus however.)

 

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.

 

If the batteries get below 96%, it waits for it to get to 100% again. This happens sometimes if there's a big burst of sunlight and then clouds when the heater is on. 

 

Potential downside is continuously cycling the Cerbo's relay, but this can be easily circumvented by using a networkable solid state relay board and talking to it over the LAN.

 

 

[peterboat]

None of this is beating my switch, to complex and guaranteed to fail or flatten the batteries 

[cheesegas]

3 hours ago, peterboat said:

None of this is beating my switch, to complex and guaranteed to fail or flatten the batteries 

It doesn’t work for most, if not all narrow boats though - they’ll most likely have three 35v panels in parallel to avoid shading under trees etc. Not enough voltage to feed the element directly. 
 

My approach is very simple hardware wise, and can be fitted with an override switch in case the Cerbo has an issue. 

[blackrose]

23 hours ago, pollip said:

I think my solution is a 12v Immersion tbh but I really don’t want to have to change the element out but then I also don’t want to have to run the inverter to get the solar dump lol. All the 230v/12v dual elements I’ve found are suited to horizontal tanks and mines vertical 

 

As far as I know the simplest method requires a 12v/300w immersion heater. I assume the dual element immersion does the same thing but just gives you the option of running it from shore power?

 

I can't see why any immersion heater wouldn't be suitable for a vertical tank provided it's fitted at the bottom of the tank? And I still don't really understand why any immersion heater would be fitted at the top of a tank?

 

You could email these people to find out:

 

https://www.surejust.co.uk/marine-immersion-heaters?fbclid=IwAR0vPKa6RUEov2ziI7y1-cBawK5iANaM97c_UUYXgykzE4eCiaenlyhwzdE

Edited May 3, 2023 by blackrose

[Tony Brooks]

24 minutes ago, blackrose said:

I still don't really understand why any immersion heater would be fitted at the top of a tank

 

I think that while active heating is going on, convection currents within the calorifier will eventually heat most of the content. If this were now so, why do domestic systems have atop mounted immersion heater. Also, how do the calorifier coils heat a tank full when they are a part way up the tank, especially in twin coil verticals.

 

When heating stops, I agree the very low cooling via the top fittings would dramatically reduce convection and allow the water to stratify according to temperature.

[robtheplod]

1 hour ago, blackrose said:

 And I still don't really understand why any immersion heater would be fitted at the top of a tank?

 

Ours is up the top and is a lot longer than usual ones and reaches the bottom (27" ?).... i suppose advantage is i can change ours without draining the tank..

Edited May 3, 2023 by robtheplod

[waterdog]

On 02/05/2023 at 16:13, pollip said:

I’ve got 1170w solar 2 panels running through an epever and 2 through a victron 100/50 smartsolar.. epever will eventually be replaced for another 100/50. I’m wanting to dump the excess solar to a 1kw 230v immersion heater. I’m running a multiplus 3000/12/120 16 amp, victron smart shunt, cerbo gx and touch 50. I’ve seen the usual way to do it on 12v boating group but I’m wanting a fit and forget auto solar dump where I don’t have to touch anything at all it just does it’s thing. I’ve heard of running it off l2 on the multiplus but that apparently can run off batts and I don’t want that (5 x 105ah lead carbon agms). Does anybody have any pointers ??

I fitted my solar dump recently as per the facebook 12v group but added in a digital timer (amazon)

 

Heschen Digital LCD Power Weekly Programmable Timer Relay Switch, CN101A, DC12V 16Amp, SPST, with Waterproof Cover, White : Amazon.co.uk: DIY & Tools

 

I just set the power controller so the batteries are still getting 2 or 3 amps when its dull, set the upper and lower voltage limits on the smart relay and set the timer to start at 9.30 and off at 2.00 in the afternoon. This is heating enough water for us and is still fully charging the batteries up by 5 pm.

It's not as hot as when on the shoreline but its hot enough for washing the dishes in and having showers etc.

 

It's a 240v immersion at the top of a vertical surecal calorifier with a 2kw mastervolt inverter. No idea about the immersion length as it supplied plenty of hot water on shorepower so I figured it would do the same on solar and wasn't taking it out to check. I have 1.2kw of panels on the roof.

 

As we move into summer I'm expecting to increase the run time and hopefully get even better results.

 

 

[blackrose]

On 04/05/2023 at 08:35, waterdog said:

I fitted my solar dump recently as per the facebook 12v group but added in a digital timer (amazon)

 

It's a 240v immersion at the top of a vertical surecal calorifier with a 2kw mastervolt inverter. 

 

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?

Edited May 6, 2023 by blackrose