Dillsue

We have a relatively new open vented DHW cylinder with indirect coils for solar thermal, WBS and LPG boiler. Were adding a 7kw Therma V ASHP and retaining the cylinder as its a waste to swap it out and there's no BUS/MCS involved. I'm going to try the HP using the existing boiler coil at .44m2 with a back up plan of adding a PHEX if the small coil doesn't work or becomes costly. We're currently on Octopus Go so can run the DHW overnight in the cheap period so even with a poor COP it's unlikely going to break the bank, but I would like thing to be as efficient as possible so..... The cylinder is 2 metres tall and I've got space to the side to fit a PHEX and tap into the CW feed at the bottom and HW outlet at the top with predominantly vertical pipework. What I'm pondering is if the circulation through the PHEX/DHW would work with gravity convection alone without its own circulation pump?? Anyone done it or know if its possible/impossible??

Here's solaredges take on bypass diodes https://knowledge-center.solaredge.com/sites/kc/files/se_technical_bypass_diode_effect_in_shading.pdf

There was a long thread on here a while ago on net metering and I think it was eventually shown that the net metering only works if youre exporting at exactly the same time as you're importing. If there's 1kw load on L1 and at the same time 1kw of export on L2 then no import or export gets recorded. If there's 1kw of load on L1 and no export on L2 then the meter starts recording the import. If the L1 import stops and 5 mins later 1kw of export starts on L2 it doesn't cancel the import already recorded on L1 Be nice if it offset total export against total import but that old thread suggested it doesn't. There'd be a massive scramble for 3 phase connections if it worked that way!

Got the tee shirt for the winter outage, with young kids at the time, and never been without a genny since. If you've got a working non electric heating system now, don't replace it but add a HP to it and use the existing system as a backup to the HP. Existing system will likely run off a small genny which will keep the heating, lights and telly going. Heat pumps are complex technology and it's you'll do well to get a quick fix if something fails so having a backup for power cuts and HP failure is a nice place to be, for me anyway:)

So even working with manufactures guidelines doesn't guarantee flawless operation. Interesting observation

Our therma v needs a minimum area around it of 2100mm x 1300mm for operation and that includes 700mm at the front for maintenace access. 700mm might be OK for a Korean midget to work on it but I used at least a meter to wire it. That would give an area of 2100mm x 1600mm before shrubs/fence/screen. That's quite a chunk of space in a small garden. It's a fact that some people find them intrusive in small gardens as our HP came from a plumber that had removed it and refitted a gas boiler for the very reason the new house owner didn't want it in their garden!!

In your shoes I'd have no problem putting it on the roof as it's just like the 1000s of AC units on all manner of buildings. My only reservation would be having it bearing on the roof below with the risk of vibration being transmitted through the roof. As you suggested I think I would hang it off the wall or or on a pair beams spanning the roof and supported by the wall either end. At the distance it is from the neighbours, I don't think I'd even mention it to them

Isnt a large part of our energy woes the fact that Joe public neither understands or cares about the realities of energy generation or delivery?? Having to pay a bit more attention and understand the cost and effort of delivering power at peak times might help reduce peak demand??

Borehole=eureka! I'm currently battling with Hafren water over a 76% rise in water only supply over the last 5 years and 100% increase if I include the current bill. A borehole sounds a dream come true but I guess there's a fair wedge of an outlay.......and regulation?

Not sure about that. The DNO will know local grid demand and supply characteristics which the suppliers won't. I think its more likely the DNOs will be managing any grid balancing, maybe via suppliers, but it would be the DNOs calling the shots?? It's not just the total number of EVs that influence this, it's the number of EVs that support bi directional charging, and those where the owners have bought a bidirectional charger, and those where the owners have gone through G98/G99, theres more to it than just owning an EV. Whilst a growing number of EVs may support bidirectional charging I think it only going to be a (small?)proportion of owners that set themselves up for V2G, under the current framework. Maybe in a few decades once ICE cars have gone and there's greater public understanding and incentives to hook up your cars battery to the grid will things need managing differently

Aren't we in that situation now with home batteries that can be exported whenever the user chooses? Given that a V2H/G charger will either have a G98 cert or need G99 consent it's likely DNOs will be limiting or involved in what can be exported?? If thats to be a variable limit then I would guess it will be DNOs controlling chargers rather than suppliers???

Could be, I don't know the details of V2G and if it's entirely regulated externally or can be forced to export by the user??

The CHADEMO interface is very limited in Europe and I don't think any new cars are using it. I think any V2H/V2G development in Europe uses CCS. As I understand it any charger, home or commercial, is specifc to the interface. I think there's someone who's developed and CADEMO plug/interface that can draw on the cars battery but I think it's a Fred in a shed job and quite expensive??

Might be mistaken but I understood V2H and V2G were the same but V2H had export limitation set to zero??

Gen 1 and 2 leafs use CHADEMO for bidirectional charging and I don't think anyone is likely to develop any more V2X kit for CHADEMO in Europe. I've been fruitlessly looking for an ex trial V2X charger but those that come up are expensive and seem to be locked to the original trial?? I think there's hacks that involve altering the car but how reliable/safe/legit they are is anyone's guess....the US one I saw wouldn't cut it over here

Yes. If you want to implement export limitation you need an inverter with G100 certification. I think someone posted on here recently about Multiplus not having a G100 cert but it may have been a specific model?? You can do export limitation external to the PV inverter but it's a specialist field likely with special price. Have you spoken to your DNO about what export limit they are likely to allow? We have consent for 7.4kw so we could use a 7kw inverter and wouldn't need to bother with G100, we actually use 2 x 3.68kw. Fair chance a 7kw inverter will accept your 10kw of panels particularly if they aren't all facing the same direction.

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?