A contrary view: There is no wasted power when charging a lead acid battery with a solar panel. While the battery is accepting charge, the battery terminal voltage (6 cell) is between 12.5V and 14.5V. That happens to be near the MPPT voltage for an 18 to 22V panel. So, no "regulator" is needed, effectively the panel should be connected directly to the battery.
It is only after the battery reaches full charge (indicated by the battery terminal voltage climbing north of 14.6V) that a regulator is needed. Since the battery is already charged, who cares if now the regulator is producing heat instead of modifying the electro-chemistry of the battery.
The regulator should be the kind that uses a PFET in the path between the solar panel + lead and the + pole of the battery. During the initial charge phase, the PFET is turned on hard, meaning that the voltage drop across it is only a few mV, and the wasted power is nearly zero. After the battery reaches full charge, the PFET progressively is turned off, so now the PFET begins dissipating heat. Same would be true if the using a shunt regulator; no power is wasted initially, charging the battery in the shortest time. Who cares if you make heat after the battery is charged...
Forget the LM317. It is not suitable for this task.
It is only after the battery reaches full charge (indicated by the battery terminal voltage climbing north of 14.6V) that a regulator is needed. Since the battery is already charged, who cares if now the regulator is producing heat instead of modifying the electro-chemistry of the battery.
The regulator should be the kind that uses a PFET in the path between the solar panel + lead and the + pole of the battery. During the initial charge phase, the PFET is turned on hard, meaning that the voltage drop across it is only a few mV, and the wasted power is nearly zero. After the battery reaches full charge, the PFET progressively is turned off, so now the PFET begins dissipating heat. Same would be true if the using a shunt regulator; no power is wasted initially, charging the battery in the shortest time. Who cares if you make heat after the battery is charged...
Forget the LM317. It is not suitable for this task.