Dillsue

Exactly. When we added more PV our DNO stumped up for a new transformer, 3 new poles, 100metres cable, pole anchors, earth loops etc. That brought the supply up to modern standards. The neighbours now run through the summer days on our PV. It's also meant that when we recently applied to hook up an EV charger and heat pump the supply was up to spec and got approved in a couple of days. I would imagine that much if not all of the cost of upgrades to hit net zero are coming from the bill payer and central government so minimal cost to the DNOs??

That's the G98 limit that everyone has a concession to export. If your voltage is going over 253v and it's concerning you then let your DNO know and they'll sort it out for you.....they're obliged to if your sticking to 3.68kw of export.

Before parting with your cash, have a read of what @JohnMo said up thread about nearby restrictions. Might be worth standing a pallet in front of your HP for the winter and see if it impacts operation before paying for and fitting something permanent

I think/hope that there's more resistance through the PHE route than through the cylinder so most HW draw off will be through the cylinder. Via the PHE there's 2 x 22mm Tees, the pump and the PHE but via the cylinder there's nothing but the cylinder itself. I'll leave some space for a 2 port valve just in case things don't work out. I looked at the Mixergy set up and as JohnMo says cooler water is drawn from the bottom and returned around a quarter of the way up. Would be nice to replicate that setup but I'm a bit wary of cutting a new hole in the existing cylinder and then feeding a new tank connector through the immersion boss and getting it into place and secured. Anyone successfully done that??

Thanks for the tip about counter flow....not sure I would have considered that. Not sure I follow where you're suggesting an NRV is needed? I'm going to pump from cold inlet, though PHE and into the HW outlet. I cant fit an NRV to block that flow when the pump isn't running as it will block the flow when the pump is running???

Shutting down at 253.6v seems overly close to the limit....my 2 solaredge inverters dont trip til they hit 262v. If that figure of 253.6 is adjustable, I'd raise it slightly whilst you sort things out with your DNO G98 allows you to export up to 3.68kw without seeking permission and your DNO should ensure that when exporting at that rate that your voltage stays below the 253v limit. If you're going over 253v with 2kw of export, things will only get worse with more export. As a minimum your DNO should ensure you can push 3.68kw into the grid and stay below 253v. Is your installer putting in a G99??

On a calibrated Fluke we're currently sat at 251v with minimal load in the house and negligible PV export as its grey and raining. A good chunk of PV export will push that to the 253v limit and a touch beyond at times!

If you look at the voltage line through the night you can see it rises as everyone gets into bed and the load reduces. Around 6am the voltage starts to drop as people wake up and the load increases. As your PV starts to generate around 7 you can see the voltage start to rise and then drop off as your generation drops off. You can see your PV pushing the house voltage up as it generates. The rest of the fluctuation will likely be the load from you/your neighbours being awake and using stuff??

I'd heard that in certain areas, maybe with higher than average PV installations, that they seasonally change the tappings to lower the voltage in the summer and raise it in the winter. No idea if thats a fact or not but it seems logical to keep local voltage within limits.

A higher supply voltage wont stop you exporting. Whatever your connection voltage is your inverter will raise the house voltage a little so power will flow out of the house and into the grid.

Well over 240v is perfectly normal. It's the DNOs way of getting more power to you by upping the voltage rather than the current. Our no load voltage is around 250v and tickles the max of 253v on a sunny day when the PV is going full chat. The move from 240v to 230v was when we harmonised our voltage with Europe....they were at 220v and we were at 240v so we met in the middle

No apologies needed. I was a bit confused by what you were saying but all is clear now.....for both of us

The DHW circulation pump will draw from the cold inlet at the bottom of the cylinder, pump through the PHE then inject the heated water in at the top. That way it circulates cylinder contents through the PHE, pushing the hotter water in at the top. Primary side of the PHE is pumped by the ASHP

I tried using the existing .44m2 coil and it was hopeless so have resigned myself to fitting a PHE. There's likely a few ways I could trigger the DHW circulation pump but anyone know of proven ways?

