And surely some miner out there has managed to figure out how to slash the overall expense by going solar...
I did
I put my 2011 ~ 2012 BTC into a 1.5kW solar system. Now my modest rig, only a Jally and some GPUs as the solar array was not cheap, continues to mine. With the advent of ASICs, I have an abudnace of power but not enough $$$ for more mining rigs.
Just curious, are you able to sell power back to the electric grid? If so, is it more economical to mine with old equipment than to sell your power back to the grid?