this post was submitted on 02 Oct 2024
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From a grid stability point, you can't produce more than is used, else you get higher frequencies and/or voltages until the automatics shut down. It's already a somewhat frequent occurence in germany for the grid operator to shut down big solar plants during peak hours because they produce way more power than they can dump (because of low demand or the infrastructure limiting transfer to somewhere else)
Negative prices are the grid operator encouraging more demand so it can balance out the increased production.
Spot on! I hoped this comment would be higher! The main problem isn't corps not making money, but grid stability due to unreliability of renewables.
To be fair, the original tweet is kinda shit to begin with. They've unnecessarily assigned monetary value to a purely engineering (physics?) problem.
The original commenter's (OC's) point has nothing to do with renewables' reliability.
It is entirely to do with generation vs demand. Grid operators could ask other generators like coal, nuclear, hydro, etc. plants to curtail so inverter-based renewables can export power, but that's not likely because those producers can't ramp generation up and down as easily.
Grid stability is a problem when you have overcrowding of generation without enough demand on given feeders. This is moreso an issue with the utilities anyways and how they plan their transmission and substation upgrades.
The issue is those coal, nuclear, hydro plants are what produce power when the sun isn't out. If you consistently shut them down for solar, they will go out of business and there will be no way to provide electricity when solar doesn't.
Well I wasn't expecting to find THE right answer in the comments already. Kudos!
And to everyone reading through this post: If you have questions, need more explanations or want to learn more about the options that we have to "stabilize" a renewable energy system and make it long term viable, just ask!
What options do we have to stabilize a renewable energy system and make it long term viable?
Piggybacking on your grid stability point, another issue I don’t see getting addressed here is ramp rate.
If we install enough solar where 100% of our daytime load is served by solar, that’s great. But what about when the solar starts to drop off later in the day?
A/Cs are still running while the sun is setting, the outside air is still hot. People are also getting home from work, and turning on their A/Cs to cool off the house, flipping on their lights, turning on the oven, etc.
Most grids have their peak power usage after solar has completely dropped off.
The issue then becomes: how can we serve that load? And you could say “just turn on some gas-fired units, at least most of the day was 100% renewable.”
But some gas units take literal hours to turn on. And if you’re 100% renewable during the day, you can’t have those gas units already online.
Grid operators have to leave their gas units online, running as low as they can, while the sun is out. So that when the peak hits, they can ramp up their grid to peak output, without any help from solar.
There are definitely some interesting solutions to this problem, energy storage, load shifting, and energy efficiency, but these are still in development.
People expect the lights to turn on when they flip the switch, and wouldn’t be very happy if that wasn’t the case. Grid operators are unable to provide that currently without dispatchable units.
One solution to what you're describing is to expand the grid. If your grid stretches half the planet, when the East starts to experience night, the West still experiences day and can ship electricity from renewables to the East to make up for their self curtailment. The same goes for wind where if one location on the planet doesn't experience wind, odds are another location does and the power can be shuffled around.
Another option is to build out more battery storage such that any clipped energy from solar or wind - that is, the energy that can be generated from your solar or wind resource but that can't be exported because it would overload your inverters or transformers or exceed your PPA agreement with your utility - is stored and can be exported for 2-4 hours as the sun goes down or wind dies out.
Not a lot of renewables sites are colocated with battery storage, but more and more are.
Store the surprus of energy from the solar panels and use that as a buffer with batteries or gravity
Why not? Just time it and start it hours before, wind energy could help in that too
Gravity energy storage doesn’t scale well. I’ve replied to other comments with more detail on this.
There are more feasible energy storage technologies out there, but these are super cutting edge and are not ready for grid-level deployment yet.
The future of grid level energy storage is almost certainly not going to be gravity based. At least not on a large scale.
You can’t have 100% of load be renewable/solar and have gas units online on top of that. That’s over generation. You have to match the supply exactly with the demand. If you mismatch, you destabilize the grid. Undersupply causes blackouts, oversupply melts power lines.
If a unit takes 10 hours to start, solar hours are from 6am to 6pm, and peak load is at 7pm with 0% solar; when do you recommend we start this unit? At the minimum, we’d have to order it on at 7am. Units have to run at a minimum load, let’s say 100MW for this unit. So now you can’t 100% solar from 7am to 6pm, you have to leave 100MW of room for this base loaded unit.
This doesn’t even factor in regulatory requirements like flex, spinning reserve, and other balancing and reliability requirements. Grids are required to have emergency units available at an instant to prevent mass destabilization if parts of the grid fail.
10hours to start oof, i though it was less, maybe individual batteries in house, like we have with water?, that wouldn't be cheap for industry tho
To be fair 10 hours is either a pretty old or pretty massive unit. 2 hours might be a little more reflective of modern gas turbines. Especially combined cycles. But depending on how big the peak is, you need every available unit, both old and new.
