Can I have 0.03V in the input of an OpAmp? If can, what type of OpAmp can I use?
If you are wanting to convert 30mVdc to 5V by using an energy harvest technique you may be disappointed. The lowest voltage energy harvester that I'm aware of is this: -



I'd be interested if anyone else can find a better one. This isn't a challenge by the way!

If on the other hand you are looking to amplify 0.03V to a 5V level then use an op-amp in non-inverting configuration with a gain of 166.7. This is easily achieved BUT you need a power source slightly greater than 5V to power the op-amp.