[philipkglass]

The author is drastically overestimating the lifecycle emissions and embodied energy of modern solar photovoltaic modules.

The article claims that it takes "3,514 MJ of energy to produce one m2 of solar panel."

The source for that assertion is this article from 2017:

"Energy Payback Time of a Solar Photovoltaic PoweredWaste Plastic Recyclebot System"

https://www.e-helvetica.nb.admin.ch/api/download/urn%3Anbn%3...

That article cites this article from 2006 as its source for energy intensity of solar manufacturing:

"Embodied energy analysis of photovoltaic (PV) system based on macro- and micro-level"

https://sci-hub.tw/10.1016/j.enpol.2005.06.018

That publication finds that silicon purification and processing accounts for the lion's share of embodied energy in solar PV.

But if you read section 6 of the paper, "Embodied energy of silicon purification and processing", you see that those authors are using material production energy intensity numbers from 2004 and 1998. They are also assuming the use of electronic grade silicon for solar manufacturing, and a silicon requirement of 12 grams per watt-peak of solar module. Cheaper and less energy intensive solar grade silicon has entirely replaced electronic grade silicon in PV since the early 2000s. Modern solar module silicon use is about 3 grams per watt-peak, not 12; see Table 1 in https://pubs.rsc.org/en/content/articlehtml/2020/ee/c9ee0245....

What first appears to be a reasonably recent citation for PV embodied energy is actually a chain of painfully outdated assumptions going all the way back to the 1990s.

[lowtechmagazine]

Author here. Good you mention this. I could have chosen a more elegant citation, but data on the embodied energy of PV modules is generally outdated and confusing. The number I chose is not especially high for panels produced since the 2000s. For an extensive literature summary from 2011 see 2.3 http://www.seas.columbia.edu/clca/Task12_LCI_LCA_10_21_Final...

Also keep in mind that all the panels we tested are much smaller than the ones oin those studies. This means that things like the frame, wires, connections become more important for embodied energy.

[philipkglass]

That study is also badly outdated. Under section 5, Life Cycle Inventory Data, it says "The authors have assembled this LCI data set to the best of their knowledge and in their opinion it gives a reliable representation of the crystalline silicon module production technology in Western-Europe in the year 2005/2006 and Balance-of-System components of the year 2006."

I would love to see a life cycle assessment using wholly up-to-date numbers. I keep reading new studies on PV LCA, energy return on investment, and/or energy payback time. People who write these sorts of papers don't seem to keep up with what industry is actually doing. You can learn a lot from data sheets and trade publications. E.g. from published glass thickness and module size and efficiency, you can calculate the quantity of glass currently needed per watt-peak. It's significantly lower than any of these studies using decade+ outdated numbers.

I think part of the problem is one of incentives. Academics writing about LCA are often comparing some hoped-to-be-up-and-coming technology against the mainstream. Like thin film PV, organic PV, or dye sensitized cells pitted against crystalline silicon PV. In that case using old numbers for silicon PV helps the newer technology look like it offers exciting improvements.

Another problem is that reviewers apparently don't care very much about these temporal effects. They don't chase the citation chains to find the really outdated measurements cited in recently submitted manuscripts.

Another problem is that the solar industry has grown large and competitive. Cutting-edge numbers about energy consumption for silicon refinement are probably retained as a competitive advantage by the biggest producers, for example.

It's possible to set tighter upper bounds on resource intensity just from teardowns of recently manufactured modules. I suppose that teardown based analysis may itself be the sort of information you only get from specialty publications like the Photovoltaics International magazine, which is expensive and not indexed by DOI or part of ordinary academic libraries. (So it's not even in sci-hub.)

It's $599 a year if you want to be able to read back issues of Photovoltaics International from their archives:

https://store.pv-tech.org/photovoltaics-international/

I am interested enough in photovoltaic technology that I have bought a couple of $100+ specialty books from academic publishers, but $599 is a bit too steep even for me.

[lowtechmagazine]

The obsolescence of life cycle analyses is a topic in itself, and the lack of accessible data is a problem for anyone who tries to investigate high-tech products.

For the solar powered website article, it's the order of magnitude that matters. You say I overestimate the energy use of solar panel production, but in our configuration it corresponds to just 1 liter of oil per year.

