AC coupled battery system

[Oldgreybeard]

It's now a couple of weeks or so since I got the system up and running properly, and I now have some numbers. Over the past 19 days we've used 448kWh during the off-peak period and 27kWh during the peak period. A good chunk of the off-peak usage was car charging, around 100kWh or so. Looking at costs, then if I subtract the car charging usage, and just look at the house usage, then we have paid an average of £1.38 per day off-peak and £0.39 per day peak, plus the standing charge of £0.2297/day, making an average cost per day of about £2.00.

That £2.00 per day is for all our heating and hot water, as well as lights, TV, PCs etc. Our background load is a bit higher than some homes as we have a water pump for our water supply, a UV disinfection unit, an air pump for the sewage treatment and the heat recovery fans, with most of those running 24/7.

Overall I'm pretty pleased with things so far, although we have had a few days where there has been very little PV production and when the batteries have shut down by mid-evening, having hit the fixed 15% SoC lower limit. There's been a delay getting the second set of three batteries, but one is arriving tomorrow, with the remaining two arriving some time in January. Just having one extra battery will probably stop us running out in the evening on darker days I hope.

One potential issue is that I really need to add some load limiting, as we have come close to hitting the maximum supply rating of 15kVA a couple of times. I've decreased the charge rate down to 1.5kW, but if both cars are charging, the hot water is charging, and the batteries are charging we are way over the 15kVA rating. The main fuse is 100 A, which is normal for a 15kVA service, and we're lucky, in that the normal maximum service now is 13.8kVA, it seems. Still, I have the paperwork from the DNO which is all clearly marked as our supply being the older maximum of 15 kVA, so that's what I'm going to stick with, as I'm pretty sure this limit is contractually binding from the way the DNO's quote for it was worded.

It does make me grateful that we have an E7 supply, though, as we really do need the full 7 hours at the cheap rate to be able to load shift to the maximum. I also wish that I had been able to find a dishwasher with a timer, as when I built the house I just couldn't find an integrated one with a timer, for some reason back then all the integrated ones I could find didn't have timers. With a bit more battery capacity I don't think this should matter too much, though, as we could afford a couple of kWh to run the thing when needed.

I still need to try and get the comms working, so I can try to replicate the display on the inverter in the house, plus I've decided to replace the excess PV diverter with one that has an adjustable threshold, as I'm finding that the inverter and the PV diverter are still fighting with each other sometimes. This happened today, the battery charged to 100%, the PV diverter started heating the hot water, then the sun went in and the battery started discharging into the water heater. I've ordered a new one that has an adjustable threshold and I'm hopeful that this will fix the problem.

I'll give another update as soon as I have the RS485/Modbus comms sorted, with whatever I manage to cobble together to try to replicate the display in the house. Thanks again for all the help!

[Stinsy]

My Neff integrated dishwasher has a (really good) timer that can be set to the minute. My Beko washing machine has a (bit rubbish) timer that can only be set by number of hours to delay.

How much power do you really need to put into the two cars every week? Do they need to be charged simultaneously?

Here is a snipet from my recent bill:

[nowty]

Stinsy, you need to work harder on your peak rate useage.

Snipet from Nowty Towers recent bill.

[Stinsy]

Ha ha. I knew you’d be along to trump me! My little battery only lasts ‘till mid-afternoon when there is little-to-no solar around.

[Joeboy]

Ha ha. I knew you’d be along to trump me! My little battery only lasts ‘till mid-afternoon when there is little-to-no solar around.

Wish I was in this club.

[Joeboy]

It's now a couple of weeks or so since I got the system up and running properly, and I now have some numbers. Over the past 19 days we've used 448kWh during the off-peak period and 27kWh during the peak period. A good chunk of the off-peak usage was car charging, around 100kWh or so. Looking at costs, then if I subtract the car charging usage, and just look at the house usage, then we have paid an average of £1.38 per day off-peak and £0.39 per day peak, plus the standing charge of £0.2297/day, making an average cost per day of about £2.00.

That £2.00 per day is for all our heating and hot water, as well as lights, TV, PCs etc. Our background load is a bit higher than some homes as we have a water pump for our water supply, a UV disinfection unit, an air pump for the sewage treatment and the heat recovery fans, with most of those running 24/7.

