PV marine battery charging

Re: PV marine battery charging

I have a fishing boat with trolling motor docked where there is no 110V. I try not to run my Lifeline AGM GPL-24T, 80ah trolling battery down more than 50% but it sometimes happens….

Please help me design a PV system to be permanently mounted on a fixed southern facing, unshaded piling. I'd like to recharge to 100%, if possible, from 40ah draw down, as quickly as possible. I have sheltered under console space to mount a controller to prevent overcharge with total cable run of less than 20 feet. This is located in Wilmington NC USA.

Scalez,

Correctly recharging an AGM battery such as your Lifeline requires a fair amount of time when the charger is in its absorb stage (three to four hours when starting from a 50% SOC), so, while “as quickly as possible” can influence the time spent in the bulk charging stage, the overall total will be anywhere from five to eight hours.

I’ll spare you all of the details, but I’ve no doubt that I can make the case for buying another 80 Ah battery and a “small” charging system, and then alternating batteries by using one while the other charges at the dock. A large system will cost a lot more money and not significantly reduce the required recharge period.

Assuming a south-facing panel tilted up ~19-20 degrees (latitude – 15 degrees), Wilmington’s average insolation from late spring, through the summer and into early fall is the equivalent of 5+ hours/day of “full" Sun. Sunny days will be better, cloudy days worse.

See: http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/sum2/13748.txt

This suggests you’ll need a PV module rated @ ~17 V x 8 A = 136 W STC. You might be able to get by with a single 130 W module (i.e., Kyocera 130), but a pair of 85 W modules wired in parallel (170 W total) would probably be better (i.e., Kyocera 85’s)

See: http://store.solar-electric.com/kc-120.html
And: http://store.solar-electric.com/kysokc85wa12.html

The Morningstar SunSaver 10L or Prostar 15 charge controller will work with either of the module suggestions above.

See: http://www.morningstarcorp.com/
And: http://store.solar-electric.com/pros15solcha.html
And: http://store.solar-electric.com/ss-10l.html

You should be able to connect both batteries to this system to keep them charged up while you’re away. As mentioned, don’t overlook security concerns, and don’t forget fuses between the PV module and the controller, and between the controller and the battery!

HTH,
Jim / crewzer

Re: PV marine battery charging

scalez,

The 130 W system is the small system. Anything smaller would probably take more than an average day to recharge the 80 Ah battery.

MPPT controllers are not cost effective in small systems. Since PV voltage drops as the ambient temperature increases, there's often not much "extra" voltage available in the summer for an MPPT controller to convert to additional charging current. My recollection is that previous discussions had found that MPPT controllers become cost effective when the PV array size exceeds ~350 W STC.

STC specs are based on a lab test simulating a PV cell temperature of 25 C (77 F). For this occur in the real world, ambient temperature would have to be ~-10 C F (~14 F) -- something you'll likely never experience in Wilmington.

The absorb / PWM voltage from a PWM controller will be ~14.4 V when the battery is 77 F. Assuming good insolation and module alignment, the output current from the KC-130 will be a bit over 7 A. Coulombic efficiency (Ah out / Ah in) of AGM batteries is typically 98% or better, so the ~7 A (mid-day) from a "small" 130 W STC system should be able to meet your recharge requirement during an above average sunny day.

HTH,
Jim / crewzer