Am I expecting the impossible

I'm looking to build a battery storage system, I'm fine with all aspects of the battery side of things, the inverter however is a different story.

My aim is to have 48kWh of storage and an 8kW inverter, what I'm hoping to achieve is a situation where the inverter provides my house power until the battery is depleted and/or off peak power time starts. If the demand exceeds the inverter capability, iwould like either, the inverter to supply its maximum output and additional power drawn from the grid or the inverter to switch over to grid operation i.e. all of the power coming from grid while the demand is exceeding it's capability. During the off peak time, i'd like the inverter to charge the battery although I'm happy to have a separate battery charger.

Every company Ive contacted seems to throw a spanner in the works and say it cant be done. My thinking is that if it cant be done with a battery input to an inverter, surely it can be done if I feed the battery into the solar input of the inverter i.e. 48v@320ah.

Am I being unrealistic here with want I'm trying to achieve?

what you are referring to is a hybrid zero-export setup...
this an be done by a number of inverters, amongst sol-ark/synsunk/deye and the mpp solar MPI / lvx6548 series.

The only thing regarding the mpp's i am not sure of the the peek load that exceeds the max of the inverter.
then again... add an inverter and that solved too....

What you want is possible: I built a DIY system that can do exactly what you want. My system happens to have a 9.6kW solar array for charging the 48kWh battery bank but that's not required (or even available at night and cloudy days). All you need is an all-in-one inverter, batteries, and the wire, breakers, terminals, etc. to hook it all together. You can always add panels (or another power source like hydrogen fuel cell or thorium reactor later).

My system (for example) has a Growatt 12k inverter connected to a 48V/800Ah battery bank that powers the AC panel for the house. It's an off-grid configuration so no complications with grid tie permits and poco (Power Company) permissions. The Growatt inverter is configured in SBU (Solar, Battery, Utility) mode so it powers the load in that priority. When the batteries are low (and there's no solar to charge them back up) the inverter automatically switches to utility power (from the poco meter) and powers the house while charging the batteries up to a level I can set in the programming (mine is set to ~25% SOC to minimize poco dependency).

This system runs my entire house (2200 sq ft, 2 AC units, induction oven/cooktop, electric dryer, and heat pump water heater) most days completely from sun power. It does dip into poco power during hot summers and cold winters when the AC heat pumps are running a lot. I do have to pay attention to what loads are running to prevent overloading the inverter: cooking (5kW), drying clothes (4.5kW), and running one or both AC's (1.5kW each) at the same time will push the system over it's limits and lead to a fault/power outage.

Do you know what your peak draw for 15 min in 30 days is? That will help you size the inverter (if you haven't already). My value (from monitoring my panel with an Emporia energy monitor was 9.34kW so i sized the inverter up to 12kW.

I don't think your being un-realistic and what you want to do is completely possible at a reasonable expense, and you'll have flexibility to add alternative power sources if you want in the future. There are lots of options and configurations you can use to create the system you want.

Thank you houseofancients and iMakerShop for your replies, I seem to be talking martian to all the suppliers Ive asked, none of them really understand what I'm trying to do.

iMakerShop - you say you have to watch the loading to avoid a power outage, in my situation, still having a grid supply could the inverter either cease operation and seamlessly switch to grid power of could it add some grid power to it's output to meet the demand.?

In your setup does the inverter sit in parallel with the grid supply or in series with it, I have seen both configurations online, I dont want to have to select certain circuits to supply by grid and others by inverter, I want to do it all via the inverter+grid when needed.

I also think it’s possible with Victron and the ESS services. I don’t know that for sure- I use it in my RV and so I was not paying attention to that part.

Good luck with your project.

"....If the demand exceeds the inverter capability, iwould like either, the inverter to supply its maximum output and additional power drawn from the grid or the inverter to switch over to grid operation...."

If I'm understand your ask correctly.....
Its the auto-supplement to "additional power beyond the max of the inverter" that (to me) is the difficult issue. I don't know the answer but that seems like the key issue.

In my case, it's either the inverters that energize the circuits or the grid, but it's not smart. My inverters would throw a breaker if the power draw exceeded their max and then the grid would take over... but its a manual process to reset the breakers to re-enable the inverters.

If you can't find a smart grid-aware unit that does what you want, you could rig something automatic to act like mine does - but before going there, I'll follow this thread to see what shakes out.

The key thing - am I understanding your ask?

OffGridInTheCity said:

"....If the demand exceeds the inverter capability, iwould like either, the inverter to supply its maximum output and additional power drawn from the grid or the inverter to switch over to grid operation...."

