comments:
80W is an enormous amount of power for a 12" fan. I'd look for lower-wattage fans. I don't see a panel wattage in your image, but it looks like it's probably 100-200W. On a typical day, a good ballpark for how many watt-hours you'll generate is panel wattage times five. So a 100W panel should get you around 500Wh/day on average. If these fans really use 80W, one of them would use your entire power budget in 6.25 hours. A 35Ah lead-acid battery only has about 210Wh of usable power (35*12*0.5), so the battery would be dead after 2.5 hours when there's no sun. I suspect that 80W is the maximum power use on the highest fan setting, but that's still a huge number. Two fans would chop all the usable times above in half. You'll either need more battery and more solar, or you'll need to buy more energy-efficient fans. I suspect you need all of that for this to be viable. Consider getting multiple 12V 120mm computer fans. They only use like 3-5W each. Also consider getting a thermostat so the fans only run when needed, regardless of which fans you use. It'd be a good idea to get a shunt so you can measure actual power usage. I'm just ballparking things here. With solar/battery systems, measurement is important. You can get a cheap shunt for like $20. You don't need anything fancy; just enough to measure real energy consumption and real solar generation so you can do the math and scale your system accordingly. If you don't already have the 35Ah lead-acid battery, don't get that. It's uselessly-small and lead-acid sucks. Get a 100Ah LiFePO4 battery. You should probably get at least 200W of solar panels, more if the fans really do use 80W each. Regarding your actual question, yes, you can wire the 12V fans directly to the battery. You shouldn't overload the terminals with too many connections, but two fans and one solar charge controller aren't unreasonable. Crimp some ring terminals on for a secure connection, rather than wrapping bare stranded wire about the post. I recommend a cheap blade fuse panel for safety and convenience for wiring. Size the fuses according to the wire gauge and the expected maximum current used by the fans (if the fans are really 80W, I'd use 10A fuses and AWG 14 wires).