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Am I severely underpanneled?

jbrobie16

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Apr 22, 2021
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So I've just finished installing three panels on the roof of my Ram Promaster which I'm in the process of converting to a camper van. I have 1 200 watt panel and 2 50 watt panels - wired in parallel. I've done the math to figure out that will give me 280 watts total. I'll be wiring these panels to 3 100ah Battle Born Lithium batteries. The system, when it's completed will also include a 3000VA victron inverter/charger. I'll be wiring up a shore power input and the ability to charge from the alternator.

I've got room to put in another 200 watt panel but I'm trying to leave room on the roof for a deck. I'm at the point now where I'm about build the deck. On the one hand I'm thinking I can always add another panel down the road if I find that I'm not able to charge as much from solar as I would like. On the other hand, it would be simpler to add another panel now than have to undo the work on the deck and wire another panel later.

We'll be cooking on propane in the van, and most of our draws on the system will be DC, we'll only have to turn on the inverter occasionally for the 2-gallon hot water heater, the small microwave and to charge 2 laptops.

Let me know if I've left out any pertinent information, and thanks in advance for any advice.
 
Welcome to the forum.

200W + 50W + 50W = 300W.

Those panels must all have comparable Voc/Vmp, i.e., around 21 and 18, respectively.

If on an MPPT, you have the potential to get the full 300W in perfect conditions. On a PWM, you'll never see more than 240W.

3X 100ah Lithium = 3.84kWh total energy storage.

Assuming you get great sun on 300W of panels, you would take about 2.5 days to charge them from empty.

Your PANELS dictate how much daily energy you can use on an ongoing basis.

Your BATTERY dictates how long you can operate without charging.

Based on your 300W of panels, and 5 hours of great sun (summer, no shading, clear skies, etc.), you might be able to produce 1.5kWh of energy per day (hence the 2.5 day charge time).

Not sure about your water heater, but a small 6 gal 120VAC water heater often uses a 1500W element. If that's the case, you should be able to run your water heater for 1 hour and use no other power before dipping into your batteries.

Your decision to add panels should be based on your computed energy needs. Aside from the water heater and the presumed short microwave use, they may not be too high.

Have you conducted an energy audit? (Link #1 in my sig)
Have you determined how much solar you have available in your expected area? (link #5 or #6 in my signature)

With the above two, you'll know if you need another panel, or if you can use the space for a deck.

Don't forget to include the power consumption of the inverter. It's published in their datasheet.
 
IMO: If your usage calls for three 100Ah Battleborns, rather than just two, then you are probably under-pannelled. Remember that the "Standard Test Conditions" STC panel wattage ratings are hardly ever reached in practice, even at Solar Noon on a perfect day. If your panels lie flat on the roof, accept another 20-30% penalty, along with the fact that you only get significant charging for a few hours per day.

You should certainly run your water heater on propane as well, But, as a total SWAG - I'd say that your 300W are marginal for just two such batteries, and definitely insufficient to support 3 batteries without plugins, and without heavy use of the Dodge engine (with a DC->DC converter).

I incidentally have 500W, for slightly less than 300Ah, in my travel trailer.
 
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Thank you everyone. Over on YouTube, I found this very informative explanation of whether parallel or serial makes the most sense with panels of different sizes. It explains in detail the math I used to arrive at 280 watts for my array when wired in parallel to an MPPT. I'm working on an energy audit with the spreadsheet that snoobler linked so I'll have a better idea of what our typical draw will be. From what I'm hearing here, it sounds like I am definitely underpanelled but perhaps not severely so. I think I'll go ahead with the deck and add another panel down the road if we're dissatisfied with how often we have to resort to shore power or the alternator.
 
I've got a similar setup (one 100AH BattleBorn, with 85W solar). I'm adding a second solar panel, but for this second one I decided to buy a SunPower flexible panel. I'm going to mount it to the roof next to the first panel, but with quick release fittings so that I can take it off and point it at the sun. This will allow me to park the van in the shade and put the panel where the sun does shine. Flexible panels are more expensive, and from what I've read SunPower is the only trustworthy brand of flexible panels. Something to consider.
 
I've got a similar setup (one 100AH BattleBorn, with 85W solar). I'm adding a second solar panel, but for this second one I decided to buy a SunPower flexible panel. I'm going to mount it to the roof next to the first panel, but with quick release fittings so that I can take it off and point it at the sun. This will allow me to park the van in the shade and put the panel where the sun does shine. Flexible panels are more expensive, and from what I've read SunPower is the only trustworthy brand of flexible panels. Something to consider.

Make sure it's one of the newer ETFE coated panels with a 20+ year performance warranty and a 5+ year defect warranty.
 
I've got a similar setup (one 100AH BattleBorn, with 85W solar). I'm adding a second solar panel, but for this second one I decided to buy a SunPower flexible panel. I'm going to mount it to the roof next to the first panel, but with quick release fittings so that I can take it off and point it at the sun. This will allow me to park the van in the shade and put the panel where the sun does shine. Flexible panels are more expensive, and from what I've read SunPower is the only trustworthy brand of flexible panels. Something to consider.
Oh, I really like this idea. I'm sure I can rig up some kind of quick release mount to the deck, but what about the extra wire that would allow me to move it? I'm thinking it's probably best to use the least amount of wire necessary when it's mounted to the van, then plug in additional wire only when I'm moving it.
 
Exactly - I'm going to cut off the MC4 connectors and use Anderson Power Poles instead, and then build a 30 foot long extension cable for when it's on the ground. Voltage loss calculators suggest that a 12 gauge conductor at 5 amps will lose about 3% at 30 foot distance. That small loss is more than countered by the much larger gain from having the panel oriented to the sun.
 
Why not put hinged panels on your deck? they make power when not using deck, then tip up and use as railing when using deck.
 
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