It strikes me that you are expecting quite a bit from a "smart" device to achieve your goals.
The problem of excess energy seems simple at first, but Mother Nature throws quite a few curves at us. For example, a nice day in the Bahamas
with solar panels
1. From sunup until the batteries
enter "float", we route
all energy into charging
(plus whatever loads (refrigerator, lights, instruments,radio, etc.) we have on all the time. We don't really care about the actual rate of charge since it's all going one place.
2. The batteries
are now at "float", hence "full" (not really, but close). We presumably can divert "excess" energy to "over and above" tasks such as heating
or making water
3. The difficulty now is in switching on those loads without negatively impacting the state-of-charge of our battery
. If we simply switch in a large load (like that 300w water
heater), it will draw down the battery
rather quickly every time a cloud drifts by. Switching a resistive load on & off quickly (using say, FET switches to get around the relay contact wear problem) based on maintaining "float" voltage could work
, but this approach won't work
for a watermaker
. If the passing cloud is large & dark enough, the voltage may drop enough to convince our solar regulator
it needs to go back to "absorption" or even "bulk" depending on how far the system voltage drops. Any "extra load" switching device needs to understand this and react properly by removing these loads.
Loads that are more complex (like a watermaker) that cannot be turned on & off at will complicate matters even more.
4. As the sun sets in the West, the "extra load" device needs to shut down properly so the last few solar
rays go into the batteries and standing loads.
changes (i.e., a bank of dark clouds) approaches - you really should shut down all the extras before it arrives to ensure you are at full charge.
b. Changing seasons means that initial, peak and ending charge times will change.
c. Changing locations (you sail to the Chesapeake or Maine) means the expectations for sunlight (and the hourly availability of charge) will change.
I suspect someone could probably build such a smart device, given enough sensors to drive it - or you could substitute a human into the loop and switch in loads as your superior "smarts" allow - for example, in the tropics with expectations of several hours of good charge available, you energize the watermaker
for a couple of hours. Upon spotting an approaching front, you shut it down.