"Concealing" 150-300W a day shouldn't raise any alarms considering all of the electrical kit we use today.
If you have a bunch of electric kit on-hand (game system, TV, computer, monitor, cell phone charger, stereo, DVD player, electric razor / tooth brush etc...) what's to say that the 150W-300W you are burning isn't coming from all that?
IMO, I don't think you will have an electricity issue with such low wattage. However, I DO think you will have a "grow issue" with your room mate when they find out, and I have NO doubt that they WILL find out, or at least suspect your grow. Even if they are not sure, the suspicion will lead to friction, which will erode your relationship, and reduce your quality of life.
Good luck regardless.