Is there any manual way to calculate the power consumed by a FPGA.
There is a tool called Xpower for Xilinx FPGAs, I just interested to know how exactly it works...
Type in google for "CLB power consumption". You will find a wealth of information on the topic. The power depends on the frequency you run your design and also how many logic elements you use in the CLB.
Manually doing power estimation for an FPGA is very difficult and Time-consuming. For a design using >70% of Device can be rather impossible. You need to know the frequency at which internal nodes are switching and the power factor of each node. I am attaching a Xilinx Document which might help u to understand how the tool does it.