Abstract: A power supply system for an a.c. resistive element (10) comprises a first input point for an a.c. mains power source (14) and a second input point for d.c. power derived from photovoltaic panels and/or wind generators (24). Switches (18, 36) are provided between the power input points and the element (10). Timers (60, 62) are provided for delaying closing of that one of the switches (18, 36) that is open on change over from one power source to the other whereby the closed switch opens before the open switch closes. The voltage at the d.c. power input point is detected by a voltage sensor (42). The output from the sensor (42) powers an optical switch (46) which operates a relay (58) which in turn supplies power to one or other of the timers (60, 62) and one or other of the switches (18, 36).

Abstract: Electrical storage batteries and methods of making electrical storage batteries are disclosed. The electrodes (122) of the batteries each comprise a hollow core (124) of electrically conductive material which is sheathed in lead to protect the core from corrosion by the battery acid. Electrochemically active positive material or electrochemically active negative material (116) is cast onto the core. The hollow core permits fluid, gas or liquid, to be fed through the core to prevent excessive increases in battery temperature during charging and discharging.