I work in the industry making hardware and software for large scale commercial and grid scale storage.

There are several challenges with this, safety, thermal runaway, and life cycle of the asset which has a limited amount of cycles.

Also the architecture of the system for the AC inverters and the DC side can come from very different places in the supply chain and aren’t as vertically integrated leaving you in a position where you can’t actually make this work without compromising something in the supply chain. That being said we are talking about a LOT of energy in these systems and to dissipate that much heat you’d need a load bank.

Couldn't the battery just do, as an example, 1 minute long charge then discharge cycles?

For example, if the electricity price is -28€/MWh (like today in Germany), and your battery efficacy is 80%, you could get paid 28€/MWh charging, then only pay back 22€ discharging, generating a 6€/MWh profit.

The wholesale energy markets don't have sub 5-minute granularity anywhere that I'm aware of. In the US, 1-hour is standard in the day-ahead markets and 5-minutes is standard for the spot markets.

There is also the problem that your battery would likely degrade fast depending on the technology.

The solution is actually what's called a "dummy load". Get paid to waste energy and heat up the planet a tiny bit more, gotta love it.

Can’t we power a big laser and point it at space or something instead? Anyone got a dumber idea?

There are so many things that are energy intensive and not really economically viable: co2 capture, crypto mining, "green" hydrogen, we could see a world soon where a large scale BESS would have an on-site dummy load that does something useful with that electricity

The problem with all those things is that they are ridiculously capital intensive to set up, and then they sit idle 80% of the time Worse, the whole point of negative electricity prices is that they're an inefficiency in the market which ideally will eventually be optimized away. Then what do you do with your billion-dollar plant that can only run with negative prices that no longer exist?

You're assuming the way they get optimized away isn't by these sorts of plants.

I guess the problem with building a pure energy waster is that it could only operate every now and then, and it's not guaranteed to see negative prices in a few years from now. So, might not be all that profitable.

Use the electricity to heat up a lump of iron to a very high temperature, than use electromagnets to fling it into space?

If you heat up iron to very high temperature (>770°C), it's much harder to fling it using electromagnets.

Ah that's annoying. Fine, we use the electricity to heat...uh...molten salt encased in stone, and to pull back a very big heat-proof slingshot, and after a threshold it lets go and launches it into space.

Obviously the complaint is about the changing atmospheric absorption properties as a side effect of the generation side, not the heat from using the power.

Either way I think people are overthinking it though.

Isn't this the basic description of what a gravity battery should provide?

No, because his situation is basically that the gravity battery is already sitting at its max height.

He's just trying to burn energy because a negative rate means he's getting paid to use it.

So sure - it's great to give that energy a functional use first (ex - charge his batteries) but eventually he runs out of functional ways to use the energy but could still be making money by using it.

Enter the desire for a dummy load.

Pumped hydro could do that if they had a way to bypass (either physically or electrically) their turbines on the downhill portion of the loop. Just pump water up and back down without extracting the energy. Then you have a dummy load that isn't just a power sink and is already designed to handle the relatively rapid switches on and off.

Yeah, but dummy loads are cheap. Probably cheaper than changing any designs in other places.

It's straight forward to add a giant resistive load that just converts electricity back to heat.

I can get 10kw heaters for just a couple hundred bucks or 1.5kw heaters for literally $20 usd. And that also switches on/off easily.

For hydro... just boiling water with a heater is going to be pretty much unbeatable if we're playing the "waste energy" game. No need to approximate it slowly with your pump motor and risk other infrastructure.

The idea was to have dual use so that they're not obsoleted when we get around to installing sufficient power storage for renewables and also a less heat intensive way to do it too.

The power is coming from energy that's otherwise going to heat the planet regardless (solar rays).

If you really wanted to be clever, your best bet would probably be to turn it into a laser beam and send it back to space. Would mimic that energy getting reflected instead of absorbed, albeit through a pretty inefficient and convoluted process.

Might make more sense to run carbon capture devices at that point, but again - in either of these cases we're back into the "it's getting pretty expensive to waste this energy" spot.

Giant resistors cooled with fans are cheaper and easier to maintain than pipes and pumps.

That is what (diesel powered) locomotives do to get rid of electrical power created by using the wheel motors for braking.

New designs store the power in batteries, but most locomotives used in the US still have a compartment filled with fans and resistors instead.

Yes of course. My idea was a way for existing facilities to also function in this capacity so you didn't wind up with facilities reliant only on negative prices. I think that's important because those prices are a bandaid on the real problem that would be solved by sufficient power storage.

You can build this at a small scale pretty cheaply but the connection to sink meaningful amounts of power would quickly become a significant part of the expense.

>"dummy load"

You mean crypto miner.

Surprisingly, not always.

If I buy a device for $100 that, given free electricity, will mine $500 of cryptocurrency in its useful life - I can easily lose money if I run it less than 20% of the time.

And I doubt electricity is negative priced >20% of the time.

Yeah, there are a ton of plans in this thread for what to do with excess energy. The problem is, that’s the wrong question. The goal is to answer the question “what should we do with excess energy where we don’t mind building the capacity, but then only rarely running it.”

