Solar PV controller/diverters

[NikNak]

This is for anyone who has Solar pv panels and who have subsequently installed a controller/diverter to their hot water immersion heater/tank.

Have any of you done/installed one.?
has it been successful.?
was it a DIY job or did it need an electrician/contractor.?
Which make/brand/model did you opt for.?

We have a 3.6kw array. Its been installed for just over 5yrs now, and very pleased with it. But we're looking to maximize the generating power by heating our water too.

Any useful hints'n'tips are welcome


Nick

 

[Myfordman]

Yes,yes,DIY and made my own so possibly not a lot of help to you
But yes the principle is sound and fully legal.

 

[Myfordman]

If you fancy DIY kit try here http://mk2pvrouter.co.uk/
Robin Emley has been working in this field for many years and is highly regarded. The software I use is based on his early work with some specific back added.

 

[Woody2Shoes]

I don't have any PV panels (yet) but have been attracted by the idea of feeding an immersion element directly with DC from a handful of panels. This would remove the cost and conversion losses in going to AC. The question I'd like to answer (and haven't really seen answered on the internet yet), is how well would this stack up against a "wet" system for supplementary heating of DHW using the evacuated thermal tubes (I guess quite well in terms of cost and complexity, but in terms of heat per unit area I don't know).

Cheers, W2S

 

[Myfordman]

I don't have any PV panels (yet) but have been attracted by the idea of feeding an immersion element directly with DC from a handful of panels. This would remove the cost and conversion losses in going to AC. The question I'd like to answer (and haven't really seen answered on the internet yet), is how well would this stack up against a "wet" system for supplementary heating of DHW using the evacuated thermal tubes (I guess quite well in terms of cost and complexity, but in terms of heat per unit area I don't know).

Cheers, W2S

Duff idea I'm afraid. to get useful power from an array of panels you will still need an MPPT controller. https://www.solar-electric.com/learning ... llers.html
This device uses an inverter too so you will still get the conversion losses (which are minimal anyway).
Furthermore your existing immersion control thermostat and switches will not be rated for DC operation and will need changing for ones that do. Finally such a scheme will not be eligible for FIT.

I use an ac inverter to get full FIT, a PV diverter as well as 30 evacuated tubes to heat a thermal store. On these sunny days we are using no gas at all for DHW but do need some for the grey days- up to two 20 minute burns per day. By mid March we will be totally self sufficient for DHW (household of 3 adults) and this will be maintained to around mid October. In the hotter months, the spare PV is used to run comfort air conditioning free of cost too.

 

[Woody2Shoes]

I thought I would only need MPPT controller(s) if I wanted to charge batteries. I'm not bothered about FIT. My back-of-fagpacket calculation says I spend maybe £60 per year on DHW, if a couple of PV panels plus £100 worth of hardware could halve that then the payback period might be about 10 years without FIT. I don't think the DC vs. AC switching problem need be insurmountable as the DC voltage could be much lower (I know that heating effect varies with square of current and that back EMF - major source of arcing I think - could be dealt with using a snubber diode, if necessary the stat could switch a relay/contactor).
Cheers, W2S

 

[Just4Fun]

The question I'd like to answer (and haven't really seen answered on the internet yet), is how well would this stack up against a "wet" system for supplementary heating of DHW using the evacuated thermal tubes (I guess quite well in terms of cost and complexity, but in terms of heat per unit area I don't know).

I have a wet system using evacuated tubes which I installed 10 or 12 years ago. At that time it was more cost effective than PV but that may not be applicable to your situation. I understand that PV has become (a bit) more efficient since then and has dropped in price significantly. Also there may be government incentives for renewables that may have an impact in your location. You need to do the sums.
In terms of heat per unit area I believe the tubes will always out-perform PV because you are converting sunlight directly to heat without the losses associated with converting to electrickery and then to heat. Is area your chief constraint? I think for most people £££s are in more limited supply.

 

[Woody2Shoes]

The question I'd like to answer (and haven't really seen answered on the internet yet), is how well would this stack up against a "wet" system for supplementary heating of DHW using the evacuated thermal tubes (I guess quite well in terms of cost and complexity, but in terms of heat per unit area I don't know).

I have a wet system using evacuated tubes which I installed 10 or 12 years ago. At that time it was more cost effective than PV but that may not be applicable to your situation. I understand that PV has become (a bit) more efficient since then and has dropped in price significantly. Also there may be government incentives for renewables that may have an impact in your location. You need to do the sums.
In terms of heat per unit area I believe the tubes will always out-perform PV because you are converting sunlight directly to heat without the losses associated with converting to electrickery and then to heat. Is area your chief constraint? I think for most people £££s are in more limited supply.

I can convert electrickery into heat with 100% efficiency! (ignoring thermal losses in the cable between panels and heating element). Area is an important consideration, but paying for itself without FITs is important too. Cheers, W2S

 

[ScaredyCat]

You could always buy yourself a Tesla Powerwall* too, that'd help store some of your free electrickery..

*other solutions are available

 

[NikNak]

Just an update....

After reviewing lots of different makes/models etc opted for the Solar iBoost+.
Got some ridiculous quotes for supply & fit :shock:
Had a mooch around on the 'tinternet, and bagged a 'bargain' from good 'ol fleebay. Brand new unopened box. Think it came as part of a PV installation package,but they didn't want/couldn't make use of it. And as my bro-in-law is a 'lecky i got it installed for a drink :wink: