14KwP Solar ONGRID possible to add DIY LiFePo Battery Bank ?

[msdmaddog]

Hi everyone,
iam very new to this topic, i probably have seen nearly all of Wills Videos very interesting, but i see only OFFGrid Setups with the batteries and iam trying to get to the point if its possible to add a battery bank explained in the videos for on ONGRID solar system in addition.

I currently have an ONGRID 14kWP solar installation with a dedicated Inverter just for solar (HUAWEI STL12000) and no battery bank. i charge my EV and other power devices automativally steered with homematic.

The house power installation panel has a 2 way energy counter (IN and OUT) so i can feed into the grid with no problem, but i dont get got rewards for feed in, so i would like to optimize the own consumption. To control the energy flow i have a energy meter connected to a solarlog 300. So my central control unit (Homematic) can switch house devices like heat pumps etc. automatically. the homematic always know the power demand of the complete house in comparison of the solar energy production.

i would like to add a DIY LiFePO Battery Bank to cover the inhouse power draw when no sun is shining.

The buildup of the battery bank itself is clear, but if it comes to the battery charge controller and the inverter to fit into my system, i dont know which one is capable to play in the present solar system i have. the battery bank itself must be charged AC 240V as the present solar converter (Huawei STL12000) has no battery integration port / feature. the charge controller must be controlled somewhere over a webaccess or json, in such way to load the battery when i have sufficient solar power and to draw power from the battery when the house requests it ? i can trigger from my homematic on a webdevice to activate possible charging for instance.
How can it be done, which battery charging unit / inverter is capable of such a feature ?
Do i need to control the inverter also, or is it driven by the demand of the house "automatically".

thx for taking your time to explain.

bb
Tobias

 

[msdmaddog]

as i understood, it need this kind of inverter / charger : https://www.aimscorp.net/4000-watt-...vdc-to-120-240vac-output-listed-to-ul458.html
but i dont unterstand how to control that device to charge batteries or to discharge to feed the house power drawings.

 

[svetz]

As you already have a grid-tied PV system and want power for grid outages you'll want to look into AC Coupling. This link should help get you started: https://www.altestore.com/store/info/ac-coupling/

I think what @msdmaddog is suggesting is an inverter with an automatic transfer switch built in. With that, you can set up a critical loads subpanel and have the grid feed it while the grid is available, but those circuits will switch to battery backup when the grid goes down. The only downside is that when the grid is down, you still won't get solar power. To get battery and solar when grid-tied during an outage, you need a hybrid inverter or an AC coupling solution.

 

[msdmaddog]

thanks for your feedback and information svetz.
maybe you got me wrong. i dont want UPS or power backup functionality when the grid is down (here in the region its pretty seldom to have no power from the grid). so if this feature is complicated its absolutely not necessary to implement.

i will have a look inside your link for more information, because i dont understand how the power distribution works between these components.
when i have surplus power of 2kw from solar i need to tell the inverter to load the batteries when no other power device in the house needs this 2kw.
otherwise the power will be feed into the grid.

as i see in your link mentioned, the sunny island SMA SUNNY ISLAND 4.4M / 6.0H / 8.0H should handle the job, but i see a problem with the integrated charge controller its only designed for certain batterie vendors. i think i need this kind of device with a more open charge controller to handle selfmade batterie banks.

 

[svetz]

I don't endorse any specific hardware, the link was just to give you an overview of AC coupling.

Apologies if I misunderstood your needs... I think I get it now... What you want to do is store excess power into batteries rather than export to the grid during the day and use that power first in the non-daylight hours supplementing from the grid only after it's exhausted. But the AIMS inverter listed isn't what you want as it's ATS will only switch to batteries when the grid is down.

There are inverters that have a priority and mode and will only export power to the grid if the batteries are full. I believe Sol-Ark, skybox, the Sunny Island, and a few others will do that; look for a zero-export or priority mode feature.

But, since your utility isn't giving you credit for exported power, you might not need a grid-tied inverter or an expensive hybrid inverter. A regular off-grid inverter might work.

Let's see what other folks think about this idea:
Sell your grid-tied HUAWEI STL12000, replace it with an off-grid inverter and a whole-house ATS. Reverse the ATS's AC inputs so power will normally come from your inverter/battery and switch to the grid when the battery runs out. Run the solar to power your batteries/inverter. In this case the cycle would be:

1. Battery low-voltage cutoff occurs and ATS switches to grid, house is powered but batteries not charging
2. Sun comes out and batteries start to charge via solar, ATS switches to battery/inverter. Solar provides enough to charge and run loads
3. Once the batteries are charged, any excess solar power is lost (not grid-tied anymore)
4. Sun goes down, batteries start to drain as they handle the house load, finally back to 1

So you loose out on #3, but it sounds like the utility isn't providing anything for the power you export anyway. Non-hybrid inverters are typically less expensive, so it might save you money. As you already have a sunk cost with your existing inverter the Sunny Island might end up being better; you'd have to run the costs to know for sure. Consider also where the HUAWEI STL12000 is in it's life cycle (if it's already out of warranty might be better to consider it at end of life).

 

[msdmaddog]

Thx so much for your input, your interpretation is completely right now. i can feed into the grid it is allowed but i only get 6 cents.

i dont want to touch the solar grid tie inverter huawei STL12000 as it is pretty new and the system was installed by a solar company (warranty)

i searched a bit further and found the SMA sunny island is pretty expensive. i would rather go with the Victron Multigrid:

MultiPlus - Victron Energy

The MultiPlus, as the name suggests, is a combined inverter and charger in one elegant package. Learn more about the MultiPlus models.

www.victronenergy.com

i have a energy meter which senses all 3 phases of the complete house with an S0 Output to report to my solarlog.

so actually i "just" need a battery charger / Inverter which can handle S0 signals or i can set parameters over a webserver on that device.
The only bad thing about the victron Multigrid is as far as i can see, that it cannot handle S0 Input from my energy meter. they propose their own energy meters with Modbus Interface which the VIctron has.
so i certainly need a energy meter of Victron in addition to report the Victron Multigrid to control the charge power of the battery upon the power demand of the complete house, or there is a possible adapter device from Solarlog to Victron maybe i have to ask them.

 

[msdmaddog]

hereby i have done a drawing of the components and supply for the future battery bank integration. maybe this one makes it more clear aswell.
can you please have a look and comment if you find anything non-working in that configuration.
thx