I have made a calculator to answer just this question. Given a specified mining rig and electrical utility rate, I can show you at what difficulty your rig will not be profitable, compared to the current exchange rate of BTC. This should be applicable to solo or pooled mining.
Here is an example:BFL 5Gh/s ASIC Miner in BLUE
Power consumption: 35 watts
Price of electricity: $0.10 USD/KWHr
Block Rewards: approx 25.5 BTC (25 for block, .5 for tx fees)
Avalon Batch 3 63Gh/s ASIC Miner in RED
Power consumption: 600 watts
Price of electricity: $0.10 USD/KWHr
Block Rewards: approx 25.5 BTC (same as above)
Result:PM me for a personalized calculation. I will work for what ever tip size you feel I deserve.16a2WVi1u3VFDcqvuWHTahk15UM9CxAnUh