I can currently do very little in the game.

For some reason I have minus -133 energy, although the bar is full.

Can anyone help me out here please?

Tried clearing cache and didn't change anything

do you have any weapons that give an energy penalty like the Ion Pulse Ballistae? try removing these and see if that helps, if not, contact Dan and he'll likely have a look for you and sort it out.

Here is a possibility (thou I've never tried it XD)
step 1: very few engineers
step 2: have some energy modules, but all at very bad condition (will break in one uninstall, for example)
step 3: install relays/energy weapons such that the -energy is greater than your engineers, make sure those are in perfect condition
step 4: fail to pay upkeep, breaking the energy modules.

Note that while you are normally unable to unistall energy module with relay/energy weapon on if it reduce your energy too much, a forceful break might do the trick.

would be fun to have -500 energy....