There are tons of reasons for doing it the US. Off the top of my head I can think of (future) tax revenue, potential to increase US exports, and yes, actually -- jobs. In spite of the high degree of automation in factories, there is still a need for large numbers of skilled and unskilled workers in manufacturing.

Also, they're not talking about a factory for building products that have a bajillion years of process engineering behind them. Having the factory would give these companies feedback on new processes for making efficient batteries more efficiently.

Sure, a lot of people assemble products using these batteries overseas. However, if that were to change the US economy would see quite a boost. If this is a key component in making that change, I'm all for it. Not to mention that I'd love to see the US make some amazing new discoveries on these kinds of fronts, especially with the rules the GP mentioned.

You're on the right track, but you're not quite there. Solar panels are more or less arrays of photodiodes. AFAIK most fiber system use PIN photodiodes to convert the light intensity over a specific band of wavelengths in a fiber to electrical current. Note that I said current, not voltage. Typically a transimpedance amplifier and some kind of comparator circuit is then used to measure the intensity of the signal. The PIN diodes can convert very small quantities of light to very small currents, and transimpedance amplifiers can deal with very small currents as well. Generally the limiting factor for low-light intensity systems like is the "dark current" of the diode you're using. If the current generated due to your light source is within the noise of the dark current you won't be able to detect any change in the system. Fiber systems operate at light intensities that generate currents well above this dark current, and they do so without a high power demand.

Power issues can be born from speed issues, though. Since photodiodes need a fairly large surface area to be able to generate enough current from light signals, the PN (or PIN) junctions act like a capacitor. Capacitors act like low-pass filters and this limits the switching frequency of the signal you can transmit. This effectively limits the data rate of the system. If you make the surface area smaller, you'll need to increase the intensity and focus of your light beam in order to make up for the change. This could cause high speed systems to have high bus power requirements and higher manufacturing costs.