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From: Don Y <blockedofcourse@foo.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Solar panels
Date: Sun, 2 Jun 2024 11:06:32 -0700
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On 6/2/2024 10:21 AM, KevinJ93 wrote:
> On 6/1/24 8:32 PM, Don Y wrote:
>> On 6/1/2024 6:29 PM, boB wrote:
>>>>> Not sure how to avoid excessive charge currents into the battery if it can't
>>>>> take the full solar output.
>>>>
>>>> I think you have to be able to "talk" to the module to tell it how you would
>>>> like it to behave, NOW.
>>>
>>> The MPPT controller simply raises the PV operating voltage above
>>> Vmp...  At Voc, the current becomes zero. Whatever Vpv gives the
>>> correct controller output voltage to the battery it is charging.
>>
>> You have to signal to the controller that the battery is charged;
>> that it can't (shouldn't) continue to accept charge.
> 
> That will happen automatically when the battery reaches the set voltage.

*If* you have a charge controller for the battery, the controller limits
what will flow into the *battery*.

But, I use loads in much the same way that one would use a battery; if
there is excess capacity available, then I will bring more loads on line.
There's no other "storage" for that excess capacity -- use it or lose it.

> Some of the charge controllers allow configuration for various parameters such 
> as 100% charge voltage so that it will work with different chemistries.
> 
> In your case your load could be directly across the battery.
> 
> The one thing that is not obvious to me is how to limit the charge current if 
> you use a small battery where the solar available could exceed the allowable 
> battery charging current.

See above.  Unlike a typical application where you would "store" the excess
produced into the grid, I am avoiding that complication.  I'll just "do extra
work" with it, storing the results of that "work" instead of the electrons
themselves.

That's why I need more intimate control and  knowledge of what the available
power, battery reserves and loads are.

Power FROM the grid is always available to supplement my needs -- but, that
doesn't want to be the main source of power.  E.g., I could find it
advantageous to charge the battery at C/100 (!) in preparation for darkness
if I can make use of all of the available solar power to "do real work"
(cuz that won't be possible, later).

Likewise, if the battery doesn't have sufficient reserves to bridge the dark
period, rely on mains-sourced power -- but, as a temporary stopgap.

I.e., you continuously are making supply and demand decisions trying to
minimize the expected cost of your usage:  "Is it better for me to delay
this 'work' until tomorrow when I *expect* to have a surplus of solar power
available?  Or, have I already 'borrowed' to heavily from that future
source?"

It's just a resource management issue:  should I wash the dishes, laundry,
irrigate the yard AND take a shower now?  Or, can I distribute those
loads to better use the available water (and hot water) to eliminate
the need to up-size my supply?

> Maybe you could add a controllable dump for when solar generation significantly 
> exceeds your load consumption?
> 
> kw