Germany Takes the Lead in HVDC | Hacker News Reader

Germany Takes the Lead in HVDC

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57 pointsEEGuy22 comments

Until recent news such as this, I didn't know it was the "conceptually simple" but practically difficult ability to switch (interrupt) a GW or so of DC energy flow preventing the implementation of better than point-to-point HVDC (i.e. multiple access point) power grids.

Evidently interruption's easier with AC because of the zero-crossings of current every half-cycle.

Three alternate solutions to HVDC circuit interruption are described in this article. Two are electronically integrated with the output circuitry of the bidirectional AC-DC converters (bidirectional energy flow AC-DC converters being an interesting, but off-topic subject in their own right).

I find it an ingenious use of an IGBT bridge surrounding a capacitor to throw the cap's charge into reversed polarity so as to stop the current flow -- effectively opening the circuit. This tells me the cap would seem to be in series with the DC side somehow. Were it in parallel, well, it wouldn't make much sense to reverse the cap's polarity as you'd only get to do it once.

I also find it fascinating that the mathematics it takes to describe AC circuits is far more complex than for DC -- one has to accept that there genuinely exists a square root of negative one, "imaginary" though we may call it.

As in programming, good nomenclature is often late to the table. I wouldn't try (and I'm certainly not qualified) to "refactor" centuries, maybe millennia [1] of mathematical terminology.

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[1] https://en.wikipedia.org/wiki/Imaginary_number

Very interesting article indeed!

>I also find it fascinating that the mathematics it takes to describe AC circuits is far more complex than for DC

Why? The math is exactly the same as for DC once you substitute complex numbers for current, voltage and impedances.

Things get more complicated in the time domain, which becomes relevant once you want to look into problems like switching HVDC on and OFF. The nonlinearities of the switching devices lead to differential equations that can only be solved numerically.

Thank you kken for your clarifications.

I don't know the physics modelling switching devices or arcs, but I do recall reading long ago that once an arc starts, its resistance drops dramatically, continuing to drop as more current flows through it (within limits).

So an arc becomes a runaway situation if current flow isn't ballasted or elsewhere interrupted. But if current flow is controlled, an arc has practical application in fluorescent lighting and arc welding.

A visual demonstration: http://www.youtube.com/watch?v=9S64r-MjBN4

You don't have to use imaginary numbers to model AC circuits. The math is just easier if you do.

Pie in the sky: if the ability to efficiently and rapidly switch DC is acquired, will we see the rise of packet switched energy networks? Data networks made the transition from circuit based to packet based networks, so why not energy networks?

If centralised generation is replaced with distributed generation there will be the need to route energy between arbitrary sources and sinks, located at any point in the network. One can envisage a network analogous to a packet based data network, where "routing algorithms" are used to direct fixed amounts of energy (a packet) from "A" to "B". A process analogous to flow control is used to govern the number of packets, and so the average power, being transferred between a source and sink. A device analogous to a buffer (capacitor?) could be used to average the power at the entrance and exit to the packet network when smooth power is required, just like running a "smooth" audio stream over a packet data network.

For DC chains, you might find yourself in need of Operational Analysis, especially when you plan to switch the flow. That beats the "simple" imaginary math just right.

http://en.wikipedia.org/wiki/Operational_calculus

Germany also stores some energy by pumping water uphill for storage behind dams, but there's only so much capacity (only so many dams). That will change if other low-cost grid-level energy storage systems become available.

https://en.wikipedia.org/wiki/Grid_energy_storage

Why mothball nuke plants when they are not in danger from tsunamis seeing as how they are miles inland in Southern Germany? Was there a public outcry after Fukushima? Seems like keeping the nuke plants running locally would obviate the need for this high euro spend on HVDC as cool and all as the tech sounds.

But, you see, nuclear plants literally consume babies.

They're fueled by babies--fission is the act of separating a baby into two or more pieces, and using the released energy (screams) to fuel your city.

