Dillsue

I'd be cautious about assuming Octopus will accept your export where there's a mix of generation from MCS and non MCS systems- they told me they wouldn't accept ours! IF the red bit on your graph is the actual clipped bit then you need to work out how many kwh that equates to then multiply by the number of days you realistically think clipping will happen multiplied by your unit import rate. You'll then see how much you'll likely loose and how that compares to the the cost of adding a second system. As PVGIS is based on historical figures you'd likely be more accurate using its prediction rather than as8ngle day snap shot from a few days ago??

If there's installation constraints to hooking up extra panels to the existing inverter then only you can weigh those up versus a G99 application, part P sign off and cost of a second inverter. We have a ground mounted 3kw array which is hooked up via a buried SWA cable which is straight forward to install to the inverter inside the garage. For the clipping, assuming you've not got batteries, do you need more/can you use more during a summers day than 3.68kw for the few weeks a year that you'd likely be clipping? With split arrays you can get a combined generation forecast from PVGIS by downloading hourly forecasts for each array and summing them in a spread sheet to see what the peak generation for each hour is. You can then see how many hours/days you'd be clipping in reality. Our second system has 8.5kw of panels spread between SE and NW to give day round generation and peak generation is 5.2kw. The 5.2kw forecast rarely happens and its probably even rarer for us to use the peak for the relatively short time it's there.

Just had a look at the spec for your inverter and it allows 200% oversizing on the DC input so theoretically you can hook up all your panels to the existing inverter so no DNO involvement and extended generation through the day. I didn't see if there was a max limit on each MPPT input so check with manufacturer if you can put 4kw on one and 3.2 on the other.

Keep things straight with your DNO as it helps manage the grid for everyone's benefit. No need for MCS. The OFGEM guidance for FIT payers requires them to actively monitor for unexpected over generation. You're not gonna be getting FIT payments but Octopus should already have mechanisms in place for monitoring unexpected FIT Generation so whether they apply those mechanisms to other export schemes is anyone's guess. Even if the did detect over generation they might not be bothered if youre not on a government regulated export scheme(FIT/SEG)?? The risk you run is they pull the plug on your outgoing payments. How big that risk is is anyone's guess!

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.

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.

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.

Sorry for the derail Garald!!

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.

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.

See section 6.8 of this https://www.ofgem.gov.uk/publications/feed-tariffs-guidance-renewable-installations Accreditted = MCS Non accreditted= non MCS

I'd be surprised if anyone would touch 400vdc as all plugs are IP2x rated. Anyone would have to try hard to touch the live bits of an MC4 connector. You'd have to ask your roofer, or you plug em in

All generation goes through the generation meter and you get paid a proportion related to the proportion of existing FIT capacity and new extension. No MCS needed to retain your FIT payments on the original capacity. Only need MCS if you want SEG or Outgoing on the extension capacity. Read the section on extensions in the guidance I linked to earlier.

With MCS the extension is eligible for SEG or a direct route to Octopus Outgoing. Without MCS youre not eligible for anything. The original capacity remains eligible for FIT regardless of who installed the extension.

No MCS needed for the extension unless you want to claim SEG on the additional generation. Once you've added capacity notify your FIT payer and they'll be expecting a jump in generation and pay you pro rata for the proportion generated by the registered FIT capacity

So who's paying for the eleccy from my self installed array....legitimately?? FIT?- not MCS= no payment SEG?- not MCS= no payment Octopus outgoing?- not jumped through their hoops= no payment So who's paying?

Get a roofer to fit the rails and panels and plug them into the existing system yourself. No spark needed as they are all factory assembled and tested- same as an IKEA table lamp which you don't need a spark to plug in.

I think you do!! Non FiT generated eleccy isn't eligible for FIT export payments so you have to be able to identify the FIT element and the non FIT element which you can't do if they are running through a single meter. They definitely dont earn the same payments.

Try this https://www.ofgem.gov.uk/publications/guidance-generators-co-location-electricity-storage-and-hydrogen-production-under-ro-fit-rego-and-seg

All he needs to do is add panels to the FIT system and change the inverter if it can't handle the new DC input. Declare the additional generation capacity and get paid pro rata for the existing generation meter. Simples!

Your correct, the FIT Generation Meter measures generation only. It's used for generation and deemed export payments. If you're on metered FIT export, then that's done by the premises smart meter. If you've got FIT and non FIT generation going through the export meter then it's not possible to measure the FIT element so you go onto deemed payments. No mention of how you've been previously paid in the Ofgem guidance.

Had a quick look at FIT guidance for eleccy suppliers which contains the following- "6.72. Where it is not possible or practical to measure export by export meter readings, export should be deemed for accredited FIT installations with a total installed capacity of up to 30kW. For the accredited FIT installations where export is permitted to be deemed, the Secretary of State determines the percentage of electricity deemed to be exported. Such a determination is published at least 1 month before the beginning of each FIT Year." I read that as its obligatory to make deemed payments if an export meter can't accurately measure FIT export. So if you've been on deemed then moved to metered export, all you need to do to move back to deemed is add some none FIT Generation which renders your FIT export meter reading inaccurate. At that point your leccy supplier is obliged to move you back to deemed???

Not sure that's necessarily correct! If you add PV in addition to your FIT system it's not possible to use metered export as there's more going through the meter than just FIT export. What you are saying is that export payments would then end??

I have long been under the belief that you can choose metered or deemed and could revert to deemed if you wanted to. Dont know where I've got that from but may be worth looking into. Deemed is certainly the way to go if you'll be daytime charging a car or battery

Sorry, replying to JamesPa!!