Immersion Heater - PV electricity

[Whip1971]

Hi Walter. It's all finished and working apart from the LCD screen which I can install when I recieve it from china. At the moment it's running a 50w downlight (instead of the immersion)so I can see when it's working. Im still waiting for my plumber to install my 27inch immersion. Fortunately I already have a immersion circuit installed so don't have to worry about that. My box/ gadget is fixed next to my consumer unit with a CT connected to my main incoming tail, within the consumer unit. Hope this helps mate!

 

[mightywalter]

Whip - I like the idea of connecting the 50W downlight as visual feedback. Something like that might be useful in parallel with the immersion once finalised. We've got a Wattson to monitor our PV & usage at present - we find its coloured visual indication useful for 'at a glance' monitoring.

So are you installing a new 1kW element instead of using your existing immersion element ? I'd understood pmcalli's design tracks & uses all surplus PV, and can work with the existing 3kW immersion element, simply adjusting the power feed to the element to provide what is available ... maybe I've missed something.

Like you I have a separate immersion circuit installed. Presumably you wire the controller in the feed to the immersion from the relevant MCB in the consumer unit (CU) that previously just connected to the line of the immersion circuit. So, how does the 13A socket on the gadget work ? Are the L, N, E feeds from the CU wired directly into the gadget and the element circuit to the plug that goes into the socket on the box ?

 

[Whip1971]

Walter, Im getting my plumber to install a new 3kW immersion. I have no immersion in my cylinder at the moment.
What I have done is to disconnect the immersion circuit at the 16A MCB in my consumer unit. I have then fed the box with this MCB. Then instead of putting a socket outlet on my box, I've taken the output back into the consumer unit and connected this to my existing immersion circuit. Once I have my LCD installed this will show me how much power I'm importing from the grid or how much excess pv power im producing. I think pmcalli said that once the pv power is 40W more than what the house is using it then sends power to the immersion..

 

[pmcalli]

Whip - I like the idea of connecting the 50W downlight as visual feedback. Something like that might be useful in parallel with the immersion once finalised. We've got a Wattson to monitor our PV & usage at present - we find its coloured visual indication useful for 'at a glance' monitoring.

So are you installing a new 1kW element instead of using your existing immersion element ? I'd understood pmcalli's design tracks & uses all surplus PV, and can work with the existing 3kW immersion element, simply adjusting the power feed to the element to provide what is available ... maybe I've missed something.

Like you I have a separate immersion circuit installed. Presumably you wire the controller in the feed to the immersion from the relevant MCB in the consumer unit (CU) that previously just connected to the line of the immersion circuit. So, how does the 13A socket on the gadget work ? Are the L, N, E feeds from the CU wired directly into the gadget and the element circuit to the plug that goes into the socket on the box ?

in a word yes. you can wire it direct if you want to but having the plug and sockets makes an easy installation for the sparky.

 

[mightywalter]

Ah, understood. Everything in our home is run on electricity, so the idea of a water cylinder without an element didn't occur to me ;-).

Thanks for clarifying the installation. Do you have the EMC filter on the MCB feed into the box, or between the box and the immersion element ? Or have you installed one for each ?

Will you mount the LCD on the controller box, or will you link it through into your home, where it'll be more readily visible ?

 

[pmcalli]

Walter, Im getting my plumber to install a new 3kW immersion. I have no immersion in my cylinder at the moment.
What I have done is to disconnect the immersion circuit at the 16A MCB in my consumer unit. I have then fed the box with this MCB. Then instead of putting a socket outlet on my box, I've taken the output back into the consumer unit and connected this to my existing immersion circuit. Once I have my LCD installed this will show me how much power I'm importing from the grid or how much excess pv power im producing. I think pmcalli said that once the pv power is 40W more than what the house is using it then sends power to the immersion..

I would recommend as a precaution if your are wiring direct to the immersion that you add a fuse to protect the crydom should your immersion go short circuit. its a bit overkill as the crydom is 50A and the cu mcb should trip but the crydom is expensive and a fuse is cheap.

 

[Whip1971]

Thanks pmcalli that makes sence to fuse it.
Walter the LCD fits onto the box, so in the garage next to my CU unfortunately. Would be good to have a remote one. Maybe my next project. The EMC filter is on the feed to the box.
Wife's just phoned to say my display has arrived!! I know what I'm doing tonight...
Just had a thought, in my airing cupboard I have a 20A double pole isolator for my immersion. I'll change that for a single socket outlet and plug my immersion via a 13A plug

 

[mightywalter]

I'd like to clarify the legal position on installing a solar PV controllers, in terms of the wiring regs.

