Hybrid system conversion

[GlenB]

New to this forum!
I have two systems now: 1. an 8kw system with two Fronius inverters going to a separate power meter. This system is under contract with GA Power Company, and I receive $0.096/kw for my power. 2. an 6kw system with an SMA inverter, grid-tie. I only get around $0.035/kw for my excess power on this system. I currently pay around $0.14/kw for GA Power usage. That is the real-world rate, taking the kwh consumed divided by the BILL! I built this system entirely by myself, panels averaged around $0.62/w and inverters around $0.35/w. Wiring and conduit not more than $0.10/w.
Anyway, I want to change over to a hybrid system. Everything I see shows that I must convert from high voltage to 48V. Is this still true?
The GA Power system will stay the same, of course. I will need a new hybrid inverter, and was considering the 8kw Outback inverter. That has enough power to run most of the house. Millions of questions...
I would like to hear from people who have made the switch from high voltage strings, grid-tie, to 48v hybrid.
Thanks!

 

[snoobler]

Or AC couple an off-grid system to your existing system?

 

[the_colorist]

A few questions:

You're wanting to switch your 6KW SMA over to a hybrid system? So you're wanting to add batteries?

If so, what are you wanting to achieve? Complete grid-zero with the grid as a backup? Load shaving?

With those answers we can give you some ideas but in general you don't need to touch your existing string configuration. You just need to add a battery inverter and probably re-configure your AC wiring to accomodate. No need to waste or otherwise retire your SMA inverter.

I do not recommend Outback for this. It's premature to say but likely you would want to use SMA's Sunny Boy Storage or possibly the Sunny Island 6048.

 

[GlenB]

Yes, wanting to switch from grid-tie to hybrid. I have had some issues with SMA, nothing really bad. The Fronius have worked flawlessly from day 1. Was looking at Schneider 6048 hybrid, but wanted a bit more power, hence the 8kw Outback hybrid. 6kw will run virtually everything important here.
Ok, my wish list:
1. Use excess solar during sunlight periods to charge the batteries. May have to expand solar field, no problem.
2. Use the batteries when there is no sun, to achieve net zero (use no grid) when possible (night time as well).
3. I understand I will still have to use the grid when battery power is low.
4. Automatic disconnect from the grid when the grid goes down.
5. I need a "grid lost" signal output somewhere that I can run to contactors to disconnect stuff like emergency heat strips, dryer, etc..

 

[Hedges]

If you install Sunny Boy Storage (400V battery inverter), it will suck up excess PV production so you don't sell it to utility at a low price.
It will return power from its batteries so you don't buy power at a high price.
Does your price per watt hour vary during the day? For people with that rate schedule, they sell power the utility at a high price.
If not, you can use PV and battery to be as self-sufficient as possible, buying more as needed from utility.

You can manually enable a 120V 2000W outlet for power during outages using just that equipment.
You can add "Automatic Backup Unit", a transfer switch and 120/240V transformer, to have complete UPS backup operation with PV and batteries during grid failures.

Alternate system, you can install Sunny Island (48V battery inverter) as backup.
I'm not clear on how well it works at "zero export", "self generated consumption"

I have net metering with same price for buy/sell to utility so Sunny Island works for me.
Potentially Sunny Boy Storage would work better by gaming high/low time of use rates. But, not clear to me cost of battery justifies that.

If you can sell power or $0.035/kWh and buy for $0.140/kWh, utility is providing service as a battery for $0.105/kWh.
I think that is a good deal, and batteries would cost more, like $0.200/kWh.
Unless you're able to buy batteries cheaper (per kWh of lifetime use) than the last time I checked, I think battery system would be a financial loss.

Better to enable loads for the purpose of use-it-when-you-make-it.
For instance, unplug refrigerator/freezer at night. Plug it in to make ice again after the sun comes up.
Enable electric water heater when excess power is being produced.
Etc.

 

[the_colorist]

I would be very interested to hear the issues you have faced with the Sunny Boy.

How much PV do you currently have installed?

If you're wanting more than 6KW for loads at night (Sunny Boys will assist during the day), the Sunny Boy Storage may not be as perfect a fit as I had initially thought.

In 2016 they said they would be adding parallel operation via a firmware update which would allow you to use multiple units in parallel to exceed 6KW. The latest firmware notes have no such ability mentioned and the SMA training portal still states a single SBS per phase. I would need to follow up on the service line to confirm though.

Alternate system, you can install Sunny Island (48V battery inverter) as backup.
I'm not clear on how well it works at "zero export", "self generated consumption"

I have not tested this so bear that in mind but I do believe an approximation of grid-zero would be possible. Essentially the SI6048 would be configured to Grid-feed during a given operating window. Any usage outside of that window would come from the batteries unless the SOC reached a predetermined state (20% etc). Once the threshold was reached, the grid would be connected and the battery would be charged.

What's unclear to me though would be a situation where the PV production fell below the load requirements during the day. In that case, the additional power is likely to come from the grid during the PV Feed-in window. Again, untested (I install off-grid systems typically) but this is something I have heard in passing from other installers.

A sufficiently large system that is 2x or 3x the nominal household usage shouldn't have any issues pulling from the grid during the day or at least not under normal circumstances IMHO.

Otherwise, I do believe it is possible to only connect to the grid when the SOC falls below a certain state. This would mean no (zero) feed-in though.

What are your thoughts on batteries? Are you wanting to DIY or buy an off-the-shelf solution such as a battery from BYD or LG Chem etc?

As a final thought, you could always have a couple of Tesla Powerwalls installed rather than a battery inverter+batteries or a hybrid inverter. Then you could just add more PV as you wanted. Either retire your Sunny Boy and switch to Fronius OR just add more. I'm not a Telsa installer (yet lol) but it's likely possible to add a Fronius while keeping your Sunny Boy. This would need to be confirmed by a Tesla installer though.