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Solar power satellites
Microwave power transmitters are capable of transmitting power from solar panels, allowing for the possibility of completely maintenance-free power stations.
This article will cover some tips and tricks that are specific to using solar power for transmission. I assume that you are already familiar with operating microwave receivers and relays and with designing launchers that can put a satellite into low solar orbit.
If you have a particular power target in mind for your microwave network, it's important to know how much power a design will have available in a given target orbit before you spend the delta-v to fly there.
Interstellar discards any power curve in a solar panel's .cfg file and applies its own inverse-square curve. At 1/2 of Kerbin's distance from the sun, a panel will output 4 times what it would output at Kerbin and display in the VAB; at 1/10 Kerbin's orbital distance, the boost is 100 times.
The largest possible yield is obtained at or near the sun's surface. Given Kerbin's orbital radius of 13,599,840,256 m and the sun's radius of 261,600,000 m, the energy available at the surface is (13,599,840,256/261,600,000)^2 = 2702.7 times what it is at Kerbin.
The thermal helper display in the VAB offers a useful shortcut. Solar panels' waste heat production is always half of their electrical output. If solar panels are the only waste heat source on a vessel, then your available electrical power will be exactly twice the displayed heat production for the selected orbital distance.
The microwave transmitter attempts to draw and transmit all of the power produced by solar panels, but it is limited by the ship's capacity to store ElectricCharge. Resource processing occurs in the Unity FixedUpdate event, which in KSP is called every 0.02 s. In each tick, the transmitter requests the amount of charge that each solar panel produced in its most recent update. If the vessel does not have enough capacity to store this charge from when the panel produces it to when the transmitter requests it, power will be wasted.
To calculate the capacity required for full transmission, multiply the generated power in kilowatts by 0.02; i.e. divide by 50.
A satellite that was discussed on the KSP forum produces 2,400 kW at Kerbin. It is placed in a sun-skimming orbit where it receives 2,700x base power, for a total of 6.48 GW.
Express the available power in kilowatts (6,480,000) and divide by 50. 129,600 EC worth of batteries will be required to guarantee transmission of the full 6.48 GW.
The microwave transmitter transmits all power produced by solar panels. Due to limitations in stock KSP's handling of resources, the code is currently unable to reserve solar power for other on-vessel loads. Depending on the order in which parts request charge in each tick, probe cores or antennas may shut down while the transmitter is active.
If shutdowns become a problem, the workaround is to add an alternative source of power. The stock RTG works well, because it requires zero maintenance and its power is simply not transmitted. An Interstellar reactor can power on-board loads and add the rest of its capacity to the transmitted power, but will eventually require refueling.
Some mod solar panels use multiple instances of ModuleDeployableSolarPanel to control multiple animations. Interstellar applies its heat production and output scaling code to only the first ModuleDeployableSolarPanel on each part. For a multi-module solar panel to be compatible, the first module should generate all charge for the part, and all other instances of ModuleDeployableSolarPanel should have their chargeRate set to zero.