It includes those systems when provide electricity for other onboard systems. Since, in space, it is practically impossible to provide large amount of power supply from earth, hence, for optimum and proper utilization of power careful designing and logic accuracy is taken into consideration. Voltage regulators are used to provide constant voltage across any onboard system and excess power if any, gets radiated away in space in the form of heat. The various power supply components are :
Batteries – provides current by c
onverting chemical energy to electrical energy. The shuttle goes through eclipse period when the shuttle does not see the sun and hence no solar power; the power during this period is provided by the batteries.
Photovoltaic Cell – usually uses semiconductor devices and solar cell which converts light energy into electrical energy. This is the most efficient mode of getting power supply as it use sunlight as the source of energy and, converts into electricity; and in space, sunlight is abundantly available.
Fuel cell – It also converts chemical energy to electricity but here, some useful by product is formed. Eg: In oxygen- hydrogen fuel all used in Apollo mission, water was the byproduct formed which was used for human consumption and as a coolant.
Solar cell panels - Solar cells are made with Si and GaAs provides the majority of power to the spacecraft. A spacecraft requires from a few hundred watts for older and small ones to over 10,000 watts for larger and newer shuttles.