[ExI] [tt] Smaller, cheaper, faster: Does Moore's law apply to solar cells?

[Eugen Leitl]

http://www.scientificamerican.com/blog/post.cfm?id=smaller-cheaper-faster-does-moores-2011-03-15

Smaller, cheaper, faster: Does Moore's law apply to solar cells?

By Ramez Naam | Mar 16, 2011 09:00 AM | 22

The sun strikes every square meter of our planet with more than 1,360 watts
of power. Half of that energy is absorbed by the atmosphere or reflected back
into space. 700 watts of power, on average, reaches Earth’s surface. Summed
across the half of the Earth that the sun is shining on, that is 89 petawatts
of power. By comparison, all of human civilization uses around 15 terrawatts
of power, or one six-thousandth as much. In 14 and a half seconds, the sun
provides as much energy to Earth as humanity uses in a day.

The numbers are staggering and surprising. In 88 minutes, the sun provides
470 exajoules of energy, as much energy as humanity consumes in a year. In
112 hours – less than five days – it provides 36 zettajoules of energy – as
much energy as is contained in all proven reserves of oil, coal, and natural
gas on this planet.

If humanity could capture one tenth of one percent of the solar energy
striking the earth – one part in one thousand - we would have access to six
times as much energy as we consume in all forms today, with almost no
greenhouse gas emissions. At the current rate of energy consumption increase
– about 1 percent per year – we will not be using that much energy for
another 180 years.

It’s small wonder, then, that scientists and entrepreneurs alike are
investing in solar energy technologies to capture some of the abundant power
around us. Yet solar power is still a miniscule fraction of all power
generation capacity on the planet. There is at most 30 gigawatts of solar
generating capacity deployed today, or about 0.2 percent of all energy
production. Up until now, while solar energy has been abundant, the systems
to capture it have been expensive and inefficient.

That is changing. Over the last 30 years, researchers have watched as the
price of capturing solar energy has dropped exponentially. There’s now
frequent talk of a "Moore's law" in solar energy. In computing,  Moore’s law
dictates that the number of components that can be placed on a chip doubles
every 18 months. More practically speaking, the amount of computing power you
can buy for a dollar has roughly doubled every 18 months, for decades. That’s
the reason that the phone in your pocket has thousands of times as much
memory and ten times as much processing power as a famed Cray 1
supercomputer, while weighing ounces compared to the Cray’s 10,000 lb bulk,
fitting in your pocket rather than a large room, and costing tens or hundreds
of dollars rather than tens of millions.

If similar dynamics worked in solar power technology, then we would
eventually have the solar equivalent of an iPhone – incredibly cheap, mass
distributed energy technology that was many times more effective than the
giant and centralized technologies it was born from.

So is there such a phenomenon? The National Renewable Energy Laboratory of
the U.S. Department of Energy has watched solar photovoltaic price trends
since 1980. They’ve seen the price per Watt of solar modules (not counting
installation) drop from $22 dollars in 1980 down to under $3 today.

Is this really an exponential curve? And is it continuing to drop at the same
rate, or is it leveling off in recent years? To know if a process is
exponential, we plot it on a log scale.

And indeed, it follows a nearly straight line on a log scale. Some years the
price changes more than others. Averaged over 30 years, the trend is for an
annual 7 percent reduction in the dollars per watt of solar photovoltaic
cells. 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.

If we look at this another way, in terms of the amount of power we can get
for $100, we see a continual rise on a log scale.

What’s driving these changes? There are two factors. First, solar cell
manufacturers are learning – much as computer chip manufacturers keep
learning – how to reduce the cost to fabricate solar.

Second, the efficiency of solar cells – the fraction of the sun’s energy that
strikes them that they capture – is continually improving. In the lab,
researchers have achieved solar efficiencies of as high as 41 percent, an
unheard of efficiency 30 years ago. Inexpensive thin-film methods have
achieved laboratory efficiencies as high as 20 percent, still twice as high
as most of the solar systems in deployment today.

What do these trends mean for the future? If the 7 percent decline in costs
continues (and 2010 and 2011 both look likely to beat that number), then in
20 years the cost per watt of PV cells will be just over 50 cents.

Indications are that the projections above are actually too conservative.
First Solar corporation has announced internal production costs (though not
consumer prices) of 75 cents per watt, and expects to hit 50 cents per watt
in production cost in 2016. If they hit their estimates, they’ll be beating
the trend above by a considerable margin.

What does the continual reduction in solar price per watt mean for
electricity prices and carbon emissions? Historically, the cost of PV modules
(what we’ve been using above) is about half the total installed cost of
systems. The rest of the cost is installation.  Fortunately, installation
costs have also dropped at a similar pace to module costs. If we look at the
price of electricity from solar systems in the U.S. and scale it for
reductions in module cost, we get this:

The cost of solar, in the average location in the U.S., will cross the
current average retail electricity price of 12 cents per kilowatt hour in
around 2020, or 9 years from now. In fact, given that retail electricity
prices are currently rising by a few percent per year, prices will probably
cross earlier, around 2018 for the country as a whole, and as early as 2015
for the sunniest parts of America.

10 years later, in 2030, solar electricity is likely to cost half what coal
electricity does today. Solar capacity is being built out at an exponential
pace already. When the prices become so much more favorable than those of
alternate energy sources, that pace will only accelerate.

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.

That’s good news for the world.

Sources and Further Reading:

Key World Energy Statistics 2010, International Energy Agency,

Tracking the Sun III: The Installed Cost of Photovoltaics in the U.S. from
1998-2009, Barbose, G., N. Darghouth, R. Wiser., LBNL-4121E, December 2010,

2008 Solar Technologies Market Report: January 2010, (2010). 131 pp. NREL
Report TP-6A2-46025; DOE/GO-102010-2867,

About the Author: Ramez Naam is a computer scientist and entrepreneur. He is
the author of More Than Human (Broadway Books, 2005), which the LA Times
called "a terrific survey of current work and future possibilities in gene
therapy, neurotechnology, and other fields." For More Than Human, Naam was
awarded the 2005 H. G. Wells Award for Contributions to Transhumanism. Naam
is a Fellow of the Institute for Ethics and Emerging Technologies and blogs
at Unbridled Speculation. He lives in Seattle, where he is currently working
on his next book The Infinite Resource: Human Innovation and Overcoming the
Challenges of a Finite Planet. You can see Naam speak at a special event at
the World Future Society 2011 conference in Vancouver, B.C.

The views expressed are those of the author and are not necessarily those of
Scientific American.
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