French govt institute ADEME executed simulation studies regarding the electricity situation in France in 2050. They concluded that:
- 80% produced by renewable would be cheapest;
- 100% and 60% by renewable would be 5% more expensive.
Their Jan.2016 final report.
They also published their simulation model such that the visitor can change parameters to find out sensitivities, etc.

Their results as well those of German think tank Agora (the best they have), are in line with those of Jacobson etal.
Note that French govt then decided to reduce nuclear share in France towards <50%, which is a first step towards the 2050 optimum concluded.

So it seems to me that Clack etal are wrong.
Especial since their rebuttal contains many inaccuracies (or worse) and they didn't do relevant simulations.

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From Clack etal...

Jacobson ... exclude ... nuclear and bioenergy, that could potentially contribute to decarbonization ... while also helping assure high levels of reliability... 

Yes  they could potentially contribute, but only at high costs while they are not needed.

Looking at experience, nuclear clearly doesn't help to assure high levels of reliability.
Electricity supply in Denmark and Germany is ~10times more reliable than that in USA and ~4times more reliable than that in nuclear France and UK (check the SAIDI figures).

Why would Jacobson increase the costs of the 100% clean situation by including not needed expensive technology which doesnot increase delivery reliability???

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Bob, 

As someone who has researched both authors for my master's research. The two major criticisms by Clack is that the Jacobson papers' assume that there is no dispatch model similar to ISO dispatch and two that the hydropower plants are upgraded to a larger power capacity but the same energy density. 

Furtheron, Clack is a RE supporter and does have confidence in a 100% RE system.

While people may attack the research by both Clack and Jacobson, but they are also paid by industry to tackle technical problems in the field. 

As someone who doesn't like Jacobson's paper, it is a theoretical paper which is pushing the conversation forward. Independently of Jacobson's report, MISO, SPP and PJM, individually have come up with similar results for mid 40s-60s penetration of wind without any major cost upgrades. 

This discussion may be interesting on its own merits, but the Green New Deal does not require 100% renewables, only net zero emissions, despite the fact that many of its earliest proponents wished it were only renewables. The flaws in the Jacobson analysis aren’t especially relevant to the GND, since there are other analysis, including Clack and NREL’s, that show the feasibility of 80% or more renewables. 

1) Solar is not counted as multi-use in his paper. For wind turbines, you may not like it but there are 100s of farmers in the midwest who love wind turbines on their farms and have not had problems with it. Also, the US specifically has an oversupply of farmland and crops, with all the programs that are there to save the croplands. Solar and wind don't harm the land or change its use.  Further on, we will be getting more data in the next few years from California and Minnesota about dual use solar that will give us a better picture. 

> https://spot.colorado.edu/~daka9342/WindCrops.pdf

Effect of wind turbines on crop yields. Also, we don't need as much land as we do for farming. 

> So while the foundations completely disrupt any other use 

Very tiny footprint. This honestly is not a great argument. Liking and hating turbines is a personal choice. You don't like it but some others do. 

2) Literally, the first thing when you search for Mark Z Jacobson. He has all his models available. If my memories serve me correct, he is sadly using AC capacity factors(which was one of my problems in his paper)

https://web.stanford.edu/group/efmh/jacobson/Articles/I/WWS-50-USState-plans.html

Check the average insolation tab. 

3) Clack et. al. is not on electrification. I was speaking about his response to Jacobson on the report.  Can you please link your studies cause I have done academic research using EPRI and the AMO's BAT papers about electrification. I was able to identify 60% of MECS data that could be easily electrified with equivalent machines which had the same throughput and heat requirement. A major problem in the electrification studies is the lack of industry data as it is a trade secret for most of the manufacturers. 

Au contraire to your argument, Jacobson is overestimating the area required. He uses 5acres per MW when we are right now approaching 2.5acre per MWdc using 350W panels and single-axis trackers. With the 450s and higher, we will be cutting down the acreage per MW. 

One of the major drawbacks of the Jacobson study is that it doesnt "site" projects in locations and averages the production over large swaths of land. It is pretty impossible to site where you can place the projects. One of his inputs is the NREL/EPAs re-powering dataset. Which identifies the best suitable land for solar and wind. Funny thing is that 5 years ago, the data was pretty optimistic. Now, that study is conservative as the industry has found better solutions that allow us to use lands which were considered previously unsuitable for solar. Also, his prices are way too high for solar and wind. The costs we have compared to what he has modeled is way to high. His biggest problem is in the dispatch of electricity. His model/assumptions on coming to the answers are correct on a larger scale but when you go into localized effects on the grid, it starts showing its weakness. 

To let you know, I am not a supporter of the Green New Deal in entirety. There are many aspects which are against my personal beliefs of capitalism and the fact that an energy transition in the utility industry in 10 years is pretty hard to impossible. 

What I support is complete decarbonization and reducing all forms of pollution.

Here it's normal to situate wind turbines in meadows with cows or in land used to grow crops:

It also not unusual that the land below and between solar panels is used as shown here:

NIMBY is always going to be a problem for large-scale energy projects, though. The question is which is better-- large renewable sources, large gas sources, large coal sources, large nuclear sources? I think most people would be less than pleased with any of those generation sources being built near their properties, so the key is siting them well, engaging the communities that will be affected, and not rushing into it. There will always be affected and unhappy people, unfortuantely-- and I certainly don't want to downplay their legitimate concerns. I guess I'm just saying there's a whole lot of darned if you do, darned if you don't to figuring this all out