Hi folks,
My trailer has a 200 AH battery bank and a 140 watt solar panel permanently mounted on the roof. It’s an older panel from Craigslist and so I don’t think I’ve ever gotten 140 watts out of it. We also tend to camp next to trees that provide at least partial shade. In a parking lot in full sun I’ve seen 7 amps of charge going from the controller to the battery, but that would only translate to 85 watts. In a typical camping spot, the most I’ve seen is 2.5 amps of charge or so, only during the hour a day where the panel gets the most sun.
We run a fantastic fan at night, which is about 2 amps. Later in the season we will have a Propex heater replacing the fan, but it’s still roughly 2 amps. We both have phones that charge at 1 amp a piece, and other electronics probably take another 1 amp. Assuming devices are on about 4 hours a day, that’s 5 amps X 4 hours or 20 amp hours used in a 24 hour period. (Very rough estimate I know.)
If my solar is providing 2 amps for 8 hours a day (doubtful), that’s 16 amp hours of recharge in a 24 hour period. I think in reality 10 amp hours is optimistic with the trees. So we are using about 2x the power we make in the shade. That’s why I have a large battery bank so we can camp for many days in a row. However, i just bought a small efficient fridge, which would add additional load. The Alpicool fridge (see Slim Potatohead on YouTube for an excellent review) is rated at 45 watts, which at 12 volts is 3.75 amps. However it would cycle on and off. Let’s say it’s only running the compressor for 8 hours during a 24 hour day, so that would be an additional 30 amp hours used. What have I gotten myself into? Lol.
Let’s sum up.
200 Amp hour battery bank, of which 100 amp hours are usable (50%)
Fan or Propex 2 amps x 4 hours = 8 AH
Phone charging 2 amps x 4 hours = 8 AH
Other electronics 1 amps x 4 hours = 4AH
LED lighting is negligible.
Total use per day adds to 20 AH
Solar charge (full sun) will bring this back to full (7 amps x 3 hours)
Solar charge (trees) would only replenish 10 AH per day
So a net of -10 AH a day means we could camp 10 days on our battery bank under trees and be fine.
Now add in the Alpicool fridge 30 AH for a total of 50 AH used per day.
That’s replenished in full sun (assuming 49 amp hours of charging), so we could be fine if we camped in the desert. But we are in Pennsylvania and there are trees.
If we only get back 10 AH per day under the trees, that’s a deficit of 40 AH so we can camp for 2.5 days until we run out of power.
Advantages to the fridge would be no more having to buy ice or have food spoil in melted ice water. We could save money on ice and food. I like the concept. Can we sustain it is the more important question, and one I should have thought about more before clicking “Buy” on Amazon! But I really want this to work.
So... this is turning into a manuscript... sorry. Here are some remedies I am thinking of.
1. Camp in sunnier spots to be able to stretch the battery bank across more days.
2. Get a portable solar panel to move into the sunny spots around us to supplement our power generation.
I really like #2. I can imagine splicing in a smaller portable panel that can be set up and angled directly at the sun in open areas. 20 feet of wire would probably be enough to stretch it out to where it would need to go. I think wiring it in series not parallel would be the way to go since it wouldn’t be identical to the existing panel. I have an MPPT controller.
Here is my question.
My controller isn’t rated for more than 140 watts of photovoltaic input. However, I would only use the additional panel when the 140 watt panel is in the shade. If my big panel is making only 2 amps, that’s only 24 watts of input, right? I am thinking a 50 or 60 watt auxiliary panel positioned in full sun could get us another 3-4 amps. It would never be utilized when the main panel has access to full sun, so as not to overload the controller. Is this doable? It should provide another 24 AH of charge at 3 amps x 8 hours, basically making our shady spot into the equivalent of full sun and allowing us to be out camping with the fridge for 5 days instead of 2.
Thanks if you read this far! Ideas? Assumptions? Warnings? Experience?