Despite a promising start to 2011, an equity sub-sector that has absolutely languished this year is solar energy, which falls in the broader category of alternative energy.

Even with the broad equity markets rallying last week, solar based ETFs, Guggenheim Solar Energy (NYSEArca: TAN) and Market Vectors Solar Energy (NYSEArca: KWT), registered new multi-year lows.

Top holdings in TAN are First Solar (NasdaqGS: FSLR) at 19.29% and GCL Poly Energy  at12.66%, so 32% of the entire index is dominated by two names.

KWT is somewhat more diversified, with FSLR making up 11.19% of the portfolio, and followed by GT Advanced Technologies (NasdaqGS: GTAT) at 10.25% and MEMC Electronic Materials WFR  at 8.80% as the top weightings. Year to date, TAN has lost 39.32% while KWT has fallen 43.85% versus the S&P 500 down 3.35%.

If you go back as far in history as you can (limited to these product’s inception dates in 2008), we note that KWT is down 84.64%, TAN has lost 83.32% versus the S&P 500 down 12.25%.