My guess would be that fires related to isolators would be due to loose connections rather than the switch contacts. The switch/contacts are extensively tested by the manufacturer. The cable terminations are installed in an often awkwardly small space and likely the only testing is a gentle tug to make sure some of the cable has has been caught in the terminal. My money would be on improperly terminated cable, likely without crimps where there should be, or the fine stranded PV cable settling in the clamp over time and coming loose.

Exactly......no point in scaremongering over what is a negligible risk

When you look at the report roof top faults only attributed to around 25% of the fires they looked at. They only looked at 46 fires and there's tens of thousands of systems installed in the UK. Whilst there is a risk, if you ensure a quality install the risks seem very low to me and certainly low enough to focus on quality of design/install rather than spending £££s on supplementary fire protection.

With an in roof system a couple of roof ladders either side of a failed panel gets you access. I don't think access for panel/optimiser/micro inverter replacement should be a particular worry.

With a scaffold tower up, removing a panel or 2 below a failed panel is only 10-15mins work. I wouldn't worry about accessing an array 3 or 4 rows deep as the bulk of the time in replacing a panel is getting to site and getting access.

The FPA report that LnP posted says its DC isolators that account for 50% of fires. These are generally easily accessible as they're not on the roof so we'll worth a night time check that connections are tight?? I have limited experience of PV Installs but a used inverter I bought a few years ago came with some cut off cables terminated in MC4 connectors. With a bit of a tug the cable pulled out of one of them and when I dismantled it you could see it had been crimped with pliers rather than the correct crimping tool. If you're getting an install done double check that your Installer has the correct tools!!

The thing that will blow is the service fuse on the house incomer so Roger will loose all power until the DNO comes out to replace the fuse. Given the property history that may be charged for but subsequent replacements would/should be charged for. If they aren't charged to the householder then you and I will pay for the call outs.

NGs assessment can be as simple as them saying "you're on a 60A supply now so a 33% increase to 80A will be enough to cover a typical house wanting to add a heat pump". It could also be a quick look on Google earth to see that your not living in a stately home. It doesn't have to be a bespoke survey of your house which is done by your installer when applying for an LCT connection. If your installer does that and shows you need the full 23kva for the house then you've got an argument for the full 23kva. You can only really comment on and challenge NGs policy if you've done the LCT application to show the house needs more than 80 amp, and then been rejected.

Your explanation has been a bit piecemeal but as I understand it you originally wanted a 3 phase supply upgrade for your workshop for which NG wanted £20k. You've backed off on the 3 phase wish but you've already shared with NG that you have quite a substantial workshop demand. If NG have assessed your domestic needs as being met with an 80amp supply, why would they go beyond that for free knowing that any extra will be feeding the workshop? The ENA statement says its UP TO 23kva for free. It's likely public money being spent and they should rightly only meet your domestic need. I think there's a bit of a difference in an average domestic garage/workshop compared to one where the owner wants a 3 phase supply to run what sounds like a commercial sized car workshop??

Our original and upgraded supply is single phase 100amp. Our DNO states the low carbon technology (LCT)connection upgrades are free and I'm quite sure the ENA statement is true. Your experience isnt for an LCT connection, it's for a workshop, for which you should rightly pay....the free LCT connections are almost certainly tax payer or bill payer funded. I'm sure if you ran your big workshop loads off a genny then an 80amp supply will be fine for an efficient electrified house and workshop basics

28mm x 7metres from the HP to the centre of the house then 3 x 22mm x 6 metres down the centre of the house, 1 for upstairs and 2 running the length of the house for downstairs. Mainly 10mm drops off the 22mm for each rad typically 6 metre run with 4 drops of 8mm in the original part of the house around 4 metres each. Distance are one way so double for flow and return. 15mm for the whole of upstairs sounds a bit constraining!