First Time System - Domestic Storage UK

[Makia2020]

Hi all,

Long time lurker here and feel reasonably prepared to jump into finally planning and executing my own Solar Storage build in the coming months.

To set the scene I currently have a residential solar install (3.6Kw) which is grid tied on the 2015 Feed In Tarif. This is reasonably generous and nets me approx 18p/KW produced whether self consumed or not (generating approx 4000Kw per annum so cira £700).

As battery prices have come down, and as energy prices are rising I have decided that the pay back period is sufficiently attractive that it is worth acting now. Additionally, as I look to install whole house aircon and have just taken order of a new electric car, a suitably sized battery storage should reap serious benefits over it's lifetime. I am also now on the Octopus Energy Go Tarriff which allows me to draw electricity at 5p/KW between 0030 - 0430hrs each night.

Currently I have an offer of 17.4KwH of storage, installed, for a very reasonable £5495 however this, coupled with a planned £7500 for whole house AC, seems relatively simple to beat with a DIY system.

My plan is as follows:

16s3p bank utilising 48x 200ah cells to give me a 30.72kwh bank at 48v. This would link to an independent battery charger/inverter to compliment my Solax X1 boost solar inverter.

As my daily usage is approx 15kwh and I would expect this to increase to approx 25 (only occassionally) due to aircon (heating or cooling on hottest/coolest days of the year) I figured 30kwh of cells, compressed (for extended life) and generally kept between 30-80% charge would enable me to be entirely self sufficient (15kwh available) during peak energy cost hours, charge during solar generating weather windows, and top up only a small amount at night. This would save me easily £600 per year.

Now a few questions as I should mention that I am an amateur at best (although I am experienced/familiar with household electrics and the safety principles associated with this sort of thing),

Batteries - where is the best place to get them. I have discussed options with Amy Wan on Alibaba however she is offering 280 or 304ah cells which put things out of my price range. I have found some very cheap cells $40 for guaranteed 175 - 195ah capacity. I could oversize the system further if these were any good (beyond the average capacity). https://www.aliexpress.com/item/100...e-5&pdp_ext_f={"sku_id":"12000024300481546"}/


BMS - with the described configuration of cells, what would the best BMS configuration be to allow control/monitoring of each cell? How many BMS would I need? Note that I would want to be able to draw 60amp sustained load. Charging would be 60amps as it would need to share the replen window with my 7.4kw car charger. Also note I would not have the car charger on the same circuit as I would want this to run independent of the battery.

Charge Controller/Hybrid Inverter - what options should I consider. For the 60amp output (14.4kw) to the main house circuit what is the best choice?

I thank you in advance for your comments. If i'm barking up the wrong tree then please feel free to correct me/advise otherwise. I will not be moving forward on this until I have settled on design of the system so your advice is key.

Stew

 

[mrzed001]

To set the scene I currently have a residential solar install (3.6Kw) which is grid tied on the 2015 Feed In Tarif. This is reasonably generous and nets me approx 18p/KW produced whether self consumed or not (generating approx 4000Kw per annum so cira £700).

This will remain as it is or you plan to make it bigger ? (usually utility needs a contract and so and ...)

16s3p bank utilising 48x 200ah cells to give me a 30.72kwh bank at 48v.

Why not 16s2p of 280Ah or 310Ah cells ? Gives you 28,8 kWh or 31,7 kWh ?

This would link to an independent battery charger/inverter to compliment my Solax X1 boost solar inverter.

Do you thinking on an AC coupled system ?
There are several ways to make your Grid-tie system hybrid.

Hybrid inverter:


Or AC coupled system:


Or a simple UPS system:

BMS - with the described configuration of cells, what would the best BMS configuration be to allow control/monitoring of each cell? How many BMS would I need? Note that I would want to be able to draw 60amp sustained load. Charging would be 60amps as it would need to share the replen window with my 7.4kw car charger. Also note I would not have the car charger on the same circuit as I would want this to run independent of the battery.

A separate BMS is needed for every battery string paralleled

 

[Makia2020]

This will remain as it is or you plan to make it bigger ? (usually utility needs a contract and so and ...)


Why not 16s2p of 280Ah or 310Ah cells ? Gives you 28,8 kWh or 31,7 kWh ?


Do you thinking on an AC coupled system ?
There are several ways to make your Grid-tie system hybrid.

Hybrid inverter:
View attachment 60790

Or AC coupled system:
View attachment 60791

Or a simple UPS system:
View attachment 60792




A separate BMS is needed for every battery string paralleled

Thanks for the reply. Very helpful.

Ref your points.

AFAIK in the UK you dont need to tell the grid that you are storing energy......anyone? I dont think I would need to make it any bigger for a number of years.

16s2p would be fine - overall price is the key issue for me and I think with 310/280 it could work out significantly more expensive?

AC Coupled is what I was thinking. Other option is a suitable hybrid inverter but which ones would allow me to output at such high watts? Also the position of my solar inverter relative to my distribution board means it would be easier to add a battery inverter at the distribution board end of the circuit.

For ref im being quoted $136 per 310ah cell (plus delivery). Is this reasonable?

........

 

[mrzed001]

Thanks for the reply. Very helpful.

Ref your points.

AFAIK in the UK you dont need to tell the grid that you are storing energy......anyone? I dont think I would need to make it any bigger for a number of years.

I do not know but most places you can have your energy storage as you like
But to sell power to the grid, that is a different thing. Then usually you need a contract with the utility company.

AC Coupled is what I was thinking.

It has advantages and disadvantages.
You need a limiter to control your output from battery (not to sell to utility)
You need an AC coupling inverter (cost a lot). Most of them need 2-400Vdc battery like Sunny Island (that cost a lot more too).
Victron is an option (expensive but good)
You need an automatic disconnect on your main to be able to use it in a blackout. The switch is 5-50sec so in this time your equipments will shut down

Other option is a suitable hybrid inverter but which ones would allow me to output at such high watts?

There are some hybrid inverters. They are grid-tie too so can sell to grid.
Voltronic Infinisolar 10kW for example is a 3 phase inverter that has all certificates needed.

The UPS solution is the cheapest. Can connect max 9 of 5kW or 6 of 8kW inverter to the 48V battery.
And everything connected to them has continuous power.