Reuters: Solar silicon makers Renewable Energy Corp (REC) (REC.OL: Quote, Profile, Research) and Advanced Metallurgical Group (AMG) (AMG.AS: Quote, Profile, Research) posted higher quarterly earnings Tuesday on booming demand for alternatives to fossil fuel energy, but challenges to production weighed on their shares. Shares of REC, one of the world’s biggest producers of solar-grade silicon and wafers for solar power systems, initially rose more than 3 percent as its earnings topped …