@jamespa 

I have self installed 3x Fogstar self build v4 Seplos upright kits, paired with a Seplos inverter.

If your DNO is UKPN it is very straightforward  to get approval.

You can use their Smart Connect online portal to get permission to install the inverter that fits your needs, you just need to make sure it is compliant.

Originally I asked for a 5kw Solis S6.

On the application you just need to work out what your incoming supply is and it's earthing situation, which you may already know and do some load calculations, which are pretty straightforward to ensure your incoming fuse is large enough. 

Mine was approved within 5 minutes, which suggests it's automated. I then went ahead and asked for a 6kw inverter approval and that was also approved, which gave me a bit more headroom.

I chose an AC Coupled Solis S6 6kw inverter as it is fanless to avoid any excessive noise (and I have no intention of installing solar panels as the ROI isn't worth it).

The 8kw and above units have fans. In an ideal world I would have gone for an 8kw inverter, but the noise was a worry. In practice it hasn't been an issue as our total load rarely exceeds 6.25kwh the inverter can handle (sustained discharge/charge).

I decided islanding wasn't worth the significant extra cost and need for an electrician to do additional work. We rarely get power cuts.

The self build Fogstar units were very easy to build and actually quite enjoyable.

Once all up and running on 1 pack I waited for a deal on further packs and subsequently picked up 2 further packs in the next 3 months, giving me about 45kwh of storage.

I submitted my sign off documents a few weeks later and that has been approved by UKPN and a certificate supplied.

UKPN have recently visited to upgrade our fuse to 100A in readiness of our HP install and had no issues with my battery installation.

The whole system cost me £5000 and works perfectly.

I am super happy and the ROI should be no more than 4yrs. It'll also mean the £3300 our HP install will cost will be paid off within 5yrs also.

So within 5yrs I'll have a fully paid for heating system (12 radiators sized for 42.5c @-3c), a new hot water cylinder, HP and 45kwh of storage.

After then happy days!

@bash Thats very helpful thanks, maybe I will just put together a G99 application (my DNO is UKPN) and see what happens!

Im really hoping that by bundling the various jobs with the CU upgrade (which isnt yet essential, but seems to be the only way to avoid lots of messy satellite CUs) I can make the cost sensible and the design more sane.  

@jamespa 

If you get your CU upgraded perhaps ask the electrician to run an appropriate isolator on its own circuit to where your batteries will be installed?

Once you have the isolator you should be able to safely switch off that circuit and work on the battery installation yourself.

You'd just need to get a data cable from the inverter to your smart meter, which is worth planning for also.

The G99 application through UKPN was pretty straightforward.

Posted by: @jamespa

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One option Im seriously considering is to have the electrician instal the battery inverter at the same time, with batteries (perhaps Frogstar?) to be added by me when they are next discounted.  This could make the whole thing particularly cost effective, finally making the battery business case pay.  The PV and battery inverters will remain separate, ac coupled initially, but when my 14 year old PV inverter finally gives up the ghost I may well combine the two functions.  The ability to operate as backup in case of mains failure would be useful, but perhaps not essential.

It makes sense to try to have a single consumer unit. One thing to consider you are looking to have circuits running during mains failure, is that that part is almost like a separate consumer unit. Could be simpler from a reg certification perspective to have a separate consumer unit for it .. I say this even if I have tried (unsuccessfully) to stop the proliferation of CU under my stairs. 😑 

My views on Frogstar is that the DIY battery kit makes it more complicated than what it needs to be- at least right now. When I buy another one, I will buy it ready made, as it is also half the cost.  I saw the following on ebay:  

- one going for £1000: Solar Energy 15kWh Home Storage Battery for Solar & Backup 51.2V 300Ah LiFePo4

- for £1100: 48V 300Ah Lithium Battery 15KWh Solar Energy For Home Storage PV BMS

- similar for ~1050: LUX-X-48100LG01 low voltage stackable LFP solar battery storage

I have a Solis hybrid inverter and this thread covers a lot of the questions with a diagram showing how we use it. 

Posted by: @jamespa

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Can anyone outline (or point me at) the main regulatory considerations (ie what triggers G98/99/100 - noting I already have a 3.68kW PV inverter - and can you avoid by setting the battery inverter not to export), what kit, apart from a suitable inverter, do you need to specify to allow islanding and inverter options (including ideally some example recommended makes).  Im finding it difficult to unpick the BS from the truth in the various sources.  I have a physics degree so don't expect to find it difficult to understand once I can get to the basics and given the basics I am confident I can complete the 'research' myself.

Any pointers appreciated!

I started a post a while ago when I realised UKPN was making it very easy to export and shared my findings. transparent and others really helped me to understand the difference between G98 and G99. UKPN approved 8kw and this required two steps, the first being what they called G98 and the G99, when they issued the export MPAN.