Rather than coming up with some grand scheme, maybe it would be good if our dishwashers and washing machines could listen to the grid and activate when power cost was negative. (We may need to coordinate a bit though, so we don’t all activate at once).

I have an electricity contract with dynamic pricing that changes every hour based on the day-ahead electricity market for Belgium. I know what the prices for the next day will be around 13h10. I charge the car whenever the prices are lowest: around noon in the sunny months, at night during winter, preferably weekends. I save around 25% of my electricity bill like this. (More in summer, less in winter.)

So it's already possible to incentivize people correctly with price signals, at least in some regions of the world. But people are not yet familiar with this. I guess that will change as the pricing between dynamic and traditional contracts keeps diverging. With a traditional contract, you are essentially paying the average evening peak price all the time. With a dynamic contract, you get access to the cheaper and even negative rates.

In some areas negative prices account for up to 25% of hours so it's a decent number but still a rough number of spins up and down and a lowish duty cycle. A solution might be to build battery capacity along side these loads to effectively buffer the negative cost power to be able to run continuously. That would skyrocket the initial capital investment though.

Yeah, batteries are just the sort of expensive/straightforward solution.

If you think of it, a dryer is sort of a combination of a flywheel and a heating element, so it should be the over-provisioner’s best friend. IMO a real failure has been not taking advantage of our appliances.

The issue there is connectivity and most residential customers don't pay spot prices so you need to upgrade their meters as well or build metering into the appliance so they can get credit for the energy they burn off. Plus you're looking at putting a lot of extra cycles on equipment not built as well as it used to be so you're burning the useful life of a hard to repair device and probably not getting paid enough to cover that, plus they more and more designed to burn as little energy as possible.

I know there are some places where this happens though but it's more along the lines of the devices delaying their start until energy is cheap rather than being used as loads to shed excess capacity afaik.

> I know there are some places where this happens though but it's more along the lines of the devices delaying their start until energy is cheap rather than being used as loads to shed excess capacity afaik.

This is what I meant, sorry for the ambiguity. Load the washer up and kick it off whenever energy is cheap. I don’t care when it happens other than, like, that it happens once a day, so why not defer this to the power company, right?

Like I said support isn't really there for a lot of electric customers. I pay a single flat rate for electricity so there's no point in time shifting consumption.

Also there are downsides to having clothes just sit there for hours potentially before you dry them. They can get pretty dank from the moisture and for dryers some clothes need to be removed immediately when the cycle finishes.

Not all crypto mining requires dedicated hardware. I'm sure plenty of datacenters would jump. I know at least one instance where certain internal use autoscaling groups increase in size with lowering electricity prices (AI training, batch Hadoop jobs, and the like) to reap the benefits. With negative prices it'd just be bounded by the total capacity.

Presumably the negatively priced energy came from solar panels, so those sun rays were going to heat the planet anyway. The same still happens with a dummy load, just with extra steps in between to convert to and from electricity.

With enough solar panels deployed, you could still argue that they change the albedo of the Earth and therefore it's temperature.

Related, do Solar PV panels need any extra equipment to curtail instead of feeding into the grid?

Aside from software integration to remotely control household PV systems, is there anything else needed to curtail during negative price events?

If the inverter is smart enough, nothing else would be necessary

Thanks! Google managed to find more details on Reddit when I searched now

https://www.reddit.com/r/energy/comments/1iu2kkz/solar_curta...

Not necessarily. There's also reflection involved.

Now to figure out how much exactly you need to take into account the solar panel absorption spectrum & the albedo of the earth.

Could we use it for some kind of carbon capture process?

I think it's pretty clear with the constantly increasing durations of negative prices, so far we haven't found a way to do so profitably. Carbon capture or anything else for that matter.

Anything that would really love free energy also cost a lot to build and maintain/operate besides electricity. So much that a few hundred hours of free (or even better than free) energy a year is far from enough when you need >90% uptime to make sense. Maybe it makes you go from 95 to 85%, but still clearly it's far more than there are sunshine hours.

It's basically the idea behind things like hydrogen electroysis with excess energy.

The problem is that things that can use bulk energy productively like electrolysers, hydrocarbon crackers, smelters, AI training farms, etc. are very expensive and having them on warm standby but idle most of the time waiting for good grid weather makes for bad returns on the capital expenditure and operational costs.

I know this is grossly pedantic, but not matter what that electricity is used for, it will end up "heating up the planet a bit more". Energy is a waterfall whose base is heat.

Fossil fuels contain energy that are not in the form of heat, so electricity from fossil fuels would heat the planet even ignoring greenhouse effect. If from renewables, however, the energy has been previously extracted from the environment, thus being neutral in terms of heating the planet.

Not that it matters, because the effect would be miniscule in any case.

I did some napkin math and the amount of energy used from burning buried coal and oil since the industrial revolution began would warm the atmosphere about 3 degrees C. The assumption that all of the energy would be dumped into the atmosphere and stay there is obviously deeply flawed, but the overall effect might not be miniscule.

