Dillsue

Yes you can and its straight forward- download the form and see what info you need. You'll likely need to supply a single line diagram of your house distribution but Google it and you'll likely find something you can doctor. If you installed without permission, you'll be breaking the terms of your electricity supply contract and the national terms of connection which I think are legally enforceable. A G99 is straight forward so why would you want to not do the right thing. No ones going to check up on you unless there's a problem. If you go for a 3.68kw G98 inverter instead of the 5kw one, then all the G99 paperwork, and fee, go away but you'll likely be drawing on the grid more often than with a 5kw unit

Incoming and outgoing capacity aren't the same. Fair chance you've already got the incoming voltage set fairly high to allow the DNO to get as much power round the grid without upping the current and requiring expensive bigger cables. When you draw 50amps from the grid it pulls the voltage down which isn't a problem if you've already started with a high supply voltage. When you try to export 50 amps it pushes the house voltage up and if your starting no load voltage is already high, your 50amp export will take the house voltage over the 253volt statutory limit. More importantly it might take your neighbours voltage over the limit which is a problem for the DNO. If you're on your own transformer it may give you more options but anything shared or potentially shared in the future and your likely stuck with the DNOs std policies

Not sure if NG publish such a thing but SPEN have online heat maps of their distribution networks showing where they have constraints for new connections(not domestic size systems) For each section of the network there's a contact email address so I just emailed that address and outlined what I had in mind. A junior engineer phoned me 2 days later, having already looked at the network serving us, and we agreed things over the next day or so. Formal application followed just to formalise what we'd already agreed. If your looking primarily to maximise self consumption then you may be best to go for a big system with export limitation as pushing the full 11kw down a single phase is quite a big ask. Its difficult to see how NG could say no if you implement export limitation and are prepared to go to zero for the addtional array and exporting only the existing 16amp

A G99 application is straight forward- download the form and have a look but there's a fee to pay. Our DNO(SPEN) was happy to look at an informal enquiry and we agreed our export limit by email/phone and then did the formal application. If you are tripling your array to 11kw remember that it's the inverters output you declare to the DNO, not the size of the array. You could hook up 11kw of panels to a smaller inverter and apply for the smaller inverters output. If you'll use all 11kw in the height of the summer then you could always go for an export limited system and do a G99/G100 application. That way you'll have the full 11kw available for self consumption but export as much or as little as your DNO will allow.

I guess it would need to be so it could power the critical loads/charge the battery from from the grid when there's no PV??

That's a grid tied set up with back up. The grid tie is the AC connection coming out of the bottom of the inverter then running to the left out towards the grid without any means of automatically disconnecting from the grid. If the grid goes off so does the inverters output to the grid and the consumer unit, so the consumer unit is dead. The inverter you are showing has a back up output for critical loads but needs a grid connection to operate fully ie power the loads off the main consumer unit. If the outbuilding supply came off before the CU, then its protected by the DNOs service fuse so a fault in the outbuilding would take out the service fuse(or fry the cable) and black out the house, likely for a long time until the DNO got out to replace the fuse. If you add your own fuse/mcb to protect the outbuilding cable then you might aswell have the outbuilding supply coming off the CU and not before it.

The OP is trying to avoid running another cable out to the outbuilding. If the existing is used for the PV DC therell be no AC supply to the outbuilding That's the way all grid tied inverters are connected as they shutdown when they loose their grid connection.

If you've paid a deposit to the kit designer, I assume you have a quote based on a fairly detailed spec. Fair chance you'll be able to do a pretty accurate heat loss calc off the spec/quote and know if an ASHP is in the running

Some things to consider- As ProDave mention volt rise could be an issue but you can mitigate it. Some inverters allow you to reduce power generation as the voltage rises. If you are happy to do this then pick the correct inverter. As loads are switched on in the house the house voltage will likely drop a bit so when measuring your base voltage do it with 1, 2, 3 and 4kw loads switched on to see how the base voltage varies at different load levels and the likelyhood of the inverter power throttling. If your no load voltage is less than 244vac, then likely you've not got a problem with voltage rise. If you've got a battery to charge that's local to the inverter then voltage rise may not be an issue if you are routing power to the battery and not down the SWA. As TonyT mentions, to charge your battery when there's no load demand from the house you'll likely need a CT on the supply leaving the house and need to consider how the CT signal will get from the incoming supply to your inverter/battery. You might be trenching If your battery is AC coupled then how are you going to limit the current that flows down the cable from the inverter and battery. If your battery is DC coupled are you sticking within the 16amp G98 limit. Ground mount PV has planning restrictions and I think you are limited to 9m2 without getting permission. You may not be concerned, but worth knowing the limitation. If you might extend the array in the future then base your design on the extended array size/location

