GetOffYourGas
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Re: GCC: Harvard team finds large-scale US wind power would cause warming that would take roughly a century to offset

Mon Oct 08, 2018 8:13 am

GRA wrote:http://www.greencarcongress.com/2018/10/20181005-wind.html


[list]In terms of temperature difference per unit of energy generation, solar power has about 10 times less impact than wind. But there are other considerations. For example, solar farms are dense, whereas the land between wind turbines can be co-utilized for agriculture.

—Lee Miller. . . . [/list]


This is why I dislike "solar farms". There are many better uses for that land (including keeping it as wild habitat!) then large arrays of solar panels. Instead, solar should be focused on rooftop installations - that way the land has true dual-use. We are a long way from saturating the usable roof space.

Now a real impact of solar is the energy-intensive production process. I was told that the EROEI for my panels was almost 10 years. It may have gotten better since, but it will always be greater than zero for any energy generation.
~Brian

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SageBrush
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Re: GCC: Harvard team finds large-scale US wind power would cause warming that would take roughly a century to offset

Mon Oct 08, 2018 8:43 am

GetOffYourGas wrote:
GRA wrote:http://www.greencarcongress.com/2018/10/20181005-wind.html


[list]In terms of temperature difference per unit of energy generation, solar power has about 10 times less impact than wind. But there are other considerations. For example, solar farms are dense, whereas the land between wind turbines can be co-utilized for agriculture.

—Lee Miller. . . . [/list]


This is why I dislike "solar farms". There are many better uses for that land (including keeping it as wild habitat!) then large arrays of solar panels. Instead, solar should be focused on rooftop installations - that way the land has true dual-use. We are a long way from saturating the usable roof space.

Now a real impact of solar is the energy-intensive production process. I was told that the EROEI for my panels was almost 10 years. It may have gotten better since, but it will always be greater than zero for any energy generation.

EROI is about 2 years.

I've seen photos of ground mounts in Europe where they continue to use the land for agriculture.
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GetOffYourGas
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Re: GCC: Harvard team finds large-scale US wind power would cause warming that would take roughly a century to offset

Mon Oct 08, 2018 9:58 am

SageBrush wrote:
GetOffYourGas wrote:


This is why I dislike "solar farms". There are many better uses for that land (including keeping it as wild habitat!) then large arrays of solar panels. Instead, solar should be focused on rooftop installations - that way the land has true dual-use. We are a long way from saturating the usable roof space.

Now a real impact of solar is the energy-intensive production process. I was told that the EROEI for my panels was almost 10 years. It may have gotten better since, but it will always be greater than zero for any energy generation.

EROI is about 2 years.

I've seen photos of ground mounts in Europe where they continue to use the land for agriculture.


Both good news. I'm impressed if we've really improved EROEI by a factor of 5 in only 7 years.

I've never seen a ground mount system in the US, where the land is used for anything else. I'm not saying it doesn't exist, but it is the exception in both the Northeast and the Southwest where I have seen large solar farms. I still think rooftop is our best option, since the buildings (and roofs) already exist.
~Brian

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SageBrush
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Re: GCC: Harvard team finds large-scale US wind power would cause warming that would take roughly a century to offset

Mon Oct 08, 2018 10:07 am

GetOffYourGas wrote:I've never seen a ground mount system in the US, where the land is used for anything else. I'm not saying it doesn't exist, but it is the exception in both the Northeast and the Southwest where I have seen large solar farms. I still think rooftop is our best option, since the buildings (and roofs) already exist.

I'm a rooftop fan too, but so far it is a lot more expensive than large scale ground mount with rotating arrays. I like the middle ground on this issue: ground mount for poor quality land or in a dual-use.

I also like to point out that the worse case use of good land for PV is still a whole lot better than growing crops for beef or ethanol.
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GRA
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Re: GCC: Harvard team finds large-scale US wind power would cause warming that would take roughly a century to offset

Mon Oct 08, 2018 5:53 pm

GetOffYourGas wrote:
SageBrush wrote:
GetOffYourGas wrote:
This is why I dislike "solar farms". There are many better uses for that land (including keeping it as wild habitat!) then large arrays of solar panels. Instead, solar should be focused on rooftop installations - that way the land has true dual-use. We are a long way from saturating the usable roof space.

