The Boy That Cried PV Extension

[Joeboy]

Thanks. Chaser sent. I do have two FiT accounts, so that may have confused the hell out of them as I sent 2x the documentation requested, so to speak.

In all my comms with them, I kept it simple and made sure my account no and any other pertinent ID info was in there. Help them to help you style of thing. Did you do the intial query through the front door application process?

Yep. there was a list of steps you had to answer and for some attach copies of documents.

Hopefully they'll let me know how it's going. But ironically ....... once I'm on their export rate of 15p, then it makes more sense for me to export excess, rather than charge the BEV. Then charge the BEV on cheap rate at 7p. That means my annual import will increase, which makes complete sense, but also spoils all my attempts over the years, to steadily reduce the amount of leccy I import.

But I have been recording 'consumption' for several years, not just import, so that will remain the same. Or will it, oh no it won't - as I'll use more cheap rate to run the A2A units, and charge the batts in the winter to run the A2A's during the day. So more import and more consumption ...... but less FF gas.

All good fun, just need to get used to the new normal.

I get those thoughts, had them myself. We are consistently importing 28.8kWh through the night and outputting up to 60kWh through the 18hrs when other humes are up and about. I'm glad to hear you prodded them Mart. Gas consumption is a good datum point to progress as it can get trippy when old solid number trends become irrelevant.

Although the more of us that are charging stacks in our WT generation areas overnight the better those WT's have of staying online and generating 24/7.

[nowty]

It is indeed a totally new normal and gets a bit of getting used to as I'd gone over a decade to get my import to as low as possible.


June 2023 on deemed export made me less than £15.
Note the high direct consumption, very low import and reasonable export.



June 2024 with paid export made me over £250 net of all import costs.
Note the low direct consumption, high import (all cheap rate) and extreme export.
All I've lost is about 20 extra battery cycles and more harder battery inverter running.
Even if the export drops to say a more realistic 8p / kWh, its still worth it, but use strategy will change again with less pump and dump, so easier on the batteries and battery inverter.

[Joeboy]

It is indeed a totally new normal and gets a bit of getting used to as I'd gone over a decade to get my import to as low as possible.


June 2023 on deemed export made me less than £15.
Note the high direct consumption, very low import and reasonable export.


June 2024 with paid export made me over £250 net of all import costs.
Note the low direct consumption, high import (all cheap rate) and extreme export.
All I've lost is about 20 extra battery cycles and more harder battery inverter running.
Even if the export drops to say a more realistic 8p / kWh, its still worth it, but use strategy will change again with less pump and dump, so easier on the batteries and battery inverter.

Congrats, mighty figures indeed! I'm going to play for logs this Winter. Not as a true per kWh comparison (that would be unwieldy) but instead as a rough end of season picture showing to the best of my ability the carbon not burnt.

My version of "The Game" will take as given the RE purity of the Octopus model, coupled with Ripple generation and I'll Game that through Winter 24, fully utilising the network technology and hardware I have to hand. I've eliminated gas from our homes in Scotland & Turkey. Those were excellent victories but done now, time to move on. I am genuinely enthused at what we can do to reduce the Winter log consumption in Scotland.

Size of the woodpile post Winter is pretty hands on tangible for progress.

Last year we finished with 3/4 of the lower store being untouched (About 3.5T). The year before that we tanked that store fully so the correct trend direction is already there.

I have strong hopes for this year and will continue solar log prep & splitting when I get home so we begin as close to like for like as possible.

[Mart]

Big surprise yesterday, the sun was out and the back of the house PV (ESE + SSW) were doing their thing. I honestly thought that a sustained peak (2mins+) of ~5kW was the best I could hope for*, and would be great too. But the system was in the high 5's and low 6's throughout late morning and early afternoon.

Only just caught it in time, telling the battery to discharge as the gen rose, to get some space, but even with export at 3.68kW through to 3.30pm, the battery still rose to 98% ....... but no capping. Result.

So what I was told was correct, the 3.68kW inverter can handle a sum of DC and AC greater than its rating. Up to 5kW DC is possible, and at times yesterday there was 3.68kW AC and nearly 3kW DC too.

Installer team are here again now, still trying to get the inverter to chat to two batteries, but they (and the tech support at Solaredge) are still a bit baffled.

But once both batts are working, it should be far easier to avoid capping, so long as there's enough battery space, and the inverter is told to discharge. So working very much as hoped, but that's rare in life!


*I'd guessed at 5kW, based on the 6.7kWp of PV being spread roughly in thirds across ESE 30d pitch, ESE 20d pitch & SSW 60d pitch. So a tad under 80% of nameplate, when hot, seemed reasonable. Yesterday wasn't extremely hot, cooling winds, and some clouds, probably all helped.

[Mart]

Quick update, looks like there is a fault with the second battery. Not great news, but it is what it is, and at least the problem has now been found.

Not sure how long it will be before the batt gets replaced but it's not the end of the World, and with the extra PV capacity, I should be fine till Oct/Nov when I might need the whole 20kWh capacity for running the A2A units during the day, to reduce GCH use.


Now on to the next project - space heating. Do I go all in with ASHP, but with low gas consumption already, and the A2A units, maybe it would be simpler to just add a small (5kW?) leccy boiler, and a HP hot water tank. Decisions decisions.

[Moxi]

Quick update, looks like there is a fault with the second battery. Not great news, but it is what it is, and at least the problem has now been found.

Not sure how long it will be before the batt gets replaced but it's not the end of the World, and with the extra PV capacity, I should be fine till Oct/Nov when I might need the whole 20kWh capacity for running the A2A units during the day, to reduce GCH use.


Now on to the next project - space heating. Do I go all in with ASHP, but with low gas consumption already, and the A2A units, maybe it would be simpler to just add a small (5kW?) leccy boiler, and a HP hot water tank. Decisions decisions.

