I'm confused - high-wattage off-grid solar - charge controllers?

[FlyFishn]

I remember Midnite being a brand that came up routinely with off-grid solar charge controllers. Just for comparison I went over to their products to look at specs compared to what I have and now I am really confused.

For an example for discussion - the chart I've been working on for a few years for the power usage at my cabins I have listed 6kw panel wattage in the calculations.

The Midnite classic 150 shows 86 amps charge @ 48v nominal bank voltage. Actually, I think lining up the numbers to be accurate in what I am putting in the thread here has partially answered my question...

With the above numbers - 86 amps @ 48v nominal battery voltage (actual voltage around 58v - lithium) = just under 5,000w.

5,000w isn't 6,000w. So if a system is above 5,000w that would require multiple charge controllers?

Is there an input panel wattage maximum? Or does the controller take what it gets and only uses what it can make use of if the input power is more than it can push out?

How do you set up, say, a 20-30kw off-grid system?

I am familiar with the grid-tie inverters where the solar power, once it reaches enough to "start" the inverter, is directly pushed out to the AC power circuit. This is not what I am referring to - with this set up there is no storage. In order to store the power you need batteries and in order to safely charge batteries you need a charge controller. Therein lies my question.

For installs where it is sunny all the time and power consumption is only when the sun is shining then I can see where "grid tie" systems are good. That does not cover night time and that does not cover periods of no solar production - like when it is cloudy and rainy for a week. If you don't have stored power through the low periods you're hosed. So how do you get the stored power - on higher wattage set ups?

[FlyFishn]

Another parallel thought on the same topic -

With a large system the battery bank would have to be scaled up. This is one thing with lead variant batteries.

If I am correct - it is entirely another animal with lithium variant batteries.

Case-in-point - when I was discussing various system voltages with a Bioenno Power rep the other day his recommendation was to start with a battery at the system voltage. Their batteries don't handle the series voltage too well beyond 2x. So, in the example we were discussing, if you ran series 12v batteries to get to 48v the controller boards in the batteries wouldn't take that configuration. However, it was possible to get the controllers to not trip out with 2x 12v batteries to use in a 24v system. The recommendation was still to get a matched voltage battery to the system voltage that it is intended to run with (12, 24, 36, 48v).

That makes sense.

How does this play out with charge controllers? More over - how does this play out with MULTIPLE charge controllers?

Using the 5kw/48v numbers from above - in, say, a 15kw system that would be 3x paralleled 5kw "systems" feeding a single battery bank.

With the charge algorithms being different for lithium batteries vs lead - can you run 3x charge controllers to feed the single battery bank? Will the charge algorithms of the 3 controllers handle the other controllers on-line?

[bigrockcandymountain]

Yes, it is normal to have multiple charge controllers on a single battery bank.  They play well together and no harm is done. 

Batteries should be sized within reason and their allowable c rating for charge rate. C5 is a good charge rate for lead so dead to charged in 5 hours theoretically.  My 428ah 48v lead bank can be charged just over 4kw with those guidelines.  I don't know much about lithium numbers but somebody will. 

The midnite controllers have a "follow me" function, so they all go to absorb and float at the same time via a com cable, but it isn't 100% necessary. 

The 6kw system with a classic 150 is probably based on the 96a max output at 60v absorb for big lead batteries.  That's 5760 watts so it kinda rounds to 6kw.

And yes, with the better controllers anyway you can have more solar than they are rated for and they will just shut down if they get hot. 

I have a south facing array and normally you won't see rated output from the panels, but when it's cold and super sunny, it is possible to see slightly more than rated output. 

If you haven't bought batteries yet, don't be afraid of lead.  Every time I check it still beats lithium in my books.

[FlyFishn]

At this point I'm just asking questions. I'm still a good ways out of building a larger system.

As to battery types - lead vs lithium - for a large system that might be a good subject for analysis down the road.

However, for portable - I don't think you can beat lithium - the power to weight ratio is far superior. I learned that with a 12Ah LiFePO4. I just bought a 40Ah LiFePO4 as an upgrade for some bigger portable power capacity - both 12v stuff and a power inverter for 120vAC stuff.

As to multiple controllers feeding the same battery bank being OK and common - that helps answer the question.

That is an excellent point about the 2hrs peak time per day. The rest of the time production will be less. So that lines up with my thought about running more wattage in panels than what a particular controller may be rated to.

In the larger system I am thinking through - it would be a combination of solar and wind power. So it wouldn't be solely solar.

[JW]

I use an 1100 watt inverter when the power goes out I use a 12 volt system.  amp how e

https://www.google.com/search?q=amp+hours+explained&rlz=1C1JZAP_enUS981US981&ei=yF6RYsyTEJ2rwbkPvOSeiAM&oq=amp+hores+&gs_lcp=Cgdnd3Mtd2l6EAEYADIECAAQDTIECAAQDTIECAAQDTIECAAQDTIECAAQDTIECAAQDTIECAAQDTIECAAQDTIECAAQDTIECAAQDToHCAAQRxCwAzoHCCEQChCgAToFCCEQoAE6BQghEKsCOggIIRAeEBYQHToICAAQHhAPEBY6BggAEB4QFjoFCAAQgAQ6BAgAEAo6BQgAEJECOgoIABAeEA8QFhAKOggIABAeEBYQCjoHCAAQgAQQCjoECAAQQzoNCC4QsQMQxwEQ0QMQQzoHCAAQsQMQQzoICAAQgAQQsQM6CggAELEDEIMBEEM6CgguEMcBEK8BEEM6CwgAEIAEELEDEIMBOgUIABCGAzoHCAAQyQMQDToKCC4QxwEQrwEQDToGCAAQHhANOgcIABCxAxANSgQIQRgASgUIQBIBMUoECEYYAFClCFiiigFg6aIBaAJwAXgAgAGPAYgBuA6SAQQ3LjExmAEAoAEByAEIwAEB&sclient=gws-wiz

[Bossrox]

Your ?: Is there an input panel wattage maximum? Or does the controller take what it gets and only uses what it can make use of if the input power is more than it can push out?

That depends on the chargers design. Some you'll fry if you exceed the recommended input value others like my growatts, even tho the manual gives a max input, I can take my full 31kw's of panels & dump it into their chargers & they don't even flinch. But you should have a charger for each set of arrays that match the chargers input & you can daisy chain multiple chargers but there may be a limit how many can be daisy chained with some brands & mixing different charger brands & even same brand with a different output rating is a no no in most cases.