Robotic Surveillance Lighter-than-air Craft

Why wouldn't this 19th century idea work?
** Since the mid '90s, I've been thinking about the potential of robotic surveillance lighter-than-air craft (RSLC) in military and law-enforcement applications. The device would be essentially a miniature Zeplin. The balloon would be filled with hydrogen, its top and side skin being covered with solar-voltaic surface to charge batteries servicing electronics and electric motors driving the propellers and controls. The payload would be several video cameras, including visible-light and infrared, and transmitters for their signals.
** The device would be commanded to approach within a few yards of designated GPS coordinates at an altitude safe from ground fire and small rockets. Barring strong winds, it should be able to hold its position indefinitely. Larger rockets and antiaircraft guns would have to be attacked when identified. The cameras would take video at about 10 frames per second, enough to keep up with moving objects on the ground. Their default zooms would be as wide as compatible with sufficient pixels per unit ground area. On command from an operator on the ground it would zoom in on any object of interest long enough to capture identifying characteristics. It would report the GPS of any object on the ground pointed at by the operator.
** Such a device could provide surveillance around anything in need of protection (a village, an installation), or it could document events in an area rich in criminal activity (Juarez Mexico). Several of them along any route could identify IEDs being planted (where the planters came from and go to), and they could locate ambushers before, during and after an ambush.
** These applications are available to the side that controls the air in an asymmetric conflict. RSLC could have been used in the '90s to monitor and control Iraq (by threats), allowing withdrawal of flyovers, embargoes and blockades (until a new regime could come to power more naturally), thereby avoiding the unethical invasion and occupation.
** It seems that the only engineering challenge in this idea is how to ensure that the energy needed to hold position in expected wind is less than that gathered in expected sunlight. That would have to be addressed in shape of the device (to get more sun exposure, to get less wind drag).