The history of solar panels begins all the way back in 1839, when Edmond Becquerel, a young physicist working in France, observed and discovered the photovoltaic effect— a process that produces a voltage or electric current when exposed to light or radiant energy. Multiple scientists and inventors made important contributions throughout the 19th and early 20th centuries, including solar-powered engines and solar cells. In the 1950s, Bell Laboratories created the first solar cell that was 6% efficient, but the product was still cost-prohibitive for most people. Interest in solar power surged in the 1970s as an energy crisis gripped America, but fell off in the 1980s as the price of traditional energy sources stabilized. However, in the last 10 years, solar has had an average annual growth rate of 50% in the United States, in large part due to the Solar Investment Tax Credit of 2006 and a significant reduction in installation costs. Today, many homes feature solar panels on their roofs and companies are working on making solar panels more aesthetically pleasing while advancing the technology.