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I think that the cells that can convert 30% of sunshine to electricity are pretty expensive but for this design they need only a small area. In the IBM published material they state that a price of 250$/sqm can be achieved. And the idea of recovering the heat for home use is a good one.
Anytime you can take an inefficiency in the process and turn it into an energy source: WIN!
Like a combined cycle Natural Gas Power Turbine, waste exhaust heat use for steam power turbine.