Solar panel regulators come in many flavors. The plainest flavor is the simple on-off type shunt regulator. It has the advantage of simplicity, extremely small power dissipation, low cost, high reliability, but in exchange for these advantages one has to accept that the voltage on the battery is always going slightly up and down, that the battery is switched between full charging current and no charging current, and that disconnection of the battery will result in high voltage output pulses from the regulator. Depending on the application, one has to choose the most appropriate type of regulator. In most solar installations I have used my linear solar regulator design, which has the advantages of smooth voltage regulation and undervoltage load dumping, at the cost of higher cost, larger size and high power dissipation. But when I was asked to build a solar regulator for a Yacht, which has just one 3.1 Ampere panel but a 300Ah battery bank, something small and simple was more appropriate than a linear regulator. So I designed and built this one, which you might find useful for similar applications: Generally those where a rather small solar generating capacity is combined with a relatively large battery, or those where low cost, simple construction and high reliability are more important than the smoothness of linear regulation.
When the panel isn’t generating, the entire circuit is off and there is absolutely no current drain from the battery. When the sun gets up and panel starts producing at least 10 Volt, the LED lights and the two small transistors switch on. This powers the regulator circuit. As long as the battery voltage stays below 14V, the operational amplifier (which is a very low power device) will keep the MOSFET off, so nothing special will happen and the panel current will go through the Schottky diode to the battery.