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.
The rain pitter-pattered on the roof top. Pitter-patter means light sounds or beats, and often is used to describe the sound of small animals (like cats) as they gently move about. It has a fairly positive and easy-going connotation, and using pitter-patter to describe rain invokes a sense of melody and calm.