Dillsue

Remember that the 5kw is the heat output to the house. What youre interested in is the energy input as that is the electrical load. If you're heating the DHW to a high temperature on a cold winters night you might get a terrible COP of 2 so the electrial input will be 5kw/2 = 2.5kw. That's the worst case load your 5kw heat pump is going to draw, not the 5kw output. For your workshop all your equipment will only draw the rated full load power when it's working at it's hardest....under full load. Unless you're an Octopus you'll only be drawing full load on one machine or the other. The machine left running will be drawing a fraction of the full load. The only significant continuous load will be your EV charger but you can schedule that to run over night when the only other load may be your ASHP and a few hundred watts background load for the house. 7kw +2.5kw + 0.3 = 9.8kw overnight load when the ASHP is working hard. Like you we have double ovens and an induction hob but once heated all of those switch intermittently so they will only ever draw the full rated load if they are all switched on at once. Diversity says that won't happen but if it did its unlikely to cause a problem as you're still well away from the 25kw supply rating. Occaisional realistic daytime load might be 1 oven, 0.5 hob, 1 workshop machine working hard, 1 workshop machine running idle, ASHP, house background = 3kw + 2kw + 2.2kw + 1kw + 2.5kw + 0.3kw = 11kw. That's less that 50% of a 25kw supply

If that's a daily variation not linked to changing seasons then using a flat average consumption as you done will likely be fine. On the other hand there's 25% difference in the 2 figures and if those are seasonal highs and lows then probably best to put the high figure in for winter months and the low figure in for summer months. As JohnMo suggests you'd probably be better using PVGIS for your generation forecasts as it takes into consideration lots of variables in producing it's predictions. If you are using daily snap shots of irradiance they're unlikely to represent irradiance for the rest of the day or what is actually hitting the PV panels as the sun moves round and up and down. PVGIS has repeatedly been shown to be pretty accurate.

On the mainland we have the Smart Export Guarantee which is government backed/regulated and pays a pittance. Octopus SEG rate is around 4p/unit which they are obliged to pay for export from a qualifying system. Octopus will also buy your export under a separate unregulated agreement and they currently pay 15p/unit on their fixed export tarriff which is a Power Purchase Agreement. Theres no obligation to offer a PPA and it could go up, go down or end due to market conditions/insolvency. That's almost a four fold difference In Octopuses rates. If export payment is important in your friends calcs then you probably need to find out what he'll get and any conditions attached to receiving those rates

Are you sure he uses the same every day all year round? If that's the case then you already have the figures in your spread sheet. If that's not the case and his usage varies then you'll likely export more in the summer and import more in the winter. Because of the difference in unit rates between import and export your figures won't be quite so rosey

How big an array you install is a personal thing dependant on lots of factors that vary in importance from person to person. We installed an additional 8.5kw of panels a few years ago on top of the 4kw we already had. No battery for us and no export payments at the time. All self installed and kit bought at discount prices. Having plenty of "free" eleccy and happy for the neighbours to use our surplus is a good enough ROI for me. Octopus now buy our surplus so a big dollop of unplanned icing on that cake:)

Will your neibours demand profile match the generation profile? Usually there's a big seasonal mismatch because you generate the most in the summer but use the most in winter. Total annual Generation can match total annual demand but because they peak at differing times they'll not balance out.

You're right that businesses can behave like that and have unbelievably biased Ts and Cs that they will throw in a customers face and stick 2 fingers up to complaints against them. Fortunately there's a piece of consumer law called the unfair terms in consumer contracts regs that effectively remove unfair terms from a consumer contract thus holding a business accountable if they've not delivered a service they've provided with reasonable care. Once the OP has worked out if he has a single or multiple contracts then anyone trying to hide behind biased Ts and Cs and shirk their responsibilities should be referred to said legislation.......it does work:) It's alway best to resolve things amicably though

G98 is factory limited to <3.68kw. Anything >3.68kw is G99. Anything >3.68kw that can be installer/user export adjusted is G99+G100 3.68kw is a fair bit of power and there's lots of G98 inverters that can have much more PV connected than 3.68. Solaredge allow 100% oversizing so their 3.68kw inverter can have 7.4kw of panels connected, and much more if the panels are facing differing directions. We have 8.5kw hooked up to one of our 3.68kw inverters but the panels are facing 3 differing compass points so the peak is reduced but generation is for much longer

The display on the front of our meter shows import and export readings. The In Home Display shows the import reading but I've not found an export reading. Can't see why the IHD couldn't show the export but maybe it just needs setting up?

