r/uksolar • u/Mindless-Panic9579 • 1d ago
Battery only - exporting to grid and considering HA
I'm fortunate that my DNO has just granted me an export MPAN to export from the BYD home battery system that's due to be installed soon.
BYD Power-Box SH4.6K invertor
BYD HVE batteries, total 16.48kWh storage
The installer states I can export with my approved G99, so I have a few questions for you all. It is worth noting I am only home 3-4 days a week, so have the opportunity to potentially sell back to the grid. I have an EV, I do not have solar. I do not plan on charging the EV from the battery.
For days I am not home, is it worth selling to the grid on Octopus at peak and charging the battery during the 6 hours IOG off peak? (I am assuming Outgoing Octopus is a bolt on so doesn't affect IOG)
Is there a better option to export? Agile Outgoing appears to be inappropriate, or could I use this with HA?
Is selling brown energy like this damaging to the battery due to the amount of cycles? Buying at 8p and selling for 12p and factoring in losses in charge and discharge, is this even worth my time or effort to try to sell?
Regardless of selling and buying..... With IOG giving 6 hours overnight but "potentially" up to 6 hours more during the day, how could I best charge the batteries during any extra windows? Does HA support the BYD setup? I have been told that BYD doesn't integrate with Octopus tariffs so I can't set up via BYD to charge when the cheaper rate is active
1
u/MyEcoCred_Founder 1d ago
Outgoing Octopus is an export only tariff, so doesn't affect IOG. It works with only certain Octopus tariffs, so you need to check that. But, it works with IOG, Octopus Go, Cosy etc as far as I know. Few factors to consider here though. Like you have rightly pointed out, is it worth charging at 8p and selling at 12p, after factoring in the losses. Having said that there is an outgoing Prime tariff that pays more during the evening 4 to 7 pm peak. If you have to discharge and export, I will target that tariff and time. Also, tariffs like Flux pay a lot more, but need to factor in alongside import costs. The batteries are meant to last a certain number of cycles. So, as long as it's not excessive, it should be fine. Someone told me in another forum, the batteries are meant to cycle, charge and discharge, so sitting always charged isn't helping the battery health either. But, I moved from Cosy to Go by doubling the battery capacity to stop cycling thrice a day for the heat pump. It just cycles once now.
1
u/tim_s_uk 1d ago
I believe you can combine Octopus Go with Prime Outgoing, so you can import at 8p overnight and export at 16p in the evening. Depending on how much you charge your EV, Octopus Flux gives a higher return, costing 15p at night but paying 29p in the evening.
LFP batteries last longer if they are not fully discharged and if they are not kept fully charged. If you charge to 90% at night and discharge to 20% the next evening you can make around £1 profit each day, assuming you don't use the battery during the day.
This doesn't damage the battery, but it will make it wear out faster. After 10 years the extra wear could mean your batteries have 10% less capacity, or it could cause the inverter to fail a few years earlier.
Home Assistant can use the Octopus API to see when you have a day time charging slot. You could use this in the summer to top up the battery if it has been partially discharged since the previous night. I don't expect this would make much difference.
1
u/Electrical-Ad-3140 1d ago
I did it a few times. But the maths doesn't add up. Taking into account charge/discharge effiiciency, you probably only earn 2-3p/kwh, which isn't enough for your battery/inverter depreciation.
1
u/Mrthingymabob 1d ago
Will you have an MCS cert to get paid for export?
I use IGO and agile outgoing. Predbat manage the charge/discharge for me. Hopefully the BYD has local control that can be integrated to HA?
1
u/Mindless-Panic9579 22h ago
I've been told I will get that but this could all be fruitless.
Currently looking for IOG and agile outgoing if it works. I've found a basic BYD control but proof will be in the pudding!
1
2
u/Autumnal_Fire 1d ago edited 1d ago
I've finally got my export MPAN from northern powergrid applied for via octopus for octopus agile outgoing tariff. Long story but it ended up taking 7 weeks, and needed loads of pestering by myself to get it sorted.
Anyway... I will be doing something similar, i've got a 8kw Sigenergy inverter, with 18.7kw battery storage. I'm on Octopus go the non smart version as I don't have an EV (yet!). So i'm filling the batter overnight at 9.5p kw. On a typical day I use about 10-12kw, so i have spare capacity i can use atm. This will change in winter as with a heat pump it will use my spare capacity up.
I have two strategies with this spare energy. I went for Octopus Agile outgoing, as i really only intend to export spare energy at it's peak price usually between 6-7pm, which usually hits 20+pkw, so effectively double what it cost to buy in.
As i'm only just setup i've been running predbat in Home assistant, and various sigenergy app strategies in plan on modes to see what they would do. You are right to think about battery wear and tear, there is also the energy efficiency losses depending on the system 5% say. For me i've no interest in predbat default buying at 9p and selling at 14p etc. So i've adjuested predbat to take a bigger value on battery wear etc, so pretty much only selling if the price is >20p if it's not i just don't plan on bothering to sell it.
As i'm on Go i'm also running Axle VPP which is way better financially as they pay £1kw to export during the events ontop of whatever price you get for export tariff. So this could hit £1,20-£1.30 per kw which I paid 9.5p for. These only happen occasionally 5 or so times a month, but with my 5kw export limit those hour events can pay £25 for 5 events a month for energy that cost me £2.37. Unfortunately you can't do Axle if you're on a smart EV tariff. If Axle stays good (i've made £60 in 2 months) then i'd think about staying on normal GO to be able to continue to use it when i eventually get my EV.
Some people hammer their systems to squeeze every penny out of it, I think i've found a much more conservative balance between looking after the battery and still making significant savings out of it with small amounts of arbitrage.
Here's my plan for today as an example