Dillsue

Would the 10% inefficiency represent an oversized heat pump not being able to modulate its output low enough to match a more usual winter heat demand and then start short cycling 24/7?? I appreciate that an oversized heat pump might perform better in cold weather if that's what manufacturers say, but cold weather only makes up a small proportion of the heating season. The rest of the time it's mild and an oversize heat pump could be short cycling for months. Do the manufacturers performance figures cover the situation where demand is less than the minimum modulated output?

We've got a calculated 8kw loss at -2 but installed a 7kw HP on the basis that it very rarely gets to low single figure temps and being undersized means the HP should run more efficiently most of the time. It's dropped to -1 a couple of times in the last month and the HP maintained the temp OK, but it worked hard when it was cold!!! We have back up heating by way of an LPG boiler and a wood burner, but would be happy running a fan heater for a few days if we didn't have the backup and the HP couldn't cope. Remember if you oversize you're stuck with potential inefficiency for the life of the HP

I think you're correct in your views on isolators but if you need a connection in the loft MC4s are the lower risk and in my limited experience far quicker to install and more reliable than screwed terminals, either in a JB or isolator. The only exception to the reliability of terminals would be to use cage clamp terminals where the terminal applies spring pressure continuously on the cable strands so they don't work loose over time. You can certainly get cage clamp terminals but I'm not sure if you can get DC isolators with cage clamp terminations.

This! Only change I'd make is have the MC4s for the last connections on the roof within the loft so they were accessible without the hassle of accessing the roof. If you've got to change either of the last panels in the string then you can easily pull the MC4 through the felt if you've got a tiled roof. I don't know if you can do that with a slate roof so maybe MC4s outside on a slate roof?? If you want to use screw terminals at each end of strings then you'll be cutting off the factory crimped MC4s and then screw terminating them, meaning a JB on the roof or in the loft. This entails 4 screwed connections in the same way as you would for an isolator which apparently is a fire risk? From posts above, MC4s are a lesser fire risk than isolators so those would be a better bet. I think you asked in another topic about crimping which you accepted was doable and from the table above is an approved way of disconnecting a string.

If you have the inverter in a ground floor plant room and that inverter has an integral isolator or there's a free standing DC isolator next to it you've surely met the requirement @Beelbeebub posted without putting a second isolator in the loft. The loft is remote and rarely quickly or easily accessible so the isolator in the loft is going to be unused. If you need to work on the cables in the void, shut the inverter down, switch off the inverters DC isolator so there's no load in the cables then disconnect the MC4s in the loft to isolate the void cables. That's in line with the PV string disconnection method in @Beelbeebubs table. Wait til its dark if your concerned about voltage on the plugs. I really dont see the point in putting an additional isolator tucked away in the loft where it's going to get forgotten about, particularly if it's seen as an unnecessary additional fire risk.

Is that requirement for an isolator as close to the point of entry as possible a mandatory requirement or a recommendation?? On the use of SWA for DC PV I read recently that SWA generally doesn't meet the requirement for DC PV as the regs require double insulation between the conductors which standard SWA doesn't have. I beleive there are some specialist SWA cables available but the common or garden SWA shouldn't be used if you want to meet the regs

Maybe Im missing something but the Isc is likely very close to the Imp so you'd need a very precise fuse/mcb that can differentiate between normal operation and a short circuit. You'll be sizing your PV cable for the Isc so adding fuses/mcbs isn't going protect anything as a short will just take the circuit to Isc unlike a grid powered circuit which can hit very high currents more or less instantaneously and where fuses/mcbs are needed to protect cabling. How you temporarily make the PV cable ends safe depends on whose gonna do the final connection. If it's you and you can connect up when it's dark then put the ends in a JB and move them to the inverter when its dark. If it's an electrician that's likely only going to want to work in the daytime then terminate them in a DC isolator assuming your electrician would be happy terminating in the dead side of an otherwise live isolator....probably best asking if you're using an electrician.

Any surplus isn't wasted as it goes to power your neighbours and offset their grid demand. For a lot of people they see that as "wasted" but it's not. As you've already bought the panels but not using them, then that is wasted money/resource.

I've described simple and useful to you that you can install and maintain yourself. The video @JohnMo linked to boils a tub of water in an uncontrolled way and that's it. I truly don't understand why you've bought the panels but won't use them?? You said you want them optimised for winter so mount them that way and get some benefit from them. What's stopping you doing that??

If you want batteries/diverter/heating you need the panels in place and connected, so get that first step done. Everything else is secondary and can be added if and when you get round to it. 4.5kw of panels will give a useful contribution to house running costs spring/summer and a bit of autumn. It's never going to heat your house or hot water in the winter. You can load shift anytime you want by scheduling washing machine, tumble drier, slow cooker etc etc to be on during the day when its bright. Do one after the other to minimise grid draw and max your self use...........but you know all this already so no one really needs to be repeating it??? Just put self installed on the G98, that's all my son in law did and all I did on our G99. Rest of the stuff is inverter details and if you've done electrical work you'll understand all that. Apparently the ENA estimates that less than 50% of PV install has been notified to DNOs so they'll probably be quite greatful of your notification

Forget trackers, forget batteries, forget diverters as none of those are needed to get your 4.5kw of panels up and running. You've said the mechanics of mounting them are fine and that's the tricky bit. You can plug and unplug the connectors on a car loom? MC4 connectors are no harder. Fix a 3.68kw inverter to the wall? Get a spark to connect up the mains if you don't want to do that. Fill in your name and address on a G98 and post it to your DNO. What else is stopping you??

Fix panels so they face the sun at some point mid morning to mid afternoon. Plug panels together. Plug the 2 unconnected leads into an inverter using MC4 extension leads if needed. Connect inverter to nearest fuse board through an MCB specified by the inverter manufacturer. Switch the inverter on. Sit back smugly and thank the part P electrician who connected it up for you

Don't forget you need DNO consent if total potential export is over 3.68kw. You can add generation to your FIT system as the rules changed a few years back. If your current system is under performing its likely beneficial to add to the FIT system rather than add a second separate system

Have you thought about how your going to keep a tank full of hot water available during waking hours on a dull day? Paying guests shower in the morning, get p**s wet through during the day then want showers when they get in and a bath for the kids before bed. Be sure to look at DHW and heating from a holidaymakers point of view ie both need to be there when they want them.

?? There's likely auto air vents on the HP circuit and almost certainly if its a pressurised system??