Renewable installations are growing fast, but we can't have huge percentages of wind and solar on the grid unless we first have grid-level storage. With the exception of pumped storage, grid-level storage does not exist at this time. (No, I don't count an occasional 2 MW project as "the answer.")
We can't grow wind and solar to a higher percentage on the grid than their capacity factor implies, unless we have storage. Moving to 50% wind on the grid is not possible, without utility level storage.
The explanation follows, based on the New England grid.
|A year on the New England grid (2008)|
Shows the necessity of being able to dispatch electricity
Note rise in gas usage while nuclear plants refuel
Click to enlarge
In a guest post on January 7, Michael Twomey of Entergy used grid operator (ISO-NE) data to show that between 2014 (when Vermont Yankee was running) and 2015 (when Vermont Yankee was closed), nuclear kilowatt-hours decreased by about five million MWh and gas-fired generators increased their output by almost exactly the same amount. Natural gas went from 46,200,000 MWh to nearly 51,900,000 MWh. Nuclear kWh nuclear went down by almost the same amount of MWh.
|Click to enlarge table|
Wind and solar growing fast: Jeff Schmidt's comment
Looking at the table above, you can see that wind went from 1,892,000 MWh to 2,135,00 MWh, growing by approximately 243,00 MWh, and solar grew from 327,500 to 436,200 MWh, approximately 108,700 MWh.
This rapid rate of growth (though still only adding up to 2.4% of the power on the grid), prompted Jeff Schmidt to write this comment on the Twomey article:
"This article seems to dismiss the growth of wind and solar. While I am pro-nuclear, and think that nuclear needs to play a vital role in our future energy mix, I think the author of the article is neglecting something important - growth of wind and solar.
It's true that they are still small. But, if you look at the year-over-year growth rate, as shown by the statistics provided by the ISO and called out by Mr. Twomey, we see that Solar grew 33% in a year, and Wind grew 41%. Of course, one can't predict future growth rates based on one year, but IF wind and solar can keep up strong growth like that, they could conceivably become a very large proportion of the New England energy mix inside of 10 years.
It's true that it's likely an overly optimistic and simplistic projection, but just for the sake of argument, if they can keep up that growth rate, then 9 years from now, Wind could produce about 50% of the energy, and solar about 5%. If you projected it to 10 years instead of 9, that would account for more than 100% of current grid generation.
However, at the same time, it's very likely that at some point, Wind and Solar's growth must slow. Still, it's a valid point to concede that Wind and Solar, while currently small in absolute terms, are actually growing at a pretty fast rate."
Why renewables can't keep growing--unless we have storage
I wrote the following response to Schmidt. I oversimplified, but I am also worried that "we can't grow wind and solar" arguments are often based on cost, or on complex technical issues that are hard to explain. So, here's my oversimplification. Basically correct, but oversimplified.
Basically, we can't grow wind and solar to a higher percentage on the grid than their capacity factor implies, unless we have storage. Moving to 50% wind on the grid is not possible, without utility level storage.
I wrote about Vermont's plans to be 90% renewables in today's blog post. Of course, renewable growth from 1 to 3 to 5% is possible and looks great. However, it simply does not scale. Let's oversimplify a little, though not a lot.
Most of Vermont is one weather pattern, with some exceptions. Hot, dry and sunny...all over Vermont. Windy at night...all over Vermont. Cold and windless....all over Vermont. Now, obviously, the mountains are different from the river valleys and so forth, but the statement "weather is the same all over Vermont" is far closer to true than its opposite would be.
Okay. We cannot turn wind on and off. Let's say that wind has a 30% capacity factor. For wind to grow to 30% of the electricity supply overall, that means when wind is on the grid (the wind is blowing in Vermont)...the grid has to be 100% wind. Without this high percentage when wind is available, wind is not going to be able to be 30% of the electricity, overall. So we have to build a lot of wind to get wind to 30% of the electricity supply, and we have to turn everything else off if the wind is blowing.
Well, what if we build more wind? If we do that, when the wind is blowing....what then? We have to curtail some of the wind, because the grid can't take more than 100% of wind. So, without grid level storage, wind reaches a VERY hard stop at 30%.
Well, it is windier in the mountains, and the southern part of the state gets less wind and so forth and this is an oversimplification. And the grid requires more power in the day, and less in the night (when the wind usually blows). So it is quite complicated in reality. But the basics remain.
IF you can turn things on and off, you don't reach this sort of hard stop. 100% of the electricity from natural gas...this could work. No "hard stop" involved. 100% from nuclear...well, current nuclear doesn't follow load well, but there is no "hard stop" involved, where you have more nuclear than you can use on the grid. You don't need grid level storage for nuclear, just plants that follow load a little better. And so forth.
This is why I am so cynical about the Vermont energy plan. The plan is kind of "We don't just hope for miracles, we expect them."
Jeff Schmidt has two guest posts at this blog:
The Nuclear Safety Paradox, which describes how experience (such as building new nuclear plants) increases safety.
Flawed Analogies, which describes the analogies nuclear opponents made in a debate against nuclear energy.
The illustration showing the need for dispatchable power
From Sustainability presentation by David Lamont
Vermont Department of Public Service
October 18, 2010
Presentation is no longer on the web, but I had saved it to my computer.