I was interested in learning how much energy was generated so I placed a grid connected PV installation on the roof. The electricity generated by the solar panels is used in the house and fed back to the grid when there is a surplus. The LCD screen on the inverter just doesn't cut it (read: isn't very hackable).
I also have a Fluksometer near my fuse box. The idea is to measure electricity, water, and gas consumption. The Fluksometer can also measure electricity generated by the solar panels.
I connected a current clamp around one of the wires, going from the inverter to the fuse box, and let it run for a day. Surprisingly, it measured a current load of around 50-60 watt at night as well. It turns out current clamps are not the best way to measure the electricity generated by a PV installation (still not sure why though).
There is also an EM10 DIN meter in my fuse box and it happens to have a blinking LED. The Fluksometer has two pulse ports. Turns out you can simply wire the S0 pulse output on the EM10 DIN meter with one of the two Fluksometer pulse ports. The connections on the EM10 DIN meter are numbered. Port 41 is the negative pulse port and 42 is the positive one. Wire those with the correct ports on the Fluksometer (port 4 and 5 are the pulse ports).
Check the side of the EM10 DIN meter. Mine says 1000imp/kWh or 1 Wh per pulse. Configure the port on the Fluksometer accordingly and wait a few minutes.
There you go, nice graphs of your solar panels:
And more importantly: access to a REST API!