If I'm understand your ask correctly.....
Its the auto-supplement to "additional power beyond the max of the inverter" that (to me) is the difficult issue. I don't know the answer but that seems like the key issue.

In my case, it's either the inverters that energize the circuits or the grid, but it's not smart. My inverters would throw a breaker if the power draw exceeded their max and then the grid would take over... but its a manual process to reset the breakers to re-enable the inverters.

If you can't find a smart grid-aware unit that does what you want, you could rig something automatic to act like mine does - but before going there, I'll follow this thread to see what shakes out.

The key thing - am I understanding your ask?

Click to expand...

Maybe I haven't understood how it works with solar? I believed that when you have solar panels if theyre generating say 2kw that 2kw is fed into your domestic supply and anything extra is supplied from the grid. So for example solar is generating 2kw, I turn on a 10kw shower, 2kw is supplied from solar and 8kw from the grid, have I understood this correctly?
I assume the inverter can load itself up by the output sinewave leading the grid sinewave, the more it leads the more load is applied.
If I have assumed correctly panel operation and inverter, whats to stop me replacing the voltage from the panels with voltage from batteries?
Powerwalls like the Tesla one appear to work in the way I want but I dont want to pay Tesla money, there must be an inverter out there that can do it, I cant believe I'm the only one wanting to work in this way.

Let me try to help the discussion along. I'll even suggest a solution but I suspect it's not how you're thinking of things.

johnb80 said:

Maybe I haven't understood how it works with solar? I believed that when you have solar panels if theyre generating say 2kw that 2kw is fed into your domestic supply

Click to expand...

How exactly is this PV fed into your domestic supply - e.g. home? It has to go into a UNIT (e.g. a piece of hardware)

johnb80 said:

and anything extra is supplied from the grid. So for example solar is generating 2kw, I turn on a 10kw shower, 2kw is supplied from solar and 8kw from the grid, have I understood this correctly?

Click to expand...

You want a UNIT that takes in PV and Grid and outputs power to everything in your house.

johnb80 said:

I assume the inverter can load itself up by the output sinewave leading the grid sinewave, the more it leads the more load is applied.
If I have assumed correctly panel operation and inverter, whats to stop me replacing the voltage from the panels with voltage from batteries?

Click to expand...

Voltage from panels is completely different than voltage from batteries. Panels have wide swings in power and need a 'charge controller' (MPPT) type functionality to convert the power into something. Batteries are a steady state source during discharge but need a charger - different than PV. PV and Batteries are fundamentally different sources of power.

johnb80 said:

Powerwalls like the Tesla one appear to work in the way I want but I dont want to pay Tesla money, there must be an inverter out there that can do it, I cant believe I'm the only one wanting to work in this way.

Click to expand...

Tesla the battery is one thing. But it sounds Tesla the UNIT (that controls things) doesn't have what you want.
You can create you're own battery.

The key thing here is you want a UNIT (a piece of hardware) that
1) Takes in PV power
2) Takes in Grid power
3) Takes in Battery power (and can also charge the battery).
4) And outputs power....
This 1,2,3, and 4 are easily found in all-in-one units such as MPP Solar or GroWatt - it's what they do.
--------------
5) Share excess PV back to the grid.
Some units do 1,2,3,4 and 5 - but you haven't expressed sharing excess to the grid.


BUT.... you want one more thing - e.g. a number #6
You want Grid to automatically assist the output power (#4 above) if the demand is greater than what the UNIT can deliver.

To me, you need to find a unit or set of parallel units big enough to provide the MAX power demands for your situation and then let the unit manage the PV, Grid, Battery. If you want it all managed, it all has to go thru the unit's management. One could start going off on DIY tangents thinking about parallel power stream management - but that's not the mainstream approach so equipment won't be easily found.

QUESTION: What is your max power you need? 240v/120v (US?) @ 200a?

johnb80 said:

Powerwalls like the Tesla one appear to work in the way I want but I dont want to pay Tesla money, there must be an inverter out there that can do it, I cant believe I'm the only one wanting to work in this way.

Click to expand...

This yt video of different types of UPS - on line, off line, line interactive, may assist your understanding.

OffGridInTheCity said:

Let me try to help the discussion along. I'll even suggest a solution but I suspect it's not how you're thinking of things.


How exactly is this PV fed into your domestic supply - e.g. home? It has to go into a UNIT (e.g. a piece of hardware)


You want a UNIT that takes in PV and Grid and outputs power to everything in your house.


Voltage from panels is completely different than voltage from batteries. Panels have wide swings in power and need a 'charge controller' (MPPT) type functionality to convert the power into something. Batteries are a steady state. 2 different sources of power.


