5 ms·

dumb question on power producing /usage: say that Germany (and countries linked to it's power lines) produce 100 units of energy but only 95 are used that momen

dumb question on power producing /usage: say that Germany (and countries linked to it's power lines) produce 100 units of energy but only 95 are used that moment /day or whatever. What happens to the extra power? Where does it go? I understand that they try not to overproduce but I'm sure it happens

sveme 8y ago
There could be different approaches: (i) convert to gas and store it in caverns, (ii) store it in batteries, (iii) store it in pumped hydro in Norway, (iv) turn up the load in the system, e.g., electricity-demanding processes like aluminium smeltering, (v) distribute it along High voltage DC lines to distant places with lower renewable energy output and probably a shitload of other parameters that can be tuned. The power grid is already a giant distributed control system and that‘s only going to increase in the future. Really interesting stuff.
Gravityloss 8y ago
There's almost always a hydro/gas/coal plant on somewhere that can be throttled down.
deleted 8y ago
[deleted]
goodcanadian 8y ago
The short answer is that they don't over produce. If there is more energy being generated than used, turbines (for example) will start speeding up. In the very short term, the extra energy goes to accelerating the turbines. This can be observed by the grid frequency increasing. Immediately, generators will be throttled back to reduce production. If this can't happen fast enough, generators will be cut out of the system entirely, and their excess energy will almost certainly be released as heat somewhere. Imagine you are driving a car downhill and the car starts speeding up. You let off the accelerator in order to not go too fast. Worst case, you apply the brakes and dissipate the energy as heat.
pjc50 8y ago
It goes into increasing the frequency of the electricity via accelerating all the turbines. Suppose you have a generator somewhere operating at 1MW: 1MW of mechanical shaft power being put in (torque x speed) and 1MW of electrical power (current x voltage) being taken out. Then demand drops slightly to 990kW. The "braking force" of the generator coils reduces, but the input torque does not, so the generator accelerates. This usually feeds back into the rest of the system - throttles in steam and gas turbines.
ferongr 8y ago
If production slightly exceeded consumption, and production was not reduced, the generators at the powerplants would end up speeding up and the frequency and voltage of the network would go up. As voltage increases, many loads end producing more power and at some point an equilibrium would be achieved. If something goes wrong and a large part of consumption disappeared (e.g. broken HVDC transmission line) the generators would start overspeeding dangerously, and as voltage went over the limit, things would start breaking downstream (transformers, loads themselves burning due to overvoltage), resulting in a cascade of failures that would end up as far as damaging the generators themselves. Grid balancing is a tough act.
hyperman1 8y ago
That's actually a very good question. My understanding is incomplete, but this is what I make of it: What you suggest turns out to be impossible. The amount of energy that goes in and out must be identical. So this means: * Either less goes in: The required mechanical effort to make the turbine turn goes down. It will have to dissipate the extra energy as heat and catch fire, or it will become less efficient, and have stronger winds behind it as less wind energy has been used. * Or more goes out: The transparting cables are not perfect, they are a kind of very low resistor. They do convert electricity to heat. A short is an extreme example of this. In this case, a smaller version will happen: cables will get slightly hotter. As I understand it, monitoring and balancing the electrical grid is a very complicated problem. Recently, and discussed on hacker news, the opposite happened in Europe: Not enough power was available on the net because of political circumstances. All the generators had to push a little harder, so they all slowed down a tiny bit. Result was the 50HZ of the european grid went a very tiny bit down to 49.999...Hz, and some clocks lost 6 minutes of time as a result.
- severine 8y ago
  > Recently, and discussed on hacker news, the opposite happened in Europe This news had an interesting discussion recently: Continuing frequency deviation in the Continental European Power System (entsoe.eu) 478 points by Aissen 80 days ago | 323 comments https://news.ycombinator.com/item?id=16535067 https://news.ycombinator.com/item?id=16535067 https://www.entsoe.eu/news-events/announcements/announcements-archive/Pages/News/2018-03-06-press-release-continuing-frequency-deviation-in-the-continental-european-power-system.aspx https://www.entsoe.eu/news-events/announcements/announcement...
  - hyperman1 8y ago
    Thanks, that's the one
  - morsch 8y ago
    For what it's worth, the clocks are back in sync. https://arstechnica.com/tech-policy/2018/04/european-grid-dispute-resolved-lost-6-minutes-returned-to-oven-clocks/ https://arstechnica.com/tech-policy/2018/04/european-grid-di...
rafd 8y ago
On a simple network, the extra energy is "absorbed" by the remaining hardware components (think: wired getting hotter, etc.), eventually resulting in failure due to operating at higher voltages or currents than designed for. Most electricity networks have a "system operator" whose job is to keep electricity generated track electricity consumed very closely. (An organization, with many automated systems, not a single person). In practice, on a large network, the most noticeable side effect would be AC frequency fluctuations. In a severe case of imbalance, sensors/switches on the network would disconnect part of the network to protect the underlying equipment (probably causing blackouts, if not cascading blackouts). The operator predicts demand and tells each of the many electricity generators how much electricity to generate. Some types of generation are easier to ramp-up o or throttle-down: for example, hydro and natural gas are very easy, while nuclear is not. Residential roof-based solar makes things complicated because it is now a new part of the system that is no longer under the operators control. Some networks also have access to sinks of energy, the most common being pumped storage (usually in connection to a hydro facility), or even, industrial consumers who are willing to "ramp up" on demand. On top of all this is usually a market layer (depending if the electricity generation is privatized or not). For example, in Ontario, the IESO (independent electricity system operator) asks for bids every 5 minutes from all the providers, and based on a modified dutch-auction, selects which providers are allowed to produce and sends them the corresponding instructions. Of course, taking into account various other technical requirements to decide who gets to power or not. In this kind of market, nuclear power, because it cannot throttle up or down, typically bids 0 or negative (because the actual price set is based on the last most expensive bid to get in). During some hours of the year, the market price of electricity is sometimes negative, because nuclear is the only bidder. In Ontario, the government phased out all coal production (yay, no more smog!), but... had to build a lot of new natural gas plants to be able to do the fast ramp-up/throttling the network requires on some days of the year. Most of the year, these plants sit idle.
