AC coupled battery system

[Stinsy]

Hi OGB,

Your plan seems to be a good one!

A few points:
- Most people prioritise charging the batteries over heating water. The energy in the batteries can be used for anything (including heating water) whereas putting it through a resistive heater is 2nd only to allowing it to spill into the grid. The easiest way to achieve this is to program the "diverter" attached to the hot water heating element to target 100W (or whatever) export and program your battery system to target 0W export.
- I have no personal experience with that inverter. However it is very popular, I've not heard of it being unreliable, and I believe it can do what you need.
- You can get EV charging points that intelligently monitor you house total demand so as to ensure you don't go over your main fuse rating. You should be able to charge 2x EVs simultaneously on a 100A fuse because that still leaves over 8kW for everything else. Even if you did have a 12kW electric shower or several 3kW loads on simultaneously, they tend only to pull full power for a short period and the aforementioned intelligent charging points can vary the charge rate of the EV during those periods.
- I have a similar setup, I use the Octopus Go 2030-0030, 5p, cheap rate period. Here is yesterdays chart:



I'll explain the chart:
- At the start of the chart you can see where the batteries are programmed not to discharge during the cheap period so my demand (orange) is matched by the power I'm pulling from the grid (red).
- From 0030 onwards the battery discharge (blue) matches demand and grid reverts to zero.
- Then when the solar (green) comes online the battery is charging/discharging to keep the grid power at zero. The jagged grid is because the induction hob was on all day (cooking batches of bolognese/chilli for the freezer). For some reason the grid usage is never flat while the hob is on but I've learned to ignore the few W in either direction as insignificant.
- Then at 2030 the batteries started charging and we ran the dishwasher (no EV connected yesterday). It was a sunny day so the batteries were already at 62% when charging started so the charging period was brief.
- Yesterday according to Octopus I used 0.69kWh of "peak" electricity and 8.11kWh of "off-peak".
- Today is overcast and the washing machine is on so unless the sun comes out this afternoon we won't get all the way through to 2030 on batteries.

I shouldn't have been so pessimistic! Batteries never got below 46%! Used 0.64kWh of "peak" electricity yesterday...

[greentangerine]

I use an ME3000 and storage to try and shift most if not all my daytime use.

The battery charges overnight (if required - I control the ME3000 with a Pi linked to all my other monitoring kit), as do the EVs.

The screenshot is my house energy usage for the past 24 hours; I have Go and hence the spike between 00:30 and 04:30 when the battery was charging back up to 70%, one EV was charging and two dishwashers and one washing machine.

[Joeboy]

How much room do you have for a ground-mount array? Going off grid for electricity isn’t out of the question but I’d suggest the following:

- An additional 12kWp of panels (minimum).
- A generator (you will need it in the darkest mid-winter days).
- An alternative source of heat (eg wood burner/bottle gas boiler).

I know some of those go against your principles but you needn’t run the generator/ aux heat source very frequently, however on the darkest midwinter days you will need them. On the other hand the grid is a great way of delivering clean electricity from a wind turbine in the North Sea or Cornwall to your house…

Sadly none, we had a real struggle to get consent to fit the in-roof panels, as we're in an AONB and a conservation area, adjacent to a listed building , just to make things even harder. We do have a possibility of putting a wind turbine up on the ridge behind us, and have been exploring putting a tower up there to give the few of us in this valley with crap broadband a mobile signal. So far we've had no specific objection to the idea of putting a tower up there, although we've not mentioned the dreaded "wind turbine" words yet, and they often seem to bring out the worst in the NIMBYs. We had enough trouble with NIMBYs when we were getting planning consent - the real problem being that it seemed many people can't read plans and visualise what something will really look like.

Our energy needs are pretty modest, our worst case heating power requirement is only about 1.5 kW when it's -10°C outside, and it's never got down that low since we've been here. The snag with that is that even the very smallest canal boat sized wood burner would overheat the house very quickly, and no one makes one that can deliver just a couple of hundred watts of heat, which is all we need in winter, normally. If we really had to burn something, then LPG would make the most sense, perhaps a small LPG water heating unit that could heat up the UFH in the slab. Something caravan size would be more than adequate, I think, and could probably be run off bottles, given the relatively low usage.

Realistically I think we are stuck with the grid, and as you rightly say, the grid is pretty clean, and getting cleaner all the time, so seems the least polluting energy source available. It's just that when you've gone down the rabbit hole of reducing CO₂ emissions to the point where the net emissions from our house and both cars is negative, there's this strong subconscious desire to do just a bit more, and try and cut free from the dependence on the grid. Not really rational, but then so much about the things we chose to do isn't really rational, anyway. Lots of people around here think I'm already a bit of a nutter for building a passive house, that has no foundations and just sits on 300mm of polystyrene foam laid on the ground!

OGB, any photos? Sounds like you are in a good place, well done!

[Oldgreybeard]

Sorry for the delay in replying, and many thanks for the kind words. Photos will follow as soon as I have tidied up - I've been wiring the battery shed today, in readiness for the inverter/charger arriving next week (bought one of the refurbished ones from eBay for £399 in the end). I've ordered the batteries, opted to go for three Voltacon packs of 5.12 kWh each (4.25 kWh each usable), as they looked to be best value, and use Pylontech cells and the same connectors and interface. Having around 15.36 kWh max, 12.75 kWh usable, should give us a useful buffer, and may extend the life of the pack, as I doubt we'll use more than around 6 kWh/day from the pack normally. Looks like my timing is good, with wholesale prices jumping up yet again today. The batteries won't arrive for a few weeks, though, it seems that no one has stocks of them at the moment.

