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Directional Ideas - Adding storage to an existing Mongrel Solar System

SolarNut

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Jul 9, 2022
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Hi,

Looking for direction to evolve my existing mongrel solar system by adding storage.

Here's what I've got:
Gen1 - 17 x Conergy 245 panels (2 strings, one nearly flat, the other about 20% north facing) with Sunny Boy SB4000 inverter. Originally installed Mid 2012 and now in asset sweating mode as its paid for itself. Its dumb and has no usable comms (bluetooth to a windows PC was all it offered at the time). Inverter out of warranty and coming up to 10 years old. Panels not suffering much degradation but efficiency pretty low per m2 by today's standards)
Gen 2 - 15 x Longi 450M panels (2 strings, one nearly flat, the other about 15% west facing to extend afternoon generation through summer peak) with SolarEdge SE6000H-US inverter. (6.75Kw of panels on 6Kw inverter) Installed Sept 2021. Its more intelligent and connected to internet and solaredge portal and app.
Gen1 is monitered by Gen2 with a Modbus Meter which clamps the output of Gen1 and provides the SolarEdge inverter with a view of Total solar input.
Gen2 also controls a Madimack Eclipse21 Pool Heat pump which consumes 0.62 to 3.02Kw via a SolarEdge Smart Relay
Both systems are grid connected single phase.

We are in Sydney Australia and have to work with some electricity distributor limitations
- 10Kw max inverter capacity per phase - i'm at max and Telsa wall is out for storage as its treated as 5Kw because its AC coupled so whatever storage I add needs to sit behind one of the two inverters.
- Net metering with ToU billing (its highway robbery during peak hours ~50c/kwh hence the desire to battery backup through peak and have "demand response" on high consumption devices such as as the pool heater.
- Very low feed in - 5c/Kwh so close to "use it or lose it"
- I export excessive amounts of power and even in winter on a sunny day, it looks like I could fill a 16Kwh battery taking into account normal day time consumption and then get close to zero net import.

So, I'm looking to add storage ... doesn't have to be home brew as I think the system is complex enough as is. Idea's:
- Easy but high $ - add LG RESU 16H prime to SolarEdge (alternative is RESU10H prime or the new SolarEdge 10Kwh battery system). Advantage is that SolarEdge can see overall production and decide when charge/discharge battery even though its only going to charge from the Gen2 system. Cost per warranted KwH looks to be about 24c. (seem to be about $1000/kw)
- Maybe more complex but less $ - add SMA Storage (eg. Sunny Island) or some other sort of storage controller with a range of alternative batteries that might have better lifespan/warranty conditions. But this may be treated like the Tesla wall as additional inverter capacity that's not allowed.
- Replace the SMA inverter with something cheaper and with a lower cost per KwH battery eg SunGrow SBR160 or 192 which looks to have cost per warranted Kwh of about 17c. But will need a new hybrid inverter which will add to the overall cost and not sure how to integrate the two systems.
- Add "storage" in the form of Heat Pump Hot water to replace old Gas Storage hot water. Seems to consume 5Kwh per day so maybe slighty lower $ per KwH but warranties on the heat pumps aren't as long as on the batteries.
- I'm trying to work out if there is some sort of option of a highly responsive smaller Lithium battery coupled with more of a deep charge Lead Acid /AGM combo to get to a better $ per Kwh situation where I could switch out the Lead acid with something like a sodium battery when they are fully commercialised.


Thanks in advance for any ideas.
 
I hear nothing but crickets in response to your post. My humble suggestion would be:
1) don't take it personally
2) do someone else a favor: dig into the research and figure out what you can (or what you think you might know :) ) and post it here.
3) maybe someone else will find that helpful OR find they can be of help...
 
My system is a bit different, but the challenge is similar. My original system is 4,800 watts of solar panels on Enphase microinverters, running grid tied.

I can't help you with the legal issues of connection in Australia.

Adding Solar Edge storage to your system does sound like a decent option, but it is not cheap. I think you would need to change out your solar inverter though. Solar Edge has specific models that work with storage, it is not an add on module. You should check your model number with Solar Edge to see if it is storage capable or not to be sure.

I looked into Enphase storage, and they were working on their Ensemble system, but it was not available yet. Once pricing estimates came out, I didn't think the cost was worth it to convert my system. It certainly is not an option for you , as it has to talk with the microinverters to work.

What I ended up doing, and we have at least 2 others on here with it, is adding a Schneider Hybrid inverter between the grid and the existing grid tied solar PV system. There are also a few others here doing it with Outback systems, either Skybox or Radian, and they have also released their new Mojave storage system. Another option is the Generac Power Cell. But all of these are battery based inverters that can potentially push energy to the grid input side, but they can also be configured to not do that. I don't know if that configuration is going to work for your legal interconnect. If they are saying no to a Tesla Powerwall, I don't see what the difference would be.

The more I think about it, a Sol-Ark might be a good choice. Swap out your older inverter for the Sol-Ark inverter, it is just a change f an outdated unit. But the Sol Ark can then add battery backup and it can grid form and AC couple to your Solar Edge as well. The Sol-Ark would also add monitoring of the old panels. I do not have one, as I felt the cost was a bit more than I wanted to go, and I didn't need the MPPT solar inputs. And back when I was looking, they did not recommend my level of AC coupled solar without also having some DC direct tied in solar panels. Since you do have that old array on an old string inverter, it makes for a good transition. The Sol-Ark also has a built in transfer switch, so you just add a panel after it for the loads you want to be able to run during a grid blackout. Here in the USA, Sol-Ark is the exclusive dealer for the Deye inverter that it is based on. You can probably save a chunk of money over there and use the Deye branded one. The software is a little different, but from their web site, it sounds like it will still do all that you need it to do. Check out this page.

 
Anything you can do to self consume more should help. The heat pump water heater instead of gas should help, although it's buying a new WH... But receiving only .05 for outflow, your gas cost might be more than that per equivalent heat into the water.

GXMnow's plan makes sense. I added SMA sunny Island battery inverters, to ac couple my older existing solar, and added more solar, when we lost net metering.
 
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