Expanding Battery Storage in a Rental — What's the Best Approach?

Hi all,
Some of you may have seen this here:

But for the rest, adding some context:
I live in a rented house that has an existing solar setup with solar panels, a 5 kWh Hubble battery, and a 5 kW Deye hybrid inverter. I can’t make physical modifications to the setup (for warranty reasons at least) but can change system parameters if needed. I want to add more battery capacity (~ 2-3 kWh) to reduce reliance on the grid given that there is surplus solar power during the day. I am leaning towards a DIY battery setup. What kind of inverter would I need to add this extra capacity, and how would it integrate with the current setup?

The ideal scenario would be where the new inverter plugs into a standard wall socket and charges the batteries with solar and discharges them the rest of the time. Bonus points for monitoring via Home Assistant. Basically, a glorified DIY UPS.

Currently available for this project:

  • 2x 25.6V LFP batteries 1280Wh each. Can always disassemble down to the LFP cells but would prefer not to.
  • In future, might extend with a number of 3.2V LFP cells depending on how flexible this setup is

Some things I have learnt:

  • Factor in inverter idle power draw
  • There seem to be Victron chargers/inverters that would talk to these batteries

Is that not called a “suicide socket”?
The charging part is no problem.
Feeding back on same socket is frowned upon.

Why not ask you rental company to connect the additional battery for you?

If I were in your shoes, I would buy a 2nd hand hubble battery (same model as existing) and just connect it in parallel with the existing one.

Fair enough - rental - just huge installation cost implications. Kills the whole point of this exercise.

Ok so let’s assume not suicide socket :smiley: . How about output through another socket. Like a UPS.

If you mean it then works like a normal stock standard UPS, charged with spare solar production, that is fine.

But could be a PITA to manage the SOC so that the UPS does not switch off when the battery is depleted.

Take your time, wait patiently, and get a extra battery and have it installed in parallel, the longer term more permanent solution.

Just make sure that WHEN you add a battery, that the panels are still sufficient.

Cause solar systems, “Down the Rabbit Hole we go” when we sit one day and start thinking of betterment. :rofl:

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Did you discuss it with your landlord? Maybe discuss with him that you buy the battery and then offset it against the rent over say 4 or 6 months?

Long done. He is not interested in spending a single cent over what’s been spent already.

Had a thought.

You want to reduce you Eskom draw.

Is it an option for you to consider, part for part, like a 3kva MPII for example, with said new battery?

Built a system that when you one day move, you have a grid-tied system to take with.

Until that day, you don’t need a MPPT/panels as he existing system will charge your new batt.

Is it an option you would consider?

Ps. Then you can also use ANY battery you want.

Yes exactly that idea. One day when I move I’d like to take with me easily. And since I have batteries, I thought I only need an inverter to get started. And yes definitely no need of MPPT and panels in this story. What would you suggest as a design?

You have the batteries.
3kva MPII, to keep costs down, or 5kva.
Rpi Venus (need so cables) or a Venus or the Cerbo.
Assuming the battery can communicate with the Venus/Cerbo, you are sorted.
If not, dumb Lifepo4 battery, get a BMV for the SOC.

Then you can start playing with the Venus / Cerbo to schedule charging.
Or some more clever moves if the rental inverter can communicate with like HomeAssistant / NodeRED.

Looks like we’re getting somewhere. But newbie so questions.

  1. 3kVa would work. Is this inverter noisy I.e. can it run next to a TV quietly?
  2. I was wondering on the comms. Didn’t know about Venus. Can it be run as a virtual machine? If not, I have a RPi so it’s all good.
  3. Deye right now is on Home Assistant, read only made basically. Scheduling charging is easy though, I have one of those smart plugs linked to Smart Life/Tuya and Home Assistant. Can use this method at worst.

The problem with feeding a plug in inverter is routing the output. How will you power the whole property? If your plan is to just provide for one or two circuits at night - things that you can power with an extension lead - then OK.

I think your best option is to buy another Hubble, with the understanding that it is yours and when you go, the battery goes. It will not be cheap (batteries are the most expensive component in most setups) but you will then have a basis for a system of your own. In the meantime you won’t have to change the DB or plug anything into something else.

In the meantime, do as much electrical work in the day whilst the sun is up as your routine allows. Heat the water. Run appliances.

I have 10kWh of battery. We get through a night easily because we try to do as much as possible during the day. So at night we run the TV, fiber/wi-fi, security systems, external & internal lighting, fridges & freezer, and use the kettle a couple of times. Then at 6:00 (sun is up in summer, but we are not getting a lot of PV) I heat the water (heat pump) and still have some battery left over.

Work out what you can do during the day, and let the sun power as much of that as possible.

Not what you asking but please accept in the kindest/friendliest manner that this forum is known for ( :slightly_smiling_face: ) that it sounds a bit like you are more motivated to scratch the itch to tinker than anything else.

