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thunderhead
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PostMon Mar 18, 2019 10:23 am 
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But you have to be careful because once the IR absorption bands are saturated, there is no more energy at those wavelengths to absorb. 

Not quite correct.  When the entire column is saturated, increasing IR absorptivity still decreases the mean free path of a given quanta of outgoing radiation, increasing the amount absorbed at any given level, thus increasing temperature and/or increasing the amount of convective energy flux, all planetary atmospheres being in a state of radiative-convective equilibrium.

CO2 does this, which causes atmospheric moisture to increase(due to the increasing carrying capacity of warmer air), though at a similar rate to temperature increase such that relative humidity remains approximately unchanged.  It is certainly a positive feedback mechanism, probably about doubling the effect of CO2 alone, although there is enough uncertainty, especially regarding cloud cover and the ice crystal/water droplet line(big differences in IR/Vis emissivitiy), so that I would not try to give an exact value.  The changes are small enough relative to our planet's overall radiative fluxes that the impacts are so far minor, often negligible.

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The biggest limitations wind and solar face in the US now are political

Not correct.  There is the massive physical hurdle in the intermittency of these sources, combined with the lack of affordable energy storage.  Solar and wind are not yet ready to take on the lion's share of US power.  Nuclear is.
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drm
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PostMon Mar 18, 2019 10:57 am 
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Parked Out wrote:
So hypothetically, if the presence (vs the absence) of vegetation increased the average amount of water vapor by 10%, the IR radiation absorbed by that increase would constitute a radiative forcing, right?

Yes, there could be small localized increases in relative humidity, but from what I've read these will not be of a magnitude to drive climate. Remember that that air is going to move to somewhere else.
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drm
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PostMon Mar 18, 2019 11:13 am 
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Sculpin wrote:
So I stand by my claim that there is currently no scientific basis for claiming that the net forcing of water vapor over long time intervals is zero.  It is still set to zero in climate models because we lack the data to set it anywhere else, not because we have verified that it is zero.

Thanks for the clarification. I was not including clouds in my comments, just pure water vapor. It is indeed much more complex when you take clouds into effect. There are many types of clouds and they have very different impacts on the amount of feedback we get, but they are usually discussed separately from water vapor when I have seen it.

Because clouds represent probably the largest source of uncertainty in climate modeling, there is a lot of research going on and I'm not going to pretend I stay up on it. The broad magnitude of positive feedback with warming comes significantly from climate history, ice cores, etc. But that doesn't tell us the specific contribution of the different components of that feedback.

So if you replace "water vapor" with "clouds" in your statement above, I agree generally with you, though there are individual studies that make various claims. So maybe not "no scientific basis", just no coming together on it yet.
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drm
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PostMon Mar 18, 2019 11:20 am 
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thunderhead wrote:
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The biggest limitations wind and solar face in the US now are political

Not correct.  There is the massive physical hurdle in the intermittency of these sources, combined with the lack of affordable energy storage.  Solar and wind are not yet ready to take on the lion's share of US power.  Nuclear is.

The solution to intermittency now is not storage, it is transmission. Plenty of studies show that it is blowing or shining somewhere in the USA enough to power us, and a modest amount of storage would help lessen the transmission required. But there is massive political resistance to large scale transmission facilities, and of course they would be expensive. But there are no technical limitations preventing it now. That is what I was referring to.

There is also massive political resistance to nuclear, and it is expensive. We can debate which resistance is more substantive (EM waves anyone?), but if either opposition were defeated, either of those facilities could provide carbon free electricity generation. The question is which is the better option.
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RandyHiker
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PostMon Mar 18, 2019 11:44 am 
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thunderhead wrote:
Solar and wind are not yet ready to take on the lion's share of US power.  Nuclear is.

Why does it have to be either or?   Solar and wind can be developed much more quickly and cheaply than nuclear.  Even if solar and wind aren't 24/7/365 ever kwh generated and used by solar and wind is that much less CO2 emitted from burning coal, oil or gas for generation.  In more southern portions of the states peak electrical demand is on hot summer days when air conditioning demand is high -- which is also when solar availability is greater. 

As nuclear capacity builds that will be reduce coal, oil and gas usage further, but realistically it will be a decade before any new plants come online.  We can build many GW of solar and wind capacity before then and reduce emissions more quickly (and ironically lower the cost of oil and gas by lowering demand)
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Parked Out
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PostMon Mar 18, 2019 7:41 pm 
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drm wrote:
The solution to intermittency now is not storage, it is transmission. Plenty of studies show that it is blowing or shining somewhere in the USA enough to power us, and a modest amount of storage would help lessen the transmission required. But there is massive political resistance to large scale transmission facilities, and of course they would be expensive. But there are no technical limitations preventing it now.

