The Boy That Cried PV Extension

[dan_b]

Aah yes my original 4kWh lead acid PowerVault install which I got as part of a DNO trial - I’m gonna say 7 years…. After replacing the batteries twice it’s been left to die. But goodness me I learned a lot

[Mart]

Just a quick update on the system and PV extension.

Problems persisted with the two new batteries. Eventually Solaredge decided they needed to have a look. Took a long time, but last week an engineer arrived and was able to get battery one talking to the inverter again, but battery 2 was still unable to complete the handshake procedures, so needs to be replaced.

But, it's all good (long term), I'm back to having a battery, which is enough (10kWh) to get me through Sep, possibly to Dec, but will need both batts to get through Dec-Feb, without needing to import dayrate leccy. Or to be clear, any significant amount.

Have been running one of the A2A units through the cheap night rate period, and haven't yet had to use the GCH. Last night I changed the battery settings to charge during the cheap rate period. This plus the second A2A unit, and hopefully a second battery (soon), should mean I can delay GCH as long as possible. Certainly hoping to get through October, maybe Nov, but will depend on how cold it gets. A fun challenge, and at the other end, as PV gen rises, temps too, and the related COP, maybe the GCH can go back to sleep when Mch arrives.

Time to switch to night rate (from excess PV) for BEV charging now.

Overall, looks like PV, A2A, BEV, batts and cheap rate make for a very good package, each boosting the benefits of the others.

[Fintray]

Overall, looks like PV, A2A, BEV, batts and cheap rate make for a very good package, each boosting the benefits of the others.

It is a good feeling when it all comes together and you have a comfortable house and it's not costing a fortune to do so.

[Mart]

Battery 2 was swapped last week, and the new one was happy to chat with batt 1 and the inverter. Finally.

So far PV is just enough to allow for poor gen days, and a fair amount of A2A use. 6hrs of cheap rate is enough to full the batts, and that should be enough for 18hrs of average demand, plus both A2A units running.

Hopefully last update on the kit, though I will be looking to see how my gas consumption changes over the winter/spring, and also consumption of daytime rate leccy, since in theory that could be reduced to zero. In reality looks like ~10kWh per month will sneak through, be it demand higher than the 3.68kW inverter, or induction hob / microwave phasing. So excellent (theoretical) position going forward.


@Fintray, yep, it looks like it's all coming together ........ famous last words.

[Mart]

Small update on plans here, I was chatting on a thread, and then pondering with some forum friends about my plan to get a small leccy boiler to fill in the gaps when my A2A units won't cope.

It had finally dawned on me, that a leccy boiler heating water via resistive heating, to pump round the house to heat radiators, was very similar to just popping some oil rads in the rooms, where needed, and when needed. Simple and cheap.

So, I'm going to experiment this winter, to see how little GCH I need, or even perhaps avoid entirely. That should let me know what my options are going forward, almost certainly involving some immersion heaters for the towel rad in the bathroom, and maybe the kitchen.


So .... this leads me on to thinking about the DHW side. The plan was to get a HW tank when changing the boiler, but I could maybe move sooner now. But I'm not sure exactly how it all works. [And there might not be enough room in the airing cupboard without removing the gas combi. I can increase the cupboard size, but a bit pointless if I'm maybe removing the boiler.]

I have looked at clever tanks, like Mixenergy, and also heat pump HW tanks. They all seem great, and I have the money, but, as we don't use much DHW, perhaps 100kWh of gas consumption per month in the summer, so given it's a 1998 combi-boiler, I assume 80% efficiency at best, probably much lower, as it will be working from cold to heat DHW, so less than 80kWh per month?

So is it silly to look at expensive but clever tanks at perhaps £2k, or should I just go for a simple tank with one or two immersion coils, such as something like this purely as an example. The HW tank will be in our spare bedroom / gym / foster room, so during the heating months, any heating loss (1 or 2kWh(t) per day?) will be a benefit.

Whatever I settle on heating wise, I can't see us not needing the HW tank, so it might be something I can move on quicker. Is a HW tank install complicated? I'm lucky to have a retired electrician neighbour who is a close friend, and he has a plumber friend around the corner from us.


Another question for sparkies, rather than running new power to the cupboard, would I be able to take advantage of the loft ring main somehow? It actually runs up the wall at the back of the airing cupboard, through the ceiling into the loft. We don't use the loft much at all, so could I 'steal' that power, and spur off to the loft from it?

