That's pretty interesting, thanks. I guess it just accumulates until it can next reach the server and then sends a single message with the amount accumulated in that interval. It makes a certain amount of sense, to avoid having to send 288 packets per day in one shot, though a little disappointing.
They could be smarter in how they store/display it, by distributing the value evenly over the time range.
I had a couple of periods shortly after installation when it lost connection and I had thought it was losing the data completely.