Apologies if this has been noted anywhere or if i'm missing something but if I recurse (apparently that isn't even a word!) a small power factory inside a larger factory (first screenshot), it messes up the production bar - it just shows as a black bar (second screenshot - have highlighted it). Any thoughts? I have the both the steam engine factory and the larger factory housing it set to output power (yellow arrow is pointing downwards) and have set them both to 100GW.

Not the end of the world, it just means I have no idea of how near I am to going low power without working out the output of all the turbines. Just thought i'd mention it!

https://drive.google.com/open?id=1gMDfgpSSAMTq5g-_LeINtXIZJk62d4aR
https://drive.google.com/open?id=1fTJHT-qJBNJKS_TX9BfFv3bXhoA4jE3B

Cheers

If you set the output to 100GW, that bar is indeed going to be pretty black. The maximum available power, used for the scale of the production bar, is determined by the production capacity as seen from outside, and from outside Factorio only sees the energy transfer buffer, which you yourself set to 100GW. If you set your buffer to something less, then more of the production bar will be visible.

Ahhhh sorry I had no idea the maximum throughput had any bearing on the production bar! Makes sense now. So actually when you setup a power plant it's a good idea to work out the max output then set the max throughput to around the max output?

Yeah, that lets you read your current load in the power graph window. Protip: When you've done that, you can very easily find the maximum load of your power plants by placing an infinite drain in your electric network (for example a factory building set to pull 100GW), and then checking the power graph. (This causes a brownout though, use with caution.)