Tesla the battery is one thing. But it sounds Tesla the 'unit' (that controls things) doesn't have what you want.
You can create you're own battery.

The key thing here is you want a 'unit' (a piece of hardware) that
1) Takes in PV power
2) Takes in Grid power
3) Takes in Battery power (and charges battery) - e.g. manages battery per settings.
4) And outputs power....
This 1,2,3, and 4 are in all-in-one units such as MPP Solar or GroWatt - it's what they do.
--------------
5) Share excess PV back to the grid
Some units do 1,2,3,4 and 5 - but you haven't expressed sharing excess to the grid.


BUT.... you want one more thing - e.g. #6
You want Grid to 'automatically' assist the 'output power' (#4 above) if the home demand is greater than what the UNIT can deliver.

To me, you need to find a unit or set of parallel units big enough to provide the MAX power demands for your situation and then let the unit manage the PV, Grid, Battery. If you want it all managed, it all has to go thru the unit's management.

QUESTION: What is your max power you need? 240v/120v (US?) @ 200a?

Click to expand...

So if I understand you correctly, fit say 20Kw inverter, battery and mains in to the inverter, the output goes to my fuseboard. The inverter will use the battery until depleted and then use mains either pass through or change to DC and use that mains to power the inverter?

johnb80 said:

So if I understand you correctly, fit say 20Kw inverter,

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OK so you have a max load of 20,000w (for this discussion). Great - that's in the ballpark with parallel'ed equipment.

johnb80 said:

battery and mains in to the inverter, the output goes to my fuseboard.

Click to expand...

The UNIT(s) would connect to grid, pv, and battery and on output - a standard AC distribution panel - which has the breakers/circuits for the loads (house).

johnb80 said:

The inverter will use the battery until depleted and then use mains either pass through or change to DC and use that mains to power the inverter?

Click to expand...

An inverter takes DC and converts it to AC. So the UNIT is not an 'inverter' but a combination of charge-controller, battery charger, UPS (sometimes), and inverter - e.g. inverter is one part of the UNIT.

The MPP Solar and Growatt UNITs have options - but one common option is to feed incoming grid -> battery and then the battery is inverted to the output. So the output is always coming from the battery - but it may be a pass-thru as you describe. The advantage of AC -> DC/Battery -> AC Distribution panel is that you gain a natural UPS function so that sensitive circuits like computers are not bothered as things switch between grid and battery.

But it sounds like you're coming around to the idea of UNIT or UNIT(s) managing the max load you need - which I think is the right direction

Not pushing any of these but using it as examples.
- MPP Solar can do 9 in parallel for 54,000w - https://www.mppsolar.com/v3/lvx6048/
- Growatt can do 6 in parallel for 6 x 5000w = 30,000w - https://tennesseevalleysolar.com/growatt-spf-5000-es-install/

Here's a youtube on 3 x GroWatts (15,000w total) in parallel - to give you some DIY visuals.


QUESTION: Are you planning to DIY this? or are you looking to hire this done?

johnb80 said:

Thank you houseofancients and iMakerShop for your replies, I seem to be talking martian to all the suppliers Ive asked, none of them really understand what I'm trying to do.

iMakerShop - you say you have to watch the loading to avoid a power outage, in my situation, still having a grid supply could the inverter either cease operation and seamlessly switch to grid power of could it add some grid power to it's output to meet the demand.?

In your setup does the inverter sit in parallel with the grid supply or in series with it, I have seen both configurations online, I dont want to have to select certain circuits to supply by grid and others by inverter, I want to do it all via the inverter+grid when needed.

Click to expand...

My system (and most off grid systems) has an output limit: 12kW peak in my case. I sized the system (max load) knowing that my homes peak 15-min consumption in a 30-day period is around 9.5kW in summer. My system cannot use grid power to go beyond that limit so I manage my loads to stay below it. That covers >98% of my use cases. To size the system to power a load greater than 12kW that could happen once or twice a year would cost more but provide little added value.
If I need more than 12kW I can always manually bypass the system and use grid power in those rare cases.

johnb80 said:

and/or off peak power time starts.

Click to expand...

I overlooked this in the original post... It sounds like you a system (battery, inverter, and charger) that:

• stores up to 48kWh of energy for use only during peak utility (rate?) times...
• recharge the storage during off-peak times when your not using power for your loads
• power your loads during peak times and ONLY draw from the grid during peak times if the load demands more than the system can supply.

Basically smart "capacitor" for the house that reduces your kWh cost.

Is that basically it?