1. Batteries 2. PV comparison

[Dillsue]

9 hours ago, Dillsue said:

Again your correct that if you opt out of FIT deemed payments for PPA(Octopus Outgoing) then yes you have forgone your right to FIT payments both deemed and metered. But what is being said is about opting out of FIT deemed payments for FIT metered payments, not PPA.

After a bit more reading it seems this isn't strictly true either. You can opt out of FIT export payments and go for SEG or PPA but you can opt back in to FIT export after a period of time. I guess that's to stop people seasonally fliting between the 2.

 

From the FIT licencees guidance-

 

5.43. Generators who opt in to receive export payments from their FIT licensee will be unable 
to opt out and sell exported electricity on the open market, and vice versa, until at least the 
first anniversary of their participation in the scheme. After that date, FIT generators shall be 
permitted to change their selection to opt in or out, but no more than once every 12 months. 
FIT licensees are required to record this change on the CFR.

[Dillsue]

Sorry for the derail Garald!!

[JamesPa]

10 hours ago, sharpener said:

 

If the capacity is already limited by the inverter rating what do you gain by adding more panels?

 

Yes there is some advantage by over-panelling a bit wrt the inverter (20% is often suggested as optimal and my second set is a bit under 10%) bc you get more at the shoulder periods of the day and in winter.

 

However I thought you were talking in terms of a lot more and if you are already over-panelled as you imply I don't quite see the benefit, can you share the numbers?

Currently I have

 

String 1 2500Wp nominal.  15deg elevation sw facing (10*250W)

String 2 1500Wp nominal 45 Deg elevation sw facing. (6*250W)

 

Although thats 4kW peak nominal the low elevation of string 1 and SW aspect means its about 3.2 kW peak actual.  However the declared installed capacity doesn't take this into account so the declared capacity is the lesser of 3.68 and 4 ie 3.68.

 

There are various options on how to connect inverter(s) but they all revolve around the same or a very similar upgrade to the panels.

 

The obvious upgrade physically is to leave string 2 alone and increase string 1 to 8*400W =3200Wp.  The inverter (SB4000) 

can cope according to SunnyDesigner.  3 of the recovered panels can be reused to make a separate, standalone 750W array on the cheapest inverter I can find and the remaining 3 set aside for future use or spares should any of the old panels fail.  Possibly a couple of panels in the new string 2 array could be connected to this inverter instead of the original one to reduce the extent to which it is over-panneled.

 

It's difficult to calculate exactly how much energy is lost from the over-panelling because clipping is of course based on the instantaneous output.  But my best estimate is that it's around 10% of the increase.  

 

It's not worth taking the design further until I can find someone who will do it.  So far the solar installers in the area have only shown interest in starting again from scratch, at which point it's not worthwhile.  I think the market might have cooled somewhat from when I did the research eighteen months ago, so I might just have better luck now.

 

Will look into roofers too but, I'm still struggling to believe they will touch a system that has 400V DC on it.

 

[Dillsue]

9 minutes ago, JamesPa said:

Will look into roofers too but, I'm still struggling to believe they will touch a system that has 400V DC on it.

Where's the 400v? It's between the two cables in the DC isolator which no-one needs to access.

 

With the DC isolator off, if you unplug an MC4 connection between any 2 panels there's 0v between the 2 connectors and the connectors are IP2x. When connecting in the new string, connect in one leg at a time and there's 0v between the connectors that your handling

If you're not happy with your roofer doing it, take a multimeter up on the scaffold, check the voltage and plug them in yourself.

Even buying a climbing harness and rope to tie yourself on will be way cheaper than battling with pro installers if they are busy and aren't interested in your job.

[sharpener]

2 hours ago, JamesPa said:

It's not worth taking the design further until I can find someone who will do it. 

 

Maybe the key is to make it less hassle/a more attractive project for them. I can see that repanelling a roof is sthg they would not want to do, either they have to re-use the old rails that someone else put up years ago (?liability) or take them off and make good where the fixings were.

 

This is where a jobbing roofer might be better. I think many will have experience of PV now and not be worried by the cabling. Also you are likely to get a better job of the weatherproofing.

 

It seems a lot of work and expense to achieve a net increase of 2450W pk (and 750W of spare panels). And to benefit properly from the extra generation, as well as adding inverter capacity somehow I think you would also need storage.

 

One alternative approach would be to leave the existing MCS-certified setup exactly as it is and just add the new 750W array (can you get any 400W size panels in the space you have?), combined with a small hybrid inverter and some of the money saved on panels spent on battery storage. This might make it a more attractive mini-project for an installer. The battery should pay for itself in <10 yrs through time-shifting.

 

Then you would get a new MCS cert so can export on OO, and also be free of the apportionment hassle as you are not adding capacity to the existing FIT system.

[Dillsue]

As JamesPa is already at his G98 limit, adding a second inverter means a G99 application. That could cover any new battery to. Adding panels to the existing inverter avoids G99 unless batteries are added.

 

The prorata payments are all handled by the FIT payer so there's no hassle for the recipient after they've notified of the additional capacity.

 

Whether adding panels at all is "worth it" is down to whoevers paying- there's so many factors that everyone attaches differing values to, its a wholly personal thing.

[JamesPa]

23 hours ago, sharpener said:

One alternative approach would be to leave the existing MCS-certified setup exactly as it is and just add the new 750W array (can you get any 400W size panels in the space you have?), combined with a small hybrid inverter and some of the money saved on panels spent on battery storage. This might make it a more attractive mini-project for an installer.

That was the original plan.  However it's visually unattractive because it means two sets of panels of radically different appearance will be adjacent (my existing panels look quite different from the panels you get today).

 

I'm honestly not convinced there is a solution and wishing I'd maxed the panels from day1.  Back then however over-panelling wasn't so well recognised as a valid technique and panels themselves were a significant part of the cost.

[Dillsue]

If you want to match your existing panels,  set up a few saved searches on ebay and you'll likely find what you want if youre happy to wait. You could also contact some of the sellers disposing of older panels and ask specifically if they've got what you want.

 

There used to be guy near to us that disposed of ex solar farm panels and he only ever advertised a fraction of what he had in his yard.

[sharpener]

9 hours ago, JamesPa said:

However it's visually unattractive because it means two sets of panels of radically different appearance will be adjacent (my existing panels look quite different from the panels you get today).

 

By chance a quick search for "second hand solar panels" turned up a load of my original Upsolar 230W ones that Bimble are offering. The later Longi all black ones are quite different, but inconspicuous on the slate roof. I might have preferred matching silver frames but had no choice other than to take what the installer had from stock.

 

These people have a lot of s/h inverters of all kinds, including once again an exact match for my Steca inverters. Can't make up my mind whether to buy them as spares.

 

Both of which suggest that it might not be too hard to find what you want.