Kevin Means
Site Team
Hi Frank... A couple of things - First, I think AGMs are the greatest thing since sliced bread. Other than dusting them off once in awhile, they require no maintenance whatsoever. You're going to pay for that, because they're pricey - and you'll want to make sure that you have a charger and solar controller that charges them properly (they have a slightly different charging profile than standard lead-acid batteries) but they're well worth it IMO.
You mentioned not going to an MPPT controller unless your panels' output exceeds 600 watts. Some PWM controllers will work near that 600 watt threshold, but nowhere near as efficiently as an MPPT controller. PWM controllers work fine on high wattage systems, but only if the battery-banks they're charging aren't drawn down very far. If the RV's batteries get drawn down overnight like most RV battery-banks do, a PWM controller probably won't be able to put enough amps back into the batteries during the next solar charging cycle to fully recharge them. PWM controllers can't convert higher voltages from larger arrays to amps like MPPT controllers can, so a lot of solar power gets wasted.
Something else to consider - In the winter months, when most RVers really use their solar, the only way the concept of, "One watt of solar for every amp-hour of battery" will work, is if the panels are tilted toward the sun. If you're not going to tilt them, you'll need more panels to overcome the array's lower output due to the low solar angle, especially if you're going to be consuming more power than what is typical.
We've got eight Group 31 AGM house-batteries (840 AH capacity) and in the winter, our flat-mounted 970 watt solar array puts out just enough power on sunny days to fully recharge the batteries (with typical use). There's no way 840 watts of solar would fully recharge them in the winter. It would in the summer, when the sun is more overhead, but not in the winter unless the panels were tilted.
Kev
You mentioned not going to an MPPT controller unless your panels' output exceeds 600 watts. Some PWM controllers will work near that 600 watt threshold, but nowhere near as efficiently as an MPPT controller. PWM controllers work fine on high wattage systems, but only if the battery-banks they're charging aren't drawn down very far. If the RV's batteries get drawn down overnight like most RV battery-banks do, a PWM controller probably won't be able to put enough amps back into the batteries during the next solar charging cycle to fully recharge them. PWM controllers can't convert higher voltages from larger arrays to amps like MPPT controllers can, so a lot of solar power gets wasted.
Something else to consider - In the winter months, when most RVers really use their solar, the only way the concept of, "One watt of solar for every amp-hour of battery" will work, is if the panels are tilted toward the sun. If you're not going to tilt them, you'll need more panels to overcome the array's lower output due to the low solar angle, especially if you're going to be consuming more power than what is typical.
We've got eight Group 31 AGM house-batteries (840 AH capacity) and in the winter, our flat-mounted 970 watt solar array puts out just enough power on sunny days to fully recharge the batteries (with typical use). There's no way 840 watts of solar would fully recharge them in the winter. It would in the summer, when the sun is more overhead, but not in the winter unless the panels were tilted.
Kev