buy an old wattmeter off ebay for 20$.
rewind the current sense coil for 2x 10 turns instead of 2 turns to make it more sensitive, typically its 7.2 watt hours per revolution, and if the meter's lowest dial is KWH x10 then you'll have to wait 10 hours to get an accurate number. so just rewind it for 10 turns and its easier to read.
did you contact the electric company about grid tying your solar?
if not, you're probably getting billed for the power going into the grid too..
the industry is moving to separately metered grid tie, and they only pay you the industry rate, which is typically half or one third the residential rate