As recently discussed here, it is possible to have a single clamp meter/sensor which can detect direction of energy flow - but since that requires appreciable additional complexity, I find it hard to believe that it would be built into any 'standard energy meter'.
Yes, I think I remember him - I think he would be the one whose question I answered in the very first response to his OP, and who obviously already has bought some sort of 'energy meter'.
All true. However, if one accepts all that (and few people really want or need accurate measurements), I'm sure that some people find them useful as rough indicators of changes in their energy usage.
As has been discussed, your energy monitor is almost certainly giving you a figure for net energy flow (without knowing about direction of flow). If you were generating 600W and using 300W, that would leave 300W to be exported to the grid, and that is probably what your energy monitor would show (and, not being able to distinguish flow in different directions, that will 'look the same' as if you were importing 300W from the grid). If, whilst you were generating 600W, you increased your usage from 300W up to 500W, that would leave just 100W to be exported to the grid, and I suspect that is what your energy monitor would show.
Without seeing more information, I don't know exactly what that current transformer is doing. However, although the output of a current transformer will be AC, and of identical magnitude no matter which way around one connects it, the phase of the AC will be reversed by swapping the connections (analogous to reversing DC polarity if you swap the connections to, say, a battery). It may have nothing to do with this but, as discussed at length above, the relationship between phase of the current and phase of the voltage can be used to determine the direction of energy flow).
As I just wrote, that it's exactly what one would expect (and, conversely, one would expect the observed reading to fall if the sun suddenly disappeared behind a black cloud). It's obviously true that "a minus sign on the display would help you" but a simple energy monitor like the Owl does not, and cannot, know which direction the energy is flowing, so it would not know when to display the minus sign - a simple monitor like an Owl cannot tell the difference between 300W being exported and 300W being imported.
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