The given pie chart presents the consumption as well as sources of different forms of renewable energy in the USA from 1949 to 2008. Overall, the total energy consumed in different forms show rose with many fluctuations during this period. If we see the graph in detail, we can categorise the data into two groups.

The first group includes hydroelectric power and wood energy consumption. We can see that rate of energy consumed by hydroelectric power is higher compared to wood energy. In 1949 both energy lines touch almost the same rate of consumption, which over years pass through many ups and downs and in 2008 again match the values with the difference of around point one percent.

The second group comprises biofuels and wind energy. Both lines show almost the same trend of stability between 1949 and 1980 and then sharp rise afterwards. In 2008 grading, the consumption of biofuels was little higher than the wind energy.

To summarise, we can say that hydroelectric power was the most popular source of energy and wind power was the least. The trend of all energy forms is increased overall but in an irregular manner. Another interesting thing can be noticed that consumption of wind and biofuels remains at zero level between 1949 and 1980.