How longs a piece of string Mart ? If the A2A Hp's do the job why keep a wet system of radiators in the house? For DHW that depends on how much you use as to what route you go - I'm guessing you can isolate the house from the grid and run on batteries in the event of a power cut - if not then do you have alternate means of staying warm on the off chance of a power cut of any reasonable duration ? Your circumstance might be best suited with a simple immersion heated hot water cylinder that can tie in to cheap power slots on your preferred tariff - I say could as there's lots of variable not known.

Good luck tho - I have spent nearly 18 months so far agonising over the pro's and con's of various options.

Moxi

[Krill]

Direct electric heating of water is dreadfully expensive. If you are going to have a water tank anyway really do look at an ASHP.

[Moxi]

Direct electric heating of water is dreadfully expensive. If you are going to have a water tank anyway really do look at an ASHP.

As I said it depends on Marts requirements installing £7,500 pounds of ASHP buys a lot of cheap rate units of electric if DHW demand is low it might be a better route for a basic 100% efficient immersion? We don’t know until the details are specified. An ASHP integrated cylinder can work as well depending on requirements but then so could some old fashioned reliable vacuum solar tubes and quite a few here know how good they can be.

We will need to see what Mart needs before we can narrow things down.

Over to you Mart

Moxi

[Krill]

Yeah, they can be be many partial solutions that add up. Immersion heater with a tank is one thing but the electric boilers that do central heating are extortionate to run, and aren't really any better for showers. That's the one I was getting at.

[Mart]

Direct electric heating of water is dreadfully expensive. If you are going to have a water tank anyway really do look at an ASHP.

You are absolutely right, and so is Moxi.

I'd suggest everyone go the ASHP route in general, but the key word(s) there is in general.

Our gas consumption is now down to about 6,000kWh's pa. During the non-heating months we use about 100kWh pm, for DHW and cooking (oven), so that takes space heating down to under 5,000kWh. Next, I played with running an A2A unit throughout the cheap night rate early this year, and was surprised how well it did. We also use the A2A units to reduce some GCH during the day when there's enough spare solar to avoid expensive day rate leccy. Didn't need any GCH in April this year, as the night rate A2A plus some solar matched (back to this crucial bit) A2A was enough.

So, fast forward, and if:
1. I run the A2A throughout the cheap periods during the whole winter, now I know it works, that should further reduce gas consumption.
2. Bigger PV system (I may have mentioned it once, but I think I got away with it), will mean more excess PV for A2A use in the spring and autumn.
3. Batts will significantly improve A2A use, as I was often exporting spare PV, but not quite enough to avoid expensive day rate top up, so I didn't use it. Now I can use the cumulated excess.
4. Batts will allow me to run the A2A units throughout the day, in the winter, by storing cheap night rate for daytime use. the 3.5kW A2A units consume about 400W on average (each), so that's around 14kWh across 18hr day rate leccy (ignoring any PV generation which in Dec/Jan will be needed for household use anyway).
5. I take the DHW off the gas, be it a leccy HW tank (charged at night), or a HPHW tank.

I should be able to seriously dent that 6,000kWh figure.

I'm still a true believer in heat pumps, but ..... is there a point where it's simply better to consume a bit more leccy, than go the whole hog ..... I genuinely don't know, it's something I'm wrestling with.

I should also add that Octopus aren't doing HP's in Cardiff yet, and many quotes I've looked at have been over £10k (£2.5k after subsidy), plus the problems with planning permission, and the disruption as our house isn't quite simple, but nothing too bad I'm sure.

Balanced against that, I was just doing the most basic Googling and finding very small and cheap leccy boilers in the 4kW+ range. So I did ponder how I might be able to 'charge up' the house, again on cheap rate during the night, then minimise day use, thanks to the A2A units.

I do like the look of the simple HPHW tanks where they don't have an outside unit, just a unit on top. Then you can vent to the room ('free' A/C in the summer?) or vent to the outside using two pipes.

Another option I pondered as an extension to the HPHW tank, was a HP thermal store, utilising a simple HPHW tank idea, and feeding the DHW and central heating. But apparently that's a bad idea, though I wonder, if again that's because typically folk need more energy. [Than I do, from that component of the space heating mix.]


Hope this makes sense, the electric boiler idea seems like a fail to me, but at the same time, might be correct given the small(ish) demand we have. I look forward to seeing how the autumn goes now, and if we can avoid the GCH through Oct (I'm hopeful) and possibly Nov (if we top up the batts from night rate). Then the biggie will be how much we dent GCH use in Dec, Jan and Feb.

Historically our worst/cold months have meant consuming about 2,000kWh of gas. So that's my worst case starting point, and our boiler is ~25yrs old. That's approx 65kWh per day, but of course some days would be more, some less. Then knock off perhaps 30kWh for the A2A units at very (very) low efficiency, and just for this example 6hrs x 4kW for the leccy boiler at cheap rate, and ~5kWh for the DHW no longer from the boiler, and it's not looking too bad.

So perhaps come Mch/Apr I'll have an idea of what is, or isn't possible based on more solid numbers.

I should add, I do also have a nagging/recurring thought about fitting a 3rd A2A unit, perhaps above the low roof on our side 'garage' (really it's a store room, as seen with nthe pic of the giant panels). The indoor unit could be near the top of the stairs, but space is tricky, as we have stairs into our loft, so that bit of wall is tight. But a 3rd unit might do the job (but I doubt it, this is a 1930's semi-detached, so not the best starting point).

Sorry that turned into a disjointed ramble. Feel free one and all to suggest ideas, I've done a lot of pondering, but I'm happy to admit my ideas are still full of holes and need better insulating.