Technically if you power a laser shooting into space with solar panels you are cooling the planet, but you are ofcourse right in practice and on the scale of the universe!

That sounds like a good way to waste tons of energy during negative electricity prices to me! Shoot it into space.

Good luck trying to get rid of such an amount of heat anyway near your batteries.

Well in times of negative energy prices wouldn't it even be good if the air conditioning ran at full capacity?

Depending on how powerful your air conditioner is, it would rapidly start cooling down the building to a temperature which is too low to still be comfortable. You could maybe buffer this with more thermal mass, but then you are back in the game of storing energy and might as well just get extra batteries.

Why not place the air conditioner next to a large electric space heater?

Many heat pumps already have a mechanism for deliberately wasting energy for defrosting the coils. I bet that the same hardware with a different control algorithm could be convinced to heat out the outdoors without much net change in indoor temperature. (The solution involving the smallest amount of extra hardware is to run the system in reverse periodically. There are other solutions.)

Whether the negative energy price is enough to balance wear on the system and potential noise is a different question.

Yes, it's not much of an issue if you have free energy.

It only makes sense if you have ‘more than free’ energy you need to get rid of, because not getting rid of it causes problems. Similar to flaring natural gas, but for actual electricity.

This is not a common occurrence or situation, or shouldn’t be anyway, or someone is screwing up pretty badly somewhere.

With variable sources of electricity it can be cheaper to have capacity at a level that you sometimes overproduce than to have a capacity that produces at a lower level, and so mostly needs a backup source of power.

It’s actually quite common. You have base load generation stations and your highly variable solar and wind. There are often times when the power at a wholesale rate dips below zero. It’s too costly to turn off your base load plants and maybe both solar and wind are generating above normal.

Solar inverters can just not draw the solar current, and wind can generally just change the pitch on their rotors at the individual level. The only ones that generally can not help ‘over produce’ are baseload power stations as they have actual physical inertia in very large turbines and can’t respond as quickly to demand.

Baseload power stations sometimes over-produce on longer timescales than just a few seconds because they'd rather not turn them off for maintenance/operational reasons. E.g. imagine you have a big biomass boiler feeding a steam turbine. Turning it off for an hour or two means everything cools down, which is a thermal stress, reducing lifetime compared to keeping it at constant power.

But yes, certainly poorly managed solar/wind that doesn't have good mechanisms to turn off in response to lack of demand is mainly the issue. In the future, when control systems are better, I'm sure negative pricing will be much less common.

Right but keep in mind these events are generally short lived and depending on the market there may be reliability guarantees that keep these open or specific federal funding rates.

But like I said before when rates go negative you will typically see it in occurrences where you have abnormal conditions (wind and solar generating at the same time) or aggressive night winds. And it does not happen long enough to need to curtail generation.

Electricity prices around here (Austria) are negative around noon on most summer days. They pay you to waste all that solar energy people are feeding into the grid.

Is it really screwing up? If solar panels are cheaper than batteries, then you can over-provision the solar panels and then you won’t need to use the batteries as much, so you can probably get away with smaller installations.

My gut would expect it to approach $0 if full communication were possible, based on the instinct that most people would run their dishwashers if the energy cost was $0.

Solar panels don’t produce excess power that needs to be dissipated - just don’t invert the unneeded current, and that’s it.

‘Overproduction’ in this sense is from something like a spinning generator which starts to overspin, or an inverter which oddly starts to overvolt the output for some inexplicable reason.

That only works if the grid operator has control over the inverters, which they often don't have.

We currently have the situation where operators of solar farms of all sizes get a fixed amount of money for each joule they feed into the grid. Of course those people have zero interest in turning down their inverters when the sun is shining and there's already a surplus in the grid.

That isn’t actually structurally true - the way inverters work is they do high frequency analysis of the output power, and then ‘push’ energy in at various parts of the waveform. That’s how DC->AC inversion works. We’re taking much higher frequency than the AC waveform for any non-terrible-quality inverter.

While they can be configured to overvolt the outputs or drive frequency higher than they should if they have the excess energy, that is certainly not a normal setup and seems pathological, frankly. Which I guess goes to your point regarding solar operators - if they have an incentive to keep pushing power into the grid even if the grid doesn’t need it, they certainly can configure their equipment to do that. But that is also a clearly screwed up situation for the grid eh? And of all the generation providers, they are the ones with the least excuse to actually do that.

It’s trickier with something with moving parts (like wind generation), where there may be some element of physical inertia or direct physical coupling to the output power. But inverters are not that.

And my understanding is that all modern wind turbines do automatic blade feathering and a significant degree of voltage/frequency regulation to avoid blowing things up ‘downstream’. So with any luck it would be a minutes at most, type situation.

Still, 90% of the problem is likely with wind farms or the baseload eh? Unless the solar operators are doing this intentionally to screw their competition.

Some years ago, I helped with battery load tests in a nuclear power station. The constant test load was just a big (~500kW) heater. We burned the battery energy for 5 hours. So it's easy possible to do such things.

