The present invention comprises systems and methods related to monitoring of energy usage on a power line. In a preferred embodiment, this system comprises (a) an electronic microprocessor-controlled digital electricity metering device coupled to the power line and comprising a non-volatile non-battery-powered data-storage device, wherein the metering device is capable of interval metering and of receiving a data request and transmitting data in response to the request over the power line; and (b) a data collector (preferably, a transponder) coupled to the metering device via the power line. The data collector is preferably capable of (i) receiving data from and transmitting data to the metering device over the power line, (ii) storing data received from the metering device over the power line, and (iii) receiving data from and transmitting data to a remotely located computer (preferably, a billing computer).