When you are harvesting solar or wind energy, you want to take most of it. For this you need efficient power converter which would take raw energy and convert it to proper voltage level for charging your batteries or powering electronics. Soldernerd have build an Arduino shield dedicated for charging lead acid battery. He used a solar panel with voltage output around 17V which had to be converted to 14V for lead battery.
This obviously required step down (buck) DC to DC converter which takes 17V – 18V from solar panel and converts it to 12V – 14V as efficient as possible. Microcontroller takes care of generating PWM signal which automatically adjusts to maintain output voltage level. Charger is capable to protect battery from overcharging when voltage of battery reaches 14V. Charger is capable to drive 30W power to the battery.