Integrating DIY LFPs with FLA and Adding Solar

Thom Price

Solar Enthusiast
I moved aboard my boat three months ago in Baltimore Harbor, and I liveaboard full-time. I absolutely love it. I've made several upgrades but have a long way to go to get things the way I want them. Energy wise, I've made a huge difference by replacing the 36 year old 21 cubic foot refrigerator with a new one and replacing all of the lights with LEDs. Now I'm ready to go solar.

What I have:
  • 1984 Hatteras 53' Motor Yacht
  • 32 V DC used for starting engines (2 Detroit Diesel 8V-71TI), running hydraulics, pumping water, flushing toilets, and some lights
  • Two 32 V, 1000 AH FLA battery banks made up of four 8 V batteries each
  • An Outback 3.2 KW inverter/charger
  • A 6 KW diesel generator for AC power
  • 50 A shore power service
  • A brand new Energy Star refrigerator and dishwasher, induction cooktop, microwave/convection (1.5 KW), and a small pizza oven (1.5 KW), which are all 120 V
  • A newish stacked washer/dryer (120 V)
  • Four reverse cycle air conditioner/heaters (240 V)
  • A 20 gallon, 240 V water heater (kept turned off most of the time because the marina has nice showering facilities and the dishwasher heats its own water)
  • A flat screen TV (Energy Star) and various small electronics
  • A forced air diesel fired heater (17 KBTU) and several small portable electric space heaters
  • Two 100 W monocrystalline panels that charge a 50 AH LFP battery for my electric dinghy
  • An electric bike used for daily commuting
What I want to achieve:
  • Reduce my need for shore power to 150 KWH/month on average when in the marina (currently 300 KWH baseload plus heating and cooling)
  • Use the generator no more than 2 hours/week when at anchor (presuming nice weather)
  • Find the most cost effective solution over a 10 year span
How I am hoping to do it:
  • Remove one FLA battery bank and replace it with LFPs
  • Add 2.4 KW of solar panels above the fly bridge
  • Insulate between head liners and outside
  • Batteries - Three of the FLA batteries need to be replaced and they cost around $600 each. It would be better to replace 4 of them so that would be $2400 if I stayed with FLA. I need one bank of FLAs to crank the engines and raise the anchor, but the other bank can be used for everything else. Since I'm wanting to use as much solar as I can, I'll be cycling the batteries frequently and so LFPs should be more cost effective over a 10 year span, especially since I'm getting 3.2 V prismatic cells from China and spending $1040 for a 280 AH bank to start off with. I may double that if needed, but I figured it would be better to start small and grow since prices tend to fall for these things. The batteries are arriving next week so now I have to get the rest of the system figured out (hence this post).
  • Solar Panels - I have a space in front of the radar arch that's 10' x 12', which currently has a canvas Bimini on tubular frames that I can cover with panels. The canvas is getting old and I'm thinking that the most cost effective thing would be to replace it with rigid panels fastened to longitudinal rails added to the existing structure. I can add more panels behind the radar arch (1.8 KW), but again want to start smallish and grow as needed.
  • Insulation - This is just part of improving the energy efficiency of the boat by reducing the heat transfer and hence the need to heat and cool as much. I'll be removing the head liners to reveal 1.5" cavities. I'll take a sheet of 1/2" foil faced polyisocyanurate foam board and glue it to the roof, then leave a 1" air gap below that, then install another 1/2" layer of foil faced foam board below the beams and install a new ceiling surface below that. In the galley it will be "stainless steel" contact paper which should reflect the radiant heat back down. I think I'll go with copper in the master state room and white bead board in the salon.
What I need your help with:
  • BMS - I think I need a 10S BMS for the LFP cells. Do I? What do I need to look for?
  • Solar Charge Controller - I was thinking of going with Outback, since I already have an Outback inverter/charger (click for details) for the FLA bank. I want to keep the two banks separated as much as possible, but it would be good to not have a hodge podge of brands. Then I guess I would need to get their Hub to link things together and the Mate, which is where you set all of the parameters. Does anyone here have experience with this brand? Which parts would I need to get? Should I just go with another brand and let the Outback take care of the FLAs?
  • Second inverter/charger? - I guess it would be better to have a dedicated inverter/charger for each bank since the chemistry is different and float charges different. I could have used 11 cells in my LFP bank and gotten away with one inverter/charger for both chemistries but I realized that after ordering the batteries. I could also go ahead and order 12 more cells from China for a total of 22, and build a 11S2P 560AH bank - spending about the same as I would on a second charger/inverter. I'll probably need them. Should I just do that or get a second inverter/charger?
  • Paralleling the two banks - Though I want to keep the two banks separate for the most part, there may be times that it will be useful to parallel them, like when I want to top off the FLAs from the LFPs when at anchor. I have a button at the helm to do that temporarily when starting if needed, but it only connects them while the button is being depressed. Would this be too hard on the LFPs to parallel them with the FLAs when starting the engines? What hardware would I install to top off the FLAs from the LFPs?
  • What's the best way to maximize the solar and minimize the shore power? I'm thinking there must be a controller which would turn off the shore power when certain conditions are met like batteries being full and plenty of sunshine, then turn it back on when the batteries are low. I'd like to start off a sunny day with the batteries depleted, ideally. Other than doing all of that manually, is there a better solution?
  • What am I not asking that I should be asking? Is there some component I have overlooked?