The US wind resource varies seasonally and tends to be lowest July-September across most of the country.  The solar resource obviously peaks during the summer, but it still produces zero energy overnight even in the sunniest months.  To install enough wind & solar capacity to meet the nation's needs when wind power is low and solar power is nil would require a massive overbuild of generation facilities, on top of new transmission lines.  Then what do you do with all the excess generation when it's windy & sunny?  You have to dump it or sell it to someone at a loss, or you store it for later.  If you go the storage route there are significant losses putting the energy into storage and taking it out again, and if you use batteries there are typically HVAC loads to consider.  At some point you run into energy-returned-on-energy-invested (EROI) issues and the whole thing becomes pointless as the net energy produced by the system is too low to bother with.

Granted, if people are willing (or can be coerced) to pay for it, you can add a fair amount of wind & solar to the grid before these problems become unmanageable, but the question is why?  Intermittent energy is a dead-end road.  Better to bide your time, don't squander your resources, educate the public on nuclear and end up with something that has a viable future.  Barring some new green deal fiasco, the amount of wind & solar the US would install over the next decade wouldn't make any difference to the climate anyway.  We'd be better off to continue the transition to natural gas.

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PostMon Mar 18, 2019 7:50 pm 
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RandyHiker wrote:
As nuclear capacity builds that will be reduce coal, oil and gas usage further, but realistically it will be a decade before any new plants come online.  We can build many GW of solar and wind capacity before then and reduce emissions more quickly (and ironically lower the cost of oil and gas by lowering demand)

To me it just seems like a token gesture and likely money not well spent.  Despite the assertions, there's really no reason to be in panic mode, and with well over a thousand new coal plants in the works worldwide, all our wind & solar isn't going to have any more effect on the climate than Germany's has.  At this point in time, money spent on deployment of existing technologies would be better invested in developing better technologies that could actually make a difference.

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RandyHiker
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PostMon Mar 18, 2019 7:52 pm 
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Parked Out wrote:
At some point you run into energy-returned-on-energy-invested (EROI) issues and the whole thing becomes pointless as the net energy produced by the system is too low to bother with.

Yep the cheapest thing to do is nothing.  That is the type of counter argument that car makers made in the '60s and early '70s against emissions controls on vehicles requiring catalytic converters and other measures to counter smog.     I remember my eyes itching and burning in those days.
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PostMon Mar 18, 2019 8:09 pm 
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RandyHiker wrote:
Yep the cheapest thing to do is nothing.

EROI isn't about profitability - it's about getting a sufficient amount of energy from the energy you expend so that you have some left with which to run your civilization.  7:1 is often considered a minimum EROI to be viable for an advanced society.  Ethanol is a classic example of ignoring EROI;  you get no more energy out of a gallon of ethanol than you expended to create it.

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RandyHiker
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PostMon Mar 18, 2019 9:29 pm 
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Parked Out wrote:
RandyHiker wrote:
Yep the cheapest thing to do is nothing.

EROI isn't about profitability - it's about getting a sufficient amount of energy from the energy you expend so that you have some left with which to run your civilization.  7:1 is often considered a minimum EROI to be viable for an advanced society.  Ethanol is a classic example of ignoring EROI;  you get no more energy out of a gallon of ethanol than you expended to create it.

Do you have any facts to back up your assertion that solar cells require more than 7x energy to manufacture and install than they will produce over their useful life?

Ethanol is only about elections that happen every 4 years.
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Bedivere
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PostMon Mar 18, 2019 9:38 pm 
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Parked Out wrote:
The solar resource obviously peaks during the summer, but it still produces zero energy overnight even in the sunniest months.

There is a solution for that.

https://www.scientificamerican.com/article/new-concentrating-solar-tower-is-worth-its-salt-with-24-7-power/

I've read about other, similar plants that simply use sand.

And molten salt nuclear reactors are really the way to go and we should be pushing for them.

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PostTue Mar 19, 2019 6:24 am 
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RandyHiker wrote:
Do you have any facts to back up your assertion that solar cells require more than 7x energy to manufacture and install than they will produce over their useful life?