Ultimately the issue is it’s very hard to meet that peak when all of your gas units have to go from 0 to 100% output. Much easier (and more reliable) to take them from 10% to 100%. Which is what grid operators do currently.
Yea an affordable battery in every home would be a slam dunk. This is kinda already happening with vehicle2grid (v2g) electric car protocols. But not everyone has an EV yet. And operators are still working out the kinks using this in the grid.
Plus the lithium batteries in cars have their own supply/recycling issues.
As someone with a technical background this is the stupidest problem with solar that I don’t get… just turn off the panels in groups until generation is closer to demand… how have engineers not figured that out. And if they have why does this still get written about.
Someone is an idiot. Maybe it’s me?
I'm in solar/BESS, and I mean more and more DER sites are making use of string inverters which break out arrays into greater chunks than with central inverters. With those, you have more granularity of control where you can drop entire blocks/strings at a time to fall to your curtailed export rate.
You might ask yourself though why DERs can't just ramp inverter outputs up or down to match curtailment automatically across a whole site. You can absolutely do that, but what happens is your solar or wind resource stays high on the DC or low frequency (LF) AC side, respectively, while power frequency AC is low on the other side of the inverters. This is referred to as DC:AC ratio in the biz, and the higher that ratio, the more losses your inverters experience and less efficient they are. This also puts a huge strain on your inverters and can lessen their operational lifetime.
But really, DERs tie into the grid at distribution level and so they don't fall under the regulations of FERC & NERC (at least in North America). This means that smaller producers don't have the same requirements for control as do utility-scale players, so the incentive to control these string inverters at that granular level isn't there. It's much easier to just trip the main breaker and wait until the utility gives you the go ahead to turn back on.
I suspect that at lot of producers may want to look into greater control capabilities in the future, but this also depends on inverter OEMs too allowing that control.
I’m adjacent to this problem, so I have a little context, but am not an expert at all.
To my knowledge, we don’t have granular control over panels. So we can shut off legs of a plant, but that’s a lot of power to be moving all at once.
Instead, prices are set to encourage commercial customers to intake more power incrementally. This has a smoother result on the grid, less chance of destabilizing.
A customer like a data center could wait to perform defragmentation or a backup or something until the price of power hits a cheap or negative number.
Thanks that’s helpful.
But right…?
Solar plants can be reduced to rationalize supply.
To my understanding. The bigger issue is you can’t as effectively do this with other non-renewables like coal/gas… so this not a solar problem but a problem of legacy power plants.
So stupid. The narrative as well.
Yea, more control over the panels will help with the overgeneration issue.
But there’s other issues like ramping supply to meet peak demand and general generation during non-solar hours that still have to be addressed.
Each have interesting proposals on how to solve them, but they haven’t been developed to the point that they’re ready to be put onto the grid at a large scale.
But the thing is, you CAN simply turn them off at the press of a button (or an automated script) so its really a complete non issue. As long as big solar installations control systems are accessible by the grid operators, it should be fine.
You can do more with them too actually. You can ramp down the AC power production incrementally to meet curtailment requirements, in theory. When you do that though you subject your inverters to greater strain/losses and less efficiency which shortens your lifetime.
If inverter-based producers in solar, wind, and/or BESS want their sites to last for 30-40 years so that ROI is achieved via operation, then it is in their interest to protect their equipment and operate as much as possible at rated conditions or de-energized conditions.
You might think that it would make sense to have more of a slider control between ON and OFF to save everyone, from producers to grids to consumers, but my guess from being in the industry is that grids don't really supply incentives for that kind of operation. If they did, maybe you'd see more variable control at utility- and community-scale levels.
If you’re spending billions to build a solar plant that has to turn off all the time during peak hours then you’re wasting your money. That seems like a fundamental issue to me, not a non-issue.
It's two sided.
Yes you waste money by not exporting the electricity-transformed version of your resource (wind, sun, chemical potential, etc.).
But on the flip side if you export lower across your whole site, this means more losses at the inverters which can shorten operational lifetimes and lead to quickened inverter failures and needs for replacement. Those maintenance costs eat into your profit as well.
As someone in the industry, I'd imagine that inverter-based producers really just react to the rate structures of whatever grid and utility they hook up to. If the incentives of that utility favor one mode of operation during supply-demand mismatches - such as complete site curtailment - then that is what generators will do. If the incentives favor partial generation where only certain blocks of your solar or wind or BESS plant are switched off while others remain on, then we could see more producers do that.
Ultimately though you need to have a way to operate your site in those conditions to help balance out operation and nonoperation. If whenever a curtailment signal comes to your site, and in response you always shut off Block B while leaving Block A on, then Block A will experience accelerated lifetime degradation over Block B. Inverters, transformers, cables, panels will fail faster in Block A than Block B. But if you could rotate your curtailment/demand response such that certain blocks/strings are used sequentially and that lifetimes are averaged out, this might solve the problem. Think about how farmers rotate which crops they plant in which of their fields to avoid famine and soil degradation.
