suntop,
I agree with others suggesting solar power and radio. Do an internet search using the terms "radio SCADA". SCADA stands for Supervisory Control and Data Aquisition, a catch-all term for remote control systems over long distances, pumping being the biggest market for it (another older term for it was "radio telemetry" but that will get you a lot of hits that are unrelated to your needs). People in the SCADA industry are very attuned to your exact problems and offer many low powered systems that come with solar power sources and radio transmitters.
A word of advice, be very thorough in your thinking of failure modes, try to cover all of the important "what-ifs" with regards to loosing communications because it WILL happen.
You still need to divulge your general location on the planet if you want anyone to be able to address your questions about cost, licensing etc. I can assume that since you used kM for distance measure that you are not in the US, but that leaves a lot of different currencies and radio regulations to guess at!
FWIW, I have seen a very innovative solution to your problem back in the days when solar was unrealistic. A farmer put a water turbine generator at the reservoir end of the fill pipe feeding a battery charger and a bank of lead-acid car batteries used to power his level controller and radio. His feed pipe dumped into the top of the reservoir, passing through the turbine first, which re-charged the DC system. By using a small pipe he had the water flowing for long enough periods of time to effectively charge the system at a rate roughly equal to the power consumption rate. Later on I heard that he added a small wind generator to suplement it because he discharged the batteries too often.
Quando Omni Flunkus Moritati
