Removal of thermal energy Why can't you extract heat from your attic and use it to supplement charge to a Tesla wall battery, while also making your house cooler?
 A: Turning heat into work requires a heat engine.  Unfortunately, the efficiency of a heat engine is determined by the temperature difference between the heat source and the heat sink.  When temperatures are expressed in absolute terms (e.g., Kelvins), the temperature difference between the hot air in your attic (the source temperature), and the outdoor temperature (the sink temperature) is so small that the efficiency of such a device would be VERY low.  For details, see http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/carnot.html 
A: The same reason why you can't leave your refrigerator open to cool the room. To cool an object you need to make the surroundings even hotter. The total energy you spend to do this will always be more than the total energy you can harness.
If you do make an ideal machine that'd do this for you, the maximum efficiency is given by: $$1-\frac{T_{surroundings}}{T_{attic}}$$
Let's take $T_s$ to be the room temperature, which on average is $293 {K}$. Let's make this attic $20 {K}$ hotter. (which is a lot) 
This gives you a maximum efficiency of just $0.063$ or $6.3\%$.. Pretty bad if you want to do something practical with this. 
