Off Grid Home Forums Technical Discussion One system or two/////////Overflow power//////Air conditioning Re: One system or two/////////Overflow power//////Air conditioning


OK, its making more sense.

If I understand correctly: 1) A second systems is pointless if one of them needs the accessories (inverter/mppt/etc). Therefore, it seems an extra battery for emergencies is the easiest way to “back up” the important low watt part of the system (unless its the inverter that dies); 2) High loads will “balance” at peak pv production (with proper planning and a mppt).

The aquaponics pump will almost certainly be an airlift running on less than 10 watts.

Priorities were almost correct.

1 Aquaponics/toilet vent(6 watts all day/10 watts all day) and I have not figured out if I need a roof vent yet

2 computer/router (100 watts 3-6 hours mostly daytime)

3 fridge/freezer (as low watt as possible without breaking the bank)

4 lights (10-40 watts 3-6 hours only at night)

5 Tools/Blender/Toaster(This is flexible…100-500 watts a day seems like plenty…and this would be a daytime need)

6 Anything I forgot

7 AC

I’ve spent a year and half in Central America. The only time I remember the luxury of AC is when I went to the bank (OH…and a really nice hotel the University put me in for a weekend…but I protested that the place was too nice and that the school should not be wasting money treating students like honeymooners…lol). I would only use the AC for 3 reasons 1) It was running on otherwise wasted power 2) If a guest had a heat stroke 3) If I got cabin fever really bad.

The way I see it, I need a system that runs the basics reliably. If its overbuilt enough for something like occasional AC then its obviously big enough that the basics are not over working the system. That gives me both piece of mind and the ability for a high demand appliance every once in a while (whatever it may be but probably AC).

Thank again. The timer idea is good and it gave me an idea.

I don’t know how it would work off-grid but I have seen timers with 2 power sources. First, they are hard wired with mains power to run greenhouse lights or any 110 or 220v appliance (AC) but the timer itself is plugged into a different circuit that only needs a couple watts to run the relay in the timer (this allows a light running at 220 to be operated by a timer relay on 110). If the main current was from the PV/Batteries and the second was from a tiny PV (like the ones used on direct feed solar fans and pumps) then the timer could only trigger the appliances when the tiny PV was sufficiently active (then set the timer to 24 hours a day so its no longer a timer but a solar triggered device). With some experimenting (finding the perfect amount of shade for the tiny PV) you could MAYBE get it where the AC only comes on during the brightest days. It would not take into consideration if the batteries are already charged but after some trial I should be able to confidently assume if the sun is that bright then the batteries are charged. I hope I explained that well enough…Its just a silly idea but it may have real applications for someone somewhere.

Thanks again for all the help. This is looking more and more doable every day!