TobiasA 8y ago
The short answer is that they sell it to other countries/nations that can't produce energy that efficiently.
- onetimemanytime 8y ago
  Yeah, but I asked what happens in a closed system. Germany, for example, doesn't sell electricity to USA, so there are limits.
filmor 8y ago
As others have said, if nothing is done about the energy excess, it goes into an increase of the frequency. In Germany, there are 3 different steps to handle this (I guess it's pretty much the same in other countries too). 1. The primary reserve power is short-term fine-grained capacity that takes effect automatically (is not requested by the TSO[1] explicitly) if the frequency leaves the +-0.01 Hz band around 50 Hz. The capacity is then provided proportionally to the distance, full capacity is supposed to be provided when the frequency goes under 49.8 or over 50.2 Hz. The tricky part is that the capacity needs to be supplied in both directions which can for example be done by modulating the frequency differences on a power plant running slightly under its full capacity. In Europe, this capacity is provided jointly spread over the whole grid and totals roughly 3 GW in both directions (e.g. simultaneous full outages of two large power plants). Broadly speaking, primary reserve power is supposed to stabilise the grid, i.e. to stop a frequency in/decrease. 2. Secondary reserve power is supposed to kick in after 5min, latest 15min of primary reserve power usage. This is done automatically by the individual TSOs (in Germany we have 4 because we can :)) if the reason for the deviation is in their grid, and sends a request to a controller in the providing power plants, which have to provide 1MW 1min after the request and full (sold) capacity after 5min. It's not as immediate as primary power as the to-be-produced capacity is not directly calculated from the frequency, but the request messages still change quite frequently, usually a few times per second. This part is supposed to move the frequency back to 50 Hz. 3. At last, if secondary reserve is drawn for too long, minute reserve power is activated. This is just a straight "you have 15min to provide 50 MW, 30min onwards after you start". It's essentially just an economical optimisation on the process, since due to the higher lead time, conventional power plants can actually start up to provide it, while for both secondary and primary reserve power they need to react so quickly, that a full ramp-up wouldn't be efficient. Back to your main question, on how negative reserve power is provided then concretely, this could be: - Downmodulating running power plants (primary, secondary and minute reserve) - Charging batteries (likely just primary and secondary reserve since minute reserve would exceed capacity) - Starting up additional consumers (minute reserve) - Running turbines without actually producing any power (worst case minute reserve) - Shutting of wind turbines by turning their rotor blades (likely just secondary, can't be provided guaranteed for long due to changes in the wind, would be fast enough for primary reserve but can only work in one direction) [1]: Transmission System Operator
Someone 8y ago
On top of what others say, the spot price of electricity decreases in the hope that that induces demand. Sometimes, it even goes negative.
Angostura 8y ago
In the UK, there is a sophisticated siren system that when sounded requires citizens to make a cup of tea with our electric kettles.
- trebligdivad 8y ago
  You're joking but see: https://www.nationalgrid.com/uk/electricity/balancing-services/reserve-services/demand-turn https://www.nationalgrid.com/uk/electricity/balancing-servic... that lets get people get paid for taking load in exactly these situations! You should probably apply to get paid for operating that emergency siren system.
- madez 8y ago
  I think that would be awesome, if correctly dosed. It would create a sense of belonging and working together.
cesarb 8y ago
The power generation system uses a closed-loop control. It's easier to visualize if you think of a single traditional rotating generator connected to resistive loads like incandescent bulbs. The electrical power being used by the lamps acts as a "brake" on the generator: it takes energy from its rotation, so you need more mechanical power to spin the generator shaft at the same RPM. Now suppose some of these incandescent lamps are turned off. The power being consumed is reduced, so the power being taken from the shaft rotation is reduced, so you need less effort to spin the shaft. If the mechanical input is the same, the shaft will spin faster. And here is the trick: there's a mechanism which senses the shaft increasing its speed, and reduces the mechanical input, for instance by partially closing a water gate, until the speed returns to normal. The same happens in the opposite direction: if more of the incandescent lamps are turned on, the shaft slows its speed, the mechanism senses this and opens the water a little more, until it's back to the correct speed. What we have on modern continent-wide power networks is basically a scaling up of that principle. So the answer to your question is: the extra power is not produced, the production automatically reduces until only 95 units of energy are being produced, matching generation and demand. What happens if that's not the case? Simple, if production and demand are not within a few percent of each other, protective relays cut the generators and/or loads until it matches, to prevent damage to the generators, power distribution devices, and loads.
tofflos 8y ago
You've already received a lot of good answers and some of them go into the underlying mechanics. Here is a simplistic ("business") explanation to go with them: If too much power is being produced the system will eventually fail and everything will go dark. The entity responsible for the system, the system operator, will pay someone to produce less in order to prevent that from happening. As you can imagine most producers are happy to receive more money for producing less!
- onetimemanytime 8y ago
  I understand the business side. Burning coal or spending water to produce something that is not selling or has a negative value (we pay you to use it) is not a good strategy, but I didn't know that it can be done in real time...given the speed of light.
  - tofflos 8y ago
    Ah, then you're into mechanics. Excess power is continuously converted into increased rotational speed of a very large turbine at a hydro power plant. But the increase in speed takes some time due to inertia. The hydro plant operator has a device attached to the turbine, a regulator, that reduces the flow of water running through the turbines in real-time - lowering the amount of power going into the system which in turn slows down the turbine. This service is the foundation of a working power system and is called "automatic" or "primary" regulation. Usually the system operator pays ahead of time for this service to be available followed by an additional payment afterwards for actual use. A single hydro plant can only do so much though - it can not reduce the flow of water below zero and the system will fail if it ever runs out of primary regulation reserves. The system operator will then have to pay an additional party to produce less in order to prevent that from happening. This is called "secondary" or "tertiary" regulation and is not real-time.

