Not much. TEDs, except for the radioactive ones, have like you said very poor efficiency. Not like 1 or 2% but like 0.01% if that. They are just not capable of producing large amounts of power given the resources required to make them work not to mention the cost of those resources. Would you rather pay $0.10/kwh for power from wind and solar or $8.00/kwh from a TED plant in a volcano?