Now a real impact of solar is the energy-intensive production process. I was told that the EROEI for my panels was almost 10 years. It may have gotten better since, but it will always be greater than zero for any energy generation.

EROI is about 2 years.

I've seen photos of ground mounts in Europe where they continue to use the land for agriculture.


Both good news. I'm impressed if we've really improved EROEI by a factor of 5 in only 7 years.

I've never seen a ground mount system in the US, where the land is used for anything else. I'm not saying it doesn't exist, but it is the exception in both the Northeast and the Southwest where I have seen large solar farms. I still think rooftop is our best option, since the buildings (and roofs) already exist.

Rooftop gives the best power density and lowest environmental impact, but the amount of it is strictly limited. Smil's book on power density includes the results of a study of rooftop solar potential in the Tokyo Metro area, which is currently the world''s largest megacity and representative of forecasts for where most of the world's urban population growth will be concentrated between now and 2050, and looking at all available roofspace in that area, it's orientation etc., IIRR the conclusion was that no more than about 10% of the metro area's demand could be generated using rooftop PV only. Germany has the highest % of rooftop solar in the world (and 44.3 GW total PV, both roof and ground mount, as of July), owing to extensive subsidies (which have been and are being gradually reduced). Per Smil the size of the rooftop systems have been increasing, with more and more going on MUDs and commercial buildings rather than detached homes.

Unfortunately I had to return the book to the library (interlibrary loan), so I don't have the exact figures handy and am working from memory. Just to remind everyone who's interested in what the actual power densities of deployed renewables are, I highly recommend it (like I do all of Smil's books I've read, especially those on energy transitions and technological change):

Power Density: A Key to Understanding Energy Sources and Uses
https://www.amazon.com/Power-Density-Understanding-Energy-Sources/dp/0262529734

Re ground mounts, parking lots show how PV can allow concurrent usage, although whether the typical monopole supports count as ground mounting is arguable:
The Design Basics for Solar Parking Lots You Need to Know
https://www.designnews.com/materials-assembly/design-basics-solar-parking-lots-you-need-know/96305277745717

Still, if there's enough room to park cars under the panels there's enough room for grazing/horticulture/silviculture (xmas tree farms etc.) if the amount of light getting through and around the panels is adequate for photosynthesis, assuming the concrete pads for the pole bases are kept small. The tradeoff for allowing concurrent use for such mounts is that the tilt angle is normally kept quite low, reducing the capacity factor. Providing water to clean panels in desert areas may be a bigger issue.

Re EROEI, ten years seems far too long, as even a decade or two back the number was around 3-4 years IIRC. However, even if it were 10 years, as the panels will be useful for 40 or more (with decreased output, to be sure) you're still well ahead.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

GetOffYourGas
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Re: GCC: Harvard team finds large-scale US wind power would cause warming that would take roughly a century to offset

Mon Oct 08, 2018 6:08 pm

Tokyo is an extreme case, Guy. And 2050 is several decades from now. Meanwhile, in 2018, most of the solar farms in the northeast reside in freshly deforested areas, and not high enough for anything to grow beneath them. In many cases, they are near large buildings with plenty of roof space. The trouble is that the panels cannot be seen from the road, so no one would know how "green" the business/college/etc is!

Parking lots are a great option, especially in hotter climates - the panels provide shade, keeping the cars cooler and reducing their energy usage for A/C.

Regarding the 10 year number, that was a number I was given. I didn't dig any deeper than that. The panels / inverters are warrantied for 25 years, so I'm sure I will end up ahead. Although, as Reg knows from another thread, my inverters have been failing at an alarming rate. I have lost 9 of the 16 inverters in the less than 7 years that my system has been operational. I'm currently running on 14 functioning inverters, while I wait for my installer to replace the most recently failed inverters.
~Brian

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DarthPuppy
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Re: GCC: Harvard team finds large-scale US wind power would cause warming that would take roughly a century to offset

Mon Oct 08, 2018 6:55 pm

You beat me to it. I was just about to say that Tokyo is a rather dense population city and therefore tilts toward rooftop solar being inadequate. The study would be quite a bit more enlightening if it looked at 2 extremes - say Tokyo vs. Los Angeles. In LA, we have tons of roof space for our population versus the roof space in Tokyo. Then for most cities, the results will be within that known range.

