RV Solar Series: How we Store Electricity is a key consideration, almost all RVs have some kind of central battery. We wish we had the best battery. Nearly all RV manufacturers put the lowest cost battery in an RV, just to give it the minimum. Thankfully when we purchased our RV, the original battery had been replaced with what was the best battery available (at the time).
AGM absorbed gas mat
Our battery is AGM (lead-acid, absorbed gas mat) and holds 300 amps electricity for later use. Of the 300 amps of electricity, we can use 150 amps without undue wear leading to premature battery failure. The previous statement isn’t really true but is a common belief. That discussion isn’t the purpose of this series, it is close enough to the truth to leave it at that.
What is absolutely true is that the deeper you discharge a battery the longer it takes to recharge it. What I didn’t know is that by using the generator to charge the battery “back to full” I was depriving the battery of a most important life-extending recharging stage called float charging or sometimes trickle charging. A lead-acid battery that is denied a trickle charge is not really full. I didn’t want the expense of replacing a dead battery. Nor did I want to live as if electricity wasn’t available. So we ran the generator and watched what we used and how to replace it. (much more on batteries later)
Solar Panel sizing related to battery size
Battery size doesn’t matter when sizing panels for two reasons. First, if you don’t have enough battery size to make it through the night, your battery is too small. If your battery is too small, the repeated deep discharge will kill it. Second, panel sizing needs to replace usage storage only matters when you are trying to use electricity at a later time, typically at night.
How to make enough
We determined to shoot for 250 amps per day covered by solar to recharge the battery and run our RV during the day and evening hours. This we calculated at another 50 amps per day. Unfortunately, it seems that every solar expert calculates collector sizing on a different method. I have not found one sizing method that met my expectations. The other factor of human nature is that we want more. Sizing the panels was a series of guesses. We ended up getting the answer right, but one of the calculations was based on a nonscientific theory — no one has yet to complain that the TV was too big or that they had too much solar.
Thumb rules are junk
Here comes a thumb rule: Some (experts, one and all) say that I should be happy with 150 watts of solar based on the usable capacity of my battery. Again, battery size has nothing to do with it. Instead, since I use 250 amps to 300 amps per day and 150 watts of solar reasonably cannot create 250 amps of useable energy per day; I would have been undersized. Others would say I would be happy with 300 watts of panels, in my opinion, that would be marginal. Instead, I installed 700 watts of solar, and I want more; but you will have to read and read and read some more to find out what I think about solar sizing. (Hint it has to do with the way batteries like to be treated.)
RV Solar Series: How we Store Electricity is important and we are doing ok, better than some and we want improvement in this area.