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Comment by undreren | Hacker News Reader

> but theptip writes below that heating water in residential and commercial settings might be better.

When I worked at Ørsted, we did this all the time. We had a huge electric kettle, which we used to produce district heating water.

But there are many more things you can do with surplus energy. You can make methane gas from pure CO2 and hydrogen when you apply electric power as a catalyst.

The methane can then be eaten by bacteria to provide protein powder to be used as supplements to feeding livestock.

Or, we can yank CO2 out of the atmosphere and store it as ethanol. I think this was discovered last year or so? Ethanol is a really good "battery", and it only discharges as much CO2 as was captured by the surplus energy used to make it, making it a clean fuel that only exhausts CO2 and sterile water.

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A banal long term way of storing energy is to pump water up to some high ground. Whenever you need it, use a turbine to get the energy back.

That requires big water deposits up in the mountains, along with a dam.

Norway is having great success with this strategy on their hydro plants.

The UK pretty much exhausted its stock of good, easy, large sites with Dinorwig.

This is exactly how the 6th largest power plant in the UK works (but the turbine is reversed to become the pump)

https://www.youtube.com/watch?v=McByJeX2evM

https://electricityproduction.uk/plant/GBR1000151/

There's a number of them all over the world. Surprisingly simple idea and amazingly powerful storage.

https://en.wikipedia.org/wiki/List_of_pumped-storage_hydroel...

this reminded me of underwater energy storage pilot:

https://arstechnica.com/science/2017/03/german-institute-suc...

Fascinating. When you pump the water out I wonder what it's replaced with? What holds back to pressure of the ocean at 700 meters depth? The article was very light on details, unfortunately.

My understanding is that they do not replace it with anything.

I'd assume the only thing they look at is not to go above the pressure differential that the dome/sphere can sustain.

The train goes up, the train goes down: a simple new way to store energy https://www.vox.com/2016/4/28/11524958/energy-storage-rail

This sounds good to me and it claims have 86% efficiency.

Interesting, I wonder how long a rail system would need to be in order to be able to pull energy from tidal effects with the moon.

considering how much trains weigh and how fast they move, perhaps the electrical trains are already being used as "linear flywheels" ?

Since kinetic energy = 1/2 m * v ^ 2 , the a slight change in velocity on the trains that are already moving fast at any point in time, could store a lot of energy (i.e. for 2 identical weight trains, from 0km/s to 1km/s is a smaller change in stored kinetic energy than from 100km/s to 101km/s ! [in fact the latter increase of 1 km/s stores 201 times as much kinetic energy than the former: ((101 * 101) - (100 * 100)) / ((1 * 1) - (0 * 0))]

Now that I think of it, this could probably explain why our local trains are suffering more and more irregular arrival times :) but why would it be kept secret or hidden in plain sight? perhaps all the negative news about negative prices for renewable energy during energy flood is just manufacturing consent to keep price hikes for the plebs palatable, or a kind of white lie to offset their airplane travels...

to be honest I'm not very impressed by the trains up/down proposal:

The trains move on a track 5.5 miles long at an inclination of 8 degrees. thats a height difference of sin(8deg) * 5.5miles * 1.609344km/mile = 1.232 km, now it may be hard to find a steep cliff 1.2km high, but you could use a smaller cliff and heavier weights, think of the steep section at the start of an amusement ride (they will probably be better equipped with safety for such systems anyway since they are used to designing crazy rides for human consumption). no need for train and electrical tracks 5.5 miles long, since the motor can reside on the top part of the cliff/hill...

One more example.

Bath County Pumped Storage Station in the US. Huge place.

https://www.dominionenergy.com/about-us/making-energy/renewa...

Amongst the best and ost efficient energy storage options, but very limited suitable sites.

The Balkans region, along the Adriatic coast, offers an interesting prospect: using the sea as a lower basin with mountaintop reservoirs. This is a rare topology, particularly near large populations.

What the results of localised salinisation might be is a concern though.

I was at a tour of Skærbækværket many years ago, and as I remember it, when you produce power, you need to be able to control the voltage somehow. If there is a surplus of power and you cannot turn down production, you need to dump it or the voltage will go up, destroying electrical systems. One of the simplest ways to do this is to heat water, and when you have well established district heating it's almost a no brainer what to do.

It's a nobrainer, but the electric kettles are rather expensive and are usually therefore only bought to ensure production capacity in the case that the powerplant's own kettle malfunctions.

Besides, district heating produced on power from the grid is taxed as if produced on coal, as the power has no traceability. This makes it really expensive, unless you are directly hooked up to a solar or windfarm.

That's the law in Denmark at least.

PS: I worked in the administrative building just next door to Skærbækværket! :)

Ahh, it doesn't make much sense to install it away from a powerplant. It captures waste heat and electricity, where as one elsewhere would only be able to capture excess electricity.

> district heating produced on power from the grid is taxed as if produced on coal, as the power has no traceability.

Sounds like there is room for improvement. E.g. an agreement with an energy provider and tracking when it was used on demand as a sink for excess energy instead of base-rate heating.

>You can make methane gas from pure CO2 and hydrogen when you apply electric power as a catalyst.

You can make methane gas from pure CO2 and hydrogen period. The reaction is exothermic, it's just the Sabatier method. You could however use electricity to split water into hydrogen and oxygen.

> We had a huge electric kettle, which we used to produce district heating water.

...and you thought you were heating with renewable energy. You were not. Much of the "surplus" power on the grid comes from coal plants (especially in Denmark!) that can't throttle down, so someone burns coal, converts the heat to electricity at an efficiency of 40% or so, and you turn it back into heat.

> ...and you thought you were heating with renewable energy.

No we didn't. As a mathematical modeller and software developer for their inhouse production optimization software, I was perfectly aware of what was happening.

> Much of the "surplus" power on the grid comes from coal plants (especially in Denmark!)

Most of the power plants owned by Ørsted are bio-converted and runs primarily on wood chips and pellets. Unless you are talking about surplus energy imported from Germany, what you say simply isn't true.

Besides, the huge amounts of surplus energy that often came from germany were caused by their massive open sea wind farms, making the energy pretty green.

Ørsed operated almost exclusively combined heat and power plants, meaning that they can produce heat and power concurrently. The utilization of energy was well above 90%, when we ran the plants this way, because we cooled the plant with the district heating water, instead of sea water. The theoretical maximum is ~98%.

We also never planned for pure power production, only to turn it into heat again. That would be monumentally stupid.

We had many, highly skilled engineers and power traders, and they absolutely knew what they were doing.

So it seems many coal burners in Denmark have switched top biomass in the past few years. I didn't know that. But someone burning wood to make electricity and someone else wasting the electricity in a resistance heater still doesn't sound like a solution, it sounds like insanity. (Not necessarily pointing fingers at you personally. Negative prices lead to insanity.)

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