[kragen]

You can get a reasonable estimate by taking the wholesale price of the thing you're analyzing, dividing by an average price of electricity for industrial use (like, around US$60/MWh, in the quaint non-SI units traditionally used in the trade), and multiplying that by some fudge factor like 20% to account for the fact that much of the cost of things is due to non-energy inputs like raw materials, skilled labor, and interest. This gives a result correct to within a factor of 3 for the vast majority of goods and services, while using LCA numbers from a quarter century ago did not. In this case the result is 2.3 MJ per watt (peak) of low-cost solar panels using €0.17/Wp from PVXchange and SolarServer. That's almost an order of magnitude lower than the 22 MJ/W you used in the article (assuming 16% efficiency; with 21% efficiency it's 16.7 MJ/W. I'm not sure which one your original number was for.) So I think you may have gotten within an order of magnitude, but only just.

If the numbers you were using were correct, then just the energy input for the solar panels would have cost more than the wholesale price for the modules.

[lowtechmagazine]

Calculating embodied energy based on costs is an option, but I have always learned that it's the last resort, as it has many problems, too.

For example, How do you account for the fact that all production facilities for solar panels have moved to China? If you look at the price evolution of solar panels, there's a gradual decrease due to technological progress (less energy use indeed). Then, from 2009 onwards, the decline in costs accelerates sharply, the consequence of moving almost the entire PV manufacturing industry from western countries to Asian countries, where labor and energy are cheaper and where environmental restrictions are more loose.

https://solar.lowtechmagazine.com/2015/04/how-sustainable-is...

[philipkglass]

The manufacturing shift to China can account for a one-time step decrease in solar PV costs due to lower wages and a lower cost, dirtier industrial ecosystem (e.g. high-CO2 grid power supplied mostly by coal plants having minimal pollution controls).

But the costs of solar panels made in China in 2020 are much lower than those of solar panels made in China in 2010. Chinese factory wages have not fallen over the past 10 years, nor have Chinese pollution controls been further relaxed. The trend of falling costs over the last 10 years of made-in-China solar panels is due to improved techniques of production.

In 2010, Chinese producer Suntech was the largest PV manufacturer in the world. It sold 1.6 GW of panels and realized revenue of $2.9 billion:

https://www.greentechmedia.com/articles/read/suntech-q4-earn...

Its panels were therefore selling for about $1.83 per watt in 2010.

Presently, Chinese high efficiency monocrystalline PERC panels are selling for no more than $0.25 per watt:

http://pvinsights.com/

This 85% drop in prices indicates that technological and manufacturing progress in the solar sector continued at a rapid clip even after its center of gravity shifted to China.

[belorn]

For an apple to apple comparison we would need to define exactly what is being compared. Should we use the exact PV module that they bought and compare that to the exact power plant that supply energy to their area? We could also compare a hypothetical PV module using the latest models and compare that to the latest models of power plants and energy grids.

Depending on incentives and purpose one can choose which facts that one want to use. A fair comparison would be quite complex and have many variables one need to define for both the solar version and the power grid version.

[admax88q]

If we are discussing the viability and sustainability of any particular thing we should be using the current industry standard numbers and a reasonable estimate of where the industry is going. There's no sense discussing whether option A is sustainable or not if nobody actually produces option A is outdated and the next decade of installations will use option B.

[belorn]

I can see value in both approaches. One is a test of what happens if you go right now and buy a PV module from a nearby store. This has the implication that the module has been in the store for a while and the raw material was mined and collected many years ago. Then you compare it to getting the power from the wall socket, which similar implications that the power plant that generates the power was built many years ago using old technology.

The other approach compare the state of the art PV module vs the state of the art power plant, both being built using the latest mining and construction methods.

The answer of what is more sustainable is going to depend a lot on context. Are we comparing what a person can do right now, or what we should be doing in the future? For powering websites the general answer from the industry is currently to build data centers in depopulated areas in countries with cold climates, near a hydro power plant and with plenty access to cooling water. This is however not a solution that you can apply if the requirement is that the server must be located in Spain.

[beerandt]

LCAs are sort of the epitome of "looks a lot easier than it is," combined with no obvious red flags for getting something drastically wrong. Mistakes like these are everywhere. And I'm afraid the average study quality is going to get a lot worse before it gets better.

A little bit of knowledge can be a dangerous thing.

At least we're not making many safety critical design decisions based off of them, yet.

[graycat]

So, yup, we need at least old common high school term paper writing standards, e.g., support every claim with good references to high quality, credible, primary sources. And, of course, as you mention, give the darned dates.

Ah, maybe a lot of media content would be seen right away of no interest if those standards had been followed. Or, about news writing, in some old movies,

"If it's not good, I'll make it good."

and

"A good reporter doesn't get great stories. A good reporter makes them great."

Now from that and not being born recently, I have learned to avoid nearly all news media.

[lowtechmagazine]

It's a bit more complex than that. The life cycle analysis of high-tech products takes many years. That's why most studies seem to be outdated even right after they are just published. It's not just solar panels. Try looking for a life cycle analysis of a recent laptop.