Solar on garage issues

[BMcN]

Looking for some advice on installing solar panels.

 

At the moment we are putting up our detatched garage, while the weather is bad, aiming to start the house kit in the new year when the weather improves.

 

I am not required to put solar panels to obtain my SAP rating  but I would quite like to, depending on costs, to work along side the planned ASHP.

 

I was looking to install the panels on the garage roof (shown in red), this is roughly south facing (possible 10-15deg North).  Currently I have a service cable (shown in yellow) run from where the meter/CU sits at the house, to the corner of the garage where the CU will be.  I presume, for this to work with solar, I would need another cable back to the house, where it could then be switched between the mains and the water heater.   Distance is around 50meters, would volt drop be an issue?  Would it be more efficient to have the inverter in the house or garage?

 

Thanks.

solar.pdf

[ProDave]

This is all a lot simpler than you think.  As long as the solar PV is connected upstream of your electricity meter (which it would be anyway) it does not matter where it connects.  You then fit either a bought or make your own solar PV hot water diverter to dump excess power into the immersion heater.  Any self generated power is used first in preferance to imported power, you don't need to think about it or even understand it, that is just how it works.

 

If you are building the garage first, I would suggest there is merit in having your electricity supply routed into the garage and having your electricity meter fitted in there. You then have a consumer unit in the garage for all the garage stuff and the solar pv to connect to.  Then run a big cable, via a switch fuse, to the house and have a house CU in the house for it's loads.  Depending where the power comes onto the site it may work out cheaper to get the power into the garage than into the house, but in any event you can get it into it's final place early on in the project.

 

If you do that, you might want some telemetry of some sort between the house and the solar PV diverter so I would install a duct and a drawstring to enable you to pull suitable cable(s) from the house to the garage later on, though wireless options are also possible.

 

Choose your house CU and garage CU locations so they are each as close as possible to the closest points in each building, at the moment your yellow cables goes all round the outside, probably twice as far as it has to go.

 

One other other off topic suggestion.  your plan shows a "septic tank"  Do yourself a favour and instead fit a small waste treatment plant, preferably one of the ones that works on the air blower principle. It will not cost much more but will give far better results with a LOT less chance of ever having issues with the soakaway.

[BMcN]

I should have given a little more info Dave.

 

The house foundations and blockwork is in up to DPC.  The power is already in and live on site with a meter and small temp CU, in the bottom right of the house where I have shown the yellow cable.  The yellow cable is a large 25mm service cable that I will supply the garage with, in the same was you suggested (but in the opposite direction).

 

The yellow cable goes to the far end of the garage, this was to save a lot of hassle as I have some thick concrete hardstanding to the front which I would rather not disturb for now.

 

The soakaway and septic tank are also already done.  Thanks, Bryan

Edited December 30, 2018 by BMcN

[ProDave]

So in that case reverse things.  Feed a supply out from the house via a switch fuse (60A fuse) to the garage and fit a garage CU. The solar PV will just connect to that with the inverter in the garage.  I would personally prefer a switchfuse to feed out to the garage rather than taking it from the house CU. There is no need for RCD protection of a SWA cable and keeping it separate to the house CU removes any chance of nuisance tripping.

 

You won't need any telemetry cable. A solar PV diverter for water heating uses a current transformer clamped on one of your meter tails in the house to determine when you are exporting and turn on the immersion heater.

 

That's all you need to do, no switching between mains and solar.  If solar power is available that will be used in preference to grid power.

 

Later on if the house proves well enough insulated that you don't get much temperature drop overnight, you can time the heating so it comes on mostly in the daytime when there is likely to be PV generation and not much if at all at night.

[BMcN]

Thanks Dave, I didnt realise the PV diverter worked via current clamps, I had presumed it was switched from the inverter and therefore the inverter and diverter had to be closeby.    That will be fine then, no extra cables needed will be a bonus.  Just need some decent quotes now.  I may be worth waiting till after the FIT ends, should drop the price of systems a bit.

 

Yes that was the plan for the garage, didn't fancy trying to fit 25mm swa into the CU. 

 

 

[Jeremy Harris]

13 hours ago, BMcN said:

Yes that was the plan for the garage, didn't fancy trying to fit 25mm swa into the CU. 

 

 

You can't normally terminate 25mm² SWA at the case of most domestic CUs, as usually there isn't enough room.  What I did was terminate the 25mm² three core SWA that runs to the CU in the house to a galvanised adaptable box, then ran 25mm² tails from there to the CU as normal.

[BMcN]

Thanks for the advice on the CU.  What terminals did you use inside the box? 

 

On the subject of solar, would it be possible to stay off grid with the system I spoke about? As I would like to avoid the cost of having a MCS installer involved and there is no point as FIT wouldn't be applicable? I presume a normal sparky won't be able to sign the system off. 

[ProDave]

You don't need to go "off grid"  Just do as I am doing and fit your own system.  It does mean anything you export you do not get paid for, so just do all you can to self use as much as possible. That will almost certainly mean battery storage at some future date.