I am about to start a science PhD and i was wondering how often do other students come up with thier own ideas for experiments that are totally original? I can read many papers and apply them to my work but I'm worried that I wont be able to come up with my ideas that no one else has ever thought of.

You arn' really expected to come up with your own - applying other methodology to your own area will still give original results. Your supervisor will be the main source of ideas.

I think that what 'a student' said is certainly true at the start of your project, when you are new to the subject area (and perhaps new to research). However, as you progress through your PhD, you will be expected to take 'ownership' of your project and to contribute your own ideas and plans for future work (although your supervisory team will still advise you too). After all, you are the one who will have to defend your work at the viva, not your supervisor! Goodluck with your project and don't worry, the ideas will come to you!