Exactly this.

And the same thing for residential scale is literally just a ceramic space heater running at ~1500w.

They're dirt cheap, usually have temp safety checks built in, work on a residentially sized circuit, and are available everywhere.

I needed a cheap and consistent load to do LFP battery testing, and I could spend $5,000 for a real test unit, or $21 for a ceramic heater that will do basically the same thing.

If you've already got the monitoring for the batteries/inverters, a heater is a GREAT load choice.

HAAS CNC mills are famous for using electric stove elements for the spindle brake resistor: https://www.reddit.com/r/CNC/comments/1es1d01/someone_didnt_...

I'm not sure that this really is a completely off-the-shelf stove element. But obviously, the technology is basically identical to what you'd have on your stove.

It is cery common for Frequency Inverter for AC Motors to have a break resistor. It's expensive to push energy back to the grid with from an inverter. So in most case just a break resistor is used. Just if you break a lot and a long time it is worth to buy an inverter who can do it. If you have multiple axis in a machine, often they are coupled with DC, so the break energy is used by another drive.

Yup. On a much bigger scale it's common for the power supplies going to electric trains to do this too. They like to use regenerative braking because it's efficient. But the electricity grid can't always handle the extra power, so in some designs they have a backup mechanism to dissipate the power if needed; diesel-electrics usually just have a big bank of air-cooled load resistors on the roof.

A neat example of regenerative braking being important is the London Underground: they've had a persistent problem with high temperatures in the subway, of which a decent % is actually heat from trains braking. By using regenerative braking rather than putting that energy into the tunnels as heat, they can transport that energy outside the tunnels, keeping them cooler.

so you're installing a resistive heater? what is the economics of that?

500kw is nothing, that is 1/3000 of the nuclear power plant electric output.

Not sure if it's discussed in the paper but apparently in Australia there have already been recorded instances of batteries charging with negative price electricity and then selling back that electricity at a still negative but closer to zero price and so profiting.

When I first heard it, it seemed wild that they couldn't hold on for the price to go back above zero, but I guess if we're talking high frequency trading it makes more sense. They might have bought and sold many times while the price is different levels of negative before switching to charging up in preparation for the later price rises.

And the round trip inefficiency helps too.

That's not as ridiculous as it sounds!

As you know, negative electricity prices mean that someone is willing to pay you to dispose of electricity they need to generate for some reason. For example, a conventional steam-turbine-based electricity plant might prefer to just keep running for a brief period of time when demand is low, rather than subject their equipment to a power cycle, which increases their maintenance costs. There's other, dumber, examples based on stupid contracts and badly designed solar... but this example is a reasonable one that exists for good engineering reasons.

The battery provider in this circumstance is profiting from their ability to accept power when demand to dispose of electricity is particularly high. When that need goes down, they can reasonably profit by dumping that energy on someone else who is also able to dispose of the electricity. But at a lower cost. E.g. imagine an big industrial refrigerated storage facility that can consume some excess energy by supercooling their refrigerators. But they can't consume unlimited excess energy, because at some point their warehouse just gets too cold, and they don't have unlimited refrigeration capacity anyway.

So in this simplified example, the battery storage service is getting paid a lot of money to quickly absorb a lot of energy, which they then dump more slowly to the refrigerated warehouse (and similar providers) as the surplus diminishes, in anticipation of another surplus in the near future.

If it was so profitable, why wouldn't the electricity utility do it themselves? Certainly, they have the scale, infrastructure, and pricing power to do it.

Oh, that's right. This is supposed to be wealth transfer.

Your electric utility could be doing this if they were more forward thinking and installed grid scale batteries, but that's not their business model so they don't do it.

Well, if other people are allowed to install batteries, then it might be fine that the utility isn't doing that. They don't need to do everything themselves.

Even if the arbitrage exists, it does not mean you are equipped to profit from it. Furthermore, the rapid installation of battery capacity means that the profit margin for this activity is likely to dwindle as more entrants try and do the same thing.

I’m just guessing but it probably isn’t so profitable. More like a “you already have the batteries, so why not?” type thing.

Someone at the generation facility ran the numbers and found that the grid was able to dispose of excess energy for peanuts but installing and maintaining a dedicated electronic load cost more than peanuts.

I'd recommend digging elsewhere for conspiracy bait. This is a mild curiosity at best.

This is why we don’t move data center load to the coldest available data center to reduce the AC power fraction of the cost. The cost of electricity is a significant fraction of the overall cost but not high enough to make up for stranded assets. Computers not running during their best years is expensive.

But I’m not sure that’s entirely correct, and maybe it’s time to revisit this.

Any system that is selling responsiveness as part of their service has to keep a certain amount of equipment sitting idle. That’s just how queuing theory works. So while you cannot move all server load to the coldest available zone, we should still be able to run that center near capacity and use the hottest one for all reserve capacity.

