There are transceiver concepts for low power consumption. Some like the Rockmite or the Pixie even fit in an Altoids can. Both can operate on 12V and the battery can be charged via solar panel or Savonius generator.
With my Rockmite I was able to easily pick up transmitters located in China claiming to use 50W of power.
The only drawback is that the Rockmite and the Pixie are CW only tranceivers.