I believe you will need a separate earth if considering island mode for off grid operation (in the event of a power cut), which will need to pass an impedance test to be compliant.

@batpred 

Thanks.  I wasnt contemplating a self build battery, life is too short.  Thanks for the info on UKPN, will check their site.

@old_scientist I think the earth requirements depends on the type of earth already present, I did once know but forget, thats another reason to get everything 230V done in one go ((including the inverter quite possibly) leaving only the 48V stuff for later

@bash I know that inverters and battery management systems speak wo each other but I cant quite work out what they have to speak about.  The inverter can measure the voltage and current, I suppose state of charge but is there anything else.  It seems, reading the literature, that the different manufacturers speak different protocols and TBH I'm mystified as to why it needs to be that complex given that, from the point of view of the inverter the battery with its own BMS is just a source of electrons!

Posted by: @jamespa

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...

@bash I know that inverters and battery management systems speak wo each other but I cant quite work out what they have to speak about.  The inverter can measure the voltage and current, I suppose state of charge but is there anything else.  It seems, reading the literature, that the different manufacturers speak different protocols and TBH I'm mystified as to why it needs to be that complex given that, from the point of view of the inverter the battery with its own BMS is just a source of electrons!

You got me wondering too, so I had a bit of a search around and found a thread on the Home Assistant community.

Reading CAN bus communication between Pylontech battery and Solis inverter - Share your Projects! - Home Assistant Community

Seems there's a bit more going on than I expected, but all understandable and sensible.

• Battery state of charge
• Battery power
• Battery's limits
• Battery temperature
• Battery alarms
• Requests between battery and inverter to do stuff (e.g. charge request)

Posted by: @old_scientist

↑

I believe you will need a separate earth if considering island mode for off grid operation (in the event of a power cut), which will need to pass an impedance test to be compliant.

I had heard the same. Perhaps it was an initial requirement the DNOs insisted on (some apparently even claim that an earth connection is not part of the service that they provide). With UKPN in my area, they did not raise any such need. 

The need for separate earthing may also be a requirement from some inverters. 

With Solis, earthing from the DNO could be used in my installation. And it provides UPS/islanding mode. 

Posted by: @batpred

↑

Posted by: @old_scientist

↑

I believe you will need a separate earth if considering island mode for off grid operation (in the event of a power cut), which will need to pass an impedance test to be compliant.

I had heard the same. Perhaps it was an initial requirement the DNOs insisted on (some apparently even claim that an earth connection is not part of the service that they provide). With UKPN in my area, they did not raise any such need. 

The need for separate earthing may also be a requirement from some inverters. 

With Solis, earthing from the DNO could be used in my installation. And it provides UPS/islanding mode. 

 

The earthing requirement (to protect the engineers who may need to work on the supply when there is a power cut) is not provided by the inverter.

The earthing to your property will depend on what supply cable you have. We have TN-S supply, so the earthing returns back to the power network. 

This however will not be effective and safe if there is a power cut. 

If you have a "live" system during a power cut, for example UPS or other battery backup, you MUST provide additional earthing at your property, usually in the form of earth rods.

This is why "islanding" is more complex than people realise and can add significant additional costs to your installation.

Posted by: @jamespa

↑

@batpred 

Thanks.  I wasnt contemplating a self build battery, life is too short.  Thanks for the info on UKPN, will check their site.

@old_scientist I think the earth requirements depends on the type of earth already present, I did once know but forget, thats another reason to get everything 230V done in one go ((including the inverter quite possibly) leaving only the 48V stuff for later

@bash I know that inverters and battery management systems speak wo each other but I cant quite work out what they have to speak about.  The inverter can measure the voltage and current, I suppose state of charge but is there anything else.  It seems, reading the literature, that the different manufacturers speak different protocols and TBH I'm mystified as to why it needs to be that complex given that, from the point of view of the inverter the battery with its own BMS is just a source of electrons!

It's not actually essential that your inverter and batteries have communication. Ours will run happily with the communication cables removed.

The BMS of the battery will ensure they are kept in check independently of the inverter.

It is however beneficial to have communication, particularity if you have multiple batteries, but certainly not essential.

Posted by: @bash

↑

It's not actually essential that your inverter and batteries have communication. Ours will run happily with the communication cables removed.

The BMS of the battery will ensure they are kept in check independently of the inverter.

It is however beneficial to have communication, particularity if you have multiple batteries, but certainly not essential.

Good to know. 

In the Solis, the soc can be used to set reserve battery levels. Also when to charge and with what max rate, which I use to try to have smooth charging overnight. The goal is to avoid discharging the batteries and also reduce losses with charge/discharge. My tariff is flat overnight.