Domestic Battery Storage - G83/G98 - Earthing Arrangements + More

vantech:

Hi,


I am looking to add a battery storage system to my own home (I am an NICEIC registered contractor, just to make it clear this is a project for myself). This will be a battery only solution, and will not feature any solar arrangements. 


If there are any experts here that can advise on a few questions, that would be superb. 

 

• GN98 (formally GN83) allows systems up to 16A per phase to be connected without the need for any sort of site inspection before the install (so the solution is notified after). I plan on doing this myself, and I am not part of a microgeneration scheme, but assume self certification is ok, following Part P requirements and issuing the relevant certs to the NIC. 

 

• The battery I plan on using is the Alpha ESS (combined battery and inverter), which is grid tied with separate backup output(s) for things like lighting circuits and small power circuits. I have a smart meter, however I do not have a feed-in tariff, therefore by means of a CT connected to the battery I plan to set the feed-in to zero using the inverters user interface, so that the battery just delivers power to loads as and when its required. My question here however leads me onto earthing - when running in backup mode, the inverter automatically disconnects the grid and provides power on its dedicated backup connection - what do I do with the Earthing? I am on a TN-C-S supply from the DNO - I would assume an earth rod is required, connected into the MET (as the DNO earthing cannot be relied upon during an outage) which would be combined the DNO earthing (so a rod in the ground connected to the MET and bonded onto the battery inverter). Assuming this is correct, does the inverter need to tie its backup output neutral and earth conductors together, forming its own TN system (it could even be doing this internally I'm not sure and need to check). 

 

• Anything else I may be missing?

Thanks.

 

What do the manufacturer's instructions say about earthing? If the whole output is floating with neither pole earthed, is there really any risk of an L to E shock? Perhaps that is a safer situation. If the output is not connected to the mains supply at all then you may prefer an independent earth electrode and an R.C.D., a TT system for the battery inverter supply. 


Z.




 

broadgage:

What is the purpose of this installation ?

If simply to provide back up power during power failures, then simply use an "of the shelf" UPS unit with an extended run time battery bank. No question of parrelal operation with the DNO supply or of returning energy to the public network. GN 98 or related documents not relevant.


If the intention is sell power back into the DNO, I would give up on that idea.

Calculate the cost of charging the battery from the off peak DNO supply, and then therevenue from selling the power back at peak times, compare with cost of battery cycling.Not worth it.

Hi,


The idea would be to charge the battery on special night time rates (and lowered tariffs for EV charging) and then discharging during the day. The battery is grid tied, so during the day and up until the economy tariff begins, it will discharge with zero feed to the grid. 


So you are saying that if I am not selling back to the grid, I don't need to complete the GN98? The battery will be grid tied for the purpose of supplying loads (so it connects into an MCB to charge the battery and also to discharge when supplying loads - the backup is a separate output limited to 16A), so does the DNO not need to know there is a generation plant, even if it isn't selling back to the grid?


Thanks. 

The idea would be to charge the battery on special night time rates (and lowered tariffs for EV charging) and then discharging during the day. The battery is grid tied, so during the day and up until the economy tariff begins, it will discharge with zero feed to the grid. 

vantech:

The issue with this is that some devices are Class 1 by nature, so would require a "ground" reference for EMC circuits etc - this wouldn't work unless the battery was ground referenced when running on backup. 

What common typical domestic items would you give as  examples of vulnerable items?

https://www.bing.com/videos/search?q=what+is+emc&docid=608010981617370857&mid=075EEAE665041D122C8E075EEAE665041D122C8E&view=detail&FORM=VIRE



Z.

RichardCS2:

vantech:

The idea would be to charge the battery on special night time rates (and lowered tariffs for EV charging) and then discharging during the day. The battery is grid tied, so during the day and up until the economy tariff begins, it will discharge with zero feed to the grid. 

Does this actually make economic sense? If your battery costs say £5k, stored 10 kWh and lasts 2000 cycles, and was charged at £0.05/kWh overnight (somewhat guessed / made up numbers), the overall cost of a daytime kWh of electricity is £0.05+ (£5000 / (10*2000)) = £0.30. Sounds pretty expensive to me, how's it look with your actual figures?

