by daveesl77 » Fri Dec 21, 2018 8:10 am
Here is a way to think about it all.
A 100 watt (rated) solar panel can possibly put on 8 amps at 12v in the very best of conditions (8a x 12v =96watts). Those conditions seldom exist and panels are never perfect, so count on like 90% efficiency at best or maybe 80 watts available. So, in full sun, no clouds, nothing blocking anything, you could theoretically run something drawing about 75 watts during the daytime hours when the sun is hitting the panel full on and less during times of less direct sunlight. The panel is charging a battery to act as storage and cushion (say a cloud comes over for 10 minutes).
A heater runs from resistance, so a 1,500 watt heater is pulling 1,500 watts the entire time it is running, unless it has a thermostat, which turns it on/off as needed. But to start, it pulls that entire 1,500 watt load. Your panel is putting out 75 watts actual, your draw is 1,500 watts. That means you are creating 1/20th of the needed power to run the heater constantly. Say you have a battery bank that has a capacity of 40 usable amps at 12 volts (50% of an 80 amp rated battery). Those 40 amps can equal 480 watts. (40x12=480). That 1,500 watt load is going to wipe out your capacity in about 30 minutes or less. So the 1,500 watt heater is a no-go, unless you have a monster setup. And remember, solar only produces when the sun is shining.
As to the AC, this is a bit different. I test ran my little 5k, Walmart $90 special window unit a couple of years. I added in a "hard start" capacitor and yes it did work ok with 150 watts of panel and 80 amps of battery. The unit, in Florida, had an average draw of about 150 watts per hour. In compressor mode the draw was large, like 500 watts, but when the compressor kicked off, the draw was like 75 watts for the fan. That is still going to whack a small solar system, but it is usable.
What I primarily did with my setup, and this worked for years, was to run a small Haier $100 dorm fridge. I would use the panels to charge the golf cart batteries (mppt controller, not pwm). The batteries ran the inverter (cheap 1,200 watt HF modified sine) and the fridge was running at about 29* F. It was perfect. While traveling, the tow vehicle charged the batteries which ran the fridge. When stopped if I had shore power then I switched the fridge over to 120v shore. If not then I used either the solar or a small 2,000w Predator gennie. I could normally run the fridge non-stop, at medium setting with just solar, if the sun was going well. Hourly draw was like 60 watts. If no sun, then I'd either fire up the gennie or plug the tow vehicle in to charge the batteries. The golf cart batteries, with no input, could easily run the fridge for 12 hrs +.
As to the location of my panels, they would ride on top of the camper in an aluminum tray I made. They could be easily removed and set-up away from the camper, if needed. I could go out about 50'.
dave