• Ramez Naam, The Moore’s Law of solar energy, Scientific American guest blog, 16 March 2011.

Executive summary: solar cost per watt is dropping on an exponential curve, and will drop below coal by 2020. As usual we see some graphs where the past is fairly wiggly:

while the future is a smooth and mathematically simple, starting tomorrow:

Both these graphs show the price per watt of photovoltaic solar modules (not counting installation), measured in 2009 dollars. Both graphs are logarithmic, so an exponential decline in price per watt would show up as a straight line.

Of course, anyone can draw a curve through points. The question is whether experts can see a way to keep the trend going!

On this, the author writes:

While in the earlier part of this decade prices flattened for a few years, the sharp decline in 2009 made up for that and put the price reduction back on track. Data from 2010 (not included above) shows at least a 30 percent further price reduction, putting solar prices ahead of this trend.

He also writes:

We should always be careful of extrapolating trends out, of course. Natural processes have limits. Phenomena that look exponential eventually level off or become linear at a certain point. Yet physicists and engineers in the solar world are optimistic about their roadmaps for the coming decade. The cheapest solar modules, not yet on the market, have manufacturing costs under $1 per watt, making them contenders – when they reach the market – for breaking the 12 cents per Kwh mark.

The exponential trend in solar watts per dollar has been going on for at least 31 years now. If it continues for another 8-10, which looks extremely likely, we’ll have a power source which is as cheap as coal for electricity, with virtually no carbon emissions. If it continues for 20 years, which is also well within the realm of scientific and technical possibility, then we’ll have a green power source which is half the price of coal for electricity.

What do you think? Is this for real?

By the way, Naam’s blog post has a chart showing efficiencies of various solar cell technologies. It’s unreadably small, but here’s a version you can click to enlarge:

What I want to caution you about is that some of the more efficient solar cells use expensive materials for which the world supply is limited. For more on this see

• Photovoltaic solar power, Azimuth Wiki: efficiency and physics of solar cells.

Here’s another article:

• Kevin Bullis, More Power from Rooftop Solar: A startup says technology inspired by RAID hard drives can boost power output by up to 50 percent, Technology Review, 29 April 2011.

Immediately below the headline they tone down the claim slightly, saying “25 to 50 percent”. But that’s still a lot. The idea sounds nice, too:

Solar cells have become more efficient in recent years, but much of the improvement has gone to waste because of the way solar cells are put together in solar panels, the way the panels are wired together, and the way the electricity is converted into AC power for use in homes or on the grid. Typically, the power output from a string of solar cells is limited by the lowest-performing cell. So if a shadow falls on just one cell in a panel, the power output of the whole system drops dramatically. And failure at any point in the string can shut down the whole system.

TenKsolar has opted for a more complex wiring system—inspired by a reliable type of computer memory known as RAID (for “redundant array of independent disks”), in which hard disks are connected in ways that maintain performance even if some fail. TenKsolar’s design allows current to take many different paths through a solar-panel array, thus avoiding bottlenecks at low-performing cells and making it possible to extract far more of the electricity that the cells produce.