As long as you don't have to lift very high, airlifts can be effective, as soon as you are lifting very high it changes things and you suddenly need air pumps that can push air down under deeper water in order to lift water higher above the surface of the water.
As to using 12 volt stuff. Mad German talks about this a bit. You need to make sure you have the capacity to charge your batteries and provide power for the pumps without the batteries draining down too far since it is the low voltage that seems to damage the pumps (I've heard people complain about the bilge pumps burning out and the explanation that the voltage drop as batteries drain down causes the pumps issues seems logical to me.)
You're right and good batteries are expensive. Even with sufficient batteries, if the sun doesn't shine you will eventually need something else, such as charger from the grid or generator. I have two expensive AGM batteries and would like to have at least one more.
Raychel A Watkins said:
The amount of battery backup then would be crucial.
I have been running my system on 95% solar, and this is how I have done it.
1) Run system with pumps only during the day for 12 hours.
2) Run air 24 hours to the fish tank.
I have had to power my system %5 of the time time with standard power when we have had those rare 4 - 5 days of very cloudy days.
As a test this winter I tried to have no heat to the fish at all but had the tank buried in the ground. The Talipia I had in the tank did not make it, but all of the bluegill and koi are doing just fine.
Other tips on batteries:
Get used golf cart batteries, and then put a desulfator on them. I have found this one awesome to add to your system
Brain dead simple, and helps rejuvenate tired old golf cart batteries.
But this is what works for me.
My inverter kicked off sometime last night and that was the 2nd time in a couple of weeks. The first event was due to clouds but this time I think the system was affected by cold - down in the mid 20s F. It was sunny yesterday and the day before (I think). I've decided to keep a grid trickle charger attached to the batteries and continue pumping water 24/7. If grid power goes out long term then I'll reduce pumping. It looks as though there is a bit of damage to brussel sprouts, lettuce and cauliflower but we'll see what it looks like after warming up. Potatoes in the ground don't look good either.
Thanks for the suggestion on golf cart batteries. I'll keep an eye out for one or two.
Here's a challenge. I live in the Florida Keys and it's warm (and hot) most of the year but we do get cold snaps. Last night I pumped warmer water from a cistern into the fish tank to keep them warm but know that in future years we'll have serious cold snaps. Aquarium heaters are real energy hogs. What would be a solar alternative? I use those large black tubed sheets to heat my hot tub. I wonder if something like that could be connected to the fish tank and run when needed. Anyone do something similar?
Solar heating can work but do some extra research and you will need to either remember to open/close valves to control temperature or some how automate it.
For your situation Michael, where the cold snaps are usually not too extreme and extensive expense on solar heating could be something that is only of use for such short periods that occasionally turning off pumps and throwing a heater in for a couple nights might make more sense as your cold spells in the keys are not usually cold enough to kill tilapia and when they are, it is usually only for a night. (And at night the sun isn't shining to heat the water and warming the water too much during the day only to have the temperature drop too much overnight can be even harder on the fish than a few days being chilly.)
The solar pool heaters with the small tubes, I would recommend not running system water through it since the bio-slime that would build up would clog those tubes right quick. If you have to run system water through black tubing, get the black HDPE drinking water pipe that is 3/4 or 1 inch to avoid clogging constantly. Don't run system water through copper pipes or any metal other than high grade stainless steel. If you must use metal pipes, I would recommend doing heat exchange instead of running system water through the pipes.
Basically you are right but last year and the year before we had very cold Januaries. Cold nearly every day. My concern is that the climate is changing and we're getting more and more anomalous weather. I will check out thermosiphons. If I can run a coil into the tank without actually circulating water through whatever I use that would be a better solution. That's how they do solar hot water up north. We have solar hot water but it would roast the fish very quickly.
I did turn off the pumps last night and didn't restart until around 9:30 a.m. today when the sun hit the grow beds. These little guys have had a lot of stress and I'm amazed that only one died.