Power plants also have to deal with fines for exceeding emissions limits, but I suspect the problem here is that Bayesian analysis tells them that if a plant has to kick on early for some reason (early school release day, or another plant exceeded a maintenance window), it will still be needed for sure an hour from now, so it’s better to leave it running for 45 minutes doing nothing than to cycle it.

> This is a mild curiosity at best.

Exactly. There are genuine economic/engineering reasons for negative prices to occasionally exist. But in a well-designed, well-run, grid price will be negative only a small minority of the time. It just doesn't make sense to install a bunch of expensive equipment to provide this service when sufficient capacity exists from "happy accidents" like spare battery storage.

In the long run, better managed solar and wind should make negative prices a fairly rare event.

Once you sign up customers for 'cheaper electricity, but you have to agree to the occasional loadshedding', you can probably also sign them up for a bit of 'oh, and please burn some more electricity, when we tell you to'.

The former is already happening and useful, the latter would be a relatively simple and easy add-on that could be used to offer ever so slightly cheaper electricity.

My washing machine has a timer. I do the wash when local electricity rates are near zero.

Yes, and you could imagine telling your utility: just kick off the laundry anytime in this time interval, in return for cheaper electricity.

One reason, that I understand has applied in Germany, is when taxes are applied both to the electricity the storage firm buys and to that which it sells. This puts a damper on the whole thing unrelated to any actual technical or economic realities.

What do you mean by electricity utility? Which organisation specifically? The electrical supply is usually formed of multiple organisations with different responsibilities, which usually works pretty well, but it generally means that e.g. storage, transmission, and generation are not one single organisation.

Yes, including because firms at one level of the supply chain (eg, transmission) are in many countries precluded from operating in another level (eg, generation).

If you find a hundred dollars on the ground you don't pick it up because in an efficient market somebody else would have already picked it up, hence it can't be real?

> That's not as ridiculous as it sounds!

I'm not sure: why doesn't someone 'just' put up a few resistive heaters and fans to benefit from negative prices?

Because it doesn't happen often enough to be worthwhile, you're better off just building a battery and being able to make profit every day.

If one is incentivized (eg, paid) to burn power, then sure: One can burn power and reap the incentive. It can happen in any market. The producer has so much abundance of a thing, for whatever reason they do, that they're willing to pay others to get rid of it for them.

It can even happen productively: "Hey, they're paying us to run the heat! Turn the glass kiln on so we can get a head start on tomorrow."

Or "Hey, they're paying us to charge our batteries! Let's charge them!"

It can also be "Hey, they're paying us to run resistive heaters! Turn on the artificial sun!"

Whatever it is: If the demand satisfies the supply, then the supplier is satiated. And then the price can go back to something more-profitable for that supplier.

> It can also be "Hey, they're paying us to run resistive heaters! Turn on the artificial sun!"

It may be difficult to dump all the heat at scale. You probably need a huge cooler with fans to get active air flow. Or a water tower (that requires water) (There are regulation about extracting water from a river and returning it too hot).

Is it possible to build one of this heat dumping facilities in a zone where there is permanent snow? (Ignoring environmental and moral concerns.)

PS: Seriously, heating a swimming pool may be a nice application.

> It may be difficult to dump all the heat at scale. You probably need a huge cooler with fans to get active air flow. Or a water tower (that requires water) (There are regulation about extracting water from a river and returning it too hot).

You could probably just boil off your water, instead of returning any?

It would be funny, to use the steam to generate electricity.

> You could probably just boil off your water, instead of returning any?

You get a lot of salt residue that you have to dispose. The usual nuclear plant tower [1] evaporates most of the water to dump heat, but returns a small part of it to avoid collecting salt. But it has to be not to hot nor too salty to avoid killing the fishes.

[1] https://www.google.com/search?q=nuclear+power+plant+cooling+... [How to I link to the images pages?!?! Google changed the format of the URL and I can't find the correct &something=xyz to make a short link to the images :( .]

Yeah, they did butcher the Image Search URLs pretty terribly.

Ye olde format still works: https://www.google.com/search?tbm=isch&q=nuclear+power+plant...

...and that ultimately lands at https://www.google.com/search?q=nuclear+power+plant+cooling+... which also works.

It definitely is sometimes difficult to dump power at scale. That's the source of the surplus and resulting negative price.

But it doesn't have to be big. A negative price is still a negative price, even on a small scale.

So, for instance: At home, I have electric hot water. I have some baseboard heaters in parts of the house (that I never actually use, but which I could use). I have central aircon.

All of these things could stand to be automated just for automation's sake, and that's something I'll probably do some day even with the fixed-rate electricity I buy right now.

With automation and price feeds, it's a programmatic no-brainer to switch on the electric baseboards on during the heating season during negative price events and get paid some non-zero amount to get ahead on the temperature game.

During the cooling season, I can probably stand to get paid to supercool the house for awhile.

And during any season: I normally run my electric water heater at a fairly low temperature because that's more efficient, but I'll cheerfully accept money to temporarily raise its temperature.

Or if I had an EV: Maybe I might normally like to keep it at 70% SoC for battery health, but if it's plugged in and the price is negative then I might cheerfully run it up to 85 or 90% or more.

