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

Ramez Naam
By Ramez Naam
Scientific American

Posted: Mar 17, 2011

If humanity could capture 1/10 of 1% of the solar energy striking the earth, we would have access to 6X as much energy as we consume in all forms today, with almost no greenhouse gas emissions.

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

This article was originally published at Scientific American. Reprinted with permission.

Ramez Naam, a Fellow of the IEET, is a computer scientist and the author of four books, including the sci-fi thriller Nexus and the nonfiction More than Human: Embracing the Promise of Biological Enhancement and The Infinite Resource: The Power of Ideas on a Finite Planet.  He writes at

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@ Ramez NAAM,

Your article on “Cost of PV Energy” was a good effort.

No doubt you will return to this issue, with later editions.
Dare I suggest that in these later editions you also consider / include:

- number of AVG days of solation (p.a.), for various locations around our planet (thus, some areas might not be able to harvest enough AVG energy for daily living)

- cost-effective storage schemes for “when the sun don’t shine”;
this could be expressed as the “cost per KWhr”, or as “cost per storage day @ nominated energy consumption”.

- pollution production (all types)  per KW of PV-cell production

- the rate of abatement of CO2/CH4 in our stratosphere (there we already have 100 years worth of CO2 and CH4 - at standard resorption rates)

- the abatement rate for Global Temperature Rise, per KW per annum, for PV installations

These are very hard questions.

But if the current acceleration of temperature rise for our planet is not stopped, or reversed, we may as well cease production of all PV cells anyway !!!

Yeah, thought that might cheer every one up grin



Thanks very much.  These are all very good questions and are topics for future posts. 

In terms of solation for various areas, if you follow the link in the article to the NREL report, you’ll find “load factors” for various cities in the US.  The price per kwh is indexed to a load factor of around 20%.  You can find load factors for other parts of the world online.

The other questions I’ll have to answer in later posts.

You build the panels using resources from the moon, install them in geostationary orbit and beam the energy down to a rectenna.

The myriad of toxic byproducts from solar panel production can’t sicken or kill more people than they already have. Once installed, the panels are in unfiltered and unblocked sunlight for 23 hours out of the day. Instead of covering tens of thousands of square kilometres of (often fragile) ecosystem with structures made from hazardous materials, you can get away with a fraction of one percent of that.

And as a wonderful byproduct it will kick-start humanity onto the next step to becoming a spacefaring civilization.

Help us solar powered energy - you’re our only hope.

2011-03-19, IEET Group on Facebook

@ Clint,

Yes Clint, that (space harvesting of solar energy) has been an excellent idea since it was first proposed by Gerard K. O’NEILL, in many quarters, but most notably to :
“1976 Subcommittee on Aerospace Technology… United States Senate”

This particular submission was titled “Solar Power from Satellites”, and can be read as an Appendix to O’NEILL’s book “The High Frontier”, (1976), now out of print, but Amazon usually stocks reprints. ISBN = 0-224-01406-4.

O’NEILL long championed the notion of “Colonisation of Space”, and in particular, the human colonisation of - firstly - the Moon, from which most building materials could be quarried and processed, and then - subsequently - the Lagrange Points L4 & L5, in the Earth-Moon gravitational system.  All engineers should read his works.

His ideas were fascinating, sound, well designed, but thoroughly rejected by 6 Senate Committees only because they wanted to fund their mates in the Oil-Arms-War machine, instead of building inspiring developments for mankind.

This deep corruption of American Business and Government finances is well illustrated and documented in the 2010 release of the movie “Inside Job”, and here is a summary of that movie:

“Inside Job” - Charles Ferguson’s film lifts lid of Wall Street
by Ian Fraser

(About) The academic economists interviewed by Charles Ferguson for his seminal film about the financial crisis, ‘Inside Job’, reveal themselves to be charlatans

I have never looked at Space Solar in detail, but it looks unlikely to be economical to me.

If current solar cells weigh perhaps 5 grams per Watt, and a Kilo delivered to low earth orbit costs perhaps $10,000, then we are looking at $50 / watt launch costs. (Not including any of the equipment to transmit energy back to the ground or to collect it on the ground.)

