Download datasheets for the part and study them to begin.
Pin 14 in the transmitter schematic is the transmit control. Connecting it to 0v makes the part transmit. In the schematic it is permanently tied to 0V so it will transmit continously.
On the receiver scjhematic pin 17 ( VT ) is the output pin. It is set to the supply voltage ( +5V ) when the address line settings on both the transmitter and receiver are set the same.
The output control circuitry shown ( after K1 ) probably needs to change. It depends on the requirements of the valve you want to use.
For power the easiest probably would be to use a battery and some form of solar charger for the battery. Pick the battery technology you wish to use and then select a proper solar powered charger for that battery technology.
Specifics about the valve control are really dependant on the specific valve you want to use. Are there 2 inputs for direction control? Or is a supply voltage polarity swap needed?
A possibility would be to use 2 HT12F decoders fed by the 1 receiver. One would provide a "OPEN" control signal while the other would provide the "CLOSE" control signal. The 2 decoders would have their address lines set differently. Then on the transmitter would be a SPST switch controlling 1 address line. This switch would choose "OPEN" or "CLOSE" function. Then another switch to assert the transmit pin ( or just the power and the transmit pin is permanently connected to 0V ). You would hold the transmit switch until the valve had completely moved to the desired operating position.