Low battery during time of use period

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Mike Curran
Forum Emperor
Posts: 1817
Joined: Sat Aug 28, 2004 6:28 pm
My RE system: Outback - Garage roof:
- 8 (2x4) Evergreen 180's into one FM80 (2007/2020 - replaced MX60)
- 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

Outback Skybox - Barn roof: (2019)
- 14 Talesun 275W in series (DC array input to SB inverter/charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input (manual switch during grid outage only) from 14 Talesun 275W,
Enphase M215 microinverters, normally direct grid tied

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

Low battery during time of use period

Post by Mike Curran » Sat Dec 28, 2019 9:51 am

If a Skybox is running off the battery during a high cost time of use period, and battery reaches the low SOC limit setpoint before that period is over, will the Skybox transfer back to grid? I don't have time of use rates here but I'm considering using this feature in Skybox to temporarily get around high power draw from the Skybox when there's little to no sun, at least until we can figure out where the problem lies.

http://outbackpower.com/forum/viewtopic ... 47&t=14520

Edit: Well, that experiment was informative. Before I set TOU rates, I was drawing about 18 kwh overnight (no sun - cumulative from 4:00pm to 8:00am) from the grid for a 300 watt load plus Skybox power draw. With TOU rates enabled (set artificially high to ensure the battery supplied loads, not the grid) and the battery supplying barn load plus Skybox, over the same time period grid use was about 14.5kwh, all because at 4:00am the battery reached its low voltage limit at a minimum SOC 20.4% and Skybox started a bulk charge from the grid at that point. If we had more daylight hours this scheme would probably make sense. As it is now during winter months, the slight grid savings (18 - 14.5 = 3.5kwh/day) probably isn't worth the wear and tear on the battery. Any opinions out there?
http://www.tigoenergy.com/site.php?95b2dca2-ca6c
https://enlighten.enphaseenergy.com/public/systems/Hctc107221

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