My understanding is that the controller would need to be installed either (i) by a certified installer or (ii) by myself, but in the latter case I would need to get it checked and approved. Either way, before CE marked products come to market, would an installation of a hand-crafted gadget be approved ?

There could be some subtleties here. For example, if the immersion element were connected via a 13A plug to a dedicated socket (fed from the immersion circuit, not the ring main) I believe that would be OK. In that scenario, however, I could plug a controller in between (except, of course, the difficulty of connecting the controller's CT sensor over a rather long distance).

Comments welcome...sorry if I'm asking an 'awkward' question !

 

[pmcalli]

I'd like to clarify the legal position on installing a solar PV controllers, in terms of the wiring regs.

My understanding is that the controller would need to be installed either (i) by a certified installer or (ii) by myself, but in the latter case I would need to get it checked and approved. Either way, before CE marked products come to market, would an installation of a hand-crafted gadget be approved ?

There could be some subtleties here. For example, if the immersion element were connected via a 13A plug to a dedicated socket (fed from the immersion circuit, not the ring main) I believe that would be OK. In that scenario, however, I could plug a controller in between (except, of course, the difficulty of connecting the controller's CT sensor over a rather long distance).

Comments welcome...sorry if I'm asking an 'awkward' question !

If you put the 13A socket from the cu immersion circuit next to the CU then there isn't a problem. As to long lead on the CT. I have tried 50 Meters of lead and it works fine. the problem is routing the sensor lead. other people have had interference problems but in my circuit the worst that could happen is the interference is integrated into an offset which affects the import/export.

 

[Trader9]

Hi Chris


I have been using an Arduino Uno since December to divert surplus solar to two 3kW immersion heaters using a 3.3kVA isolation transformer toggling between 55V and 110V and have been looking to upgrade to a triac circuit using PWM from the Arduino.

However, because of the zero cross sensing and triggering of the triac at 100HZ there was no processing time left for the current sensing and calculations needed to provide the trigger levels using a single Arduino. I believe you may need two Arduino's. A good place to look for a PWM circuit is by Googling “Using Hardware Interrupts to Control A.C. Power” it has notes and a Arduino sketch it also works I have built it.


I am still going to replace my transformer, but with an adjustable SSR and instead of the PWM I am going to step through eight different voltage levels to give me eight loads 100W 200W, 300W, 400W, 500W, 750W, 1,000W and 1,500W. I have found that this is all I needed to keep my water hot and the low loads give me lots of flexibility in the winter when spare solar is in short supply.


Let me know how you get on. If you get stuck I have a sketch that calculates PV and load power using two efergy CT's and a sketch for PWM control (as above) and I even have two spare Arduino's and the opto-isolation PCB, so I could get it operational, but it seems overly complicated.


My eight step system will be easier to build, as all the components are readily available and I was hoping to come up with a simple system that anybody could make for less than £100. And this system will meet that criteria.


Regards, Trader9

 

[chris_cronin]

Hi Chris


I have been using an Arduino Uno since December to divert surplus solar to two 3kW immersion heaters using a 3.3kVA isolation transformer toggling between 55V and 110V and have been looking to upgrade to a triac circuit using PWM from the Arduino.

However, because of the zero cross sensing and triggering of the triac at 100HZ there was no processing time left for the current sensing and calculations needed to provide the trigger levels using a single Arduino. I believe you may need two Arduino's. A good place to look for a PWM circuit is by Googling “Using Hardware Interrupts to Control A.C. Power” it has notes and a Arduino sketch it also works I have built it.


I am still going to replace my transformer, but with an adjustable SSR and instead of the PWM I am going to step through eight different voltage levels to give me eight loads 100W 200W, 300W, 400W, 500W, 750W, 1,000W and 1,500W. I have found that this is all I needed to keep my water hot and the low loads give me lots of flexibility in the winter when spare solar is in short supply.


Let me know how you get on. If you get stuck I have a sketch that calculates PV and load power using two efergy CT's and a sketch for PWM control (as above) and I even have two spare Arduino's and the opto-isolation PCB, so I could get it operational, but it seems overly complicated.


My eight step system will be easier to build, as all the components are readily available and I was hoping to come up with a simple system that anybody could make for less than £100. And this system will meet that criteria.


