You may want to look into Solarcoin.

As I understand it, it's "mined" by producing solar power.  I've never looked too far into it, but it may interest you.

Additionally, if you want an easy answer to this question, just fire up any mining calculator (Google has several) and set the "power cost" field to 0, using your hashrate / etc.

A staking wallet, run on a cellphone powered by a small solar panel would effectively be "free" coins, not accounting for whatever your Internet access costs may be.