So anyway, it's hypothetically pretty easy for an individual like me to dump a few kiloWatts in a useful way.

A thousand such people make it easy to dump a few megaWatts.

A million such people make it easy to dump a few gigaWatts. (And a million sounds like a lot, until one counts the eventuality of smartly-connected EVs.)

Freight trains have very powerful versions of those onboard. You'd just have to repurpose them. It's called "dynamic braking".

https://en.m.wikipedia.org/wiki/Dynamic_braking

Some electric cars have that as well.

Btw, many passenger trains have something like that as well, especially in the metro or tube: the stations are deliberately built slightly higher than the normal lines, so that you can convert kinetic and potential energy back and forth.

People do - but the actual answer to your question is as you’re implying: it’s not as simple as “you get paid to consume”.

There are negative spot prices in Europe all the time - but they are not usually negative enough to make up for the grid fees and taxes. Or they are in countries like Germany that hasn’t rolled out smart meters, so consumers have no way to access spot prices

Oxygen capture and liquid nitrogen seems like a great use of negative prices.

> and then selling back that electricity at a still negative but closer to zero price and so profiting.

How is it not better to discharge the batteries instead? I guess if you don't have that hardware option integrated into the platform maybe, but otherwise...

I know a country, the national train company turns lots of outside lights on (daytime), if the price is negative.

Great for the local insect population.

Yes that is the SBB in Switzerland but they do not turn the lights, instead they turn on the heaters for the track switches. Not sure if that is all rumours.

> Surely the power electronics or even just the control algorithms in a BESS could be slightly modified to consume power, get warm, and not transfer any current to or from the battery cells, effectively taking advantage of the BESS’s heat sink to sink excess power and sell that service.

Unless you specifically design for it (specifically, with a dummy load), the efficiency of the system is inversely proportional to its ability to do this. You need a secondary system.

The power system can connect the battery terminal to in or to out, so if you switch both on at once you effectively bypass the battery. It's called shoot-through current and is generally considered a destructive process. If you can switch on and off fast enough you could limit it to a non-destructive level, but in practice most systems will not switch fast enough. They are designed to operate with the battery load, which is at minimum ~10x higher resistance than the transistor itself. In practice it is often 100s of times higher.

That's where the efficiency comes into it. If a power system is 98% efficient (pretty normal- this does not include power lost to heat in the battery itself), that means the electronics can only burn 1/50th as much power as normally passes through the system. Worse, when you put the switch into shorted position it will try to pass 50x its rated current. You need to switch much faster -certainly more than 50x faster- and that will probably put it outside its operating region.

It is relatively easy to just have a large resistor, but it is not very well suited to use battery power systems. Batteries are very low impedance, and the power system exists to transform to a lower voltage and higher current. Resistors are cheaper when they are higher voltage, so the power system is a hacky kludge.

The overall solution is just more batteries. Oversupply is a transient problem and always will be.

> Unless you specifically design for it (specifically, with a dummy load), the efficiency of the system is inversely proportional to its ability to do this. You need a secondary system.

Many multicell BMS already have this kind of "power shedding" capability. They use it for cell balancing - to equalize voltage between cells with slightly different characteristics. This is desirable despite the power waste, because it reduces wear, increases charging efficiency and allows battery packs to last longer.

Some battery packs are also designed to be able to dump enough power into heat to be able to keep the batteries warm during extreme cold.

The amount of power you can dump for balancing is just a fraction of the charge/discharge power (because it only needs to offset differences in self-discharge rate). So you still need a proper dummy load when you want to dump more.

Similarly, the heatsinking capacity of the battery is designed for charging/discharging losses (say 5% of charge/discharge power).

Our house have geothermal heating (heatpump conncted to 160m drilled hole, pretty common in Scandinavia). The heatpump supports having a coolant loop for cooling the house in the summer. Thus the heat pump pretty much exchanges heat from the house to the well (heating it up ever so slightly). It would certainly be possible to insert a resistive dummy load on that loop and just store that heat in the bedrock as well.

This! Or, if you don't have geothermal heating but have an electric water heater, maybe temporarily increase the temperature it goes to: maybe it's normally set to go to 65C, then when you detect that you have negative prices and your batteries are full and your water already hot, maybe heat the water to 70C and store that little bit of extra energy as heat! If you have thermostatic valves in your bathrooms, you won't even notice the difference except by the fact that your water heater now can apparently hold a little bit more water than usual :)

Assuming regular negatives (more than once a day) you could also tie the heating to the grid prices with maybe an hour buffer around your high water usage times to make sure you are up to temp.

Modern water heaters will keep temp for a shockingly long period of time.

I have a heat pump for hot water and calculated this with an offered floating energy tariff. It is not economical because the high net tariffs are not floating but fixed per kwH and negative / very low prices are seldom here and only for a short period of time available.

If you have free energy the obvious thing to use it for is carbon capture.

