Next, some of the key features that are necessary for a power management IC being used in an energy harvesting system will be covered. First and foremost, the quiescent current of the part must be extremely low, as the amount of harvestable energy is usually quite small in most systems. Low quiescent currents enable greater efficiency at small loads, as well as low inputs. This results in greater run time. Having the ability to extract energy when a source is at a low voltage is critical. Single cell solar cells operate around 500 millivolts and thermal electric generators can produce voltages much smaller than this, depending on the temperature differential. When the storage element is not charged, being able to start the PMIC and begin charging is also important. This is called cold starting. Cold starting with the smallest input voltage possible, and with as little power as possible is ideal.