Now Xively has stopped working I have made the move to a Raspberry Pi running Measureit.
Data is uploading OK but the rule I used to use to stop small amounts of -ve generation uploading when the system was off has failed. Now I see maybe 12 - 20W during the night.
I modified my original feed rather than starting afresh.
The Rule I used is;
if(power < 40) power = 0;