I already have solar, how do I add batteries?

I have 10.5kW of solarpanels on the roof, and a 15kW inverter to supply the grid.

Now I want to start with a DIY powerwall, but I want to do it right. Do I replace the 15kW inverter with a hybrid inverter?

Or do I just do the batteries separately, with a charger, BMS and a second grid inverter?

I wouldn't mind creating the rules/switching/controlby myself (when should the batteries charge, how much amps should they use to charge, same for supplying the grid), but I'm thinking this would go wayyyyyy easier with an integrated hybrid inverter, as not all inverters/chargers can be easily monitored/controlled through a communication bus I believe.

I am not off-grid, but I pay more for electricity I take off the grid at night than I receive for the power I supply to the grid, and that difference will continue to rise over the next 10 years or so.

If your inverter can use battery input you can use that. Or you'd need to have a separate charger/inverter setup.

More information would be needed from you to get a better answer. Like what "brand/model" inverter you currently have. Are you backfeeding into the utility grid?

Korishan said:

If your inverter can use battery input you can use that. Or you'd need to have a separate charger/inverter setup.

More information would be needed from you to get a better answer. Like what "brand/model" inverter you currently have. Are you backfeeding into the utility grid?

Click to expand...

I'm sorry, I'm new to this, I thought it was implied I was feeding into the utility grid if I'm not off-grid.

Right now I have a Delta RPI M15A 3 phase 15kW inverter tied to the grid, which cannot connect to batteries (which means it is not a hybrid, if I have my terminology right). So I'd need a separate charger/inverter setup, or replace my inverter with a hybrid inverter. I got that far.

My questions are:

How much do I lose if I use a separate charger/inverter setup instead of replacing the inverter I have with a hybrid inverter than can handle batteries? Is this inherently a bad idea?
If I'd go for a separate charger/inverter setup (grid-tied), what should I look for in terms of terminology (so that it can be grid-tied, and not just a UPS)?
What would be the best way to ensure I'm not dumping battery energy back to the grid, but only supply the energy to the home( grid) that would otherwise be pulled from the grid? Same goed for charging, I only want to charge with excess energy that's otherwise dumped onto the grid.
Are there 3 phase charger/inverter setups for batteries that can do different loads on different phases? Or would I need 3 different charger/inverter setups?

MrAlfabet said:

I'm sorry, I'm new to this, I thought it was implied I was feeding into the utility grid if I'm not off-grid.

Right now I have a Delta RPI M15A 3 phase 15kW inverter tied to the grid, which cannot connect to batteries (which means it is not a hybrid, if I have my terminology right). So I'd need a separate charger/inverter setup, or replace my inverter with a hybrid inverter. I got that far.

My questions are:

How much do I lose if I use a separate charger/inverter setup instead of replacing the inverter I have with a hybrid inverter than can handle batteries? Is this inherently a bad idea?
If I'd go for a separate charger/inverter setup (grid-tied), what should I look for in terms of terminology (so that it can be grid-tied, and not just a UPS)?
What would be the best way to ensure I'm not dumping battery energy back to the grid, but only supply the energy to the home( grid) that would otherwise be pulled from the grid? Same goed for charging, I only want to charge with excess energy that's otherwise dumped onto the grid.
Are there 3 phase charger/inverter setups for batteries that can do different loads on different phases? Or would I need 3 different charger/inverter setups?

Click to expand...

Depends on how far you are willing to rewire stuff, if you're looking for off-grid capability (ie. backup power) and how much you are willing to spend, the sky is the limit!

Try searching for the term 'AC coupled'. It will bring up some post regarding an AC coupled system, which is basically using existing grid-tie inverters and then having an AC charge/inverter to store and export the energy. This has some loss in it due to the DC->AC->DC->AC, but may be simpler to install. Now having a 3 phase does complicate things, but still doable. One way is to just export through one leg, which if you have one meter for all the 3 phases then it doesn't matter since it's net overall. May not do well for balancing so as long as you limit the output so the balance isn't that bad it may be ok. You talk about efficiency, so how much do you currently use vs. how much is sent back to the grid? If you use 30% and send 70% back to the grid, then you still net out ahead, but if you're using 90% and only sending 10% back to the grid then having a battery system may not be worth it once you factoring the losses.

