This Adafruit part is likely as close as there is.
(from a google search of the form “fritzing part Portable-Charger-Power-Bank”.) There are a variety of solar charger parts available in the forums (people have asked for them over the years.) That said your circuit still will not work. The relay module only provides a switch function, it does not supply any power on the contacts. Without a power source the solenoid valve will not function and thus as it stands this sketch will not work.
Peter