Remote mounted PV

[Russell griffiths]

I’m thinking of putting PV in at a later date, my main concern at the moment is actually having the cash to finish the house without things like PV 

so im thinking of a remote setup on the garage roof that will be built some time after we move into the house

what I’m after is what sort of ducting to put in place from the garage back to the house. 

 

Is there a distance where where it gets unviable to have it remotely, I presume the further away the larger a cable is needed. 

Where do I run back into the house. To the consumer unit? Or to a place that has the space to store all the solar gubbins

can the solar stuff be in a utility cupboard that houses the hot water tank and ufh manifold, but it doesn’t have the CU, that is in a cupboard just across the hall. 

 

Any thoughts @ProDave  @Jeremy Harris

[ProDave]

If you put the inverter in the garage, then you need do nothing more than a mains connection to the garage.

 

Voltage drop on the cable is critical (it manifests as voltage rise with a generating inverter)  If that is too high the inverter may trip.  So fit what you probaably think is an over sized cable.  Give us some idea of the distance and we can give you some help.

[ToughButterCup]

Thanks @Russell griffiths, you have saved me a post ...

[Stones]

This is how I remotely fitted our PV:

 

 

[ToughButterCup]

13 minutes ago, Russell griffiths said:

.. . 

Where do I run back into the house. To the consumer unit? Or to a place that has the space to store all the solar gubbins

can the solar stuff be in a utility cupboard that houses the hot water tank and ufh manifold, but it doesn’t have the CU, that is in a cupboard just across the hall. 

....

 

Can anyone point me to a post or Internet resource that gives a Ladybird version of what's needed between the inverter and arrival at the CU please? 

 

In Russ' words, the '... solar stuff ...' 

[Stones]

The picture in my blog entry shows the basic set up. CU to AC isolator to inverter to DC isolator to PV panels. I also have a meter so I know what I'm generating (fitted between the AC isolator and inverter)

[Pete]

2 hours ago, AnonymousBosch said:

Thanks @Russell griffiths, you have saved me a post ...

And me!!

[Pete]

4 hours ago, ProDave said:

If you put the inverter in the garage, then you need do nothing more than a mains connection to the garage.

 

Voltage drop on the cable is critical (it manifests as voltage rise with a generating inverter)  If that is too high the inverter may trip.  So fit what you probaably think is an over sized cable.  Give us some idea of the distance and we can give you some help.

I have a distance of about 25m from house CU to garage CU so what size cable would I be better using pls @ProDave? Probably be a 4KW system. TIA

Edited February 18, 2020 by Pete
To add more information

[Jeremy Harris]

If the cable run is 30m (allowing for a bit to run up walls etc) and the system is a 16 A one (so nominal 3.68 kWp, often referred to as "4 kW") then I'd opt to keep the voltage drop well below the normal 5% allowable, just because of the potential nuisance of having the inverter start to limit on voltage a bit earlier than it otherwise might.

 

4mm² SWA over that distance would have a voltage drop of about 5.77 V at 16 A, so when the inverter hits the upper cut off voltage of 253 VAC, the voltage at the incoming supply end would be about 247.3 VAC.  This is probably a bit tight, TBH, and if it were me I think I'd up the cable size to 6mm², as that reduces the voltage drop to about 3.79 V, so the supply voltage at the incomer can rise as high as 249.2 VAC before the inverter will hit its limiting voltage.

 

Also, if the garage is that far from the house and incoming supply, I would consider installing an earth electrode and making the garage a TT installation.  It's OK to export the earth out to a detached garage, but IMHO I think it's preferable to have it referenced to the local true earth potential.

[ProDave]

Me too.  In fact 25 metres is about the distance to ours and that is done with 6mm SWA and has not been a problem.

[Russell griffiths]

9 hours ago, ProDave said:

If you put the inverter in the garage, then you need do nothing more than a mains connection to the garage.