As the client, the level of insulation and air tightness is up to you. Get your head round your energy saving options and tell your architect what you want- build to passive house or building regs or somewhere in between, but it's your call

You asked if you could use the existing SWA or needed to run another one and the answer is you can do either. Concerns over distance from the incoming supply for monitoring wasn't mentioned but why are you considering a dedicated SWA if you think the shed is too far away??

Connect wherever you like so long as you consider circuit protection, discrimination and voltage rise when the inverters at max production.

Sorry I read another thread and replied on yours!!!! Ignore me

If your existing inverter is a 3.6kw unit and you're thinking of adding micro inverters to the garage you'll need DNO permission. If you want to avoid DNO permission you'll need a single 3.6kw G98 inverter and wire each of the 3 arrays to its own mppt input, or use optimsers. If you're going down the DNO route then it's likely cheaper to install a dual mppt inverter in the garage, where your big loads are, and split the east and west panels over the 2 inputs. If the existing inverter has dual input then move that to the garage and get a basic 2 kw inverter for the house.

Quick Google search says Enphase IQ8s will handle 560w panels. Avoid the junction box if you can which should be doable with micro inverters.

If the garden room panels are on an east/west split the you'll probably want the east and west arrays on separate strings so you'll need 2 spare mppt inputs on the inverter and 2 loops of cable running down to the garden room. The mix of directions and shading would make your set up an ideal candidate for optimisers/microinverters

The prices you've highlighted are 2018 and 2021 prices. May not be quite the same as we've got now??

Maybe you are looking pre 2023? Just scrolled through what I think we're the N Scotland figures for 2023 and I could only see one instance from 1/4 to 1/10 where it went just over 24p. If you go beyond 2023 then you've got all the turmoil of the start of the current energy crisis

Where did you get the 2023 figures from? I've just looked at the N Scotland graph for the last 365 days and they don't go above 24p/kwh and the average looks to be low 20s??

For our MCS system only the MCS number for the panels is listed with no mention of the inverter so I suspect an inverter change won't matter to your MCS registration. Your DNO will definitely be interested in the new inverter to ensure its compliant with their grid standards, if its a change of inverter make/model. If the replacement inverter is the same make/model then you don't need to do anything. If its a change of make/model then you'll need to let them know the new inverters details and the new inverter will almost certainly need to be listed on the ENA database and be G98/G99 compliant. Check before you buy a new inverter! What's the original Inverters rated output? 16 amp/3.68kw or less? Changing the inverter is the same as changing a socket in the house ie anyone can legally do it. You only need a part P spark if you are adding or altering a circuit. If you were going to change the MCB for the inverter, change the supply cable size or increase the inverters power output, then you'd need a spark but a like for like change doesn't need a spark. Obviously work safely.

If your install has been done under G98, it's a notification that you need to do(have done) rather than an application- you tell them what you've done rather than ask their permission to do it. If your DNO is referring to a G98 submission as an "application", they're getting their wires crossed! If you Google G98 commissioning form, you'll find the commissioning form that you need to send them but it sounds like you've already sent it? Certainly for our DNO, SPEN, they don't seem to issue an export MPAN until all the paperwork is in place, they didnt for me at least! Last I heard from Octopus If you want them to buy your non MCS export you have to- pay them a £250 fee, get building control approval for the install, get a part P electrical installation cert, get a smart meter installed, get a confirmation letter/email from your DNO. With a 1.7kw system there's a fair chance its not worth it for the amount you'll export at 15p/kwh

Yep if you've got you're own and want to use it for luxuries like AC then fill your boots. But if you think the grids got plenty of spare solar on a sunny summers day that's a bit away from reality sadly

Unfortunately not. Have a look at gridwatch.co.uk to see how thin the yellow solar sliver is.

Google "Octopus tracker rate" and there's at least one website with the last year's rates.

You only know the future price 1 day ahead so you'll not know what a particular nights rate is until the day before. Historically I believe the tracker tariff has worked out cheaper than their standard variable price capped rate, but you take the risk that it doesn't stay that way!! I'm guessing that if the OPs use is only/mainly in the summer then there could be some quite low rates to be had??