One Watt at 12 V (I presume, since you have a car charger clipped to it)?

That would yield you 0.083amps. That's less than 1/10th of an amp. 1100mA less than what the N900 calls for.

1 watt/12 volts = 0.08333333 amps.

That solar panel has to have a higher rating than one watt.