Feasibility of TEG Power
Off-the-shelf thermoelectric generators cost today what PV cost about 10 years ago. However, the price of the modules themselves is relatively low. Easily accessible modules put out 3W (5% of 60W) and cost $2. Thus we have a 70 cent per watt cost in TEG modules at maximum efficiency - so $70 for the 100W module of interest. The balance of system involves the heat exchange mechanism. This should be doable at low cost of approximately $250 in parts, making this very competitive with PV prices if one builds it themselves.
A 100W system can produce as much power as a 400W PV system - because TEG can run 24/7, while PV assumes 6 hrs of light per day - or only quarter the duty cycle. Thus, the equivalent PV cost would be 65 cents per watt.
The conclusion is that the cost of a TEG generator can be competitive with the cost of PV. This indicates feasibility of TEG power production in off-grid homes.
See more notes and back-of-envelope calculations on this at Thermoelectric Generator.