Dillsue

Next to nothing to go wrong if you've done your homework. I guess if your builder is responsible for building regs compliance and sign off then he may be a bit hesitant to hand responsibility to you but if you make it clear he's not responsible for the heating system performance it's hard to see why he'd be concerned. If you put it writing it's a valid change to any contract you have. If he's got a mark up on the heating system then he's potentially a bit out of pocket if the HP installer is out of the picture.

So you need to decide who's taking on responsibility for the systems performance and providing the warranty for that. If you want things done your way then make it clear that you take responsibility. If you want someone to blame if things don't work then you probably need to leave the design and install to the builder/plumber/HP guy. As mentioned above its straight forward to install a HP........if you understand what needs to be done!!

Dont forget everytime you change or add water you're adding to the scaling potential. I'd be tempted to buy a pump that will alow you to return any drained water back into the system rather than adding fresh water.

Given that the changeover switch is wholly cable connected and doesn't need busbar alignment/compatibility with the CU, what hazards would you envisage being on the sparks risk assessment if you used a different manufacturers unit??

I guess the Geya description trumps the symbol on the unit....a 0 printed on the unit would make it clearer. If you are having the changeover switch in a separate enclosure to the CU then having the standard 2 pole main switch in the CU would remove the need for the changeover to have an OFF position?? If you need to pacify your spark by having an OFF position then the Geya or Hager units seem to do that. I'm pretty sure all the units you've posted will fit in standard CUs so it might be neater to have a slightly larger CU and house the changeover switch in that rather than a separate enclosure??

I think that's a 2 position unit? The I and II show the 2 positions

I've got 2 of those changeover switches, one in each of the main house consumer units. They let either of the CUs be fed from the grid or the backup output from the inverter. One is normally fed from the grid, the other normally fed from the inverter backup output. I'm not aware of any regs that prevent that configuration but it's such a niche that I'm not sure those producing the regs will have detailed if and how they should be use??

Ask them for a breakdown so you can see where the money is going

An extra inverter on top of an exiting 4kw unit would need a G99. Might be easier to let your FIT payer know about the extension as thats just a phone call/email??

At 13 degrees your roof will likely be below the level where the panels are self cleaning so you'd probably get best results by setting up an automatic cleaning system that sprays them once a week. You can change out the panels if you want but you'll likely need to extend the mounting rails so factor that in. If the total generation capacity goes over the FIT registered capacity you need to let your FIT payer know and they'll pay you the proportion of generation attributable to the original capacity only. You won't get FIT payments for the extension!

If you want a "ladder" so you can climb the roof, just slide every other tile up in a vertical row. Your tiles look exactly the same as ours and sliding them up and out of the way makes a great way to move around.

Exactly. It's very basic school level physics

The other rationale for a DNO limiting inverter size could be customer tampering with G100 settings?? AFAIK G100 settings are supposed to be password protected with an installer/manufacturer password that the customer doesn't know. There's been several posts on here where people have said they'll lift the export limit above the DNOs approved limit as they have the installer password. The battery inverter I've just installed has a single password that protects G100 settings and all "advanced" settings including TOU charge scheduling. Technically I shouldn't have access to the G100 settings but legitimately have access to the TOU settings so this inverter is poorly designed from a G100 compliance perspective.

If a DNO does limit the inverter size then effectively they're saying they dont trust the ENA standards and/or the G100 certification/self certification process

This is basically an off grid setup with the inverter taking one or more energy sources to power the house. Intended to use batteries and PV with a generator as a backup. In terms of the inverter generating anything, and being regulated by the DNO, it only generates power to supply the house as so far there's no grid connected. Now swap the generator input for a grid connection and as far as the grid is concerned the inverter is only a load but no generation capacity on the point where the grid is connected. MCS isnt required for any installation works. If the video is suggesting otherwise then take it with a pinch of salt As stated use a changeover switch to choose if your house is supplied from the grid OR from an off grid system that the DNO doesn't regulate. What's your concern about what is said above??