Solar Rule Of Thumb....
I was wondering with so many variables is there a rule of thumb on how large of a solar system you need to keep your batteries charged so not having to run the generator. The factors I would includ...
Forum Discussion
Whether to apply the "don't discharge more than 50%" rule of thumb depends on how much you'll use the battery.
If you're less than a full-time boondocker, the difference may simply not matter. Only 4% of campers do over 30 days per year. The majority camp less than 15 nights. And even fewer if only considering boondocking.
You can find pessimistic estimates for generic deep cycle lead acid of 200 cycles @ 100% discharge. Then look at a premium battery - Trojan Battery's literature for their SPRE 06 255 solar battery (same size as a T-105) shows a life expectancy of about 1900 cycles @ 50% discharge, and about 1200 @ 80%.
The inexpensive Interstate GC-2's sold by Costco are supposedly 650@80.
So, take the extreme high end of 30 full battery cycles per year, and use the pessimistic expectation of only 200 cycles of lifetime, and that's still almost 7 years. Not many RV batteries last longer than that regardless of how well they're treated (now someone will describe their 20 year old battery bank).
But let's say, age and cycles combined, the battery lasts 6 years instead of 7. We did that by limiting how much battery capacity we used - 50% instead of 80%. So, over those 6 years, we avoided using 30% of the available capacity to save (7/6=1.17) 17% in battery cost. It's still a false economy.
Use more realistic figures, and things only get better. Use the Interstate 650@80 numbers, and that's over 21 years. Cycles simply aren't a significant factor at that point. Even a battery on constant float charge isn't going to last that long.
If you're less than a full-time boondocker, the difference may simply not matter. Only 4% of campers do over 30 days per year. The majority camp less than 15 nights. And even fewer if only considering boondocking.
You can find pessimistic estimates for generic deep cycle lead acid of 200 cycles @ 100% discharge. Then look at a premium battery - Trojan Battery's literature for their SPRE 06 255 solar battery (same size as a T-105) shows a life expectancy of about 1900 cycles @ 50% discharge, and about 1200 @ 80%.
The inexpensive Interstate GC-2's sold by Costco are supposedly 650@80.
So, take the extreme high end of 30 full battery cycles per year, and use the pessimistic expectation of only 200 cycles of lifetime, and that's still almost 7 years. Not many RV batteries last longer than that regardless of how well they're treated (now someone will describe their 20 year old battery bank).
But let's say, age and cycles combined, the battery lasts 6 years instead of 7. We did that by limiting how much battery capacity we used - 50% instead of 80%. So, over those 6 years, we avoided using 30% of the available capacity to save (7/6=1.17) 17% in battery cost. It's still a false economy.
Use more realistic figures, and things only get better. Use the Interstate 650@80 numbers, and that's over 21 years. Cycles simply aren't a significant factor at that point. Even a battery on constant float charge isn't going to last that long.
