This post on the Moore’s Law-like exponential gains
in solar power per dollar went up at Scientific American yesterday. Reprinting
here with permission.
by Ramez Naam
http://rameznaam.com (March 17 2011)
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 fifteen terrawatts
of power, or one six-thousandth as much. In fourteen 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
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 one
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 thirty 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 thirty 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 eighteen months. More practically speaking, the amount of computing power
you can buy for a dollar has roughly doubled every eighteen 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 pound (4500
kilograms) 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
US 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 thirty years, the trend is for an
annual seven 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 thirty
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 thirty years ago. Inexpensive thin-film methods have
achieved laboratory efficiencies as high as twenty percent, still twice as high
as most of the solar systems in deployment today.
What do these trends mean for the future? If the seven percent decline in costs
continues (and 2010 and 2011 both look likely to beat that number), then in
twenty years the cost per watt of PV cells will be just over fifty 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 fifty 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 US and scale it for reductions in module cost, we get
The cost of solar, in the average location in the US, will cross the current
average retail electricity price of twelve cents per kilowatt hour in around
2020, or nine 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.
Ten 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
twelve cents per kilowatt hour mark.
The exponential trend in solar watts per dollar has been going on for at least
31 years now. If it continues for another eight to ten years, 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 twenty
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 US from
1998-2009, G Barbose, N Darghouth, R Wiser, LBNL-4121E, December 2010
2008 Solar Technologies Market Report: January 2010, (2010). 131 pages. NREL
Report TP-6A2-46025; DOE/GO-102010-2867