This 12V solar charge regulator meets most small-scale application requirements. With a current rating of 6A, it can handle up to a 100W solar panel. Its principle of operation is very simple and there is only one adjustment: cut-out voltage. Many inexpensive commercial solar charges available use, I believe, this technique.
This solar charge control combines multiple features into a single design: 3A current rating, low dropout voltage (LDO), range of voltage adjustment (accommodates 6 & 12V lead-acid batteries), reverse polarity protection, low parts cost ($5.90) and low parts count (14 components).
Max solar panel rating (12V): 43W (open circuit solar panel voltage = 18 to 20V) Max solar panel rating (6V): 22W (open circuit solar panel voltage = 9 to 10V) Output voltage range: 4.5 to 15V (continuously adjustable) Max power dissipation: 17W (includes power dissipation of D3)