The big problem there is you have these intensely capital expensive capture plants sitting idle around 75% of the time. Also the processes may not gracefully start and stop though maybe you could smooth that out by building a huge battery bank along with the CC plant to effectively run a full duty cycle with 'free' energy. That bumps the capital costs up again though so the economics get tricky.

Yeah. Anything that's designed to use nearly-free or negative-priced energy from the grid needs to be cheap to build and easy to start and stop (The former being one of the main issues with the 'bitcoin mining as grid management' idea).

In theory if you run it using negative priced energy you could maybe run with older less efficient hardware that's not viable for current mining that would be much cheaper, if you can source it. I'm thinking older ASICs for BTC for example where the best in class kHash/W has moved on and the price doesn't support running the older devices but the negative price would offset that by giving a reliable return on time to offset the extra energy burned.

It'd take a far amount of math to figure out if that tips it over though I don't feel like tackling haha.

I wonder if desalination would be another good use. But, yeah, it is probably just a matter of how fast the processes can absorb extra power.

District heating and cooling would be an excellent sink for the power.

Water needs a lot of energy to cool or heat, concentrated at a district, you could easily absorb a lot of energy at negative prices.

Electric heating elements aren't free nor infinite in capacity. You'd pay a lot of money for a rarely used asset that has to be replaced by something else most of the time because people want their heating to be reliable.

But it is not horrible. A lot of people have resistive water heating for their solar setup because grid sell prices are super low and a 2kw water heater cost basically nothing.

Which they use all the time. If you did this at a district heating level, you'd just be running an electric district heating system, resistively, which you run all the time - it wouldn't be a dump load, it would just be the load and a very inefficient one at that (compared to a heat pump).

The point is all this stuff costs money to build, money to maintain, so if you don't use it most of the time the time you do needs to be incredibly valuable.

A 10kw heating element costs 250 euros, lets double that to make it able to switch off by the smart meter. Now if you used it 1% of the year and saved 5ct per kWh you would gain 43 eur a year. Not a super convincing ROI but compared to your 10kw peak solar array a very small investment. If you used it just 2% of the year it would already be pretty good and the switch might become very cheap in the future if most houses use load steering for all kinds of things

> Electric heating elements aren't free nor infinite in capacity.

They are about as close to an ideal load as one could imagine.

And capacity is easily expanded with a water tower. You can scale the total thermal energy stored and the efficiency of that storage by simply building a very large water tower. You don't even need special insulation because the water insulates itself.

> You'd pay a lot of money for a rarely used asset

Assuming you've converted over to district heating and cooling, it'd be frequently used as climate control for surrounding buildings.

> that has to be replaced by something else most of the time

What? No. District heating is the most efficient way to provide climate control, bar none. The only thing that needs to happen is setting minimum and maximum temps. Maintain the minimum temp and when negative power price events hit heat to the maximum or cool to the minimum.

And if you want to get super clever, part of your storage can be sand which can store huge amounts of energy.

> because people want their heating to be reliable.

District heating/cooling is as reliable as plumbing. That's because that's effectively all that it is. It's super reliable. If the incoming water is 60C or 90C, it doesn't make too much of a difference in terms of heating a home.

It's a proven tech. Many universities use it because it significantly reduces the heating and cooling cost for their buildings. My own city uses district heating in the downtown to great effect.

The problem is desalination plants cost billions. You're not going to make money building one then running it the 1% of the time the price of electricity is negative.

The real low hanging fruit is energy use you were going to do earlier/later anyway but where timing isn't important.

Heating water, cooling water, pumping water, charging batteries, running power hungry machines.

It's half century old tech and usually the only thing missing is a financial incentive to do so.

Wouldn't that discharge the battery and hence contribute to battery wear, by wasting a charge cycle?

Balancing.. thats probably 1-0.5% of the BESS capacity. The impedance of LFE cells are so high when charged pretty small amounts of energy can slosh around before a protection disconnect, over voltage for example

I don't know why it rankles me to think that generated power should be fed into a dump load just to make the storage owners extra money. Even though it's inefficient at the system level, it shouldn't be harmful releasing energy that would have been eventually dissipated as heat anyways. And yet it still just feel wasteful to me.

I had to go search my bookshelf for this one:

  "There has been an increasing awareness among engineers of the last two decades that machines can perform a useful purpose in many applications, even though their characteristics do not conform to the orthodox standards of goodness.  The main objective of the engineer is to make money -- to exploit economically the physical properties of materials.  Economic considerations, however, do not stop at the first cost of an article, nor at the running cost, but extend to everything connected with that article in the situation in which it is to be used."

Eric R. Laithwaite, Induction Machines for special purposes

>I don't know why it rankles me to think that generated power should be fed into a dump load just to make the storage owners extra money. Even though it's inefficient at the system level, it shouldn't be harmful releasing energy that would have been eventually dissipated as heat anyways. And yet it still just feel wasteful to me.

This is one of those efficient market things where you need to manage the market in order that wasteful things happen sometimes... but that waste is an opportunity.

If you and your competitor are both in the business of dumping energy into heat, you're going to compete with each other for access to that money.

