Converting sunlight to electricity with solar cells has an efficiency of 15%%. It's possible to achieve a higher efficiency (though currently at higher cost) by using concentrated sunlight as the hot reservoir of a heat engine. Each dish in (Figure 1) concentrates sunlight on one side of a heat engine, producing a hot-reservoir temperature of 470 CC. The cold reservoir, ambient air, is approximately 30 CC. The actual working efficiency of this device is 30%%.

[What is the theoretical maximum efficiency?]<--- Question