Direct current( DC) is characterized by the fact that the current always flows in the same direction. The level of the DC voltage and the current intensity can change, but the direction is always the same.
Direct current can be generated by DC generators, photovoltaic systems, batteries, accumulators and fuel cells. It can be obtained from AC voltage by rectifiers and used as supply voltage for electronic devices, chips, components, modules and appliances. On the other hand, alternating current can be produced from direct current using inverters. Direct current always has a fixed reference polarity, which can be positive or negative. The designation itself says nothing about the polarity or voltage level.
Direct current can be transmitted in direct current networks. Since consumers usually have AC-based power grids installed, the DC current must be converted to AC current with the grid frequency of 50 Hz in inverters before it is made available to the consumer.