An odd thing about the "climate" debates is the lack of much discussion of the practical challenges and costs of trying to convert production of energy for a modern economy to something near 100% "renewables," or maybe even something close to 100% from just wind and solar.  Currently, according to the EIA here, only about 10% of U.S. energy usage comes from all "renewables" combined -- and about half of that is from hydropower that is almost as much reviled by environmentalists as fossil fuels.  Trendy but intermittent wind and solar account for less than half the "renewable" share, at about 4% of the total usage.  Over in the "real energy that actually works" category, we find that more than 80% of U.S. energy usage comes from fossil fuels (coal, oil and natural gas), and the remaining about 8% comes from nuclear.   

So what is the problem with converting the U.S. economy over to almost entirely wind and solar over the course of the next few decades?  Can't we just build some more wind turbines and solar panels until we have enough of them to satisfy the demand?  In my post on Tuesday about New York Governor Andrew Cuomo's energy schemes, I cited Mark Mills's article for the proposition that New York already has wind turbines with about the same "capacity" as the Indian Point nuclear plant, but they produce only approximately one-fourth the amount of electricity over the course of a year.  So then, how about just building wind and solar facilities with four times the capacity of the existing fossil fuel or nuclear plants?  It might be a little pricey, but isn't this the complete answer to the problem?

If you think that might work, I suggest that you consider this January 10 article from something called Energy Post by prominent German economist Heiner Flassbeck.  The title is "The End of the Energiewende?"  Recall that Germany has managed to get its electricity production from solar and wind up to 31% of its consumption, averaged over the course of the year.  According to charts at a Wikipedia article here, as of 2014 Germany had installed wind "capacity" of about 40,000 MW, and installed solar "capacity" of another about 40,000 MW.  Presumably those numbers have gone up somewhat since.  Per a chart in Flassbeck's article reproduced below, Germany's average electricity demand is around 70,000 MW, with peak demand around 90,000 MW.  Doesn't that mean that the wind and solar should be supplying essentially all of the demand, rather than less than a third?

And of course the problem is that electricity production from wind and solar swings wildly and unpredictably back and forth from supplying all or nearly all of Germany's power some days to almost none on other days.  Flassbeck:

This winter could go down in history as the event that proved the German energy transition to be unsubstantiated and incapable of becoming a success story. Electricity from wind and solar generation has been catastrophically low for several weeks. December brought new declines. A persistent winter high-pressure system with dense fog throughout Central Europe has been sufficient to unmask the fairy tale of a successful energy transition, even for me as a lay person.

Here is Flassbeck's chart of total German energy demand and energy production for the first half of December 2016, with wind, solar and other "renewable" energy production broken out separately:

You can see that, although wind plus solar production sometimes met up to about half the demand, there were also two extended periods -- December 2 - 7, and December 12 - 16 -- when production from wind and solar was catastrophically low.  The worst days were the 12th and 14th:

Of power demand totaling 69.0 gigawatts (GW) at 3 pm on the 12th, for instance, just 0.7 GW was provided by solar energy, 1.0 by onshore wind power and 0.4 offshore. At noontime on the 14th of December, 70 GW were consumed, with 4 GW solar, 1 GW onshore and somewhat over 0.3 offshore wind. The Agora graphs make apparent that such wide-ranging doldrums may persist for several days.

At both of those times, they had sufficient wind and solar "capacity" to supply all of the electricity demanded; but the wind and solar facilities only provided about 3% of the demand at one of the times, and about 7% of the demand at the other time.  Fortunately, they had enough "conventional" facilities to supply the full demand.  But really, what good are the wind and solar facilities if, after building enough of them to have "capacity" to fulfill all of your need, you still literally can't afford to get rid of any of the fossil fuel facilities?

And then Flassbeck points out what he calls the "futility" of building still more wind turbines and solar panels:

[Even] three times the number of solar panels and wind turbines (assuming current technologies) could logically produce only three times the amount of electricity. The deficiency of prevailing winds and sunshine will affect all of these installations, no matter how many there are.  Even threefold wind and solar generation [on a day like December 14] would then fulfill just 20% of requirements. . . .    

So, to deal with a day like December 14, you would need wind and solar "capacity" equal to 15 times actual usage.  But even that wouldn't help you on the afternoon of the 12th, when it would have taken wind and solar "capacity" more like 35 times the usage to supply the demand.  

Many of the comments to Flassbeck's article are interesting.  Substantial numbers of the commenters agree that trying to get to 50% or more of a first world country's energy from just wind and solar is a complete joke.  But others think they have easy answers.  For example, commenter Helmut Frik says that on the same days of low German wind and solar production in December there were production records in Scotland and Sweden, presumably due to high winds there.  So, all they need to do is to build a big enough connector!  But of course, that assumes that on the maybe 20 or 30 days a year when Germany has no wind, Scotland and Sweden -- countries with combined population of less than 20% that of Germany -- will consistently have enough surplus wind power to sell to make up Germany's deficit.  As of now, Scotland and Sweden combined don't have remotely enough wind "capacity" to cover for a calm in Germany (their combined wind "capacity" is less than one-third that of Germany), and it's hard to believe they will be willing to essentially cover themselves over with wind turbines just so that they can bail out Germany a few days a year.  Who or what is going to pay for all those excess wind turbines the rest of the time?  And then, couldn't there be a day (or several days) when it is calm in Germany, Scotland and Sweden all at the same time?  It might be rare, but the big problem here is that you need to have a system that works all the time, even in the most extreme circumstances.  

Meanwhile, many of the commenters dismiss the proposed easy solutions as "fairy tales" or something similar.  I'm with them.  I would say that this is an enormously complicated engineering problem, where any potential routes to get a majority of energy from wind and solar are extremely expensive and still likely to work imperfectly.  Private investors are way to smart to even try, when we have abundant fossil fuel energy that works just fine and is ready for the taking.