I learned about solar companies by attending an investment workshop on this topic. Other resources are investment periodicals. Google "solar companies" and see if they are being traded publicly.
First Solar (FSLR) recently announced it is investing in China. Trina Solar (TSL) recently obtained a large loan to expand their capacity by 500 megawatts. A non-public company called Brightsource has several articles talking about investments by Google and Chevron. There are many solar companies right now, be careful as there is bound to be some companies drop out.
First Solar is the leader in thin-film solar modules, ticker FSLR. Trina Solar is a Chinese solar company that is the global cost leader in crystalline modules, ticker TSL.