AC Coupled Battery

[johnb80]

I have a 6.7 kWh Solar Array, with a 6kW Growatt Inverter and a 7kWh Growatt battery. The system works beautifully and is easily capable of meeting my needs in the summer. In the winter however, this will be an issue.

I'm trying to add another invert and battery to my system. I have read so much documentation and threads my eyes are bleeding and I cant come up with a solution. What I'd like to do is to install my DIY 16 kWh battery in an outbuilding along with another inverter. Normal grid tied operation i.e. it sees energy being imported it increases it's voltage, energy going out to the grid it decrease its voltage. I want to have the option to charge my battery off peak, no problem there. Where I come unstuck is how do I make the inverter use excess energy to charge the battery eg my solar PV system is driving 1.5kWh back to the grid, how can I harness that to charge the battery on inverter system 2? Does such an inverter exist?

Ive outlined LifeP04 eve 300Ah batteries, DALY BMS etc, any suggestions / comments appreciated

My other thoughts was to get a 10kW inverter with a battery charging unit to feed it and charge my batteries, the house to run off this inverter completely i.e. the house not connected to grid. Excess power when detected increase the charging current when it starts to import from the grid, reduce the charge current.

I assume the likes of Tesla Power Wall work in this manner.

Many thanks in anticipation - J

 

[newbostonconst]

Is it pushing back power to the grid when the battery is almost full or at least above a certain percent? If so adding more battery capacity might help or is there a Float/Absorb setting you can rise the voltage on?

 

[johnb80]

Is it pushing back power to the grid when the battery is almost full or at least above a certain percent? If so adding more battery capacity might help or is there a Float/Absorb setting you can rise the voltage on?

Hi,
Thanks for the reply. I haven't put the 2nd inverter / battery together yet, I need advice on what's possible and what should be trying to purchase etc

 

[newbostonconst]

Hi,
Thanks for the reply. I haven't put the 2nd inverter / battery together yet, I need advice on what's possible and what should be trying to purchase etc

But on the current setup, what is the Absorb and Float voltage set at?

 

[johnb80]

But on the current setup, what is the Absorb and Float voltage set at?

I assume the defaults within the internal BMS of the Growatt battery, I cant see a way to get to that and I'm not sure chages at that point would help?

I'm really wanting to AC couple a battery for several reasons:-
1) To get more inverter power into the system to cover odd peaks eg 2 ovens running, hob and washing machine.
2) To get more capacity in there, in winter time I can charge on off peak tariff.
3) Physical space with the existing installation is limited, AC coupling would allow me to install it in an outbuilding.

Thank you again for your help.

 

[acdoctor]

On my contract so long as the amount I send to the grid is equal to or greater than my consumption I don’t get billed. My shop is strictly grid connected ( same meter though). If grid goes down it has not power but the house does.
Daytime: when running A/C in the shop and selling at the same time. The meter doesn’t see all of that just a tiny fraction in one direction of the other.
Night time: shop A/C buys from the grid.
I set my thermostat so that the net is zero. I sell some during the day and buy some at night.
I could set my Schneider to sell from batteries at night but don’t want to wear them out.

 

[johnb80]

On my contract so long as the amount I send to the grid is equal to or greater than my consumption I don’t get billed. My shop is strictly grid connected ( same meter though). If grid goes down it has not power but the house does.
Daytime: when running A/C in the shop and selling at the same time. The meter doesn’t see all of that just a tiny fraction in one direction of the other.
Night time: shop A/C buys from the grid.
I set my thermostat so that the net is zero. I sell some during the day and buy some at night.
I could set my Schneider to sell from batteries at night but don’t want to wear them out.

Here in the UK its just a little different. If I buy from the grid I pay 29.2p per unit, if I sell to the grid I get 4.2p per unit. Thats why I need to get more storage etc to avoid paying 29.2p.

J

 

[newbostonconst]

I assume the defaults within the internal BMS of the Growatt battery, I cant see a way to get to that and I'm not sure chages at that point would help?

I'm really wanting to AC couple a battery for several reasons:-
1) To get more inverter power into the system to cover odd peaks eg 2 ovens running, hob and washing machine.
2) To get more capacity in there, in winter time I can charge on off peak tariff.
3) Physical space with the existing installation is limited, AC coupling would allow me to install it in an outbuilding.

Thank you again for your help.

Only way I know of to do what you want is to stack inverters.....like add a second set of growatts but I don't know if that is an option with that brand.

You can stack with Sol-Ark, and some of the Outback stuff and I am sure others.

I have been searching for a way to "AC couple" a battery to get rid of my 300 watt base load at night cheaply. I have 35 kWh of battery so I am happy there. I have tried Enphase inverters hooked to my battery but haven't been able to repeatedly to get that to work.

 

[johnb80]

Only way I know of to do what you want is to stack inverters.....like add a second set of growatts but I don't know if that is an option with that brand.

You can stack with Sol-Ark, and some of the Outback stuff and I am sure others.

I have been searching for a way to "AC couple" a battery to get rid of my 300 watt base load at night cheaply. I have 35 kWh of battery so I am happy there. I have tried Enphase inverters hooked to my battery but haven't been able to repeatedly to get that to work.

I dont think I have the option with the Growatt inverter for them to work together.

 

[johnb80]

Ive been burning my brain to come up with a solution, do you guys think this could work

The second inverter on the right has it's own CT and battery but no PV. It would also have an RS485 comms link to a supervisory PC which will instruct it to charge the batteries and whatever rate it needs if energy is bang exported.