Affordable Option for Solar Li-ion Home Battery System?

[Hedges]

Thank you, I'm about to install (ok, next year, not really about) a grid tied system with micro inverters. A big help.

Consider your battery-backup options. Better to plan for it than want it later and find some existing equipment is incompatible.

Enphase offers a battery add-on which works with some of their microinverters.
New Enphase microinverters do frequency-watts, making them compatible with AC coupled battery inverters that do frequency shift, but older models do not.
Some other microinverters don't have support for battery backup.

Microinverters address some system issues, but string inverters and hybrids are worth considering too.
It is common with micro inverters to over-panel (e.g. 400W panel on 250W inverter) which has some benefits but misses out on some power production. It may be possible to make arrays which are better utilized with string inverters.

 

[Hedges]

Thanks! My bad, I meant the battery side. I'm already all Enphase IQ7X with 10kW of SunPower and would love to throw in a good battery inverter/switch wherein I can use anything, even if there's some loss. I know I can use Enphase's batteries plug and play but a bit more freedom would be nice.

For example, I'd love to try a stack of those Gyll batteries. I'm just barely starting my due diligence. I permitted and installed all of the solar myself. The user summaries are great and finding the latest and greatest tech via Google isn't very reliable.

If those IQ7X to frequency-watts, you may be able to feed them through Sunny Island or Skybox or other similar inverters for grid-backup.
Those take 48V batteries so multiple options. Compatible BMS is best. I would DIY.

Some guys here do that (Enphase microinverters AC coupled to a battery inverter), but there have been firmware issues so read up on it.

 

[dd36]

If those IQ7X to frequency-watts, you may be able to feed them through Sunny Island or Skybox or other similar inverters for grid-backup.
Those take 48V batteries so multiple options. Compatible BMS is best. I would DIY.

Some guys here do that (Enphase microinverters AC coupled to a battery inverter), but there have been firmware issues so read up on it.

Ok, I'll dive into frequency-watts. Thx!

 

[Hedges]

Arizona bumped the allowable grid tie to go to 20kW last year or else I wouldn't be stuck at 10kW (I installed prior to the bump up - thanks Tesla for lobbying). I want to oversize and go off grid slowly, load-by-load. Besides the 5-ton A/C, which I can smooth down, the biggest load is the induction stove. I already switched to a Rheem heat pump hot water heater. That thing is amazing. At the prices I'm seeing for LFPO, going off grid seems viable if I oversize my array. Before I do that, I went to get comfortable with batteries.

But is LiFePO4 at any price cheaper than net-metering? If DIY lasts a decade of daily deep cycling, I think it costs $0.05/kWh.
What could make sense is peak shaving/shifting, due to spread in price.
Net metering is a good way to store power to be used several months later. A good deal at the $10/month fee I pay (although PG&E wants to boost that.)

If you have 10 kW of GT, you might add 10 kW of PV tied to a hybrid, for 20 kW total. Within limits of grid current for the hybrid, might require splitting in two.

Off grid (so no issue with feed-through current) Two SI-6048 makes 11.5 kW from battery and can manage up to 24 kW of AC coupled PV. That might be a good fit for your plans. Retail they are expensive, but for a while I saw eBay listings for two in a metal box with some other pieces, around $5000. You can AC or DC couple additional PV. For Lithium, REC is one of the compatible BMS.

 

[dd36]

But is LiFePO4 at any price cheaper than net-metering? If DIY lasts a decade of daily deep cycling, I think it costs $0.05/kWh.
What could make sense is peak shaving/shifting, due to spread in price.
Net metering is a good way to store power to be used several months later. A good deal at the $10/month fee I pay (although PG&E wants to boost that.)

If you have 10 kW of GT, you might add 10 kW of PV tied to a hybrid, for 20 kW total. Within limits of grid current for the hybrid, might require splitting in two.

Off grid (so no issue with feed-through current) Two SI-6048 makes 11.5 kW from battery and can manage up to 24 kW of AC coupled PV. That might be a good fit for your plans. Retail they are expensive, but for a while I saw eBay listings for two in a metal box with some other pieces, around $5000. You can AC or DC couple additional PV. For Lithium, REC is one of the compatible BMS.

No, it's not cheaper. My costs are near net zero for the next ten years. I would be doing it mostly for experience. I also fear AZ will pass laws preventing people from going off grid once it's a popular no-brainer. I think it's inevitable that those that can afford it will go off grid and all that will be left is business loads and multi-family, low income.

That's a good idea. I could have two systems and the new, off grid one could be string inverters?

 

[Hedges]

String inverter by itself isn't off-grid, but some hybrids use high-voltage PV strings plus batteries. Sol-ark, Skybox, Schneider all 48V battery I think. Some drop PV to battery voltage first, but Sol-Ark uses a high voltage DC rail (more efficient if consuming AC immediately.)

My suggestion was the existing PV capacity of microinverters could be put on the island grid of a hybrid or battery inverter which performs frequency shift. It becomes part of the grid-backup/off-grid system so available for protected loads and charging battery.

Just like the Sunny Island/Sunny Boy system I have.
See diagram at bottom of data sheet with AC coupled Sunny Boy and house loads on protected side of Sunny Island.
If all PV is AC coupled, you should have a "load shed" relay to disconnect loads at low battery so system remains up until sun comes up and recharges. Having some DC coupled PV is an alternate solution. Something like Sol-Ark would turn off inverter but keep its DC coupled PV input charging (only your AC coupled microinverters would be disconnected until battery comes up enough.)

https://files.sma.de/downloads/SI6048US-DS-en-27.pdf