Considering a second Solar system on a 3phase supplied house

pip895

We are considering installing a second solar array on a roof we originally rejected mainly because it is very visible at the front of the house but also because it has considerable shading issues in winter.    Our existing array sits on Phase 1 with a single phase inverter.  Looking at our energy usage we will use the great majority of the energy a new system would generate even on a sunny day in summer.  We are also potentially interested in a battery system but that is less obviously beneficial economically.

We have had one quote in from a national company which is quite a bit more expensive expected principally because of the high cost of the three phase inverter and the inclusion of a 3 phase voltage optimizer which they insist we need.  We have a second installer popping round tomorrow and I would like to get a few issues straight in my head before he arrives.
1.  How does the house metering cope with our existing array sitting on a single phase?  If we generate more than we use on Phase 1 but are still importing on the other Phases does the meter net the total so that we still get the benefit or do we end up exporting from Phase 1(at no benefit) whilst being charged for the import on Phase 2 & 3...and will this change if/when we get a smart metre installed?  The current metre is about 12 years old so not smart but also not the spinning wheel type.
2. Is there any reason why we shouldn't just install the panels with a single phase inverter on Phase 2? (which includes the EV supply to the garage)
3. Do I really need that voltage optimizer - what does it actually do?

Martyn1981

Obviously you need expert advice on this, and I'm as far from an expert as is possible. However, my sister is currently getting PV installed on 3 phase, so I have comments from what I've heard (and heard on other forums in the past), which may start you off.
She is has a large install which will run through a 3phase inverter. But when I asked the installer about a second array in the future (on a yet to be built small barn/stable) with a different orientation, and it's own inverter, they said that this would throw out the phases and not be a great idea. Another installer said pretty much the same to my sister previously.
I also remember someone on a different forum mentioning that they have had PV exporting on one phase, whilst they imported leccy on another, which is a tad annoying!

I suggested a solution regarding the two inverters mucking up the phases, which was to run the second array through the same 3 phase inverter in the future, making sure what is installed today is suitable, but again all installers point blank refused this idea as the second array would result in a long DC cable raising safety concerns. But perhaps your arrays would be closer, and could all go into the same 3 phase inverter?

Regarding the optimizer, I'm not a fan of these, but I have no idea if a 3 phase is different, and if it perhaps solves some of the issues I've heard of (and mentioned)?

[Take all of this with a massive pinch of salt, I know nothing, but I thought it might be useful to share as different installers all raised exactly the same concerns, which may be a coincidence, or useful knowledge.]

EricMears

Martyn1981 said:

 all installers point blank refused this idea as the second array would result in a long DC cable raising safety concerns. But perhaps your arrays would be closer, and could all go into the same 3 phase inverter?

Why on Earth would they think that - let alone say it  ?   Any cable -  AC or DC,  long or short  - might have "safety concerns" if it wasn't properly installed but methods of making them safer should normally be used.  I hope anyone living near Southsea doesn't get to hear of such 'concerns'  as I understand there's a very long DC cable running across their beach !  

pip895

Martyn1981 said:

Obviously you need expert advice on this, and I'm as far from an expert as is possible. However, my sister is currently getting PV installed on 3 phase, so I have comments from what I've heard (and heard on other forums in the past), which may start you off.
She is has a large install which will run through a 3phase inverter. But when I asked the installer about a second array in the future (on a yet to be built small barn/stable) with a different orientation, and it's own inverter, they said that this would throw out the phases and not be a great idea. Another installer said pretty much the same to my sister previously.
I also remember someone on a different forum mentioning that they have had PV exporting on one phase, whilst they imported leccy on another, which is a tad annoying!
This does worry me a bit - Phase 1 does most of the heavy lifting with the big single phase loads and is offset by the current solar.  Having a big array sitting on Phase 2 wont give us that much benefit - we will be lucky to use more than 30%.  If this is the case then we would be better off having two smaller arrays attached to phase 2 & 3..
I suggested a solution regarding the two inverters mucking up the phases, which was to run the second array through the same 3 phase inverter in the future, making sure what is installed today is suitable, but again all installers point blank refused this idea as the second array would result in a long DC cable raising safety concerns. But perhaps your arrays would be closer, and could all go into the same 3 phase inverter?
Regarding the optimizer, I'm not a fan of these, but I have no idea if a 3 phase is different, and if it perhaps solves some of the issues I've heard of (and mentioned)?

