Advice for AC coupling - Radian vs Skybox

Discussion about adding energy storage to grid-dependent inverters using OutBack Power technology
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Plum
Forum Junior Member
Posts: 3
Joined: Wed Mar 11, 2020 10:12 am
My RE system: GridTied: 16X245 watt - 3.9 kW Inverter- Enphase M215

Advice for AC coupling - Radian vs Skybox

Post by Plum » Wed Mar 11, 2020 10:31 am

Hi,
I am looking for advice on whether I should consider a Skybox or a Radian for AC coupled backup to an existing GTI system.
3.9 kW existing GridTied with Enphase M215 micro inverters.

1st, I think I would be looking at the Radian 8048 (over the 4048), given what I have and suggested ratio?

2nd, what are the pros and cons on the Radian vs the Skybox?

I hope this is appropriate for this forum,
Thanks for your thoughts.

Mike Curran
Forum Emperor
Posts: 1393
Joined: Sat Aug 28, 2004 6:28 pm
My RE system: Outback - Garage roof:
- 8 (2x4) Evergreen 180's into one MX60 (2007)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied GVFX3524's classic stacked for 120/240VAC (2007)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar - Barn roof: (2012)
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied, no longer AC- coupled

Outback Skybox - Barn roof: (2019)
- 14 (2x7) Talesun 275W (DC array input to SB charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 modules

All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Advice for AC coupling - Radian vs Skybox

Post by Mike Curran » Wed Mar 11, 2020 5:23 pm

Hi Plum - I chose a Skybox after considering a Radian, as you are.

Some pros for SkyBox:

I needed an inverter that could be mounted outside. The Radian cannot unless you mount it in a NEMA 3R enclosure, and the cost for one that would fit would make the entire cost comparable to a Skybox.

I was also adding a DC array and the Skybox has a built-in charge controller. With a Radian I would've had to buy a separate charge controller. In addition, the SB CC can accept up to a 600 volt DC input. OB's highest capacity, stand alone charge controller, the FM100, has a max 300 volt DC PV input.

With a Skybox, you don't need to have a battery, whereas a Radian must have one connected to it.

A SB also has its own built-in monitoring and control mechanism. With a Radian you must purchase a Mate3s.

With a Skybox, you get a built-in termination cabinet they call BOS (Balance Of System). For a Radian, OB offers a GSLC, another sort of add-on.

Some cons:

Skybox uses about 150 watts whenever there's low to no sunlight. I'm not sure how this compares to the Radian, but it seems excessive to me.

Compared to my older system with the 2 GVFX inverters, Skybox data updates on Optics RE (OB's free on-line monitoring and control software) are very slow. Each day when I open Optics for my Skybox system, it never has graph data beyond 1:00 a.m. It takes about 5 minutes before continuously refreshing my browser yields current data. Perhaps a minor quibble, but noticeable to me at least.

With the Enphase M215 microinverters, the maximum power sell to the grid with a Skybox is 5kw. I think the Radian has a higher max but I'm not sure. For you, this probably isn't an issue since your array size is under 5kw, but if you ever decide to enlarge your PV array, it could be an issue. A Skybox with more recent microinverters (that meet new grid-interactive standards) will allow up to about 7kw to be exported to the grid. Again, don't know how this compares to a Radian.

I'm sure others with Radian inverters can provide good input from their perspective. Good luck! - Mike
http://www.tigoenergy.com/site.php?95b2dca2-ca6c
https://enlighten.enphaseenergy.com/public/systems/Hctc107221

Plum
Forum Junior Member
Posts: 3
Joined: Wed Mar 11, 2020 10:12 am
My RE system: GridTied: 16X245 watt - 3.9 kW Inverter- Enphase M215

Re: Advice for AC coupling - Radian vs Skybox

Post by Plum » Wed Mar 11, 2020 9:01 pm

Hi Mike,

Since I will be installing inside, with batteries for backup and will not have DC in, I am leaning toward the Radian.
I think the output power would be slightly higher with the Radian.

That said, the SB is still quite tempting for its all inclusive set-up and function.... difficult choice.

