Apologies for a slightly technical and wonky post about a recent paper I came across....

It addresses a major solar 'naysayer' issue....the (supposed) low EROEI of solar PV, and its (supposed) resulting inability to support modern civilization.

Many here have a current or former 'energy doomer' bent.....this is a story for you. FYI...I do not intend 'doomer' as a prejorative, no offense intended....I am a recovering doomer myself.

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The good news: future projections of current (exponential) growth rates of solar PV production would result in all global electricity and all primary energy needs being satisfied by solar PV in 2-3 decades.

Major roadblocks for this 'clean energy eco-utopia' are not obvious:

--solar PV kWh are already cheaper than fossil kWh in many locations in the world (mostly sunny developing countries, and the US SW). Many of these locations are now driving global PV capacity growth with minimal or no subsidies.

--falling costs (due to tech learning curve) mean that the regions for which the above is true will expand to cover most global population in a decade or so

--the available energy resource (global sunshine) is more than sufficient for anticipated needs.

--the materials required, silicon, oxygen, aluminum are all earth abundant (being what the earth is primarily made of) and ubiquitous.

The hypothetical problem:

There are still energy doomers out there. They will cite a couple related issues. Some say that the EROEI of solar is too low to support civilization. Recent studies have determined that the 'energy payback time' for solar PV is 1-2 years; it takes that long for the panel to generate as much energy as it took to manufacture. A similar figure for greenhouse gas emissions (from initial manufacturing versus saved) comes up with a similar payback time 1-2 years.

On its face, this seems ok...the panels last 20-30 years...so we get an EROEI (energy return on energy invested) of 15-30 or so.

Some current doomers will cherrypick studies that have higher payback times, so EROEI is less than 10. These same folks often say that the EROEI of 10 is a magic number that if a technology is below it, then civilization collapses. Or climate doomers say that energy payback is ok, but that manufacturing PV requires fossil fuels, so 'you can't make PV with PV', so it won't work (this latter point is silly...PV is often made with electric furnaces).

I never understood the above doomer math/logic, so I won't say anything else about it. I think its weak.

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This post is about another, subtler issue. Imagine that solar PV payback (energy or GHG) takes 3 years. And imagine that the amount installed doubles every 2 years. The math says that installing PV would then be a net loss for both energy production and GHG avoidance **forever**...no savings are realized until a couple years after we stop the exponential growth curve. In fact the 'bad' grows exponentially in proportion to the installed capacity!

This is cited as a concern by some (more sophisticated) doomers...that the installed amount of PV will always deliver less than the amount of energy needed to make next years (larger) amount of installed PV.

A (free access) peer reviewed study in

http://www.nature.com/articles/ncomms13728

The bottom line is that, while obviously 'doubling time' needs to be less than 'payback time' to see a benefit, the payback times (for energy and GHG emissions) are also falling due to learning curve, just like the prices have been. And should continue to fall.

In their extensive analysis it appears that solar PV may have been a net negative for global energy supply and GHG emissions as recently as

IOW, solar PV is a net good for the global energy supply and GHG emissions, at current growth rates, and the good will grow exponentially going forward.

Happy New Year

It addresses a major solar 'naysayer' issue....the (supposed) low EROEI of solar PV, and its (supposed) resulting inability to support modern civilization.

Many here have a current or former 'energy doomer' bent.....this is a story for you. FYI...I do not intend 'doomer' as a prejorative, no offense intended....I am a recovering doomer myself.

--------------------------------------------

The good news: future projections of current (exponential) growth rates of solar PV production would result in all global electricity and all primary energy needs being satisfied by solar PV in 2-3 decades.

Major roadblocks for this 'clean energy eco-utopia' are not obvious:

--solar PV kWh are already cheaper than fossil kWh in many locations in the world (mostly sunny developing countries, and the US SW). Many of these locations are now driving global PV capacity growth with minimal or no subsidies.

--falling costs (due to tech learning curve) mean that the regions for which the above is true will expand to cover most global population in a decade or so

--the available energy resource (global sunshine) is more than sufficient for anticipated needs.

--the materials required, silicon, oxygen, aluminum are all earth abundant (being what the earth is primarily made of) and ubiquitous.

The hypothetical problem:

There are still energy doomers out there. They will cite a couple related issues. Some say that the EROEI of solar is too low to support civilization. Recent studies have determined that the 'energy payback time' for solar PV is 1-2 years; it takes that long for the panel to generate as much energy as it took to manufacture. A similar figure for greenhouse gas emissions (from initial manufacturing versus saved) comes up with a similar payback time 1-2 years.

On its face, this seems ok...the panels last 20-30 years...so we get an EROEI (energy return on energy invested) of 15-30 or so.

Some current doomers will cherrypick studies that have higher payback times, so EROEI is less than 10. These same folks often say that the EROEI of 10 is a magic number that if a technology is below it, then civilization collapses. Or climate doomers say that energy payback is ok, but that manufacturing PV requires fossil fuels, so 'you can't make PV with PV', so it won't work (this latter point is silly...PV is often made with electric furnaces).

I never understood the above doomer math/logic, so I won't say anything else about it. I think its weak.

-----------------------------------------------

This post is about another, subtler issue. Imagine that solar PV payback (energy or GHG) takes 3 years. And imagine that the amount installed doubles every 2 years. The math says that installing PV would then be a net loss for both energy production and GHG avoidance **forever**...no savings are realized until a couple years after we stop the exponential growth curve. In fact the 'bad' grows exponentially in proportion to the installed capacity!

This is cited as a concern by some (more sophisticated) doomers...that the installed amount of PV will always deliver less than the amount of energy needed to make next years (larger) amount of installed PV.

A (free access) peer reviewed study in

*Nature Communications*addresses this very issue:http://www.nature.com/articles/ncomms13728

The bottom line is that, while obviously 'doubling time' needs to be less than 'payback time' to see a benefit, the payback times (for energy and GHG emissions) are also falling due to learning curve, just like the prices have been. And should continue to fall.

In their extensive analysis it appears that solar PV may have been a net negative for global energy supply and GHG emissions as recently as

*a few years ago*. But even the most pessimistic estimates for energy and GHG payback show PV pulling into the black no later than this year, despite solar's current amazing rate of growth.IOW, solar PV is a net good for the global energy supply and GHG emissions, at current growth rates, and the good will grow exponentially going forward.

Happy New Year

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