Enough to keep drinks cool in a small cooler, but not much more.
Actually Bob , I used to have a Coleman 12V cooler with the TEC module and a small fan , we used it for camping , it was a large size cooler.
If we didn't open it at least once a day , everything in it would start to freeze , so they may have more capacity than you think.
The fan on that one packed it in after a few years and I couldn't find a replacement , so it got trashed.
The thickness of the insulation would dictate the size of chamber you could keep cool with it , within reason that is.
It seem like an interesting option , but still , by the time you buy the TEC , the wood and the insulation (Good high density foam insulation is very expensive) , a cheap refrigerator may be just as effective.
I'm going to look at some options in our local used appliance store today , as I need to make more cheese this weekend and my cave is FULL !