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.

CdTe is still out there, from First Solar, but it's not much of the market (and has scalability problems due to the need for tellurium, even if the active layer is much thinner than in silicon cells.)

One little advance that swept the industry a couple of years ago was replacement of boron as a dopant by gallium. Boron doped silicon has light induced degradation, which was determined to cause a small loss in efficiency due to formation of boron trapping centers under prolonged light exposure. Gallium-doped silicon doesn't have this problem.

You're in luck! The author's earlier piece on the subject attempts to address that exact question. Learning curve effects and piggy backing off the computer chip industry are major factors if I recall, but I haven't reread the piece in a while.

https://www.construction-physics.com/p/how-did-solar-power-g...

My understanding is that China recognized the potential of solar power around 20 years ago and decided they wanted to be the world's manufacturing hub for solar panels. The government invested in R&D early, and today we are reaping the fruits of that investment.

The same thing is happening now with storage, but western governments are weary of losing that battle as well. To address this massive tariffs were put in place by the previous US administration, and are likely to be increased by the current administration. Hopefully this doesn't slow down the production of batteries, but instead just moves the production out of China and into other countries, but that remains to be seen.

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.

In terms of resource extraction needed for the batteries and the panels, how sustainable is it? The way I understand it is that you can't really repair broken panels and batteries... Can we still make these after, let's say, 500 years? I have no conception at all in this topic...

No, but I don't see a good reason why you can't recycle the cells especially given they contain a thin layer of silver. Google already finds local recycling firms, since it's required by WEEE.

(The 500 years question has issues for all the other sources of energy as well!)

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.

It's a false assumption that technological progress happens automatically or even that it's based upon the passage of time.

Progress happens as a result of many choices made by individuals to invest time and energy solving problems. Why is solar rapidly improving now? Because way more people are invested in making it better.

Nascent technologies almost always face an uphill battle because they compete against extremely optimized legacy technologies while themselves having no optimization at first. We only get to the current rapid period of growth because enough people pushed us through the early part of the S curve.

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.

Sure, that makes sense. This is where I'm coming from with my interest in history:

I heard an interesting argument somewhere that solar cells are an ideal manufactured good. Whether you are building a module for a calculator or a GW scale plant, the modules are the same. This is fundamentally different for steam turbines. On the "concrete-internal combustion engine" spectrum of complexity, solar modules are closer to concrete and turbines are closer to ICEs.

Shouldn't this have led to a special interest in advancing solar module research? Or widespread understanding that eventually the unique set of attributes that define a solar module would lead to it's takeover of a significant portion of global energy generation? Shouldn't that have been apparent from the earliest days of photovoltaic research as a sort of philosophical truth before the advances in material science, extraction or manufacturing of the last fifty years?

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?

> 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

I think this is a really important distinction, that between research in the lab versus research on the factory floor. Tesla in particular has talked about how much they value engineers that get down in to the production process versus those that are working in the lab. That's the "doing" that needs to happen. As well as shaking out parts of the upstream supply chains and making all that cheaper.

We can theorize about what's going to work in practice, but the price drops are the combination of 1% savings here, 0.75% savings there, 0.5% there, and until you have the full factory going you won't be able to fully estimate your actual numbers, much less come up with all the sequential small improvements that build on each other. And all that comes together in the design of the next factory that's the next magnitude up in size.

Yes, batteries are getting better at such a rate that you can recycle old batteries at end of life, lose 10% of the material in that process and build a new battery with new tech and less material that is better than the original.

The resource extraction issue is more than these are so useful we're going to build an ever growing amount of them.

Luckily they're made from widely available materials, with even more widely available substitutions possible e.g sodium batteries.

> why didn't progress in solar and batteries happen sooner?

The rate of progress in cost reduction has been astonishing. It's unlike anything except Moore's Law. This catches people out.

As well as the usual suspects: cheap fossil fuels, failure to take global warming seriously, belief that nuclear power would see similar exponential cost reduction rather than opposite, and of course anti green politics.

But if 95% cost reduction is the result of not taking it seriously, would taking it seriously earlier have been even better? Hard to say.

Right! Good points for optimism here, and acknowledging broken mental models.

We have silicon solar modules in the 1950s, Moore's law in the 1960s. Another take on the question then: today we use Moore's law to describe progress in solar modules, to what extent was that realization possible in the 1960s from the fundamentals, or "first principles"?

If it was clear, why did we not see rapid prioritization of solar and energy storage technology research? Or did we and I don't know the actual history? Or what influences am I undervaluing or not recognizing?

If it wasn't clear, why not? Gaming out many positive impacts of solar technology feels easy today in a way it appears was not easy in the past. Why wasn't it clear in the past?

I hear that, it seems a common observation. Maybe a fundamental truth of enterprise.

> until you have the full factory going you won't be able to fully estimate your actual numbers, much less come up with all the sequential small improvements that build on each other.

Why not? Is there a theory or school of management or industry that establishes this foundational principle that seems so commonly invoked? It feels true, but I don't really know why it might be true. There must also be great examples of counterpoints in this too!

Maybe it goes back to learn by doing: it's a common refrain in outdoor recreation that safety rules are written in blood; that many of our guidelines directly follow from bad things that happened. But certainly we can also design safety rules by thinking critically about our activities. Learn by doing vs theory.

Wary not weary

It's literally studied as "learning" in the management science literature.

For example: https://pubsonline.informs.org/doi/abs/10.1287/mnsc.2015.235...

> We find that productivity improves when multiple generations of the firm’s primary product family are produced concurrently, reflecting the firm’s ability to augment and transfer knowledge from older to newer product generations.

I think another important part is that solar has low minimum useful quantities and customization. Lots of the problem with nuclear power is that you only need ~100 to power the US, and each one takes years to build, so getting scale is basically impossible. With a 50-100 year lifespan per plant, that means you only get to build 1-2 a year, and you can't learn much from the 5 you've most recently started since they're still under construction.

You can't repair, but you can recycle (although doing so likely isn't very profitable until the exponential price decrease stops)

Battery progress was in some ways slowed but also accelerated by oil companies who kept buying up patents on solar and battery stuff that looked promising, and then sat on the patents, refusing to license it.

One oil company bought Cobasys, which owned all the NiMH patents. Thereafter, Cobasys refused to license NiMH batteries to anyone making a vehicle, except large ones like transit busses. Several early EVs used NiMH batteries until Cobasys was acquired and set up the restrictions.

This really lit a fire under researchers and battery industry to try and improve lithium ion, which had hit the market in the early 90's. Once the price of Lithium Ion started falling, the market very quickly forgot about NiMH batteries. In about ten years prices have fallen to one fifth of what they were. That fall has slowed, but it's still dropping.

The resources all start off chemically bound in rocks that aren't famous for spontaneously generating or storing electricity.

I don't see it being meaningfully more expensive to process smashed up old PV or batteries than starting from the natural state, and my expectation is that it would be easier.

The exception would be if some of the chemical pathways turn into low-concentration atmospheric gasses that then diffuse all over the world, which is how we got the problem with CO2 (and unrelated problems with CFCs).

The US policy doesn't seem very smart.

invest in R&D -> reap fruit

tariff barriers -> inefficient industries

The current administration seems to be doubling down on that.

Aside from silver for contact wires, PV panels are made (or could be made) with mundane materials available in essentially unlimited amounts. The total mass flowing through new PV panels each year if the US were fully solar powered would be much less than the volume of mundane material flowing through the system already. For example, the EPA estimated that in 2018 the US generated 600 million tons of construction and demolition waste (of which 143 million tons went to landfills.)

https://www.epa.gov/facts-and-figures-about-materials-waste-...