Dillsue

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??

Our calculated heat loss is 8.5kw at -2. We put in a 7kw LG Therma V and it's kept us warm all through this winter but it's worked very hard for the few days it's been freezing. I was wary of oversizing for the reasons JohnMo mentions and was wanting to install an 8.5kw Ecodan to exactly match our heat loss. The LG came up on ebay secondhand for a few hundred £ so went for that with a plan to run a fan heater or light the woodburner if the smaller LG unit couldn't cope. No fan heater or woodburner needed as the smaller LG has coped throughout and I'm very pleased with how things have worked out. We'll hopefully have benefitted from efficiency gains in running a smaller unit but the older Therma V doesn't calculate COP or energy produced so I'll never know for sure.

I've not looked at it and have no need to but good on you for doing it and making it available

If you go for 2 single phase HPs they can likely be wired on separate phases so you'll use 2/3 of your 3 phase supply;) Your spark will sort that out and hopefully balance the third phase with other house loads, as best he can. On the sizing of your heat pump, if its sized for -2 as ours is, it will rarely be running in those conditions. This winter we've had -2 for 1 night, zero for maybe another 4-6 nights and the rest above zero. With a single big unit, especially if it's oversized, you'll likely hit its modulation limit quite often and see short cycling so youll be paying higher bills for the life of the HP. I'd seriously think about getting an independant heat loss calc done from the likes of Heatgeek just to sense check the size of HP needed.

Our solaredge inverters run way beyond that at default settings:) Grid can be up to 253v so you'd need to legitimately run higher than that to export anything.

If you're paralleling the inverters and they are grid tied to the house AC, then you can connect multiple inverters, subject to the usual DNO restrictions. Unless there's some quirk of the inverter, they just autonomously pump power into your house/grid. We've got 2 PV inverters and soon to have a battery inverter all running in parallel with no control between them. Just watch out for voltage rise in the house if you're producing alot of power. The DNOs obligation is to limit the voltage at your service fuse to 253v. If you're trying to push alot of power into the grid through undersized cabling within the house, then you might find the house voltage rising significantly!!!

Solis confirmed you need a DC input from either or both the PV or the batteries....will have to get the batteries charged and assembled!