Solar. - Here is Circuit Schematic and Project 6A, 6V SSS Based Solar Charge Control using LM339. This is a Solid State Switch upgrade to the 6A, 6V Relay Based Solar Charge Regulator. Solid state switching provides longer life, smaller size and higher efficiency than a relay. In addition, the clock frequency may be doubled in order to better track battery load /charging requirements. The parts cost is essentially identical. One drawback is the loss of the secondary output feature. For more information go the above link as this write-up contains mostly supplemental information.
Effect of parallel MOSFET devices
While the above exercise indicates an acceptable, conservative temperature rise using my favorite, inexpensive TO-220 heatsink, parallel devices have merit. Simply paralleling two FQP27P06 MOSFETs, reduces the Rdson by a factor of two to 0.035Ω. This also reduces the total conduction loss to half, but there is an additional benefit here in that the power is split between the two devices. So the worst case power dissipation of 7W @ 10A is now reduced to 1.75W per device.
The Original Article: "6A, 6V SSS Based Solar Charge Control"