After another week or so of research and many exchanges with the awesome folks on this forum and others, I have decided on my final config! I figured with all the great setup information on this mile long thread I'd toss my final setup on here to add to the compilation. Especially because I went Lithium!
I re-examined my FWC specs and manuals and got much more accurate picture of energy needs for both summer and winter:
So I'm looking at ~60 ah a day max and will more likely be in the ~50 ah per day range most of the time. I'd like my system to run for 2 days without any driving or charging, so ideally I'd like a battery in the ~100 ah usable range. Unfortunately, that's a lot of weight which led me to consider lithium over conventional lead acid.
Initially I thought LiFePO4 batteries would be too expensive for me. I even looked into building my own until I found a company in Nevada called Battle Born Batteries. Their prices were actually comparable to building my own. These guys are making a 100 ah 12v battery with a built in BMS (very important) and a 3 year warranty for $899. When I called them to chat they ended up giving me $50 off and they don't charge for shipping. So $850 for a 100 ah usable delivered right to my door step! Plus, and this was a huge consideration for me, the entire thing weighs only 29 lbs. 100 ah usable on a comparable lead acid system would have weighed 132 lbs and (for Lifelines) cost $590. So for a difference of only $260 the advantages are pretty hard to ignore. The pros of LiFePO4 for our kind of applications seem to be these:
- drastically lighter
- can be discharged well into the 80-100% vs 50-70% for LA
- performs better at higher loads
- faster, more efficient charging
- 3000-5000 cycle vs 400-1500 LA
So I pulled the trigger on Lithium.
As for panel sizing, I looked at the average solar radiation for Denver as a baseline for the areas this rig will camp most. (UT, WY, CO, NM). It's 5.54 kWh per square meter. Multiplied by my panel kW (.29) I get 1.6066 kWh per day, or 1606.6 Wh per day. Divide by 12.8v for 126 amp hours per day, per square meter. I have .99 square meter of panel. So if I'm doing all of this math right, 126/.99 means I can expect to generate ~125 ah a day as a daily average in any season. But of course that's assuming I get my theoretical maximum amount of power, which of course, I won't. Considering my bad math, what other people have measured with similar setups in real life, less than ideal panel location in the morning and evening, shading from parking under trees, etc, bad weather, the ~%70 efficiency of panels to begin with, and fudge factor in general, I opted to go with 50% of that number. So hopefully I'm still around ~60 ah per day which is more than enough to meet my likely 50 ah a day energy needs.
I plan on achieving 290 watts of solar using a combination of flexible, lightweight panels. Two 120 watt Solar Cynergy panels and a 50 watt HQST panel came in at a total of $1.29 per watt. It was the best price for the size I could find. Also -- and again, weight is important -- a comparable rigid array would have been well over 40 lbs whereas these combine for a total of less than 10 lbs. I'm opting to wire them in parallel rather than series as shading on a single panel will make the entire array less efficient in series and the existing wire in the FWC is in the acceptable range to handle the parallel current.
To choose a controller, I looked at size and programability. 290 watts (divided by 12.8 = 22.7a). Even at 70% panel efficiency that is still 15.9a and I would like a little wiggle room in case I ever want to add more solar without adding another controller. So I opted for the Victron MPPT 100v/30a controller. I saw some mention in my research that MPPT wasn't as effective with LiFePO4. I can't see how that is true because the MPPT specifically provides a boost during bulk, and LiFePO4 batteries charge to nearly 99% in bulk. MPPT seems more advantageous for lithium than for LA considering this. Also, the Victron algorithm is fully programmable which is important considering my battery's different chemistry (although with the built in BMS the manufacturer says 14.4v bulk and 13.6v float is ideal which is very typical in many LA configurations).
Lastly, I want to know what is happening within this setup. I need good data! One of the most troubling things in my old rig that I drove the pan am with was not having very good insight into my setup. So, for this rig I'm adding the highly praised Victron BMV700 to the mix. Both the solar controller and the battery monitor store the data within the device, so I'm also buying a single bluetooth dongle that I can switch back and forth between the two to pull the data into my phone. If switching becomes a pain and the data is as useful as I hope, I'll add a second dongle later. It might very well turn out that just monitoring the battery by itself is sufficient, so I'll start with one. Having at least one also allows me to program both devices from my phone.
Not the cheapest setup. It comes in at about $1600. But it meets my energy needs, is extremely light, and should well outlast any comparable LA setup. My stoke is high!
