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Motrukdriver

Motrukdriver

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So you are sitting in your lawn chair on a nice, not hot, sunny day.  You don't have any drain on your house batteries and they are fully charged.  What do you do with the excess voltage your panels are producing?  Does anyone use a water heater (6 to maybe 10 gallon) with 12 volt heater elements?
 
Charge gadgets with batteries or a secondary bank that

Make ice or freeze packs for the cooler.

Heat water.

In cold weather heat the living space.
 
I charge lipo batteries for my RC planes or ham radio. Always something to top off...
 
> Charge gadgets with batteries or a secondary bank that

one whose chemistry doesn't require getting to Full
 
I have a 6 gallon Hott rod for the water heater, I can switch the propane fridge over to 120v, run a small oil filled heater on cold days, a small A/C on hot ones. I can even use a hot plate for cooking but it is likely I'd be using a solar cooker already.
 
Motrukdriver said:
So you are sitting in your lawn chair on a nice, not hot, sunny day.  You don't have any drain on your house batteries and they are fully charged.  What do you do with the excess voltage your panels are producing?
Click to expand...

This is one of my favorite hobby horses.

Basically anything that can be timeshifted can be an opportunity load:
  • water heating is a natural, as it can consume lots of power
  • charging laptops (or just using them, like doing email in the afternoons)
  • dehumidication
  • running items off  inverter
  • etc
I suspect that folks could get by with smaller solar installs if the loads were used when it would least affect charging.  Particularly important with PWM controllers, since they produce more power when battery voltage is highest (ie, closer to Vmp during Abs and Float).  PWM output for a Renogy 100W panel under lab conditions:

Code: 
		 Vbatt   PWM Watts
50% SOC	        12.2	    64.54
Float	        13.2	    69.83
Float	        13.8	    73.00
Absorption	14.6	    77.23
Absorption	14.7	    77.76
Absorption	14.8	    78.29


Adding loads in late Absorption can also help reduce MPPT temps when overpaneling the controller.
 
I'm attempting to operate a 12v fridge on that general strategy before upgrading my battery bank. I turn on the fridge after the absorption phase of charging, the first 2-3 hours of full solar. It works great as a fridge, will be attempting as freezer on this next trip out, in cooler weather.
 
Just to be clear Bulk/CC stage is first, batt accepting highest amps.

Absorb then continues until bank is (should be) 100% Full.

Then when bank charging is all done comes Float, to handle loads and combat self-discharge.

If your peak solar is 12A output, and your fridge + other loads pulls 8A, you should wait to turn on the fridge until the bank is only accepting 4A. That is then "free, excess" power that would otherwise be wasted.

Or a bit earlier as you gain experience, just make sure you're not preventing getting the bank to 100% Full.

But of course you should not risk food spoilage either.
 
Been doing the 2nd tier dometic for ten days on surplus no battery power. It runs continuously for 5-6 hours a day and max temps around 70.
 
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