I am also wandering when AC coupled with the Radian, will I be able to take advantage of some of the Operating Modes (GridZero, Support, etc)?
I might have to post this question separately and/or in another topic...

Thanks so much for your reply - very helpful!

Plum
Forum Junior Member
Posts: 3
Joined: Wed Mar 11, 2020 10:12 am
My RE system: GridTied: 16X245 watt - 3.9 kW Inverter- Enphase M215

Re: Advice for AC coupling - Radian vs Skybox

Post by Plum » Thu Mar 12, 2020 9:04 pm

Hi Mike et al,

It's my understanding that when AC coupling to the Radian, the only Operating Mode that can be used is GridTied. The batteries would therefore only be used in a grid down scenario. So, the Radian option would basically be backup for power outages without losing the solar power.

If I understand the SkyBox correctly, when AC coupled you can utilize the time of use and load shifting features. And therefore making more use of the battery bank and the PV on a daily basis.

I suppose another consideration might be: is it better to have batteries that are cycled infrequently (as with the Radian back-up) or batteries that are exercised (SkyBox scenario). Perhaps longer battery life / lower cost over time with the Radian? I suppose this also depends on the battery chemistry...

Is this a fair general assessment?

Regardless, I can now see how the SkyBox might be a good (better) choice for our purposes.

We are in California and experience short (<6hr), but occasional (6/year) outages.

Thanks again for your thoughts!!

Mike Curran
Forum Emperor
Posts: 1393
Joined: Sat Aug 28, 2004 6:28 pm
My RE system: Outback - Garage roof:
- 8 (2x4) Evergreen 180's into one MX60 (2007)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied GVFX3524's classic stacked for 120/240VAC (2007)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar - Barn roof: (2012)
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied, no longer AC- coupled

Outback Skybox - Barn roof: (2019)
- 14 (2x7) Talesun 275W (DC array input to SB charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 modules

All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Advice for AC coupling - Radian vs Skybox

Post by Mike Curran » Fri Mar 13, 2020 5:46 am

Plum - I don't use time of use or load shifting with my Skybox so can't speak to how it utilizes them, vs. the Radian.

As far as best practices for long battery life, I have both FLA and LiFePO4 batteries and both are pretty much in float mode most of the time. My FLA's are going on 13 years old and seem to be going strong. They do get a mini-absorb cycle each day so strictly speaking, they're not held in float 100% of the time, and I occasionally cycle them (disconnect from grid for a day or so) to give the acid a good stir. I don't have as many or as prolonged grid outages as you do, but the FLA's still serve me well. Based on their comments on this forum, most owners of FLA based systems swear by having to cycle them to prolong their life, but my experience isn't as clear cut as that.

The Simpliphi lithium batteries attached to the Skybox are pretty much in float all the time, and Simpliphi has assured that this kind of operation isn't harmful to them. But they are relatively new compared to FLA's so maybe only time will tell.

Hope this helps.

Edit: Having said all that, if you're also trying to choose FLA vs. lithium, I'd go with lithium if you can afford it.
http://www.tigoenergy.com/site.php?95b2dca2-ca6c
https://enlighten.enphaseenergy.com/public/systems/Hctc107221

raysun
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Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower One: FX3048T, (2) FM80, MATE3s, FlexNetDC
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Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: Advice for AC coupling - Radian vs Skybox

Post by raysun » Fri Mar 13, 2020 6:34 am

Mike Curran wrote:
Fri Mar 13, 2020 5:46 am
Plum - I don't use time of use or load shifting with my Skybox so can't speak to how it utilizes them, vs. the Radian.

As far as best practices for long battery life, I have both FLA and LiFePO4 batteries and both are pretty much in float mode most of the time. My FLA's are going on 13 years old and seem to be going strong. They do get a mini-absorb cycle each day so strictly speaking, they're not held in float 100% of the time, and I occasionally cycle them (disconnect from grid for a day or so) to give the acid a good stir. I don't have as many or as prolonged grid outages as you do, but the FLA's still serve me well. Based on their comments on this forum, most owners of FLA based systems swear by having to cycle them to prolong their life, but my experience isn't as clear cut as that.

The Simpliphi lithium batteries attached to the Skybox are pretty much in float all the time, and Simpliphi has assured that this kind of operation isn't harmful to them. But they are relatively new compared to FLA's so maybe only time will tell.