If you go for a larger than 3.68kw system but export limit it, you can draw what you want but just not export it. Save peeing around with a second off grid system and the headaches that could come with 2 differing systems.

?? You said you can export all your PV through one hybrid inverter so its AC output likely powers the house/grid and would have your FIT generation meter in the output?? Maybe you've got a FIT system inverter feeding the hybrid inverter via the FIT generation meter??? I seem to remember you've got a complex system??

Unlimited export?? Are you sure it's unlimited? Why wouldn't you need to involve your FIT provider if you've increased your TIC?

Depends is the honest answer. If currently on a combi then you'll likely need a new DHW cylinder. If your emmitters are predominantly radiators then there's a fair chance some or all of them will need replacing/swapping round or additional ones fitted. To get the best out of the ASHP system you want accurate heat loss calcs so the HP and rads can be sized correctly. Having excess solar is primarily a summer issue so will likely have little impact on the economies of running a HP predominantly in the winter. Finding someone who can design and commission a system for you may take some doing. My advice would be spend a good while researching how to get HPs to work efficiently and what constitutes a well designed/commissioned system before you start talking to suppliers. You'll be better placed to know if they know what they are doing!

For G98 compliance the inverter must be factory limited to 3.68kw and manufacturer certified as such. If it can do more but you limit it to 3.68kw then it's not G98 compliant. It then needs a G99 application plus a G100 supplement to cover the set up of the export limitation. My very limited experience of G99 is that it's straight forward and worth the effort to get consent for the max your local grid will support. Imagine export payments being £1 a unit and your neighbours had grabbed all the spare export capacity:)

There's a circulation pump for the secondary/cylinder side of your PHEX in the schematic you've not long posted????

Isnt that the same as heating an indirect cylinder via an internal coil?

No idea if cool energy provide this but on post 2020 LG Therma VS there's two inputs for thermostat control, one to call for heat and the other to call for cooling. Might be worth having a trawl through the cool energy manual to see if they provide similar

Thanks for that. Hopefully Dave can share how he's "powering" the cylinder side of his PHEX without a pump.

So PHEX I'd heating the DHW whenever the HP is running regardless of which way the 3 port is routing flow?? Intrigued to know how flow is achieved on the secondary side of the PHEX feeding the cylinder- gravity?? The coil we have available in our cylinder is undersized for our HP so looking at options to get HP energy into the cylinder without replacing it.

Doesn't the intelligent version of Go need Octopus to control your EV charger to get the very low unit rates? How would that work if you're adding your own, presumably uncontrolled, loads such as night time HP running?

It gets quite complicated and eveyones circumstances are different!! You don't automatically get paid for export as you need MCS or jump through a few hoops to get a non MCS system accepted for export. Either way there's ££s to pay. Without export payments then diverting to DHW could be beneficial. I specifically said intermittent PV as you can't run a heat pump on intermittent PV without a significant draw off the grid. Heating DHW overnight is fine if a TOU tariff works for you. We're on Octopus Go so we get 5 hours cheap overnight but pay a premium unit rate the rest of the time. We want to run weather compensation on the HP I'm putting in just now so for 19 hours a day we'll be paying premium rates to run the HP. If we went for Octopus Cosy then we'd lose the heavily discounted EV charging period and only be able to run the heat pump intermittently on cheaper eleccy. Again we'd be paying a premium outside the cosy periods and a big premium to cook tea! Buying a cylinder with a lower immersion boss defers making complex decisions now and gives flexibility in the future

If you're only going to heat DHW with a HP then you'll likely only need a pocket for a temperature probe. If you've got or might get solar PV then a second immersion lower down the cylinder allows you to divert excess solar into the cylinder when the solar is intermittent

Google "heat geek" and get a local guy to do detailed heat loss calcs for you. Youll need to pay for it. Be very wary of accepting a heat pump much larger than the Heat Geek calcs- running costs could be massive if you significantly oversize the heat pump

Octopus didn't ask us for proof of an EV but only wanted the model. I think its fairly easy for them to see the load profile during the night time cheap rate but whether they monitor that is anyone's guess??

If the meter is supposed to be read every half hour and they miss a few half hourly slots or a whole day/week then surely when they eventually capture a read everything will even out?? Won't show you half hourly figures but you'll not miss out on payments for total export?? Not sure if every smart meter displays it, but ours shows total export so probably best to take a reading every so often if you don't trust remote readings from Octopus??