As in other industries, clean tech companies can get funding from public markets. When looking at performance, Because of its diversity, it's best to look at the performance of specific sub-sectors.
Solar Stocks 2011/12
As an example, we looked at share prices of 12 solar companies from July 2011 - March 2012. We included Solarworld, Firstsolar, Yingli, LDK, MEMC, Trina, Jinko, Hanwha, Suntech Power, Conergy, Phoenix Solar and Aleo Solar. We plotted the development of the average share price along with minimum and maximum in that pool. For comparison, the plot also shows the S&P 500 as well as the price of oil (Brent).
As the solar industry is suffering from over-capacity and is undergoing a serious consolidation, unsurprisingly, solar shares have underperformed the market over that period. The average lost 40% while the oil price was almost steady.