Dillsue

An option to resolve all your queries would be to get a secondhand unit and play with it then either use it yourself or resell as a proven working unit. Ours is secondhand and I hooked it up to a 45 gallon drum of water to confirm it worked. Not sure what options you've got in Shetland but you can pickup HPs with controllers for a few hundred £. Maybe your installer would have a unit you could borrow?? Ours had been removed because the new householder didn't like it in their small garden and the installer who removed it and refitted a gas boiler wanted shut of it.

I'd guess as a backup for a failed HP a log stove with fireplace/chimney/flue/wood store/logs/back boiler etc isn't gonna be any cheaper than a boiler and oil tank/propane bottle?? Needing only a small genny to run either means another few hundred £ saved to use a boiler or WBS also as a back up for a power cut rather than a larger genny to run the HP.

Your 4 days trumps the max 3 days we've been without power. That 3 days was over Xmas a long time ago but it leaves a legacy of us always having a backup for essentials.

Maybe not for you but our 2.2kw honda unit is as much as I'd want to carry around when the lights go out. A backup heat source other than the HP also covers you for heat pump failure.

Whether you have back up heating or not is entirely down to individual circumstances. Unless someone's in the same circumstances their needs/wants are unlikely to be the same as yours. A heat pump requires a fairly beefy supply and would need a beefy generator to keep it running, an oil/lpg boiler wouldn't so a small generator and a few gallons of fuel will keep the heating and lights running for days. If there's a major storm which are likely to get more frequent and youre on a remote supply then you could be off grid for days which a typical battery bank won't cover. If your in an urban area sharing a supply with 1000s of others you'll be top priority for repairs to get you back on supply. If you're remote and share a supply with few other houses you'll be lowest priority to get back on supply. That's how the DNOs prioritise things when dealing with widespread storm damage. I don't know how the Ecodan interfaces to a back up boiler but the Therma V that I'm installing just now provides a volt free contact to enable a backup boiler to run. The configuration seems to allow the outdoor temperature value to be set that shuts the heat pump down and activates the boiler contact.....the manual isn't the best written but that seems to be what it says??

So are they all on their own DNO meter and have their own MPAN? How many flats are there?

Page 65 is within the section on eligibility criteria for FlT installations/payments and I read that as applying only to the FIT accredited part of your installation?? The section on extensions talks about accredited and non accredited installations and the tariff rates you are entitled to on p23 section 3.18. It gives 3 scenarios which I read as follows- Original accredited installation-MCS, entitlement to FIT tariff(80% in their example) Extension accredited installation-MCS, no FIT entitlement but entitled to SEG tariff(20% in their example) Extension non accredited installation- non MCS, no FIT or SEG entitlement. (20% in their example) You may get PPA from Octopus and Co., but no entitlement to anything. These 3 senarios suggest to me that self installed/non MCS extensions to a FIT system are allowable An inverter swap may impact DNC but not TIC which is driven by the panel capacity, as I read it! You'd be increasing the TIC if you added panels so wholly notifiable as an extension. From what's on our original MCS cert the G98 limit is what defines the DNC. Our FIT install has 4kw of panels and a declared TIC of 4 kw. The inverter is limited to 16amp so the DNC is declared as 3.68kw. Yep!!

I dont believe that MCS is required for any alteration or repairs/replacement to a FIT system. As an example, if you extend a 4 kw system by 4kw to give an 8kw system you get paid FIT rates on the original 4kw. If the 4kw extension element is MCS installed you can claim SEG on the extension. If the 4kw extension isn't MCS certified then you can't claim SEG but you could get paid under a PPA by the likes of Octopus. It's all in here https://www.ofgem.gov.uk/sites/default/files/2024-09/Guidance_for_FIT_Generators_V18.pdf

If your inverter supports it or you can change it for one that does, I believe you can DC couple within the FIT rules. If you can charge from the grid and potentially export it again through the generation meter then you need to replace your generation meter with a bi directional meter that gives a net reading so the net reading only represents the PV generation.

