PV power back from Garden Room to feed immersion heater

[muh3]

Hello,

I just had an electrician in to size a cable to my garden room but he could not answer my question.

I'm running SWA cable from the house to my Garden Room, I'm planning on installing Solar Panels on the Garden Room. Both, Garden Room and House will have a hot water cylinder. I was planning on using one solar power diverter to feed both tanks.

Can I run a 4 core (L, N, Earth, L from diverter) SWA from the house to the Garden Room, PV on Garden Room, Solar Diverter in Garden Room feeding the tank in the garden room and use one core from the SWA to feed back to the house directly to the tank.

Only issue I can see is if somebody comes in to do any work and turns the power of on the fuse board for the house would assume that the power is off in the house but there would still be a live feed to the tank in the house.

Any thoughts?

 

[jj4091]

Would it not be easier and cheaper to just use solar thermal panels to heat the tank water in your garden room and. continue your current method of heating house tank. I would think you would need a lot of power to operate 2 immersion heaters.

 

[bsr]

Seems technically possible, my iboost has two outputs for two immersions. You can get stickers that warn of needing to isolate at multiple points, I would want to make it really clear to someone who didn't know the house.

 

[muh3]

Hi JJ, the garden room tank is only 120l and used rarely, so all it needs is a top up. Once hot it would feed the main tank in the house. I would like to avoid any feed back to the grid.

 

[Murdochcat]

Why the 4 core?

 

[muh3]

Why the 4 core?

L,N,E, 1 Core to feed back to the house immersion.

 

[Murdochcat]

L,N,E, 1 Core to feed back to the house immersion.

= almost certain tripping or 2 or more RCD's

 

[muh3]

= almost certain tripping or 2 or more RCD's

Fair point, probably easier to chuck a separate cable in the trench.

 

[Murdochcat]

Fair point, probably easier to chuck a separate cable in the trench.

I think you are missing out on the understanding of how these divertors work ........

 

[ericmark]

I am waiting for an iboost to be fitted, I thought it would be fitted where the solar panels are, but seems they want to fit it where the tank is. Reading the instructions it seems they are radio linked. Radio Range 1 to 30m indoors (dependant on construction and local conditions). So looking at this.

I only need it in the summer, in winter the central heating does the water heating, the solar panels are remote from the inverter, there are in my case four dc cables between solar panels and the inverter, which is mounted near to the DNO supply, but the cables reading the spec, are extra low voltage (under 75 volt DC) so there is no 230 volt at the location of the panels.

There has to be paperwork raised, and loads of hoops to jump through, so not really a DIY job, and I have even as an electrician not gone down the DIY route, I am sure there are other methods, but you would need to down load and read all the instructions first.

 

[SUNRAY]

= almost certain tripping or 2 or more RCD's

Fair point, probably easier to chuck a separate cable in the trench.

or use a 5 core

 

[SpecialK]

Are you having a grid connected inverter? Most diverters won't off-grid work as they detect the excess being sent back to the grid.

 

[Adam_151]

... And even if they could, the means of control is not suitable for where the available energy is a hard limit. They work the same as a phase cutting dimmer, so for example to run at 50% of power, they activate at the peak of the sinewave, so while they reduce the RMS current in relation to the required power, the peak power doesn't follow the same trend, it'll stick at the same value until you get below half then start reducing.

Its not a problem when there is infinate energy available, although I'm not quite sure how the meter ends up integrating it all (whether you end up buying the peaks from the grid, or whether it gets averaged out over one cycle) but if you are on a strictly limited energy supply from a off grid system, you could find yourself with not enough energy to hit the peaks even though in RMS terms its perfectly loaded and the inverter might start dropping the voltage/ shutdown / or actaiavte a bypass contactor

 

[cjcoffin]

Your original idea with the 4 core cable should work. Personally I would use 5-core so the circuit back to the immersion in the house has its own neutral. You will need to take the immersion circuit out of the CU in the house and connect it to the 5 core with an MCB in a separate enclosure suitably labelled or a fused spur box.

You may need a separate earth rod for the Garden Room so it is TT earthed, rather than exporting the earth from the house presuming that is T-N-CS.

 

[Murdochcat]

Why would you not let the iboost heat your water in the winter, spring and autumn?

Sunny day, excess production = free hot water