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.
Well, I personally use the phrase cash a check to mean that I'm taking a check to the bank to get the amount in cash. Others probably use it interchangably to mean deposit a check, which I'd say means taking a check to the bank with the intent to deposit it (either in full or partially) into an account. YMMV.