Dillsue

We're almost into May already and without any firm plans you probably want to get the oil boiler ship shape to see you through next winter. Then do your research and build a plan as to the work you want to do. Once you have a plan you'll be able to size your heat pump more accurately based on the draught proofing and insulation levels in the plan. Remove the loft insulation and buy a box of 10 little nipper mouse traps. Once youve cleared the mice, seal up all the pentrations where cables/pipes come through the ceiling, fit rodent proof vents to the eaves and refit the insulation. You might want to use PIR over the tops of the walls to give decent insulation between rafters but leaving enough of an air gap to get airflow across the loft space. Don't expect any solar PV to contribute much to running your heat pump as solar generation is at its lowest in the winter when heat demand is at its highest

One of the not so publicised benefits of optimisers/micro inverters is that they allow you to have mismatched panels on the same string which is great for phased expansion of a system. We have 310 and 320 watt panels on one string and 335 and 405 watt panels on a second string with the smaller panels not affecting the output from the larger panels.

I think that to do what the OP is doing you'd need a few extra bits and bobs off the roof to get the same functionality with micro inverters. The thing to be conscious of with anything active up on the roof is replacement if they go wrong. I don't know what the failure rate is of micro inverters but we're waiting delivery of the 3rd failed optimiser from one of our systems. They come with a 25yr guarantee but that's not an indication of how long they'll last, just means we get the part free. Fortunately I have the kit to replace them so it's just my time to put up a scaffold tower but if you have to pay someone to change them it can be £100s

Google "Ofgem fit guidance" and youll find- https://www.ofgem.gov.uk/publications/feed-tariffs-guidance-licensed-electricity-suppliers And- https://www.ofgem.gov.uk/publications/feed-tariffs-guidance-fit-generators

The FIT rules changed in December 21 to allow alterations and batteries so make sure you find the version dated then or later

Read the FIT rules!! Your config is likely allowable with a new bidirectional meter doing net metering. Anything drawn from the grid and put into batteries is deducted from energy flow to the house/grid giving a net reading of what was generated from solar. It's all covered in the FIT generator rules and/or guidance docs from Ofgem. Don't expect or trust that BG staff will understand the finer details so you could well have a bit of an uphill struggle but you'll get paid in the end if you know and stick to the rules. There's also a guidance doc for FIT payers(BG) detailing how they should manage you so that's worth a read of the sections covering what you want to do. Have fun!

Great that you got your 8kw export. If you've not already done it have a read of the FIT rules re system extensions so you get all the total and net installed capacities correct

That's a G100 concept doc. Have you checked the ENA type test register for a compliance cert as a previous post reckoned Victron weren't going through certification?? Is it a G99 application you made to your DNO rather than a "notification"?

SEG is the government's successor to FIT and is regulated and must be paid if you apply with a qualifying system. Outside of SEG, Octopus and maybe others can buy your surplus on a Power Purchase Agreement(PPA) which is an unregulated contract between you and them. Octopus offer both a PPA and SEG but no point in going for SEG when you can get much more on their Fixed or Agile Outgoing tariff

Title is "help with first solar PV system". Bit confusing when you're actually expanding an existing system! The answer to your question about getting paid for FIT generation and separately paid for metered export on a PPA, is yes you can. We do exactly that. Scottish Power pay the FIT generation on our 4kw FIT system and Octopus pay the 15p/unit on the export from the total 12kw we have. You can only change between metered and deemed payments once every 12 months. If your extending your FIT system to 8kw you'll only get FIT payments on the original registered capacity of 2kw so as you say you'll get paid on 25% of what goes through the generation meter

The FIT scheme ended in 2019. If you mean SEG, last time I looked that generally pays a pittance- Octopuses 15p rate isn't SEG, it's a power purchase agreement that Octopus offer, can end anytime, and doesn't carry any government backing which SEG has, hence the G on the end

If you can't get consent for 8kw then you wont(shouldn't)get approval as your inverter eemingly doesn't have G100 certification to limit export below 8kw. Anything with more than 3.68kw rating and your DNO should always be your first port of call. Your MCS installer shouldn't power up, commission and certify for you without DNO consent. I'd speak to your DNO ASAP and hope you can blag 8kw.

AFAIK you need the system designed and commissioned by an MCS certified outfit to get the grant.

Up until the last few days we'd had 1 day of rain in the last 2 months.....witness the wildfires we've been seeing in the media. The nearest reservoir to us is only half full as we come out of winter. Might be worth being a bit conservative with something we really don't want to run short of??

Just a heads up for what they may offer. Our detailed heat loss cals show a heat loss of 6.5kw at -2. This winter when it was zero outside, we maintained house temp around 19/20 degrees with 4kw of fan heaters running so I'm quite confident the calculated loss is fairly representative at 6.5kw Seeing the Coolenergy offer of a free kit of parts with me sorting the installation I made an enquiry and fell off my chair when they quoted for an 18kw unit. The 18kw unit won't even modulate down to my max heat loss so will spend its life short cycling and putting a significant dent in my bank account. When I shared my detailed calcs with them they stopped talking to me! By all means go down the Coolenergy route but get your heat loss worked out by someone else and don't accept a massively oversized heat pump