Not another one!

Just want a system that works well and ideally has full off grid back up during short powercuts.

Average annual consumption from the grid is 8500kWh.

ASHP 3000kWh.

Solar PV 3500kWh.

Our Current Setup :

• Solar PV: 3.74kWp array installed back in 2011, that has averaged 3,500kWh of generation annually. Works a treat.

• Diverter & DHW: We have a V1 Myenergi Eddi (Model 16A1P01) sitting in the plant room, diverting our daytime solar surplus straight into our hot water cylinder immersion.

• House Spec: We are an all-electric household (no gas or oil). Heating and DHW from Mitsubishi Ecodan, monitored by an Elster meter.

• Outbuildings & Sub-Main: A sub-main supply loops out 8 metres from the plant room to a garage consumer unit. This zone houses a separate full-time live-in space with its own appliance baseline.

• Data Link: We have a pre-installed, active Cat6 data cable running the 8-metre span between the house router/plant room and a network switch in the garage.

I am looking at the Myenergi Libbi 5kW 230V IP65 Hybrid Inverter & 15kWh Battery Kit (LIBBI-KIT-5.0K/15KWH).

The plan is to install the inverter and three 5.12kWh battery blocks out in the garage outbuilding, running back to the garage consumer unit. To hook up the grid-boundary sensor, we want to split our existing Cat6 cable, to hardwire a direct RS485 Modbus data loop from the house plant room straight to the garage inverter.

We will configure the system via the Myenergi ecosystem so that the Libbi Battery acts as Priority 1 and the legacy V1 Eddi acts as Priority 2 (with "Avoid Drain" enabled).

I have found the 5kW / 15kWh Libbi kit online for £5,628 including 20% VAT (approx. £4,690 trade/wholesale at 0% VAT).

Two options.

1. Supply Only + Electrician Friend: Buy the kit myself and have a close friend who is an industrial electrician (he installs large-scale commercial solar and container-sized utility battery networks) fit it for me.

2. Supply & Fit Quotes: Contact local independent installers to quote for the package.

Your thoughts much appreciated. Thank you.

If I understand you correctly, you are not changing the solar system but adding a battery system?

There might be part P issues with option 1. Your friend might not have the ability to do the part P compliance stuff. (You need Part P compliance for any work in a house, work outside of one, maybe not, but if the garage contains a live in unit then it likely counts)

Assume you aren't bothered about MCS certification? Good reasons not to be (markup by MCS folks) but MCS questions are common when selling a property so something to consider.

Do you have FIT with your current system? (Maybe your existing install predates that??) If so you want to make sure that nothing you do affects that.

1 hour ago, -rick- said:

If I understand you correctly, you are not changing the solar system but adding a battery system?

There might be part P issues with option 1. Your friend might not have the ability to do the part P compliance stuff. (You need Part P compliance for any work in a house, work outside of one, maybe not, but if the garage contains a live in unit then it likely counts)

Assume you aren't bothered about MCS certification? Good reasons not to be (markup by MCS folks) but MCS questions are common when selling a property so something to consider.

Do you have FIT with your current system? (Maybe your existing install predates that??) If so you want to make sure that nothing you do affects that.

Yes , keeping existing PV system with FIT with no alterations. It is upstream of the house on another outbuilding sort of on its own loop.

I will get some quotes from MCS certified installers but not really bothered.

My friend who has been very busy recently with these large solar + battery farms is a residential electrician but will check with him.

I assume the grid export limit on the Libbi will be set to 0.0kW so cannot back feed to grid and compromise the FIT.

Think will need a formal pre installation G99 grid notification certificate.

Thanks Rick.

Only going from what I've read here do check the FIT regs. You should be able to do what you want but you might have to follow some registration process or ensure things are done a certain way. Can't say more than that as not an area I know that much about.

15kwh battery is unlikely to power an all electric house for a day if that's what your after. We're almost all electric with a lodger in a separate flat and a single 16kwh battery with 91% depth of discharge is flat by tea time now the ASHP is running. Just added a second battery to see us through the winter on cheap TOU tariff

2x Fogstar 16 kwh batteries is £3600 plus Solis 5kw inverter at around £700 gives £4300 for a 32kwh set up.

2 hours ago, Nestor said:

I assume the grid export limit on the Libbi will be set to 0.0kW so cannot back feed to grid and compromise the FIT.

Are you on metered FIT export payments or deemed? An AC coupled battery won't upset deemed payments but likely will if youre getting metered FIT payments

12 hours ago, Dillsue said:

Are you on metered FIT export payments or deemed? An AC coupled battery won't upset deemed payments but likely will if youre getting metered FIT payments

Thanks Dillsue, I have read a lot of your posts about this topic.

Did you self install as you seem to have a lot of knowledge about the subject?

Our export is deemed from the onset so the 50% rule.

Had not planned on running the whole house on battery storage for any length of time, just for short power cuts.

If the Fogstar is available at those prices I could install up to 32kWh, I assume there is a limit on how much you can charge in the cheaper overnight rates limited by the inverter, did you install an 8kW inverter?

What happens with the DNO approval.

Our 2015 4kw FIT system was professionally installed by an MCS contractor. I've added a second 8.5kw system and the 32kwh batteries. I read the FIT guidance so I knew what I could and couldn't do......I've also had disputes with our FIT payer so needed to understand the rules to resolve those!!!

If youre on deemed payments then adding an AC coupled battery won't affect your FIT generation, so long as you don't connect it between the FIT inverter and the generation meter. If you connect batteries to your FIT inverter then you can do that but it's more complicated and will likely need to change the generation meter. The FIT guidance for generators covers all of the scenarios of adding batteries and making alterations.

Ours is a 5kw inverter that can charge at 5kw and can fully charge the 32kwh batteries in the EDF 7 hour off peak window:) it did it for the first time last night!! It's got 5kw backup capacity so I've split the house circuits across 2 consumer units as 5kw isn't enough for the whole house.

If you just want backup for short power cuts then 32kwh of batteries is likely more than you need. Like many batteries ours is expandable so you could add more if you changed your mind. We ran for the summer on 16kwh but always intended doubling that for the winter with a plan to run as much of our usage at off peak rates:)

You'll need G99/G100 approval from your DNO, which personally I think is straight forward

Edited just now1 min by Dillsue