From large panels to harvested microwatts from a few photodiodes, solar power is increasingly prevalent in autonomously-powered systems. In low-power solar systems, it may be critical to assess whether there is sufficient sunlight at a given time to power the system. In some cases, there may be not even sufficient power to wake the microcontroller. Learn how with some simple analog circuits that an ultra low power op-amp—perfect for critical “always on” supporting circuitry around the microcontroller—can be used.