Most of the CubeSats have Electrical Power System (EPS) as a dedicated module on a single PC104 like PCB. Depending on the required capacity of the secondary (rechargeable) batteries, they can be housed on the same PCB or as additional modules.
Solar cell arrays, with bypass (required in case of cell shadowing and failures) and blocking (stopping from current flowing back into the cells and acts as a good protection against several failure modes) diodes are assembled in solar panel units that are electrically connected with EPS and thermally with the structure. Both of these connections needs to be well designed to avoid unnecessary power losses.
EPS contains Maximum Power Point Tracker (MPPT), which is a DC-DC converter with ability to adjust its load to the solar cells variable (dependent on the incident sunlight) current-voltage curve. Depending on the solar cells number in an array and whether they are connected in series or parallel, the output of the DC-DC needs to be upscaled or downscaled to match the batteries charging voltage needs. Battery charging, protection and disconnection circuits are usually present, as well as battery heather. Further, from batteries to the power distribution for the rest of the system, additional DC-DC converters are added, usually for 12V, 5V and 3.3V. Unregulated battery line is distributed in some cases. Sometimes, switches are integrated into the EPS to control dedicated power lines. A processing unit is often present to control the MPPT and the output DC-DC converters and switches, as well as for other housekeeping and telemetry needs. Additionally, EPS is in charge of powering up the system after the deployment from the launch vehicle, for which deployment switches and a delay timer are required. Sometimes, EPS also performs automatic deployment of antennas and deployable solar panels. Redundant components and submodules are common.
- How is this power distributed to run the various subsystems on the CubeSat?
CubeSats (at least 1U to 3U) have scarce available volume and many designs opt for custom integrated interconnection buses and there is no single standardization on the power distribution. However, just as with the PC104 standard, majority of the modules are interconnected with stack connectors, through which some lines are dedicated for power distribution.
- Is the CubeSat power output from solar cells usually in a standardized form?
No. Best strategy is to find a suitable parallel/serial connection configuration of solar cells individually for every solar panel. Sizes of solar panels on a single CubeSat can differ. Furthermore, scaling from 1U to 2U to 3U and larger provide different preferable configurations.
- Are there standard connections used for the subsystems to tap into the CubeSat power supply?
Stack connectors, as in PC104 standard is the closest to a standardized connections you can get. This is often preferred by subsystem providers, but there are a lot of custom solutions.
Here you can find an overview of available solution by subsystem providers: https://blog.satsearch.co/2020-06-10-satellite-electrical-power-systems-eps-on-the-global-marketplace-for-space