I think demand response is taking off in the utilization markets like in buildings and industrial settings, but really I think the principles we've learned from that should be carried over to generation markets as well. It's only a matter of time as the industry matures and smart technology penetrates the grid and generation markets.
Are there any solar plants that cost a billion dollars each?
Secondly, you want to over build solar, so that you have enough capacity during off peak hours. Grid storage is obviously the better solution, but seems not widely available enough yet.
It doesn’t matter how much solar you build; without storage you’ve got zero power available at night.
The issue with overbuilding solar is that you drive daytime electricity prices to zero so that everyone is losing money on all these solar plants. Furthermore, base load plants such as nuclear plants also start losing money and they have no ability to shut down during peak hours. So you end up driving the base load plants out of business and they shut down permanently. Now you have even less capacity available at night! This causes nighttime power to become extremely unreliable, potentially leading to rolling blackouts and skyrocketing nighttime energy prices.
Another issue that people rarely discuss is the quality of power on the grid. All the grids in the world operate on 50/60 Hz AC which must be carefully maintained at an accurate frequency and synchronized with the grid. The main base load turbines are the source of this waveform which is carefully monitored and adjusted to remain stable.
Solar panels produce DC power which needs to be converted into AC with an inverter and synchronized with the grid. The problem is that if all the base load turbines are taken off the grid then there is nothing for the solar inverters to synchronize with! Turbines are nice and stable because they’re literally an enormous, massive spinning flywheel. Without them you’ll have an extremely unstable system where all of the solar plants are trying to adjust their frequencies and phases to match each other and the whole thing wanders all over the place.
Ok, but what do you do when you're short of power at night? Keep in mind to turn on conventional power stations it's expensive & time consuming. Once they startup they need to stay on for a long while to be efficient & cheap.
The real solution is to store excess power in batteries. Lithium ion is too expensive to scale, Sodium ion batteries are economically & capacity viable AFAIK.
Thats just not what this post is about. Obviously storing is the way but until then yiu just gotta turn em off
I don't think you realize the work involved in integrating a new unreliable power source into the grid. Its a delicate dance to anticipate demand to keep power always available. Having more power than you need is bad for the grid, which is why the costs go negative: power companies want it off the grid ASAP.
Conventional power stations can stay on all the time & that's awesome for the grid stability. There is no power gap renewables are filling. So to turn solar on we need to turn off a coal powered plant. If this new source cannot match the reliability it hinders to grid than help. So there's no question of "turn it off when you don't need it".
We need to turn off fossil fuel power generation for more renewables, sure, but it doesn't alleviate their problems right now.
I’ve read that gravity batteries and sand batteries are ecologically sound options that work on the scale needed to support large sections of the electrical grid.
https://interestingengineering.com/innovation/two-massive-gravity-batteries-are-nearing-completion-in-the-us-and-china
https://www.bbc.com/news/science-environment-61996520
I hesitate on
That first link is for a 10MW, 8 hour battery. 10MW is on the smaller end of generators, you’d need quite a few of these to start making an impact. For example, a small gas turbine is like 50MW, a large one is over 250MW.
And you could say “just build a lot of them” but the capacity per unit of area tends to be pretty low for these types of technologies.
Building them where we have ample space is okay. But now this power has to be transmitted, and we are already having a lot of problems with transmission line congestion as-is. The real advantage of energy storage is when it’s done local, no need for transmission lines.
Plus there’s permitting/stability issues as well. These wouldn’t work if the area was prone to earthquakes or other natural events.
That’s fair. They’re certainly imperfect, but a large improvement over electrolytic cells for large scale storage.
I think a more feasible potential technology for the grid are flow batteries.
They work through some kind of ion-exchange. Where they have two liquids, one charged and one not. By running power through a catalyzer, they move charges into one tank. Then you can apply a load across the catalyzer, and remove the charge as power.
I’m by no means an expert, but these are already pretty popular in Japan, and have started to make their way into the US.
Still definitely an expensive technology, but I’m hopeful that scale and investment can drive the cost down.
One of their biggest advantages over other technologies like Li-Ion is that their duration is independent of their capacity. Because the duration is only determined by the size of your tanks and the amount of liquid you have.
Meaning that you can take an existing 50MW, 4 hour plant and upgrade it to an 8 hour plant by doubling the size of the tanks and filling them up with the electrolyte. All without having to upgrade the catalyzer.
Edit: also worth mentioning they don’t have the same supply/environmental/recyclability concerns that lithium batteries do. I believe the electrolyte is relatively inert and does not degrade over time.