Also, rooftop solar is an excellent route to take until the rooftop space is consumed. If we can produce 30% of our solar that way, that is a lot less other land that has to be consumed for solar production.

One area of consideration I'd like to know more about is the merits of rooftop solar versus rooftop gardens. On Facebook, I recently saw an interesting article touting rooftop gardens and how some cities are moving in that direction. Both are clearly a better use of rooftops than most cities have in place. But which of these two uses is better?
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RonDawg
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Re: GCC: Harvard team finds large-scale US wind power would cause warming that would take roughly a century to offset

Mon Oct 08, 2018 7:10 pm

DarthPuppy wrote:You beat me to it. I was just about to say that Tokyo is a rather dense population city and therefore tilts toward rooftop solar being inadequate. The study would be quite a bit more enlightening if it looked at 2 extremes - say Tokyo vs. Los Angeles. In LA, we have tons of roof space for our population versus the roof space in Tokyo.


There's also the fact that Los Angeles gets much more sunshine than Tokyo:

Image

Image

LA's least-sunny months (Dec and January) are still better than Tokyo's most sunny. In fact, Seattle (despite its reputation for being eternally cloudy and rainy) actually sees more sunshine between mid-March and mid-September than in the sunniest months in Tokyo:

Image
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DarthPuppy
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Re: GCC: Harvard team finds large-scale US wind power would cause warming that would take roughly a century to offset

Mon Oct 08, 2018 7:19 pm

Wow, I had no idea that there was that much of a difference in sunlight between Tokyo and LA. That further accentuates these two belong at the opposite ends of the spectrum. Tokyo has very dense population so less rooftop space per capita and less sunlight throughout the year vs. LA has lots of roof space per capita and pretty good sunlight to make use of that space.

Using these two as measurement points would do a pretty good job of establishing the relevant range into which many cities would find themselves. And that would be much more useful than a study of just one of them. A study that picks just one, and it is one that is an extreme case in one direction, raises doubts about the intent of the study.
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GRA
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Re: GCC: Harvard team finds large-scale US wind power would cause warming that would take roughly a century to offset

Mon Oct 08, 2018 7:29 pm

GetOffYourGas wrote:Tokyo is an extreme case, Guy. And 2050 is several decades from now. Meanwhile, in 2018, most of the solar farms in the northeast reside in freshly deforested areas, and not high enough for anything to grow beneath them. In many cases, they are near large buildings with plenty of roof space. The trouble is that the panels cannot be seen from the road, so no one would know how "green" the business/college/etc is!

It's an extreme case in that it's the world's largest megacity now, but megacities, especially in Asia, are going to see the majority of urban growth (which is to say the majority of population growth period) for at least the first half of this century (also the greatest number of car sales), and the power density demands of their tall tower blocks are high. Smil also discusses studies about actual power densities, available roof (and wall) areas of other cities, including in the U.S., and they are in the same order of magnitude. Phoenix is obviously better than Berlin, both because of insolation but also because of the types of buildings. Even so, no city can provide more than a minority fraction of its electricity use from rooftop PV - the power densities of variable renewables are too low, even though rooftop PV is the highest among them. I really can't type the details of the whole book in, even if I remembered them all accurately, so again I recommend people who are really interested to read it. His data is provided from numerous real-world systems.

In fact, let me give Smil's books (who's Bill Gates' favorite author, FWIW) a general recommendation, as so many of the subjects he writes about are of interest to people on this forum. I've got his "Should we eat meat? : evolution and consequences of modern carnivory" en route, but "Harvesting the biosphere : what we have taken from nature" might also be of interest, along with many of his other books.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

The 'best' is the enemy of 'good enough'. Copper shot, not Silver bullets.

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