No need to overcomplicate the design ....

https://www.victronenergy.com/live/ess:quick-installation-guide

3ph specific detail:
https://www.victronenergy.com/live/ess:design-installation-manual#three-phase_ess

Thanks for narrowing it down! I'll answer your questions/remarks so that we can narrow this down further.

I intend to die in this house (probably not, but we'll see), so I care less about ease of installation and more about doing things right.

As far as I can tell with the readout of the P1 port of my 3 phase smart meter, it only counts kWh delivered and returned for daytime and nighttime. I'm pretty sure they indeed don't care about each leg. That eases things up!

I use around 7000kWh a year, which my solar panels hit early september this year. The panels are only a year old, so will degrade a bit. According to my energy supplier, I've exported 3900kWh this year. Some of that will be used up by the A/C we'll be installing next year/this winter, but the rest I'd like to store for nighttime usage. I've got a homelab running, which uses around 300W 24/7, and a bit more when we're watching movies or tinkering with it during the night. My average day usage is around 25kWh, and is pretty equally distributed across the 24h, aside from some peaks (cooking, washing, drying, midnight snacks). I'd like the battery system to pick up on those peaks if we're drawing from the grid, and supply a bit more. As an example, today around 14:00 (end of summer here) I was sending back 4.5kW to the grid. On a peak in July I was sending back 7kW around 14:00.

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Sean said:

No need to overcomplicate the design ....

https://www.victronenergy.com/live/ess:quick-installation-guide

3ph specific detail:
https://www.victronenergy.com/live/ess:design-installation-manual#three-phase_ess

Click to expand...

Thank you! Nice to hear some Dunglish in the video I'll dive into those links.

The first thing to be aware of (and not a lot of people know this) is that you are allowed to have a panel array with a peak power up to 133% of your inverters rated peak power.

Examples:
If you have a 1.5kW inverter, you can have up to 2kW of panels attached.
If you have a 3kW inverter you can have up to 4kW of panels attached.
If you have a 5kW inverter you can have up to 6.65kW of panels attached.

And if you dont go over the 133%, you can claim the solar rebate (STCs) on those extra panels which will cover a big chunk of their of their cost (excluding installation costs and installer margin).

3kW of panels will generally only produce 80% (2.4kW) of their rated peak power due to losses.

4kW of panels, after losses will produce a peak power of 3.2kW. A 3kW inverter will safely clip this down to 3kW. So you are only losing 0.2kW of power. And that is only for a couple of hours each side of midday on a summers day. In the mornings, evenings and winter the peak power will be way less than the rated 3kW of thew inverter.

So oversizing your inverter by 133% is a good way to squeeze more energy from it.

Two big caveats here are that:

1)Unless your original solar installer does the upgrade you will void your existing system warranty.
2)It depends on your installer finding the same or very similar panels to your existing ones.

Just to keep in mind!

joeparker73 said:

The first thing to be aware of (and not a lot of people know this) is that you are allowed to have a panel array with a peak power up to 133% of your inverters rated peak power.

Examples:
If you have a 1.5kW inverter, you can have up to 2kW of panels attached.
If you have a 3kW inverter you can have up to 4kW of panels attached.
If you have a 5kW inverter you can have up to 6.65kW of panels attached.

And if you dont go over the 133%, you can claim the solar rebate (STCs) on those extra panels which will cover a big chunk of their of their cost (excluding installation costs and installer margin).

3kW of panels will generally only produce 80% (2.4kW) of their rated peak power due to losses.

4kW of panels, after losses will produce a peak power of 3.2kW. A 3kW inverter will safely clip this down to 3kW. So you are only losing 0.2kW of power. And that is only for a couple of hours each side of midday on a summers day. In the mornings, evenings and winter the peak power will be way less than the rated 3kW of thew inverter.

So oversizing your inverter by 133% is a good way to squeeze more energy from it.

Two big caveats here are that:

1)Unless your original solar installer does the upgrade you will void your existing system warranty.
2)It depends on your installer finding the same or very similar panels to your existing ones.

Just to keep in mind!

Click to expand...

Thanks! I oversized my inverter to be able to easily add more panels in the future. I installed the panels myself, and bought them through the company I work at. However, as we're still heating with gas instead of heatpumps and have no A/C it is not yet needed to place more panels. Also: I'm not in the states. No clue what an STC is.