I have a 300 watt solar panel whose voltage and current need to be monitored by installing a device there. There is no source of power supply that I can use for this monitoring device but the solar panel itself. How do I extract this small voltage from the panel? Note that the solar panel is a variable source of energy. Hence, Just voltage divider won't work. The panel produces voltage in the range of 0-40 V depending on sunlight. In absence of sunlight my circuit can switch off.