No civilized nation would continue to use such an awful and dirty power source.

> Was there a public outcry after Fukushima?

Yes. Originally, the social-democrat/green government of 1998-2005 planned to shut down all nuke plants until 2020 or so, but the conservative/liberal democrats government that took over in 2009 stopped that, mostly against the will of the public. After Fukushima, there was such a huge backslash that our dear chancellor decided it might help her popularity more if she changed her mind.

And while tsunamis are rather rare in Stuttgart, the upper rhine rift is an active earthquake zone, and since we unfortunately are not allowed to just sell the waste to Russia to dump in Siberia, we also have to dispose of it somewhere in Germany. If you look at a population-density map, you will find few places with few enough people to accept highly radioactive nuclear waste.

You are right, however, that it is economically somewhat senseless to shut down the nuke plants basically shortly after the subsidies/initial costs paid off, but, well.

>You are right, however, that it is economically somewhat senseless to shut down the nuke plants basically shortly after the subsidies/initial costs paid off, but, well.

How is it more senseless than shutting them down any other time before the end of their useful life? Sunk costs are sunk.

Sunk costs are sunk, yes, but at the moment they provide cheaper energy than during most of their previous lifetime. Or put another way, the earlier you shut down a plant, the more you pay per kilowatt-hour generated.

You answer your own question. The amount of useful life they have left that goes unused is an opportunity cost. The earlier they are shut-down the larger that cost (which necessarily must be taken up in providing power through some other means).

> and since we unfortunately are not allowed to just sell the waste to Russia to dump in Siberia, we also have to dispose of it somewhere in Germany.

Isn't it actually sent to France for reprocessing ? (La Hague factory).

At least part of it is.

Yes, but it has to be permanently stored within Germany (if it comes from a German plant), i.e. is sent back here after reprocessing. Furthermore, you cannot reprocess this stuff indefinitely, so you’ll have to store it eventually.

Really, just dumping it in a large area somewhere in Siberia with a sufficiently scary fence around it and generous compensation for the few people who have to relocate for it would be the best solution.

The Rhine valley is an active tectonic fault, so after Fukushima it does not sound like the best idea to build nuclear power plants there. Furthermore, the region is one of the more densely populated one in Germany and it is one of the economic powerhouses (BASF, SAP) and one of the important transport corridors in Europe (ports of the Netherlands -> Bavaria, Switzerland, Italy).

The Biblis power plant (http://en.wikipedia.org/wiki/Biblis_Nuclear_Power_Plant) is located directly at the core of this region, is one of the oldest reactor in Germany and one of the most powerful. It was built in the early 70s, so there is no protection against plane crashes, no secondary remote control room. If it was destroyed, roughly a million people would have to be evacuated immediately and because it is situated right at the Rhine river, major cities like Cologne and Dusseldorf downriver would have to deal with radioactive water flowing by.

Just a worst-case scenario, but people just felt uncomfortable with risks like that.

I was surprised recently to see that there have been some fairly large volcanic eruptions in what is now Germany in what is, at least in geological terms, very recent history (12,900 years ago):

http://en.wikipedia.org/wiki/Laacher_See

When I was little, we visited Laacher See and my parents told me of the recent (well, geologically speaking) eruptions.

Spend days dreaming and hoping that the Eifel volcano would erupt again :)

Near the end of the Rhine valley in Switzerland is Basel which was devastated by an earthquake in the 14th century (http://en.wikipedia.org/wiki/1356_Basel_earthquake)

According to the Wikipedia page the last eruption at Eifel was 10,000 years ago and it looks like 10,000 to 20,000 years between eruptions, so you might get your wish!

http://en.wikipedia.org/wiki/Eifel

Germany has a problem. It has a desire to increase renewables (mostly from wind), which is found in the north. The primary consumers of the energy (manufacturing) are not in the north, in fact many are in the south. They need to master the transmission of that energy from north to south.

a couple of schematics of the various configurations of IGBT based converters in the article would have helped a lot.

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