Overall I'm pretty pleased with things so far, although we have had a few days where there has been very little PV production and when the batteries have shut down by mid-evening, having hit the fixed 15% SoC lower limit. There's been a delay getting the second set of three batteries, but one is arriving tomorrow, with the remaining two arriving some time in January. Just having one extra battery will probably stop us running out in the evening on darker days I hope.

One potential issue is that I really need to add some load limiting, as we have come close to hitting the maximum supply rating of 15kVA a couple of times. I've decreased the charge rate down to 1.5kW, but if both cars are charging, the hot water is charging, and the batteries are charging we are way over the 15kVA rating. The main fuse is 100 A, which is normal for a 15kVA service, and we're lucky, in that the normal maximum service now is 13.8kVA, it seems. Still, I have the paperwork from the DNO which is all clearly marked as our supply being the older maximum of 15 kVA, so that's what I'm going to stick with, as I'm pretty sure this limit is contractually binding from the way the DNO's quote for it was worded.

It does make me grateful that we have an E7 supply, though, as we really do need the full 7 hours at the cheap rate to be able to load shift to the maximum. I also wish that I had been able to find a dishwasher with a timer, as when I built the house I just couldn't find an integrated one with a timer, for some reason back then all the integrated ones I could find didn't have timers. With a bit more battery capacity I don't think this should matter too much, though, as we could afford a couple of kWh to run the thing when needed.

I still need to try and get the comms working, so I can try to replicate the display on the inverter in the house, plus I've decided to replace the excess PV diverter with one that has an adjustable threshold, as I'm finding that the inverter and the PV diverter are still fighting with each other sometimes. This happened today, the battery charged to 100%, the PV diverter started heating the hot water, then the sun went in and the battery started discharging into the water heater. I've ordered a new one that has an adjustable threshold and I'm hopeful that this will fix the problem.

I'll give another update as soon as I have the RS485/Modbus comms sorted, with whatever I manage to cobble together to try to replicate the display in the house. Thanks again for all the help!

OGB, what is your standing background load? I ask as when I first installed my first pylontechs I was caning through the SOC. Turned out I was up close to 0.5kWh of vampires. Now down to 0.135kWh. An astonishing 9.125kWh wasted each day. Tv's and sound bar were some of the vampires along with a few old fridge freezer units. Well worth a run thru the house and see what you can catch? I found it worthwhile to use hive plugs to time shift my power use around where I could. Not as pertinent these days as we are charging thru the night from the grid yet still so in the Summer months. I am around two years into my freezers shutting down thru the night and kicking back in when the sun is rising (Summer scenario). Found this to be of benefit when I only had two batteries and was trying to preserve the SOC for better use elsewhere. No detriment to the food at all.

[Oldgreybeard]

OGB, what is your standing background load? I ask as when I first installed my first pylontechs I was caning through the SOC. Turned out I was up close to 0.5kWh of vampires. Now down to 0.135kWh. An astonishing 9.125kWh wasted each day. Tv's and sound bar were some of the vampires along with a few old fridge freezer units. Well worth a run thru the house and see what you can catch? I found it worthwhile to use hive plugs to time shift my power use around where I could. Not as pertinent these days as we are charging thru the night from the grid yet still so in the Summer months. I am around two years into my freezers shutting down thru the night and kicking back in when the sun is rising (Summer scenario). Found this to be of benefit when I only had two batteries and was trying to preserve the SOC for better use elsewhere. No detriment to the food at all.

Higher than I'd like, but down to as low a figure as I can reasonably get it. Overnight it's about 200W to 250W, made up from about 50W for the heat recovery ventilation (runs 24/7, as our house is airtight), 40W for the air pump in the sewage treatment plant, 30W for the ultraviolet lamp that disinfects the water, plus other stuff that has to stay on, like the fridge freezer, internet and network stuff, heating controls etc.

The TV gets turned off with one of those E-on plug-in adapters (bought mine from ebay), that kill all the power to up to two connected devices when the TV remote off signal is detected (turns of the TV and sound bar in our case). The set top box stays on, as it does updates overnight, plus it's often recording stuff when we're not watching TV.

