Hi,

I have seen multiple methods to calculate the charging time of a lithium battery via solar panels/inverter.

What is the correct way to calculate the charging time of a battery assuming the continues battery charging current being 100A that the inverter can output to the battery.

The setup I am referring to is roughly 21kWp of solar per hour, 50kW inverter and then 2x freedom won 60/48HV batteries (614V per battery battery with cont charge current of 100A each)

Would appreciate the input. 

51 minutes ago, schalkvstaden said:

The setup I am referring to is roughly 21kWp of solar per hour, 50kW inverter and then 2x freedom won 60/48HV batteries (614V per battery battery with cont charge current of 100A each)

This doesn't sound quite right...

If the batteries' Voltage is indeed 614V (six-hundred and fourteen Volt) and you are charging at 100A (one-hundred Ampere) at that Voltage, then that would be:
614 V * 100 A = 61 400W aka 61.4kW, which is more than the panels can supply, or the inverter, and since there are 2 batteries with 100A each, according to your writing, that would require 122.8kW to come out of thin air (not out of the solar panels or the 50kW inverter, I'd think) to recharge the batteries in one hour... give or take, so I think your numbers seem off, sure 100A max charging current, but I suspect you never get even close to this number especially per battery, in other words 200A continuous charge current at 600-odd Volt. I'd think you may be charging more like at 20A per battery, maybe, around 20kW or so, and then the batteries would recharge in 5 to 6 hours, assuming a fairly low SOC (10% or so) when the charging cycle starts, I'd think...

so the batteries can be charged at 100A cont. I am not saying that is is charged at that current although it can. So these are the HV batteries rated at 614V, which is correct.

The question is what the correct method will be to determine the average charge time with the amount of panels (36x600W panels).

 

4 minutes ago, schalkvstaden said:

The question is what the correct method will be to determine the average charge time with the amount of panels (36x600W panels).

That would depend on a lot of factors. For instance, if it is night, the charge time will be infinite. If it is day, it would depend on how much power you are getting from the panels, and how much of that is going to the batteries.

correct that I understand. This is for a off-grid setup.

During the day these panels can produce roughly 21kWp per hour. The question is relative, I want to know if these panels can charge the batteries from 20%SOC to 100% within a 6 hour peak sun span with the assumption there is no load connected hypothetically. Thus the solar panels is only there to charge the batteries during the day. This is just a theoretical exercise I want to do in order to determine if the amount of panels is sufficient.

3 minutes ago, schalkvstaden said:

During the day these panels can produce roughly 21kWp per hour

You are unlikely to see that except with cloud edge effect, you can probably work on 70% of that at noon and lower the rest of the day. Then insolation also depends on location and weather etc.

To get an idea of how often your batteries will be full or empty, use this tool: (Azimuth is -180° for North).

https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html#SA

thanks this is a great tool

 

A simple thumbsuck would be to look at the average peak sun hours for your location throughout the year.

Weather-dependent, and depends on if you've got other loads running during the day, but on average you can expect your 21kW of panels to generate anywhere from 90kWh to 130kWh per day, less in winter, more in summer, but still enough on most days to charge your 60kWh battery capacity from zero to 100% before the sun sets.

The exact charging time will vary throughout the year and from day to day. On a bright winter day you should be charged up by mid-afternoon, and in summer probably by noon.

Average Peak Sun Hours (South Africa) - Climatebiz