Regards, Trader9

Hi Trader9

thanks for the info.

I'm still waiting for the Kemo kit to arrive but will post results as soon as I have them.

I also like pcmalli's solution so I don't know which system I will adopt yet but I would prefer a 'continuous' rather than a 'stepped' solution

regards

chris

 

[Thomas101]

Hi - new to the forum - haven't (unlike some new joiners) spent the full 2 days reading all 39 pages, but I have browsed thro' quite a few, suitably impressed with what seems to have been happening here over the past 18 months. What started out as a simple question, and thoughts of switching in an extra 1kW heating element, seems to have evolved almost into an online multi-participant product development workshop, with some deep discussions and brilliant ideas emerging.

Like others we've just had solar PV installed and have now realised the desirability of using it to heat our water also - at present we have no gas, so water & space heating are all electric (storage heaters for the latter). From the forum discussions I'm persuaded that I need to look beyond the Parsons Switch plus 1kW element towards a fully responsive device that will track the generation and use all the surplus available using the existing 3kW immersion element.

If I understand correctly a couple of the regular posters - echase, pmcalli, and a couple of others - have fairly advanced product designs. Is there an FAQ listing these, or links to obtain more information ? I'd like to get something installed in the next month or so, so I can benefit from the increasing sunshine

Many thanks,


Walter

Hi

I also have had a new system fitted Feb 2012 and have been looking into how to heat the immersion heater but taking into account the electricity used in the house. I have a 4kWp system and am trying to look into the best solution. The Parsons switch won't do what I need it to do. However, just stumbled across a product called solardivert who appear to have an intelligent system which will also run the immersion at half power as well as full power. Anyone know now this compares to the other solutions out there?

Thanks Thomas

 

[mightywalter]

Hi

I also have had a new system fitted Feb 2012 and have been looking into how to heat the immersion heater but taking into account the electricity used in the house. I have a 4kWp system and am trying to look into the best solution. The Parsons switch won't do what I need it to do. However, just stumbled across a product called solardivert who appear to have an intelligent system which will also run the immersion at half power as well as full power. Anyone know now this compares to the other solutions out there?

Thanks Thomas

I've not come across this product previously, so quickly Googled it. Based on what I read on the website and what I've learnt from this forum I'd make the following observations:

1. More expensive than a Parsons Switch - one webpage comments "10x cheaper than solar thermal" (cited as £4500)

2. A simple 2-step controller, switching the immersion on to take either 1.5 or 3kW, but nothing else - thus better energy capture than a Parsons Switch but not as good as the proportional controllers that pmcalli, echase and others on this forum have in the works.

3. Looks like it works with an existing 3kW immersion element, rather than needing a new extra 1kW one, as does the Parsons Switch

4. ??? Available now, maybe not ???? Not obvious how to buy it, so perhaps they're just creating product awareness while the product is CE certified/tested etc ? If you drop them your email and get a reply on availability, be sure to post it here so we know. If its availability is the same as the proportional controllers then why go for stepped ?

One of my concerns is that once some good CE approved products are out there, and we are all using them, it won't take the utility companies long to realise that their 50% feed-in assumption has gone to pot, and to start visiting to install smart meters...(although of course at present they're probably getting much more than 50%). If this happens, product pricing will need to reflect an RoI in 2-3yrs max. At £450 I wouldn't go for this one...

Walter

 

[inie meanie]

One of my concerns is that once some good CE approved products are out there, and we are all using them, it won't take the utility companies long to realise that their 50% feed-in assumption has gone to pot, and to start visiting to install smart meters...(although of course at present they're probably getting much more than 50%). If this happens, product pricing will need to reflect an RoI in 2-3yrs max. At £450 I wouldn't go for this one...

At 4000 kwhr / year. so 50% at £0.03 / unit= £60 This is the max that you can be paid a year from 4kw system. Even using as much as I can, I still export power so the loss to the supplier would be somewhere between £30 to £50 per year. I am not sure that they would consider this worthwhile fitting export meters and all the billing that goes with it, as they would have to fit them for every body.

Analogue control rules ok!

 

[mightywalter]

Inie - yup, I agree with your numbers. However the issue may not be what they're paying for export electricity theyre not getting, but rather the cost they otherwise have to invest to get those MW of electricity from somewhere else ? That cost could be much higher than the cost of fitting smart meters....