 

Voltage drop on the cable is critical (it manifests as voltage rise with a generating inverter)  If that is too high the inverter may trip.  So fit what you probaably think is an over sized cable.  Give us some idea of the distance and we can give you some help.

Brilliant answer dave, it hadn’t even crossed my mind to put all the junk in the garage, I was trying to envisage stuffing it all in the services cupboard. 

Will measure distance tomorrow. 

[joth]

10 hours ago, Jeremy Harris said:

4mm² SWA over that distance would have a voltage drop of about 5.77 V at 16 A, so when the inverter hits the upper cut off voltage of 253 VAC, the voltage at the incoming supply end would be about 247.3 VAC.  This is probably a bit tight, TBH, and if it were me I think I'd up the cable size to 6mm², as that reduces the voltage drop to about 3.79 V, so the supply voltage at the incomer can rise as high as 249.2 VAC before the inverter will hit its limiting voltage.

 

 

At a rough approximation, if the mains supply pre-PV istall regularly hovers around 250V, would this likely be a warning sign for the PV inverter regularly hitting 253V and having to cut out?

I only started logging voltage in the house a week ago, but I've not seen it drop to 240V at all, and it's regularly hitting 250V

 

The DNO have approved 8kW G99, but I'm wondering if they saw this area is regularly overvoltage so figure there's no need to reinforce as the inverter will be regularly cutting out anyway....

I guess real question is what happens outside of winter.

 

 

I see there's a really annoying failure mode here that if the inverter does cut out, it will stop dead any export meaning any dynamic loads (immersion divert or car charing) would also then cut out, which would allow the observed voltage to rise further. Whereas ideally you want to tackle the overvoltage by adding additional loads to pull it down and hence allow the inverter to re-engage.

 

 

 

[Jeremy Harris]

6 hours ago, joth said:

 

At a rough approximation, if the mains supply pre-PV istall regularly hovers around 250V, would this likely be a warning sign for the PV inverter regularly hitting 253V and having to cut out?

I only started logging voltage in the house a week ago, but I've not seen it drop to 240V at all, and it's regularly hitting 250V

 

The DNO have approved 8kW G99, but I'm wondering if they saw this area is regularly overvoltage so figure there's no need to reinforce as the inverter will be regularly cutting out anyway....

I guess real question is what happens outside of winter.

 

 

I see there's a really annoying failure mode here that if the inverter does cut out, it will stop dead any export meaning any dynamic loads (immersion divert or car charing) would also then cut out, which would allow the observed voltage to rise further. Whereas ideally you want to tackle the overvoltage by adding additional loads to pull it down and hence allow the inverter to re-engage.

 

 

 

 

 

Yes, the inverter will limit or cut out at 253 VAC.  I'm in a similar, but less severe, position, where our voltage never drops below about 243 VAC, even in the coldest, darkest, weather, and often rises to around 250 VAC.  Our inverter often limits at 253 VAC on sunny days.  I've been trying to get the DNO to reduce the tap on the local transformer, to no avail.  They could easily drop a few percent and still be well within the allowable supply tolerance, and we're close to the end of the run from the transformer, so if we're seeing high voltages then those closer will be seeing even higher voltages.

 

In theory, if you report a consistently high supply voltage the DNO will come out, put a voltage logger on the supply and then take action if they record the same.  In practice they seem to just ignore requests like this, or have in my case.  The UK supply voltage that the DNO must keep supplies within is 230 VAC +10% -6%, so 216.2 VAC to 253 VAC.

[Nickfromwales]

@Russell griffiths

Will this be facing true south, or can you get an E/W or E/S/W array? I assume it’ll be mono pitch to match the house though? 
We’ve not long done one which was 135m away from the garage, where the AC batteries and CU2 reside, and that’s spewing electricity out. No issues with remote install whatsoever. As said, just hook into the garage CU, but, knowing you, I’d put a 25mm2 SWA between the house CU and the garage to allow you to run some big stuff in there too.
Don’t forget the laundry room will need a decent supply also, so allow for a 16mm2 to that too. Price hike in buying bigger cables now vs future costs of up-sizing later are pennies .

