Designing solar power satellites

The amount of light falling on a solar panel varies inversely with the square of the distance from the sun. If you take a panel to 1/10 of an AU from the sun, it will receive 100 times the light that it would at 1 AU. This is why KSPI's microwave power transmitters have the ability to transmit power from solar panels: because getting close enough to the sun makes it feasible to produce megawatts or even gigawatts of power from a solar array.

Using solar power to drive a microwave transmitter has two advantages over using reactors to put the same amount of power into the network. First, a well-designed solar satellite will never require refueling or maintenance after it's in position. Second, the sun is an easily visible target for your receivers anywhere in the solar system. No matter where you are, you know that if you can see the sun, you have power.

This article will attempt to assemble what you need to know to design a successful solar power satellite on the first try. I assume that you are already comfortable operating microwave receivers and relays and transmitting reactor-generated power. I also assume that you are comfortable with the launcher design and mission planning to deliver your satellite to low solar orbit.

Battery requirement

Resource consumption in KSP occurs in the Unity FixedUpdate event, which in KSP occurs every 0.02 seconds. In each "tick", the microwave transmitter attempts to consume and transmit as much ElectricCharge as the vessel's solar panels produced in their most recent update. But no matter how much power is available, it is impossible to produce or consume more charge in one tick than the vessel is capable of storing.

KSPI defines one EC per second as one kilowatt, so the available power in kilowatts is the amount of EC that will be drawn and transmitted in one second. Divide that number by 50 to get the amount of charge that the transmitter will request in each 0.02-second tick. If your battery capacity is less than that, your transmitted power will be capacity-limited.

Example

I estimated that a satellite generating 2,400 kW at Kerbin would produce approximately 6.48 GW in a minimum solar orbit. Express the power available as 6,480,000 kW, and divide by 50. A power satellite of this size will need to be able to store 129,600 EC to transmit all of the power available to the panels.