I didn't assert that.  Calculating EROI so that a meaningful comparison can be made of one system vs another means drawing appropriate boundaries around each, such that important differences are accounted for from production to distribution.  If an intermittent source requires external storage (as opposed to e.g., fossil fuel where the energy is stored in the fuel) or requires a substantial increase in transmission lines, the energy costs of those elements fall within the boundary of that system.  So the energy invested in a PV solar system includes a lot more than just the manufacturing & installation of solar panels.

A few sources:

Energy in Australia – Graham Parker  https://bravenewclimate.com/2014/02/09/book-review-energy-in-australia/

Spain’s Photovoltaic Revolution: The Energy Return on Investment – Pedro Prieto & Charles Hall  https://www.springer.com/us/book/9781441994363

Energy intensities, EROIs (energy returned on invested), and energy payback times of electricity generating power plants  https://www.sciencedirect.com/science/article/abs/pii/S0360544213000492

Energy Return on Energy Invested (ERoEI) for photovoltaic solar systems in regions of moderate insolation  https://www.sciencedirect.com/science/article/pii/S0301421516301379

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PostTue Mar 19, 2019 7:07 am 
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Bedivere wrote:
Parked Out wrote:
The solar resource obviously peaks during the summer, but it still produces zero energy overnight even in the sunniest months.

There is a solution for that.

https://www.scientificamerican.com/article/new-concentrating-solar-tower-is-worth-its-salt-with-24-7-power/

It doesn't look totally hopeless but it does look like the plant is significantly underperforming.

https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Project

It would be interesting to see daily production data.  10 hrs of storage isn't really very much so I wonder if it has a gas plant backup.  Most CSP plants burn gas every morning when they start up but most don't have storage so I'm not sure if that's the case with Crescent Dunes.

Bedivere wrote:
And molten salt nuclear reactors are really the way to go and we should be pushing for them.

Definitely agree.

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PostTue Mar 19, 2019 8:10 am 
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thunderhead wrote:
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But you have to be careful because once the IR absorption bands are saturated, there is no more energy at those wavelengths to absorb. 

Not quite correct.

I should have written "incoming solar energy."  Back-radiation washes across the IR spectrum and so does indeed allow for more absorption at lower elevations.

thunderhead wrote:
When the entire column is saturated, increasing IR absorptivity

Not sure what you mean by that.  Can you clarify?

thunderhead wrote:
relative humidity remains approximately unchanged.  It is certainly a positive feedback mechanism

These are assertions, not facts.  I doubt that they are correct.  Humidity can drive both enhanced convection, as with the tropical thunderstorm theory I mentioned before, and also affect the radiation budget in different ways if clouds form.

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RandyHiker
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PostTue Mar 19, 2019 9:09 am 
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Parked Out wrote:
RandyHiker wrote:
Do you have any facts to back up your assertion that solar cells require more than 7x energy to manufacture and install than they will produce over their useful life?

I didn't assert that.  Calculating EROI so that a meaningful comparison can be made of one system vs another means drawing appropriate boundaries around each, such that important differences are accounted for from production to distribution.  If an intermittent source requires external storage (as opposed to e.g., fossil fuel where the energy is stored in the fuel) or requires a substantial increase in transmission lines, the energy costs of those elements fall within the boundary of that system.  So the energy invested in a PV solar system includes a lot more than just the manufacturing & installation of solar panels.

A few sources:

Energy in Australia – Graham Parker  https://bravenewclimate.com/2014/02/09/book-review-energy-in-australia/

Spain’s Photovoltaic Revolution: The Energy Return on Investment – Pedro Prieto & Charles Hall  https://www.springer.com/us/book/9781441994363

Energy intensities, EROIs (energy returned on invested), and energy payback times of electricity generating power plants  https://www.sciencedirect.com/science/article/abs/pii/S0360544213000492

Energy Return on Energy Invested (ERoEI) for photovoltaic solar systems in regions of moderate insolation  https://www.sciencedirect.com/science/article/pii/S0301421516301379

It looks like you got the 7x figure from Weißbach's paper.

Here is a paper that analyzes those assumptions.  Using Germany as a model for solar is good if the goal is to discourage solar development as Germany as some of the worse solar potential.

http://rameznaam.com/2015/06/04/whats-the-eroi-of-solar/

Also your assertion that solar generation capacity must include storage increases the financial and energy costs, but many GW of solar and wind capacity have been added and produce useful capacity without it.   Is this based on "one solution" type thinking ? E.g. any form of generation must be able to provide 24/7/365 energy independently?     Why do seem to exclude using a multiple sources strategy ?
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