Then one of you is going to try to find a way to make _more_ money with that energy and find something quickly scalable with not-too-high idle overhead costs to do with that energy besides just flowing through a resistor.

Negative prices are a sign of an inefficient market or just the lag time between a changing landscape of resources and someone to utilize them.

If there's a free resource someone's going to figure out how to use it, just let it hang out for a while and the problem fixes itself.

Especially with solar energy, this is just going to be a thing. There's a certain balance where overprovisioning is cheaper than storage and so you just do that. Then you wait for industry (or consumers) to figure out how to take advantage of the intermittent cheap energy.

> Then one of you is going to try to find a way to make _more_ money with that energy and find something quickly scalable with not-too-high idle overhead costs to do with that energy besides just flowing through a resistor.

Yes, exactly.

Which reminds me of the occasional story about how one native group or another was so in tune with nature, because they used every part of the (insert important animal here).

Modern economies obviously use all parts of the animal, for exactly the reason you outline.

> Especially with solar energy, this is just going to be a thing. There's a certain balance where overprovisioning is cheaper than storage and so you just do that. Then you wait for industry (or consumers) to figure out how to take advantage of the intermittent cheap energy.

Yes, though you also need to make sure that regulations don't get in the way. Or at least not too badly.

One example I can think of is forcing utilities to charge people by net-metering, forcing the utility to implicitly pay the same price for electricity as they charge. We don't do that for eg used car salesmen.

>One example I can think of is forcing utilities to charge people by net-metering, forcing the utility to implicitly pay the same price for electricity as they charge. We don't do that for eg used car salesmen.

A large proportion of the cost of consumer electricity is distribution built in to the per kWh cost. Their buy price needs to be lower than their sell price. I think most people would be surprised by how much of the cost of their electricity is incurred between the power plant and their home.

My shallow understanding is that utilities and grid operators need to manage the supply/load ratio carefully to keep the grid's operating frequency in a very narrow band, centered around 50 or 60 Hertz. If supply outstrips demand, and assuming supply can't react [quickly enough], the operating frequency starts to rise as all the rotating masses connected to the grid gain momentum from the additional power. If the operating frequency increases too much outside of design parameters that could end badly.

So one solution is to incite demand (with negative rates) for folks to ramp up their use of electricity (into e.g., a dump load resistor bank), bringing demand back in line with supply, and bringing the operating frequency back under control.

I hate the waste, agreed. But it would be irresponsible of the operator to bank that extra supply energy into the momentum of spinning things owned by the consumers just so they could pull it out later by intentionally under-supplying. E.g., an aquarium's big water pumps designed to spin only so fast or produce so much pressure might not like being operated at 110% the rated speed at random times of the day.

related links:

https://fnetpublic.utk.edu/frequencygauge.html (you can watch the grid frequency fluctuate in real-time, here!)

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

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

The grid connected thermostats, where the energy provider has (some amount of) control over when you heat/cool your house are pretty unpopular (I know people who have had their AC turned off during heat waves and were not very pleased). But this seems like an application of that that people would like? And most people would probably even be happy with just dramatically reduced/free heating/cooling and not actually needing to get paid. And of course it has the added benefit of actually using the energy in a useful manner, rather than just wasting it.

I suspect you can make these things work, but it's not 'free': organising a bunch of retail customers and dealing with them takes a lot of effort.

> (I know people who have had their AC turned off during heat waves and were not very pleased)

I suspect they probably agreed to pretty harsh control in the name of cheaper electricity, but actually were only willing to tolerate relatively small amounts of loadshedding. I wonder whether better contracts can help align expectations here in the future. Eg allow the electricity company to set your aircon's thermostat up to 3K warmer (or something like that), but not turn it off completely?

Find area near shore, stick two big electrodes in water a mile apart, energize circuit when price is negative, profit!

I am in the power generation industry and I have honestly wondered why nobody does this. I figure getting the interconnect big enough to make meaningful money is both prohibitively expensive and a lengthy delay.

Or put them closer together and generate all of the chlorine gas, H2, and O2 a girl could want!

there are no circumstances under which it makes sense for energy prices to actually be negative. it is a sign of a market behaving very badly. propping up prices by intentionally wasting energy only treats the symptom not the cause.

It’s only ever brief and essentially a penalty to power generators for not turning off the generation in a reasonable time

In most markets, it happens because one player is being given some subsidy - ie. 'we will guarantee all power you sell sells for $X/MWh', or 'You get a contractual green bonus of $$$ if you produce XMWh this year'.

Those contracts mean the person producing the power is still incentivised to do it even with negative prices.

exactly. all i'm saying is that if you have this problem it makes way more sense to pay the offending party to stop producing excess power (or fine them for not stopping) than it does to pay someone else to intentionally waste it.

Supercapacitors ready to soak up power to charge batteries whenever rates stabilize.

Supercapacitors are much more expensive then batteries with much shorter lifespans to boot (years, versus decades).

I think they just don't understand how such a market would work. You'd trade futures on the power and if you hold the contracts to maturity you'd be on the hook for delivering/accepting the power. Everything before maturity happens on paper.