Reuters: First Solar is entering the U.S. residential market with a five-year deal to supply 100 megawatts of thin-film solar modules to installer SolarCity, the manufacturer said on Wednesday. First Solar, which produces the lowest-cost solar cells in the industry, will also take a minority stake in SolarCity with a $25 million equity investment in the privately held company, which installs clean-power systems in California, Arizona and Oregon. Tempe, Arizona-based First Solar has …