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comment by WanderingEng
WanderingEng  ·  616 days ago  ·  link  ·    ·  parent  ·  post: Coal is dead, because nobody wants to build coal-fired power plants.

The wind tech is way better than it was even ten years ago. The expiration of GE's patent on variable speed turbine generators opened the versatile technology up to everyone. These turbines can control voltage more dynamically.

Separately, the cost of power electronics have come down, so now some turbines use full converters to change the generator output to the power system frequency. These can eliminate gearboxes, too, and also control voltage.

In the US, FERC has made a number of rulings that forced wind plants to improve. FERC Order 661-A (pdf) required wind turbines have low voltage ride through, forcing them to remain online during system faults. 661-A also mandated a power factor range, relating back to the GE patent and full converter turbines with their ability to control voltage.

We're also able to push the power system harder than ever. Fifty years ago we still had manned substations. People would sit there and call the control center every so often to tell them what the analog meters showed. Today we scan every analog and digital point every few seconds. And every few minutes the entire system is simulated to see what would happen if a failure occurred. That lets the system accept more wind. The output is variable, of course. The system was easy when it was the same generators running all the time. The variable wind output means one day to the next could be drastically different. The tools allow us to be confident the system is still reliable.

There were a couple wind output records broken in the US a week or two ago. I think MISO topped 13,000 MW. For comparison, that's about double the maximum output of Grand Coulee.

To me, the issue is wind doesn't provide capacity like a gas, coal, nuclear or hydro plant does. I think MISO allows something like 16% of wind nameplate capacity to count as capacity to serve load. So you build a 100 MW wind farm, and you get 16 MW of capacity. Build a 100 MW gas combustion turbine and you get 100 MW of capacity. Load needs capacity to ensure all load can be served.




goobster  ·  615 days ago  ·  link  ·  

It seems to me that all this discussion about efficiency and output levels, etc, is like a group of engineers debating what shape the electrical outlet should be; it all kinda misses the point.

The real weakness is storage and transmission. We have plenty of methods for making power. What we don't have is a good way to store it for when we need it, and to transmit it from one place to another (ex: from a solar plant in Nevada to NYC in the winter).

We need a good way to store vast amounts of power, and transmit it with much less loss, over much larger distances.

Generating power if/when you want it, seem backwards to me. Shouldn't we take power when we can get it (solar, wind) and then store it for when we need it?

I've been thinking a lot about that plan somewhere to store the energy by pushing a bunch of water up a hill into a reservoir... and then thinking of a series of dams, like a fish ladder... and we push water uphill when power is being generated... and let it flow downhill and generate hydro power when we need it...

I dunno. That still means we have the power transportation problem, but if cities had hydropower generators instead of water towers, then power could be transmitted in stages, from city to city to city... and...

Ok, it's a huge infrastructure project, but hey... it worked for the WPA! (Which, incidentally, would also get a whole bunch of people trained into the Trades - concrete, electrical, plumbing, etc - and provide a boost to the Trades industry with newly trained, skilled workers, and, and, and provide people with options other than going into enormous debt for a college degree... and help people in depressed areas get good-paying jobs, and...)

WanderingEng  ·  615 days ago  ·  link  ·  

    Shouldn't we take power when we can get it (solar, wind) and then store it for when we need it?

Having more flexible load has been talked about for years, but nobody has made much progress on it. Little load is flexible. Around a home, refrigerators have to run regularly to keep food safe. Businesses have to keep running to sell their goods. Industry needs to keep running because while they may have high energy bills, if they aren't running they can't pay for their capital needs.

Storage is definitely a big deal. Today, energy is stored in piles of coal and gas pipeline pressure. Doing a little math, this link says a 500 MW coal plant burns about 1.4 million tons of coal per year. I think coal plants usually store about two weeks worth of coal, so let's say they have 50,000 tons on hand.

Wolfram Alpha says coal has about 7000 kWh/ton, so that coal plant has about 350 million kWh worth of energy sitting in a big pile outside. Only about 35% of that will go out the wires; the rest will go up the stack or into the lake or river. But that's still 120 million kWh of usable energy.

As far as I know, this 120 thousand kWh battery is still the largest single battery out there. It would take a thousand of these just to equal the storage capacity of a coal plant's backyard, and you still haven't produced a single watt.

The problem isn't impossible, but we're still so far away from the solutions being easy.

goobster  ·  614 days ago  ·  link  ·  

Thanks for engaging with me on this.

I really think that our power grid needs to be way more like plumbing: a base level of water is always available, and then if Nevada needs to water their lawn tonight, there is additional capacity in store to draw on.

A radical rethinking of where we get power, how we store it, and how we make it available to the places that need it, especially when that need spikes...

It's a Big Problem, but one I can't imagine we aren't going to have to solve in the next 20 years.

WanderingEng  ·  613 days ago  ·  link  ·  

It's definitely a Big Problem. The challenge with flexible load is finding load that's flexible and manipulating it to the advantage of the system. Some load can be shifted pretty simply. My refrigerator is currently running. If it had waited five more minutes to run, my food would still be cold and safe. But it will need to run eventually.

Storage is the potential miracle here. Despite press to the contrary, batteries aren't economical today to store energy for any significant length of time. They've been deployed economically for extremely short duration energy shifting, seconds to maybe a minute. I think they need to come down in price by an order of magnitude to really change anything. Maybe they will; it'd be great if they did.

kleinbl00  ·  615 days ago  ·  link  ·  

1) The storage is the grid.

2) The efficiency of a wind farm matters a lot less than the availability and quality of wind.

3) Yes we have "plenty of methods for making power" but if that power is only made at midnight on every fourth tuesday then you're well beyond storage problems because nothing holds megawatts for days at a time.

4) You're discussing compressed air energy storage or pumped storage hydroelectricity both of which I'm sure WanderingEng could talk a lot more knowledgeably about... as well as DC power transmission, which kinda licks the "grid" problem.

WanderingEng  ·  615 days ago  ·  link  ·  

I think you and goobster are saying pretty much the same thing here. You're completely right that the grid is the storage mechanism, at least today. With demand inflexible and wind and solar inflexible, as long as the flexible parts of the grid can make up the differences, everything works. That hits goobster's point about transmitting energy over longer and longer distances. When one part of the grid becomes saturated, whether it's one neighborhood or a group of states, the grid has to be expanded to pull in more flexible resources. HVDC is awesome for that, but it's also pretty expensive. Ballpark estimates are like $150M per converter station and $2M/mile of line. Projects quickly reach billions of dollars.

Any transmission line also has public opposition. They cross rivers and backyards. While some impacted don't mind and don't mind the payment that comes with, some will fight it to the bitter end.

I'd say the technical aspects are pretty well understood. It wouldn't be hard to design a system around mostly wind and solar, but nobody would be willing to pay for it.

Devac  ·  615 days ago  ·  link  ·  
This comment has been deleted.
Devac  ·  615 days ago  ·  link  ·  

Out of curiosity, do you know of wind plants that mix their turbines? Savonius' turbines seem like a great safety measure for the situations of lower wind speed (or too high for that matter).

WanderingEng  ·  615 days ago  ·  link  ·  

As far as I know, nobody is doing that. At this point, anyone putting up the capital for a wind plant wants to maximize output. Utility scale, horizontal axis turbines will produce more energy overall, even if it's less optimal at some wind speeds.