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.
Re: Rain in Breaker Box. You may want to at least consult a Lic. Electrician to check on the condition of the wires before trying to seal the moisture out. After wires are deemed safe to re-use I would then and only then find the location(s) where the water is coming in and re-seal.