Yep Dave and Knight have pretty well summed it up. I might add, X10 cameras are not known for their light sensitivity OR their wireless range. Even the X10 B&W "low light" cams need substantial auxillary lighting at night, and I wonder if an X10 wireless cam can even transmit that far(?).
Running power to the barn is the logical solution, and really the only solution if you are intent on using X10 cameras. But an alternative might be to use a wired IP camera with supplemental IR lighting, over CAT 5. Dave's suggestion of two CAT 5 cable is great advice. I think a single 150 foot run will drop too much power to the cam due to wire resistance. Doubling up the power leads in a single CAT 5 (if you can. If the IP cam has audio, you probably will not have any spares) or paralleling the two CAT 5s may help. You may even need to "goose up" the camera power supply to a higher voltage unit. i.e if the camera supply is 5V DC then you *may* need to go to a 9V DC supply at the house.