I've noticed that the manual for the ME300Sp states that there are four time of use slots that can be used, but have been just told by someone with one of these units that this is not true, and in reality there is only a single slot. If so, then that might make things a bit more complicated, as I'll need to do something like set up a RPi to control the thing, perhaps. Because I've bought a second hand ME3000SP (updated to the latest software, apparently) I have no easy way to get support. Anyone happen to know if the latest manual, that mentions the four time of use slots, is correct or not, please?

[nowty]

I've noticed that the manual for the ME300Sp states that there are four time of use slots that can be used, but have been just told by someone with one of these units that this is not true, and in reality there is only a single slot. If so, then that might make things a bit more complicated, as I'll need to do something like set up a RPi to control the thing, perhaps. Because I've bought a second hand ME3000SP (updated to the latest software, apparently) I have no easy way to get support. Anyone happen to know if the latest manual, that mentions the four time of use slots, is correct or not, please?

The four rules are supposed to be used at different times of the year so usually they don't work if you try and use more than one rule on the same date. However Sofar did release a special firmware version where more than one can be used on the same day as long as the times don't overlap which is v2.41.

I believe later versions of firmware, certainly v2.50 took this feature back out.

Also is the ME3000SP compatible with the Voltacon batteries ?

[Stinsy]

Also is the ME3000SP compatible with the Voltacon batteries ?

The Voltacon batteries look like repackaged Pylontech hardware, so I guess that they’ll work as long as you tell the inverter they’re Pylontech (probably). My back is twinging at the thought of 51kg batteries!

[Oldgreybeard]

The four rules are supposed to be used at different times of the year so usually they don't work if you try and use more than one rule on the same date. However Sofar did release a special firmware version where more than one can be used on the same day as long as the times don't overlap which is v2.41.

I believe later versions of firmware, certainly v2.50 took this feature back out.

Also is the ME3000SP compatible with the Voltacon batteries ?

Absolutely brilliant! thanks very much for this, although I do wish the manufacturers could write proper manuals for their products, it would make life a lot easier. Looks like I will need to load v2.41 then, which shouldn't present too big a problem (I hope!).

The Voltacon batteries look like repackaged Pylontech hardware, so I guess that they’ll work as long as you tell the inverter they’re Pylontech (probably). My back is twinging at the thought of 51kg batteries!

Yes, I've had this confirmed, they use the same connectors and the same comms protocol as the Pylontech units, and use Pylontech cells, so as far as the ME3000SP is concerned they are Pylontech packs. Not sure what the tie up is between Voltacon and Pylontech. There must be some link between the two, given that the packs are so similar.

I am beginning to wonder at the wisdom of heavy 51kg packs up into a rack! As usual, the very reasonable price swung me towards buying them, without paying full attention to the weight of the things!

[Oldgreybeard]

Had to change my plan, as it turns out that the Voltacon batteries I'd ordered aren't compatible with the SoFar ME3000SP after all, despite the ad saying they were at the time I placed the order. I've changed the order to Pylontech US3000C packs, but these won't arrive in the UK until December. I have managed to get three Pylontech's from ITS, though, that should arrive in mid-October.

This means I'm spending a lot more money than I'd planned to, but I think that having more capacity (around 20 kWh by December) is probably a sensible thing, given the wake up call we're getting from the present energy crisis. The more of our PV I can store and use the better, I think, as I have a nasty suspicion that the energy supplier market is likely to get a lot worse over the winter. I just wish we had a practical way of generating more zero carbon electricity during the winter, but it's just not really practical.

[Stinsy]

Pylontech batteries have had long lead times for the last few years. I guess they’ve been “suffering” from high demand, supplies have been flowing regularly but preorders and long lead times have been normal. I guess a lot of people have been thinking about the need to store energy locally.

Local green electricity generation, in winter, is unsolved. An oversized solar array requires space and even then makes little difference on the gloomiest winter days. Vanishingly few people live somewhere suitable for a WT.

This winter is going to be “interesting” that’s for sure! You should be grateful for every bit of insulation! Wholesale gas prices will be high, spectacularly so if Europe has a cold winter. Every month more people will come to the end of their fixed tariffs and face big price rises. If it isn’t windy we’ll rely on gas for a huge proportion of grid power generation too, this transfers the high gas price to electricity prices.

[Oldgreybeard]

With luck we should be up and running within three weeks with a ~10 kWh usable system, that will then get doubled up to ~20 kWh in early December. That should make a useful difference, I hope, but as PV generation pretty much falls of a cliff around November, and doesn't really come back again until March, I doubt we'll gain much extra from that for a while.

I'm hoping that we can max out the cheaper off-peak rate though, and reduce our peak rate consumption to near-zero, with a bit of luck. That should make a useful difference.

I really feel for all those who are either going to be victims of their supplier going bust, or are coming to the end of a fixed price tariff, as they are bound to get hit with massively higher bills. We got caught out on a supplier going bust a few years ago, cost us an absolute fortune, both because of the higher tariffs with our new supplier appointed by OFGEM, but also because of errors made in the transfer process that meant a lot more money was taken by DD than there should have been.