Individual solar cells are somewhat difficult to solder to. Self-adhesive metal stained-glass tape makes for the easiest soldering job--the tape holds itself in place while you solder. Use electronics solder that contains 2% silver. One side of the cell is (+), the other (-).
rain check (plural rain checks) (idiomatic) Any voucher or note from a merchant to a customer to provide an item the merchant has run out of at a later date for the item's current price, or (in a more literal sense) to provide a service at a later date.
Definition of rain. 1a : water falling in drops condensed from vapor in the atmosphereb : the descent of this waterc : water that has fallen as rain : rainwater. 2a : a fall of rain : rainstormb rains plural : the rainy season.