 

Hi,


This isn't a cost exercise, its a "nice to have", so we would have backup for power outages, as well as a lower rate during the day. The initial upfront investment of this type of setup without solar isn't economical for sure.

 

Zoomup:

vantech:

The issue with this is that some devices are Class 1 by nature, so would require a "ground" reference for EMC circuits etc - this wouldn't work unless the battery was ground referenced when running on backup. 

What common typical domestic items would you give as  examples of vulnerable items?

https://www.bing.com/videos/search?q=what+is+emc&docid=608010981617370857&mid=075EEAE665041D122C8E075EEAE665041D122C8E&view=detail&FORM=VIRE



Z.

LED drivers (I have DALI drivers which are all Class 1), server power supplies. They should be OK without it, and agree it could run as an IT system - your idea is good, but I would need to make sure the inverter is 100% isolated from anything that could provide contact with Earth, and this may be impossible. 

vantech:

RichardCS2:

vantech:

The idea would be to charge the battery on special night time rates (and lowered tariffs for EV charging) and then discharging during the day. The battery is grid tied, so during the day and up until the economy tariff begins, it will discharge with zero feed to the grid. 

Does this actually make economic sense? If your battery costs say £5k, stored 10 kWh and lasts 2000 cycles, and was charged at £0.05/kWh overnight (somewhat guessed / made up numbers), the overall cost of a daytime kWh of electricity is £0.05+ (£5000 / (10*2000)) = £0.30. Sounds pretty expensive to me, how's it look with your actual figures?

 

Hi,


This isn't a cost exercise, its a "nice to have", so we would have backup for power outages, as well as a lower rate during the day. The initial upfront investment of this type of setup without solar isn't economical for sure.

 

Sure, but you are planning to use power from it in the daytime, even though that power may end up costing you more (battery replacement required sooner) than if you drew the same amount of energy from the grid and used the battery only as backup. Having solar doesn't make a lot of difference, the dominant cost is cycling and wearing out the expensive battery, not the energy to fill it.


Not everything has to be a cost exercise of course, and "because it's cool tech" is a perfectly valid reason. It just sounded like you were trying to save money with the overnight charging daytime discharging thing and I am doubtful you will in the long term.

RichardCS2:

vantech:

RichardCS2:

vantech:

The idea would be to charge the battery on special night time rates (and lowered tariffs for EV charging) and then discharging during the day. The battery is grid tied, so during the day and up until the economy tariff begins, it will discharge with zero feed to the grid. 

Does this actually make economic sense? If your battery costs say £5k, stored 10 kWh and lasts 2000 cycles, and was charged at £0.05/kWh overnight (somewhat guessed / made up numbers), the overall cost of a daytime kWh of electricity is £0.05+ (£5000 / (10*2000)) = £0.30. Sounds pretty expensive to me, how's it look with your actual figures?

 

Hi,


This isn't a cost exercise, its a "nice to have", so we would have backup for power outages, as well as a lower rate during the day. The initial upfront investment of this type of setup without solar isn't economical for sure.

 

Sure, but you are planning to use power from it in the daytime, even though that power may end up costing you more (battery replacement required sooner) than if you drew the same amount of energy from the grid and used the battery only as backup. Having solar doesn't make a lot of difference, the dominant cost is cycling and wearing out the expensive battery, not the energy to fill it.


Not everything has to be a cost exercise of course, and "because it's cool tech" is a perfectly valid reason. It just sounded like you were trying to save money with the overnight charging daytime discharging thing and I am doubtful you will in the long term.

Absolutely agree with you, but this has been factored in, its a nice to have setup and generally the battery life is 10 years: 


Current: 5500kWh per annum @ 15pp kWh = £825 

Battery: 5500kWh per annum @ 5pp kWh = £275 (which is a saving of £550 per annum)


Saving per annum @ £550 x 10 years = £5500 - so it pays for itself, in the long run, with the added cool tech and backup features (of course this is all give and take)