Trying to build a better planet. Read more from this special report.

With all the ups and down in the energy business, it is sometimes difficult to see the forest through the trees. Solar module costs -- the actual energy conversion hardware -- have been falling for the past several decades and the past couple of years have seen sharp declines.

But there are a lot of other components in the cost of a solar installation. What you see above is a chart of all the solar installations since 2006 tracked by the National Renewable Energy Laboratory for which cost information is available. What we see are substantial cost drops in the total installed cost of solar. In the last six months of 2006, the average project paid $8.58 per watt. In the last six months of 2011, the average project paid $5.91. Not bad.

All the data is available here.