So far we've only had a couple of evenings when the battery has run down an hour or two before the start of the cheap rate period, and with the extra battery that should arrive today I think I'll have enough capacity to sort that out. It looks like another 1kWh of storage might be enough to sort that, and I'll be adding about 3.5kWh later today. When the remaining two batteries that I have ordered arrive then we should be able to cope without needing to bother to watch consumption at certain times of the day too much, I hope. Right now I still have to keep an eye on the battery SoC late in the day, to see if we're just going to scrape in on battery power before the start of the off-peak slot.

[Joeboy]

OGB, what is your standing background load? I ask as when I first installed my first pylontechs I was caning through the SOC. Turned out I was up close to 0.5kWh of vampires. Now down to 0.135kWh. An astonishing 9.125kWh wasted each day. Tv's and sound bar were some of the vampires along with a few old fridge freezer units. Well worth a run thru the house and see what you can catch? I found it worthwhile to use hive plugs to time shift my power use around where I could. Not as pertinent these days as we are charging thru the night from the grid yet still so in the Summer months. I am around two years into my freezers shutting down thru the night and kicking back in when the sun is rising (Summer scenario). Found this to be of benefit when I only had two batteries and was trying to preserve the SOC for better use elsewhere. No detriment to the food at all.

Higher than I'd like, but down to as low a figure as I can reasonably get it. Overnight it's about 200W to 250W, made up from about 50W for the heat recovery ventilation (runs 24/7, as our house is airtight), 40W for the air pump in the sewage treatment plant, 30W for the ultraviolet lamp that disinfects the water, plus other stuff that has to stay on, like the fridge freezer, internet and network stuff, heating controls etc.

The TV gets turned off with one of those E-on plug-in adapters (bought mine from ebay), that kill all the power to up to two connected devices when the TV remote off signal is detected (turns of the TV and sound bar in our case). The set top box stays on, as it does updates overnight, plus it's often recording stuff when we're not watching TV.

So far we've only had a couple of evenings when the battery has run down an hour or two before the start of the cheap rate period, and with the extra battery that should arrive today I think I'll have enough capacity to sort that out. It looks like another 1kWh of storage might be enough to sort that, and I'll be adding about 3.5kWh later today. When the remaining two batteries that I have ordered arrive then we should be able to cope without needing to bother to watch consumption at certain times of the day too much, I hope. Right now I still have to keep an eye on the battery SoC late in the day, to see if we're just going to scrape in on battery power before the start of the off-peak slot.

You're on it! Great you have the additional cap arriving today. Shall there be photo's?

[Oldgreybeard]

Much trials and tribulation with the arrival of the extra battery(s). Not wholly sure what's going on with the supply chain, probably just the disruption with shipping that seems to be affecting lots of stuff recently. One consequence is that I may have accidentally doubled up on an order for more batteries, and I have a choice of either accepting this and having a pack made up of nine US3000C's or trying to cancel an order and sticking with just 6 batteries. Right now I am in two minds. Part of me thinks that a usable capacity of around 20kWh should be enough but another part of me thinks that having around 30kWh would allow more of our solar generation to be stored for use during cloudy days, remove all worries about running low on battery capacity and also run the batteries a bit more gently, which might make them last longer.

What seems clear now is that just three US3000C's is not enough, as we seem to be running out of battery power in the evenings if we don't get any appreciable PV during the day. Another factor is that I have to keep an eye on things all through the day, and manage consumption a fair bit to try and eke out the remaining capacity in the batteries. I would quite like having enough battery capacity to not have to bother to look at the SoC through the day, and worry about whether we're at risk of running out. The good news is that the 3kW from the inverter meets 99% of our demand during the day, the only time we use more than that is for very short spikes when we happen to have the cooker on and something like the water pump kicks in for a minute or two. The energy in these short spikes is so small as to have a negligible effect on the bill, I think.

Ignoring the cost, what does the hive mind think? Should I stick with the pack of six US3000C batteries, or would it make sense to go the whole hog and go for a pack of nine US3000Cs? My gut feeling is to go for nine batteries, really because I think it may make things a bit more fit-and-forget.

[Tinbum]

I'd go for the 9. As you say you have piece of mind and its also their for the unexpected like power cuts or a faulty battery. It also will place less strain on the batteries. Payback will be longer though.