The best solution, as it seems people also pointed out on Carb, is likely to add another Hubble to the existing setup (installation costs or not liking the brand/customer service do not seem like very good reasons to not do it).

Other than having a UPS for when/if (ever?) you move, to then power essentials during power failures the “take with me” is also a red herring. You will likely struggle to use the UPS as a base for a full PV system for an entire household. Other than Pylontech I will not easily place bets that you will be able to add batteries to the system without all kinds of weirdness happening - assuming the “brand” is still around. 3kVA will be too small as far as inverters go and 24V overall not well suited to large household loads.

Unless you were gifted all the components or picked up really good bargains somewhere there does not seem to be much benefit in throwing money at this system.

Turn down the brightness on the 300W TV/save electricity costs without spending money and use the money from the Frankensystem to rather start/add to your funds for a deposit on your own place where you can install your own a system properly.

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Agreed it seems routing the output is tricky, so let’s assume UPS mode - 1 in and 1 out to some extension lead. (In theory, my understanding is that inverters feed power back to the grid simply by having their voltage slightly higher than the grid, so that power flows to the grid and not from. Open to understanding better. So I thought, a plug in inverter would work similarly except that the grid is the home wiring)

Let’s assume I get another Hubble - I guess we just wire it to the existing Hubble, and take it when I go right?

Electrical work, yes we have already done the behavioural optimisation. So we are left with pretty much what you described. TVs, etc. We have about 15 kWh being generated daily, only 5 kWh of storage vs about 7-10 kWh of usage. That’s pretty much the issue.

Keeping this in mind too:

What the others said.
But I read, the questions you are asking, you want to learn a bit more …

Answering the questions:

  1. No it is not UNLESS it is working flat-out and/or the ambient temp it is high, the fan will come on.
  2. Read more here: Raspberry Pi running Victron's Venus firmware - Victron Energy
  3. What I would try and figure, at your leisure, others can jump in to help: How to get the Deye HA to tell the Venus to start charging the battery.

Steps I would take:

  1. First decide If this is the route for you, or not?
  2. Then setup the Venus Rpi, following that link I posted above, and play a bit.
  3. Then see if you can get the HA (HomeAssistant) to communicate with the Venus. Others can help.
  4. Decide if you can make that battery, would want to, into a 48v 16cell battery?
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Remember to tell him he needs an mk3-USB if he goes this way. People sometimes forget that.

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@Village_Idiot - what is this forum known for :smiley: ? But you’re on the right track, I do have a motivation to tinker - not as much as most, but some definitely. That said, only went down this road because the incomplete maths looked promising. Of course, it will cost time and effort. So absolutely, I accept the friendly feedback.

On the carb answer- Add a Hubble AM-5 - it was something like R 30k for 5.12 kWh of added capacity i.e. R 6000 per kWh. This wasn’t making much sense. Was cheaper to go Eskom. Also with the caveat of Hubble. I really don’t mind paying, but not for the shit service experienced with them - unless that’s the benchmark with all. A good workaround, would be if I got an in warranty used Hubble!

As for a move, I expect it within say 12-18 months. It is definitely not intended as a base for an entire system, but I get your point. The ideal in hindsight would have been a Deye or some other reputable battery, to which I just added an extra one now.

Nothing, I can do on the TV more really. It isn’t a fancy OLED so I can’t watch some of the shows in the day - the contrast ratio isn’t that great (assuming I had the time to watch TV in the day). So it leaves it to the night.

Given real estate here, no plan on buying. Shitty return. But yes, the point of investing into a proper own system stands.

Was going to be my next question - cost of connecting everything up. It adds up! But I’ve got some homework for now thanks to @TheTerribleTriplet and the rest.

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Remember the MK3-USB cable you will need.

Maybe someone has one for sale here, or elsewhere, cause they are not that used anymore, all the upgrades from Victron, so there is one laying in someone’s drawer who wants to sell it to you. :slight_smile:

Mine, I have used it a few times on very old Victron 2nd hand equipment to bring the firmware inline with the latest updates. So I say, if you tinker, you need one in a drawer for that one day in the future where you REALLY need to access a inverter when all else has failed.

And you can use yours for the RPI.

Note: Need to run the Rpi direct off the battery when you go live. Today it makes no difference. Use the PSU.

Titbit:
New Rpi and all it needs.
New MK3 cable.
VE-Direct to USB cable/s for future MPPT’s
All adds up that if you shop right, a new Venus can be similarly priced.

If you have a Rpi, can get a “pass it on” MK3 cable and no need for VE.Direct to USB, that is THE cheapest Venus OS (the brains of the system) you will ever get.

Is there a thread here (so that I don’t ask repeat questions) for the commonly used Victron monitoring things (VE.Direct, these cables, GX, etc.) apart from the Victron website?