This install is close to the existing single phase installation but we cant touch that, as its getting the full feed in tariff  - these issues make me wonder if the current quote is "competent" - the last thing I would want is to impact my existing array.  Maybe though the 3 phase optimizer solves the problem...
 
[Take all of this with a massive pinch of salt, I know nothing, but I thought it might be useful to share as different installers all raised exactly the same concerns, which may be a coincidence, or useful knowledge.]

Thanks for your help - it sort of underlines the concerns I have..  We will see what the next guy has to say later today.

Solarchaser

In terms of current fit array, if you add another array, but don't put it through the fit meter, then your fit will not be compromised, May be your most simple choice 

pip895

Solarchaser said:

In terms of current fit array, if you add another array, but don't put it through the fit meter, then your fit will not be compromised, May be your most simple choice 

I don't think anyone will suggest touching the existing system except to add the Tigo optimizers to the WSW set of 8 panels.  So far one is suggesting adding the optimizers to 4 of the 8 and the other to all eight panels in the array - basically saying if we are up there then we may as well do the lot as they are relatively cheep.  

pip895

My second potential installer came round and spent an hour surveying and going through the options.  He is suggesting adding a slightly smaller single phase array and attaching it to Phase 2 he also wants to include a battery system.  He mentioned that it would be worthwhile getting Octopus to upgrade us to a new smart metre so we could go onto agile.. 
He did confirm that currently I will be exporting excess electricity on phase 1 whilst importing and being charged for importing on phases 2 and 3 
If we move a few things from phase 3 to phase 2 then in conjunction with the battery we will be able to use a good proportion of the power generation on phase 2.

Solarchaser

Does phase 2 go through a different meter?
If so.... since its been discussed on here recently... it would make more sense financially to get money for export rather than fit batteries, as they are not yet able to wash their face within 10 years.

Solarchaser

pip895 said:

Solarchaser said:

In terms of current fit array, if you add another array, but don't put it through the fit meter, then your fit will not be compromised, May be your most simple choice 

I don't think anyone will suggest touching the existing system except to add the Tigo optimizers to the WSW set of 8 panels.  So far one is suggesting adding the optimizers to 4 of the 8 and the other to all eight panels in the array - basically saying if we are up there then we may as well do the lot as they are relatively cheep.  

Do you have alot of shading on these panels?
My wsw array suffers badly from shading in the darker months.
If so, I'd work out which ones suffer, and those would be the ones requiring the tigo's, if its all, then it makes sense to fit them to them all.

Worth noting you can get tigo's that cover 2 panels,  so may be that your other quoter was planning on using those if all suffer from shade 

pip895

Solarchaser said:

Does phase 2 go through a different meter?
If so.... since its been discussed on here recently... it would make more sense financially to get money for export rather than fit batteries, as they are not yet able to wash their face within 10 years.

No its just one meter - I must admit I'm not sure how it operates - I was hoping (and originally assumed) it just netted out over the phases but the last installer didn't think that was the case..  He didn't actually look at the metre though..

Economically I have already come to the conclusion that batteries don't really cut it. OH is keen though - we have the house set up with the lighting and a few special sockets on a separate circuit - it includes things like the pump for the solar thermal array, gas boilers, internet and fridge/freezer - We have once run this circuit with a small petrol generator but a battery would be much cleaner/neater and easier to set up.

I cant help feeling that in the event of a bad outage using the EV sitting in the garage with comparatively huge (62kWh) battery & probably a second EV in the near future makes a lot more sense than a poultry 8-10 kWh in a stand alone battery.  Not sure if that's practical/available as an option yet though.. 

pip895

Solarchaser said:

pip895 said:

Solarchaser said:

In terms of current fit array, if you add another array, but don't put it through the fit meter, then your fit will not be compromised, May be your most simple choice 

I don't think anyone will suggest touching the existing system except to add the Tigo optimizers to the WSW set of 8 panels.  So far one is suggesting adding the optimizers to 4 of the 8 and the other to all eight panels in the array - basically saying if we are up there then we may as well do the lot as they are relatively cheep.  

Do you have alot of shading on these panels?
My wsw array suffers badly from shading in the darker months.
If so, I'd work out which ones suffer, and those would be the ones requiring the tigo's, if its all, then it makes sense to fit them to them all.

Worth noting you can get tigo's that cover 2 panels,  so may be that your other quoter was planning on using those if all suffer from shade 

Yes there is an issue with a chimney - not much of an issue in summer but a big issue late autumn/winter. The first quote was for just 4 of the 8 but the second guy suggested that whilst they were up there they might as well do the lot..