Calculate instantaneous power from kWh feed

Is there a way to calculate (and display a graph of) instantaneous power, if I have only a Wh (energy) feed available ?
I need some kind of “derivative” function, or calculate “(current feed value - previous feed value) / time interval between these values”
My power monitoring system is my EDF energy meter that has a digital interface (UART) sending the total meter value every ~2s. I log this through a Raspberry Pi receiving the UART messages and pushing it to emoncms.

I use a eastron kWh meter which outputs a led blink and pulse every kWh consumed. By measuring the time between pulses I have been able to get quite a nice Watts value when you have a reasonable high > 1000W consumption. This method also serves as a filtering.