Understanding Solar Energy

Good longread.

What I'd like to have a better understanding of, and I'm hoping to crowdsource here, is exactly how the solar panel cost has come down so precipitously. Part of it is simply manufacture scaling - almost everything is much cheaper in large quantities. But part of it must be a thousand incremental tech advances. Things like the reduced kerf diamond wire saw.

Also of note: I think monocrystalline has won completely? People experimented with all sorts of alternate chemistries and technologies, like ion deposition and the extremely poisonous CIGS, but good old "Czochralski process + slice thinly" has won despite being energy intensive itself.

Perovskites remain an unknown quantity.

The article posted by wolfram74 is part one of two, covering solar PV history up through the early 1980s.

Here's part two of the series with more recent history: https://www.construction-physics.com/p/how-did-solar-power-g...

Even this fairly long two-part discussion misses some of the more important technical developments of the past 20 years.

Converting trichlorosilane to pure silicon via CVD growth in Siemens-type reactors is now much more energy efficient due to changes in rod geometry and heat trapping via reactor design. A significant minority of purified silicon is now manufactured via even more efficient fluidized bed reactors.

The solar industry is dominated by Czochralski process monocrystalline silicon, but it's now continuous Czochralski: multiple crystals grown from a single crucible, recharging the molten silicon over time; the traditional process used a crucible once and then discarded it.

The dominant silicon material has switched from boron doped p-type silicon to gallium doped p-type silicon (mentioned by pfdietz) to phosphorus doped n-type silicon (used by the currently dominant TOPCon cell technology as well as heterojunction (HJT) cells and most back contact cells).

Changes in wafering that you mentioned (like the reduced kerf diamond wire saw) have reduced silicon consumption per wafer and therefore per watt, even holding cell technology constant.

The dominant cell technology has moved from Al-BSF to PERC to mono-PERC to TOPCon. Heterojunction and back-contact cells are not yet dominant, but they are manufactured on a multi-gigawatt scale and will probably overtake TOPCon eventually. Each one of these changes has eked out more light conversion efficiency from the same area of silicon.

Cells mostly still use screen-printed contacts made from conductive silver pastes, much like 20 years ago, but there has been continuous evolution of the geometry and composition of applied pastes so that silver consumption per watt is now much lower than it used to be. This is important because silver has the highest cost per kilogram of any material in a typical solar panel, and it's the bottleneck material for plans to expand manufacturing past the terawatt scale.

Wafer, cell, and module manufacturing have become much more automated. That reduced labor costs, increased throughput, and increased uniformity.

Thank you and other commenters for the great rundowns here. I'm interested in a related question and I wonder if you or others could point me in the right direction: why was the mainstream consensus around solar power (and/or batteries) apparently so wrong for so long? More specifically -- and maybe a better question -- why didn't progress in solar and batteries happen sooner?

I'm less interested in blame than in a systems analysis of how in the last half century powerful players seem to have missed the opportunity to start earlier investment in solar and battery technology. Solar and batteries are unique in energy infrastructure, as even any casual observer knows by now, and is certain to change many aspects of politics, industry and culture. It seems an inevitability that energy infrastructure will evolve from large complex components towards small and simple components, and I'm interested in engaging with the history of why "now" is the moment, rather than decades ago.

Solar and batteries got cheaper when we scaled up and built a lot. You have to pay current prices to get the next price drop, because it's all learning by doing.

If we had pushed harder in the 80s, 90s, and 2000s, solar might have gotten cheaper sooner. Solar fit in at the edges of the market as it grew: remote locations for power, or small scale settings where running a wire is inconvenient or impractical. The really big push that put solar over the edge was Germany's energiwende public policy that encouraged deploying a ton of solar in a country with exceptionally poor solar resources; but even with that promise of a market, massive scale up was guaranteed.

It's in many ways a collective action problem. Even in this thread, in 2025 you will see people wondering when we will have effective battery technology, because they have been misinformed for so long that batteries are ineffective that they don't see the evidence even in the linked article.

Also, most people do not understand technology learning curves, and how exponential growth changes things. Even in Silicon Valley, where the religion of the singularity is prevalent and where everyone is familiar with Moore's law, the propaganda against solar and batteries has been so strong that many do not realize the tech curves that solar and batteries enjoy.

A lot of this comes down to who has the money to spend on public influence too, which is largely the fossil fuel industry, who spends massive amounts on both politicians and in setting up a favorable information environment in the media. Solar and batteries are finally getting significant revenues, but they have been focused more on execution than on buying politics and buying media. They have benefited from environmental advocates that want to decarbonize, without a doubt, but that doesn't have the same effect as a very targeted media propaganda campaign that results in zealots that, whenever they see an article about climate change, call up their local paper and chew out the management with screaming. Much of the media is very afraid of right wing nuts on the matter and it puts a huge tilt on the coverage in the mass media in favor of fossil fuels and against climate science.

Indeed. You widen the conversation here, and remind me of the idea that moneyed influence is underrepresented in analysis and understanding of the world. Maybe the most appropriate way to understand big questions is who is funding the various players.

I like to think about "learn by doing". While I have of course lived it, I try to think of counterpoints. It seems clear that solar owes it's growth to Germany and California policies which subsidized the global solar industry with taxes on their economies, most disproportionately placed on individual ratepayers. But why couldn't solar research have been long-term funded based on it's fundamental value? Talk about national security, or geopolitical stability -- especially post 1970s! Skip the intermediate and expensive buildouts of the 2000s, failed companies heavily subsidized and fund research instead to hopefully bring the late 2010s forward in time?

What's a good model here, or concrete example? We see the same side of the history in electric vehicles. I think Tesla and Rivian, to pick two, both lost money on every sale in early years. Why not skip that expensive step in company history, and develop better products to sell at a profit from the beginning of mass manufacturing? Are there industries or technologies where this expensive/slow process went the other way?