Given that cells now cost less than $1/watt to manufacture on earth, that is a huge price difference.

Insolation would be greater in space, perhaps as much as by a factor of 7.  However, that is insufficient to make up the difference.

Space solar, as best as I can tell, would be roughly an order of magnitude more expensive than solar on the ground, making it highly unlikely to take off.

I would be delighted if someone could critique my rough numbers and prove me wrong.

One of the other problems with the solar satellite idea I heard is trying to keep the microwave beam focused on the designated area for power collection. If it drifts then anyone and anything caught in it gets Kentucky fried (or Texas or Florida etc) in pretty short order.  And of course, nowadays we have to seriously consider that terrorists would enjoy trying to find ways to do that deliberately. However I understand that space solar is being looked at again.

The other major objection is a philosophical point that it’s another gigantic project that centralizes everything in the hands of the people/country which it belongs to. Solar on the ground offers the possibility of small-scale, decentralized power generation which has social and political consequences. Little chance I would have thought of terrorists being able to do anything with it.

Ramez, you’re rightfully dubious of ‘conventional’ wind power giving us anything more than a tiny fraction of what we need.. Have you looked into the skypower project which is attempting to gain energy from the jet stream by the use of tethered gliders? Reports (from Discovery magazine) suggest it’s making good progress and that the engineering problems are much less severe than for fusion.

The report said there is a massive amount of energy up there constantly blowing (so no problems of cloudy weather or storage though storms are an issue but not insuperable) if we can only bring it down.

@ Ramen,
INSOLATION:  I have seen figures that predict 100% (24*7) harvesting of solar energy
[by eccentric satellite orbits that never fall in Earth’s shadow, and then pumping the microwave energy beams down to of rectennas (large!, so Watts.sq.m are small, and NOTHING gets fried), floating near shore (so umbilical cables can easily pump the received energy to shore].

I hope that answers some of the “chicken-little-can’t-be-done” objections grin))

@ Ramez:

As for launch costs, you’ll have to send me an email address, so I can send you an EXCEL spreadsheet (and detailing how to reduce space launch costs (of high gee, non-living payloads) to ... “frack-all” (as is technically used in the Engineering literature grin).

I would love to see the spreadsheet and documents. 

My email is

Colin: didn’t say it couldn’t be done, just mentioned a danger posited quite a few years ago when I first heard of the idea. The solution you mentioned sounds like it would sove that except of course that the beam would be diluted. Since much of the planet is bathed in sunlight that we don’t use already it might be easier simply if the efficiencies of solar cells get high enough, to cover buildings and/or desert areas with solar power cell concentrations as it already being done somewhat differently with solar-thermal plants.

But if as you say, they’ve truly worked out a way to cheaply and feasibly sent payloads into orbit (and that maintenance is practical since space is a harsh environment), then perhaps a pilot project could be tried. I’m not against space solar as such; as far as I’m concerned anything that works economically let’s go for it It’s already late in the day for a problem that I feel could have been solved years ago if the political will had been present.

The article says, “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.”

As you know, the Earth is a sphere, and it’s night half of the time which means that only 1/4 of that 1360 watts per meter shines on the surface. 

How do errors like this get past editors?

@ Steve,

Luv the fact/reason checking.  Absolutely necessary!

But Steve, don’t forget the world is also hungry for positive proposals for solving our problems, and ever more quickly it now appears.



The 1,360 watts / m^2 figure reflects insolation when directly facing the sun.

However, the numbers in the rest of the article takes into account the day/night cycle, cloud cover, lattitude, etc…

All of these numbers are combined into a figure called ‘load factor.’  A typical load factor is around 20% - meaning that the area gets 20% of the insolation that is theoretically possible (the 1360 number) after you factor in day/night, clouds, lattitude, etc..

The cost numbers I cite in the article, as well as the fraction of land required to meet the world’s current energy needs using solar, take this into account.  Indeed, the costs to date aren’t a theoretical calculation - they’re based on actual prices charged.


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