ISS power supply

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Power on the ISS for lighting, electricity and experiments is provided by the four solar arrays on the outside of the Russian modules, and the twin arrays mounted on the Z-1 “Mast” attached to Unity (eventually, if the ISS is ever completed, there will be 8 arrays attached to the Truss).

The electrical power system (СЭС, Система Электроснабжения – SES, Sistema Elektrosnabzheniya) is designed to:

• Provide DC (Direct Current) power to all loads of the Functional Cargo Block, Zarya, and U.S. segment modules during the early operation of the ISS;
• receive supplementary power from the U.S. segment;
• transfer power from the U.S. segment modules to the Russian segment space vehicles;
• recharge storage batteries of the transport vehicle (Soyuz) docked to the FGB.

User voltage in the U.S. segment is ~124 V dc and in the Russian segment is ~28 V dc; thus a converter unit is required for electricity from one side to be used by the other.

The power systems (СЭС) in both Zvezda and Zarya are separate and self-contained.

Zvezda and Zarya have two solar arrays (СБ, Солнечная Батареа – SB, Solnechnaya Batarea) each (these were folded during launch and then deployed in orbit, as are the arrays of the Soyuz and Progress). Electromechanical drives keep the arrays orientated towards the sun (they can also be controlled manually by the crew). The load-bearing surface of the solar arrays is fiberglass, to which the semiconductor photovoltaic cells are attached (these are metallic blue in color). Solar energy is converted into electricity and distributed throughout the Russian segment. Any excess electricity is stored in batteries.

The solar arrays on each module are designated СБ4 (starboard plane) and СБ2 (port plane).

Nickel-cadmium storage batteries (АБ, аккумуляторная батарея – AB, Akkumulyatornaya Batareya) provide a secondary source of power when the ISS is in orbital night, and also serve as a backup source of power.

From Peggy Whitson’s “Letters Home”, #10:

The arrays are reddish-gold when the sun lights them, and during sunrises or sunsets the edges of the arrays look like glowing coals in a fire. The Russian solar arrays are much smaller and mounted directly to the Service Module and FGB. In contrast these arrays are white in the sun, but during darkness, they have an opalescent quality of blues and greens.

Diagrams

• Electrical Power System (ECS) (external link, 219 KB). This describes the power of the U.S. segment (which is also converted and fed to the Russian segment). Page illustration from the Reference Guide to the International Space Station PDF.
• SB wings location on the module (41 KB)

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