Also consider people coming with EV’s so the outside feeds will then be future proofed against that too. 
 

[Cpd]

10 hours ago, Nickfromwales said:

We’ve not long done one which was 135m away from the garage, where the AC batteries and CU2 reside, and that’s spewing electricity out. No issues with remote install

That’s very interesting as I ruled out PV as the best location was up a hill at the side of the house, similar distance to above I think..... will have to rethink my long term plans.  

[Russell griffiths]

I thought you lot @Jeremy Harris @ProDave Had answered this for me. Thank you. 

But it has now led to a new question which could be a bit silly so cut me some slack I’ve just got up. 

 

If I put the pv on the garage I need a cable to take the newly made electricity back to the Cu. 

Got that. 

Do I have a separate feed from the Cu to the garage to power the garage itself ?

does the electric travel both ways down the cable. 

Or is a separate cable needed. 

 

oh god as I’m typing this I can imagine you all laughing at this. 

Im just thinking about water you couldn’t have water pushing both ways. 

Thats my justification for a silly question. 

[Russell griffiths]

@Nickfromwales garage could be twisted around a bit to get the roof facing the best way. 

At the moment this could be a year away. 

[Jeremy Harris]

Just the one cable is all you need.

[BotusBuild]

Russell,

If you put the inverter and a CU in the garage, then you can run just the one cable back to the CU in the house. Stuff you want power to in the garage can run off the CU in the garage

[Russell griffiths]

10 hours ago, Jeremy Harris said:

Just the one cable is all you need.

Only one cable cool. 

Tbh I’m a bit disappointed, I came home imagining loads of Micky taking, especially from @AnonymousBosch, I had loads of good comebacks planned and not one bit of random p##s taking. 

 

You lot are far  too nice. 

[joth]

On 19/02/2020 at 07:51, Jeremy Harris said:

 

 

Yes, the inverter will limit or cut out at 253 VAC.  I'm in a similar, but less severe, position, where our voltage never drops below about 243 VAC, even in the coldest, darkest, weather, and often rises to around 250 VAC.  Our inverter often limits at 253 VAC on sunny days.  I've been trying to get the DNO to reduce the tap on the local transformer, to no avail.  They could easily drop a few percent and still be well within the allowable supply tolerance, and we're close to the end of the run from the transformer, so if we're seeing high voltages then those closer will be seeing even higher voltages.

 

In theory, if you report a consistently high supply voltage the DNO will come out, put a voltage logger on the supply and then take action if they record the same.  In practice they seem to just ignore requests like this, or have in my case.  The UK supply voltage that the DNO must keep supplies within is 230 VAC +10% -6%, so 216.2 VAC to 253 VAC.

 

It's intended for an australian market, but this article is quite interesting.

 

Aside from learning the fact Australia has the exact same 230 VAC +10% -6% requirement as the UK (wonder how that came about...) they have a few more options for recourse- it seem the rules over there are that if the grid is just at 252V but your local observed voltage is rising above it due to the inverter (and a long cable run from the grid), you can seek permission to set the inverter's trip points slightly higher. This is called Volt-VAR mode, perhaps named after California "Rule 21 Volt-VAR requirements"

 

Another option (both there and here) that some people have been sold up to is installing a so-called voltage optimizer (examples: PV+, EdgeIQ) which reduces the local voltage as seen by the inverter. I truly can't understand how this is morally any better than going and fudging the voltage trip-points in the inverter to be +10% higher, but still these things seem widely recommended upsell by PV companies so I presume they're at least legal and maybe even effective. (They're only good for 4kW though so no use for our planned install.)

 

Finally, perhaps the most practical suggestion is to go for a 3 phase supply from the grid to reduce the local voltage increase per phase.   Damn- wish I'd thought of that 4 months ago :-( 

 

Edited May 26, 2020 by joth

[Onoff]

Late to reading this. @Russell griffiths.....totally random thought.....how about a floating PV array on the lake?