Hope this helps.

Edit: Having said all that, if you're also trying to choose FLA vs. lithium, I'd go with lithium if you can afford it.
Hey Mike,

Have you run a capacity test on the FLA battery? It would seem a perfect case study on the long term effects of holding a Deep Cycle FLA in Float service.

Did SimpliPhi mention how their battery can be held at, what I presume is 100% SoC? Is that a correct presumption? There's not much practical experience out there that I'm aware of (and I'm admittedly not all that aware.) Most of the research stuff I've read points to the accelerated formation of dendrites that grow to pierce membranes, leading to cell failure. Maybe they've addressed the issue somehow?

Mike Curran
Forum Emperor
Posts: 1393
Joined: Sat Aug 28, 2004 6:28 pm
My RE system: Outback - Garage roof:
- 8 (2x4) Evergreen 180's into one MX60 (2007)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied GVFX3524's classic stacked for 120/240VAC (2007)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar - Barn roof: (2012)
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied, no longer AC- coupled

Outback Skybox - Barn roof: (2019)
- 14 (2x7) Talesun 275W (DC array input to SB charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input from 14 Talesun 275W, Enphase M215 modules

All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Advice for AC coupling - Radian vs Skybox

Post by Mike Curran » Fri Mar 13, 2020 8:47 am

Hey Mike,

Have you run a capacity test on the FLA battery? It would seem a perfect case study on the long term effects of holding a Deep Cycle FLA in Float service.

Did SimpliPhi mention how their battery can be held at, what I presume is 100% SoC? Is that a correct presumption? There's not much practical experience out there that I'm aware of (and I'm admittedly not all that aware.) Most of the research stuff I've read points to the accelerated formation of dendrites that grow to pierce membranes, leading to cell failure. Maybe they've addressed the issue somehow?
Ray, no, haven't run a capacity test but no doubt, my FLA battery doesn’t have the capacity it had when new. However, it will easily support my backup panel loads for a couple of days (I've moved some of that load to the new barn battery, making it easier) which is all I need. That said, if I were off grid and was cycling my FLA battery more deeply every day, I'm not sure that it would have lasted this long. Last set (4 of 12 cells) of SG's were taken last September (I'm due, I know) and all were around 1.290.

Here's a relevant forum post with comment from Simpliphi (which you've seen before):viewtopic.php?f=47&t=14591
In it, they say 54 volts is considered a full charge.
http://www.tigoenergy.com/site.php?95b2dca2-ca6c
https://enlighten.enphaseenergy.com/public/systems/Hctc107221

raysun
Forum Emperor
Posts: 1668
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower One: FX3048T, (2) FM80, MATE3s, FlexNetDC
Outback 200NC batteries (8 @ 48v)
Outback IBR3 battery enclosure
Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: Advice for AC coupling - Radian vs Skybox

Post by raysun » Fri Mar 13, 2020 9:13 am

Mike Curran wrote:
Fri Mar 13, 2020 8:47 am
Hey Mike,

Have you run a capacity test on the FLA battery? It would seem a perfect case study on the long term effects of holding a Deep Cycle FLA in Float service.

Did SimpliPhi mention how their battery can be held at, what I presume is 100% SoC? Is that a correct presumption? There's not much practical experience out there that I'm aware of (and I'm admittedly not all that aware.) Most of the research stuff I've read points to the accelerated formation of dendrites that grow to pierce membranes, leading to cell failure. Maybe they've addressed the issue somehow?
Ray, no, haven't run a capacity test but no doubt, my FLA battery doesn’t have the capacity it had when new. However, it will easily support my backup panel loads for a couple of days (I've moved some of that load to the new barn battery, making it easier) which is all I need. That said, if I were off grid and was cycling my FLA battery more deeply every day, I'm not sure that it would have lasted this long. Last set (4 of 12 cells) of SG's were taken last September (I'm due, I know) and all were around 1.290.

Here's a relevant forum post with comment from Simpliphi (which you've seen before):viewtopic.php?f=47&t=14591
In it, they say 54 volts is considered a full charge.
Thanks Mike.

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