I think a ring main is 7kW?, So if we powered the tank on 2-4kW, would a 3kW spur for the loft be a safe and correct way to do the job, or am I suggesting something stupid/dangerous?

[Countrypaul]

Mart,

You are suggesting a HW tank that will lose round 2kWh per day so close on 60 kWh/month to provie 80kWh of HW per month with a tank costing £600 (though Gledhill seem to do ine around £400). An inline HW heater suchas https://www.toolstation.com/ariston-aur ... ter/p82443) costs only around £100 and would avoid the standing losses of a HW tank.

Installing a HW tank oi not difficult if you are any good at plumbing, but I think unvented ones require "G3 unvented cylinder qualification" which probably means more expense. I have installed an vented indirect tank and a some of vented thermal store, the former ws very straigh forward, the latter much more involved (but has at least 12 pipes, 2 TMVs, PRV, and 3 immersions) so I did have the help of a plumber

[SporranMcDonald]

Small update on plans here, I was chatting on a thread, . . . . <snip>

Having just read the above. I wondered if you had considered a DHW-only heatpump to complement your A2A units.

It's not something I'm considering as I use minute amounts of hot water ( and don't want a tankful sitting around here ).

I follow this YouTube Channel ( below ) in which Tim & Kat have A2A units for space heating and have replaced the gas-fired DHW for a Mixergy iHP.

https://www.youtube.com/@TimAndKatsGree ... ry=Mixergy

Best to search through the set of relevant videos, depending on where you need to start with this subject.

[Stinsy]

Small update on plans here, I was chatting on a thread, . . . . <snip>

Having just read the above. I wondered if you had considered a DHW-only heatpump to complement your A2A units.

It's not something I'm considering as I use minute amounts of hot water ( and don't want a tankful sitting around here ).

I follow this YouTube Channel ( below ) in which Tim & Kat have A2A units for space heating and have replaced the gas-fired DHW for a Mixergy iHP.

https://www.youtube.com/@TimAndKatsGree ... ry=Mixergy

Best to search through the set of relevant videos, depending on where you need to start with this subject.

I’ve looked into DHW HPs and decided it isn’t worth the cost/complexity vs a cylinder, immersion, and ToU tariff.

[AGT]

Immersion heaters need to be on their own radial circuit not off a socket circuit..

[Mart]

Thanks guys.

@ SporranMcDonald Yes, I have considered a HPHW tank, in fact that's were I was leaning before. Such as the Mixenergy HP model. I kinda fancy the high tech, efficiency idea. Wanted one with internal or external venting. So in the summer months it could actually cool the house down a bit. But when I realised it would be £2k+, v's perhaps £500, it dawned on me that it would never payback. And introduced additional equipment to fail. Hence why I'm now starting to work backwards looking at other ideas.

@ AGT. Thanks. Does that include having the immersion on its own circuit, but the circuit having a spur coming off it? I was wondering if that was some sort of cheat? So take the 7kW ring mian for the loft, turn it into a 'ring main'? for the immersion, but spur off it for a lower power (3kw?) ring for the loft? Maybe I'm just talking nonsense?

To describe it another way, where the cabling goes up the back of the cupboard, if I cut off the loft, then it would now be a dedicated circuit, with no other users, presumably that's fine. Could I then take a spur off that 'immersion circuit' for the loft? In reality, the tank would probably only need 2kW, maybe 2x 1kW.

@ Stinsy. Yep, our low(ish) demand is why it dawned on me that a basic tank possibly makes more sense. Charged from PV for ~7months of the year, and cheap rate when PV gen is lower.

@ Countrypaul, thanks, I hadn't actually thought of that. You are right that 60kWh of loss is a lot when you add a month's worth together. But that room does get a bit cold, especially with the door closed (when we have a cat like our foster Cookie in there). I'm hoping it will improve a bit with the door open, and heat leaking up from the A2A units downstairs. But even so, it's where I expect to deploy a small oil rad as temps drop, ideally running mostly off cheap rate. So during the heating months it will be fine, just leaked resistive heating from the tank, v's deliberate heat from a rad.

The summer waste is a concern to me, but it's OK from an economical point (not sure about environmental) as I will now have spare PV gen Mch to Sep, and it simply coming out of my ears Apr to Aug.

So the issue I think is simply the cost of the leccy for the 'no waste' option, since it looks like for showers, the in line heaters are around 7kW to 10kW, and the PV/battery inverter is 3.68kW limited. So we'd be buying 50%+ of the leccy at day rate prices, rather than night rate, or PV. But I feel like I'm trying to justify some naughty waste now.