Have a look here https://www.ofgem.gov.uk/sites/default/files/2024-09/Guidance_for_FIT_Generators_V18.pdf section 5.6

Ouch. Through all that sunny weather too!

It is the lower value but definitely worth checking your own figures before jumping from deemed to metered as you can't go back for 12 months. One of our systems is 4kw on 2015 FIT rates and it's only because we have a second self installed system that it was worth giving up the deemed element from the 4kw system and going for metered export from both systems.

That setup needs prior approval via a G99 plus G100 to cover the setup of the export limitation. I think there's an awful lot of inverters that support export limitation but unless the limit is factory set to 3.68kw and G98 documented as such, then you need consent before connecting.

Yes...I missed the presence of 3 phase! If the 3 phase inverter distributes the PV equally over all 3 phases but the house loads aren't evenly balanced across the 3 phases then it may be more beneficial to have a single phase inverter hooked up to the phase with the bulk of the load on it??

Hopefully you're aware that if you want to connect an inverter greater than 3.68kw output you need prior permission from your DNO so a 5kw inverter is a no no without approval

SEG is a government backed scheme that typically pays 4-6p/unit. The 15p/unit rate is a Power Purchase Agreement ie a contract between you and an eleccy company. There's no government involvement/backing and in theory could end at anytime. Lots of people including me sell under a PPA but best that you understand it's different to SEG

Your FIT generation payments won't get affected by switching to a smart tariff. If it's an export tariff then you'll loose your deemed export but still keep the lucrative generation element.

Putin added a bit of fuel to the fire that was already raging with post covid recovery....we were on our 4th eleccy supplier when Russia invaded!!

The SEG is the governments replacement for the FIT scheme but... only pays for actual export and pays a pittance per unit, typically 4-6p/unit. Being on early FIT rates you might be best sticking with your generation and deemed export payments but if you know what you'll likely export in a year you can run the figures. Octopus Outgoing will pay you 15p/unit based on actual export from your smart meter. I don't know what deemed rate you get but you'll probably be better off sticking with what you've got??

Don't you want to export everything you can and charge the battery and hot water overnight on the 7.5p rate....assuming your battery and DHW tank are large enough for a days use??

And watertight insulation if its going underground

I think there's a bit of a difference between a light switch and a thermostat.....one is used frequently through the day and the other is/should be used infrequently. If it's a digital stat then it needs to be at viewing height whereas a switch definitely doesnt want to be that height. If everything was put within easy reach of a wheelchair user/kid then where does that leave the likes of my son in law who's 6'4" and would need to kneel to see a thermostat positioned for a wheel chair user. Its your house so put the stat wherever best for those who are going to use it. Leave a bit of surplus cable in the back box so future owners can lower it easily if they want to.

I think with the Octopus non MCS option you pay £250 to join but get back £100 if they reject you?? How lucrative it is depends on your own circumstances but we'll hopefully be around net £0 over the year for eleccy, so well worth it for us and no batteries needed:)

Without knowing what lies over the boundary, my thoughts would be- Sticking out from your wall 3m up in the air sounds very prominent and may not be to everyone's taste including your neighbour or any future buyer of your house. There's quite a blast of cold air blowing out of most units so think how this might affect your neighbour. Remember that there is statutory nuisance legislation that will trump planning rules. Maintenance access is usually from what would be most installations boundary side ie the side furthest from your house. Typical HP needs 300mm gap from your wall and are min 300mm deep. This would leave 400mm Maintenance access before you needed to work from you neighbours property. Be sure that you can get access for maintenance and repair

When they know in advance then that's probably true. If they're asked to be on standby then it's probably also true. If they need to start unexpectedly then it can take a long time. The turbines have to be gently preheated with steam which I beleive takes hours or maybe days if starting from stone cold. Before you can pre heat you have to get a boiler house up and running to provide the steam for preheating Even if you only want gas generation for an hour or two at tea time each day there's a full team at work round the clock and boiler house running 24/7 keeping the turbines warm for the couple of hours they're needed