ripple4
Posts: 37
Joined: Tue Sep 18, 2018 1:45 pm
Delivery Date: 18 Sep 2018
Location: Toledo, Ohio

4000w hybrid inverter for grid assisted solar charging

Sun Dec 23, 2018 9:33 am

I've done a google site search for “grid assisted charging” and I don’t think that I saw this exact topic. I’m talking about grid assisted solar charging, not direct-to-battery solar, Not L1 6amp, not off-grid solar, not grid-tie solar, not anything with DCQC. The goal here is to incrementally change over from grid charging to solar without that need to get a utility permission for grid tie and still get 2012 full-power 3.8kw L2 charging. I've heard that this is called 'selfish solar.' Where I live, in coal/shale country, grid tie is discouraged and requires the full system to be running on day 1 and repermitting for any changes.

What might be new information here is this so-called hybrid inverter product which is grid/generator interactive without grid feeding.

They key feature is that it cannot feed the grid, which in this case is a requirement, but it can interact like a UPS with grid priority or it also can preferentially use solar/battery and then go to grid when the battery is flat. When the battery is flat and solar is off-line it can allow utility pass through with >98% efficiency, so its not a net loss when beginning with low power PV. And as solar and battery is added it can use more and more renewable before switching over to grid. The total solar input for this unit is 80amp*48v with a single mppt, which is around 4kw. I had read on this sub-forum and understand the benefit of the 1 inverter per panel arrangement, this product is not setup like that, but with add-on mppt charger from paralleled inverter units the array could be split up into up to 6 mppt segments. The one I linked to is stackable up to 6 units, which would be whole house capability. For 120v loads a cheap, used 240x120/ 480x240 single phase industrial Xmer could be used.

The one I’m researching (link) has three stage battery charging and compatibility with lifepo4 cells which tells me it has CC/CV capability, 18s LiFePo4 and 14s LiPo have the exact same max cutoff voltage as 24s (48v) lead. There are many 14s BMS options for cell balancing but I cannot find one that allows me to tailor max charge voltages to 4.1 or less, but that can be set by limiting the maximum charge cutoff voltage to 57.4 on the mppt inverter. Also I was not able to find inexpensive 14s BMSs that have much more than 60ma balance current, which in a 14s 10p module (1.4kwh each) would provide 6ma on average per 18650 cell, is that enough?

realistically, this inverter could be part of a system that may included many 10’s of kwh of lipo batteries with several 14s10p BMS strings of 18650’s like a DIY powerwall, and maybe 2-4kw of used solar panels. What kind of problems could come up with such a system? Am I missing a fatal flaw?
Last edited by ripple4 on Fri Dec 28, 2018 8:08 pm, edited 1 time in total.

ripple4
Posts: 37
Joined: Tue Sep 18, 2018 1:45 pm
Delivery Date: 18 Sep 2018
Location: Toledo, Ohio

Re: 4000w hybrid inverter for grid assisted solar charging

Fri Dec 28, 2018 8:06 pm

Here is the manual for one version of this grid-assisted solar device and verified it can do CC/CV battery charging with custom charge voltages for a lipo storage battery. the 48v model has a bulk charging range of 48 to 58.4v, a float charging within the same range and the low battery cut off is 40-48v. I would think that a bulk charge voltage of 4.05v/cell 56.7v/pack, a float voltage of 4.1v/cell 57.4v/pack and a low battery of 3.3/cell 46.2v/pack would give long life and are within the range of this unit. if I was not in another project at this time I would try it out myself.

this model is $532 shipped: https://www.aliexpress.com/item/5000W-8 ... 23289.html

here is the manual page 22 has the battery info for custom settings.
https://www.scribd.com/document/3964827 ... l-20150128

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