Solar Panels for Marine Lithium Batteries
Design yacht solar for LiFePO4 batteries with MPPT charging, shading, array size, daily kWh and Australian cruising conditions.
Solar is often the most valuable renewable charging source on an Australian cruising boat.
What matters more than sticker wattage
- usable mounting area
- shading from mast and rigging
- boom position
- panel temperature
- controller efficiency
- array voltage
- cable loss
- orientation
- seasonal sun
- latitude
- cloud
- salt and dirt
- battery charge limits
Planning formula
Daily solar Wh = array watts x peak-sun-hours x system factor
For early planning, a system factor such as 0.7-0.85 can account for a mixture of real-world losses.
Example only:
800W x 4.5h x 0.8 = 2,880Wh/day
That is not a guaranteed Australian yield. Actual output can be much higher or lower depending on location, season and shading.
Shade is a yacht problem
A mast, boom, backstay or radar pole can shade a surprisingly small portion of a panel.
Consider splitting arrays across more than one MPPT, separating port and starboard arrays, avoiding permanent rigging shadows and monitoring each controller separately.
Check the whole charging path
A charger setting is only one part of the result. On the boat, charging performance depends on the source, regulator, cable path, temperature, battery limits and what happens when the BMS asks the source to stop.
- Record sustained output after the alternator, controller or charger is hot—not only its nameplate rating.
- Verify voltage limits, temperature sensing and shutdown behaviour against the battery manufacturer’s instructions.
- Compare daily energy used with energy that can realistically be replaced in the available charging window.