What is the difference between AC and DC power?

Grid supply is alternating current, the direction of flow reverses cyclically, at 50 Hz in Australia. Batteries and solar panels produce direct current, flowing in one direction. Most industrial control, communications and signalling equipment runs natively on DC (12, 24, 48, 50, 110 or 125 V), which is why those sites use DC power systems rather than AC with local rectification.