Looking to get solar panels

isvana

michaels said:

Raggs_2 said:

...they've just offered 20 panels, so 7.4kW, for £6500. That looks pretty good to me? Now I just have to sell it to my mum about the looks!

Previously DNOs (the poeple who run the local grid) use tod have specific extra hoops to jump through if your invertor was over 3.68kw - does this remain the case?

This is something I'm curious about. If DNOs are limiting input to the grid, how does that work with maximizing solar installation sizes? Is there a certified gadget to limit the power to the grid? If that's the case, don't you need a battery (or thermal store if you have electric water or CH) to absorb the difference at max-PV-output times? 

Raggs_2

isvana said:

michaels said:

Raggs_2 said:

...they've just offered 20 panels, so 7.4kW, for £6500. That looks pretty good to me? Now I just have to sell it to my mum about the looks!

Previously DNOs (the poeple who run the local grid) use tod have specific extra hoops to jump through if your invertor was over 3.68kw - does this remain the case?

This is something I'm curious about. If DNOs are limiting input to the grid, how does that work with maximizing solar installation sizes? Is there a certified gadget to limit the power to the grid? If that's the case, don't you need a battery (or thermal store if you have electric water or CH) to absorb the difference at max-PV-output times? 

I guess this could be why they're telling me I need 2 inverters, rather than 1 bigger one.

Exiled_Tyke

I big inverter is likely to be three phase rather than single phase which complicates matters (I think) which I think is why the installer wants to use two inverters..   To export to the grid the export voltage needs to be higher than the current grid voltage. Too high a current will push the grid voltage up which becomes unmanageable which then imposes costs on the DNO to rectify.  Which is why the DNO have the right to veto.  But I could be wrong on my understanding of all this.  

michaels

We have built in micro-inverters, helps as we have a 12 panel one aspect 4 another and this would have been too unbalanced for the normal '2 strings' of a standard inverter.  WE have a nominal 4kw of panels but out inverter is 3.68 so can not export more than this, any extra potential generation is just 'lost' in some way

Re the DNO, the issue is too much energy in the local part of the grid, the 3.68 limit was some sort of 'small enough not to worry about so automatically ok' limit but I don't know if this still applies.  If you go for an export tariff then think about having west facing panels as if you choose a time of day export tariff the output after 4pm  which w facing panels generate a lot more of is worth a lot more per unit than units generated earlier in the day.

Martyn1981

Raggs_2 said:

Not sure on the ettiquette here, but going to post again. Just received a mail saying we'll require 2 inverters given the size, normally an extra £750, but they'll waive it if we install on a range of days when they'll already be down (yeah right, I'm not getting rushed if I'm not happy).

Is 2 inverters better than 1?

One inverter should be best, as that'll be more efficient than two smaller ones, and cost less than two. Not sure why they would suggest two, as the bigger inverters will be dual MPPT models, this means that you can put two strings into them, even if the two strings don't match (different panels, number of panels, orientation, pitch etc), and each string gets a MPPT which tries to maximise generation on that string.

gefnew

Hi Raggs_2
You could try this from sma ag free software to help calculate inverter and different panel configuration. so when the the solar companies say its this,
you can test this out in sunny design easy to use and free.
https://www.sma.de/en/service/downloads.html
Regards
gefnew

Raggs_2

gefnew said:

Hi Raggs_2
You could try this from sma ag free software to help calculate inverter and different panel configuration. so when the the solar companies say its this,
you can test this out in sunny design easy to use and free.
https://www.sma.de/en/service/downloads.html
Regards
gefnew

Cheers.
I have to say, given that the panels will be equally split between south facing and west facing, two inverters does make sense from what I've read about it best using them all facing the same orientation on a single inverter.

michaels

Raggs_2 said:

gefnew said:

Hi Raggs_2
You could try this from sma ag free software to help calculate inverter and different panel configuration. so when the the solar companies say its this,
you can test this out in sunny design easy to use and free.
https://www.sma.de/en/service/downloads.html
Regards
gefnew

Cheers.
I have to say, given that the panels will be equally split between south facing and west facing, two inverters does make sense from what I've read about it best using them all facing the same orientation on a single inverter.

As above, I thought most invertors have two 'strings' so can support up to two orientations assuming there are no shading issues. (Our issue with the strings  was one of our aspects did not have enough panels to suit the string minimum)

Martyn1981

michaels said:

Raggs_2 said:

gefnew said:

Hi Raggs_2
You could try this from sma ag free software to help calculate inverter and different panel configuration. so when the the solar companies say its this,
you can test this out in sunny design easy to use and free.
https://www.sma.de/en/service/downloads.html
Regards
gefnew

Cheers.
I have to say, given that the panels will be equally split between south facing and west facing, two inverters does make sense from what I've read about it best using them all facing the same orientation on a single inverter.

As above, I thought most invertors have two 'strings' so can support up to two orientations assuming there are no shading issues. (Our issue with the strings  was one of our aspects did not have enough panels to suit the string minimum)

Sorry for any pedantry, but crucial to understand that two strings is fine if the two sets of panels match, so same number orientation, pitch etc. But if there is any difference between the two strings, then the inverter will need to have multiple MPPT's not just multiple strings.
To further complicate it, you can of course have both, such as inverters with 2 MPPT's, and 1 + 1 strings, or 2 + 1 strings, or 2 + 2 strings feeding those MPPT's.
So best combo is one inverter with 2 (or 'dual') MPPT's, for two non identical strings, and if there is any shading on a string(s), then a Solaredge inverter with power optimisers, which should still be cheaper (and far more efficient) than two inverters.

Raggs_2

Martyn1981 said:

Sorry for any pedantry, but crucial to understand that two strings is fine if the two sets of panels match, so same number orientation, pitch etc. But if there is any difference between the two strings, then the inverter will need to have multiple MPPT's not just multiple strings.
To further complicate it, you can of course have both, such as inverters with 2 MPPT's, and 1 + 1 strings, or 2 + 1 strings, or 2 + 2 strings feeding those MPPT's.
So best combo is one inverter with 2 (or 'dual') MPPT's, for two non identical strings, and if there is any shading on a string(s), then a Solaredge inverter with power optimisers, which should still be cheaper (and far more efficient) than two inverters.

Solaredge inverters only seem to go upto 6kw for the single phase. That's not going to be sufficient for a 7.4kw system right? I know you aim for a bit under, but that seems significantly under?

I can see that I can purchase (from a wholesaler so I assume without vat) a 3.3kw single phase single mppt inverter for £383, even a second one is going to be significantly less than 20 solaredge micro inverters/optimizers and a £900 6kw solaredge inverter.

I presume they'll link the West facing 10 panels to one inverter, and the south facing 10 to the other.