Physics played an extremely important role in the electronics technology. Now nanotechnology is playing a leading role in the future technologies as important as physics did. Understanding the physics at the nanoscale is essential to the advancement and commercialization of any nanotechnology that is being studied. As two examples, I will talk about how the understanding of physics and nanotechnology will help to improve the solar energy conversion efficiency using photovoltaic and thermoelectric materials. With the potential of both technologies fully realized, we will have a transformative change in energy harvesting and conversion, which will certainly help reduce the dependence of oil, gas, and coal, ultimately will change the climate and make the earth more livable for our children.