sveme 8y ago

There could be different approaches: (i) convert to gas and store it in caverns, (ii) store it in batteries, (iii) store it in pumped hydro in Norway, (iv) turn up the load in the system, e.g., electricity-demanding processes like aluminium smeltering, (v) distribute it along High voltage DC lines to distant places with lower renewable energy output and probably a shitload of other parameters that can be tuned. The power grid is already a giant distributed control system and that‘s only going to increase in the future. Really interesting stuff.

Gravityloss 8y ago

There's almost always a hydro/gas/coal plant on somewhere that can be throttled down.

deleted 8y ago

[deleted]

goodcanadian 8y ago

The short answer is that they don't over produce. If there is more energy being generated than used, turbines (for example) will start speeding up. In the very short term, the extra energy goes to accelerating the turbines. This can be observed by the grid frequency increasing. Immediately, generators will be throttled back to reduce production. If this can't happen fast enough, generators will be cut out of the system entirely, and their excess energy will almost certainly be released as heat somewhere. Imagine you are driving a car downhill and the car starts speeding up. You let off the accelerator in order to not go too fast. Worst case, you apply the brakes and dissipate the energy as heat.

pjc50 8y ago

It goes into increasing the frequency of the electricity via accelerating all the turbines. Suppose you have a generator somewhere operating at 1MW: 1MW of mechanical shaft power being put in (torque x speed) and 1MW of electrical power (current x voltage) being taken out. Then demand drops slightly to 990kW. The "braking force" of the generator coils reduces, but the input torque does not, so the generator accelerates. This usually feeds back into the rest of the system - throttles in steam and gas turbines.

ferongr 8y ago

If production slightly exceeded consumption, and production was not reduced, the generators at the powerplants would end up speeding up and the frequency and voltage of the network would go up. As voltage increases, many loads end producing more power and at some point an equilibrium would be achieved. If something goes wrong and a large part of consumption disappeared (e.g. broken HVDC transmission line) the generators would start overspeeding dangerously, and as voltage went over the limit, things would start breaking downstream (transformers, loads themselves burning due to overvoltage), resulting in a cascade of failures that would end up as far as damaging the generators themselves. Grid balancing is a tough act.

hyperman1 8y ago

That's actually a very good question. My understanding is incomplete, but this is what I make of it: What you suggest turns out to be impossible. The amount of energy that goes in and out must be identical. So this means: * Either less goes in: The required mechanical effort to make the turbine turn goes down. It will have to dissipate the extra energy as heat and catch fire, or it will become less efficient, and have stronger winds behind it as less wind energy has been used. * Or more goes out: The transparting cables are not perfect, they are a kind of very low resistor. They do convert electricity to heat. A short is an extreme example of this. In this case, a smaller version will happen: cables will get slightly hotter. As I understand it, monitoring and balancing the electrical grid is a very complicated problem. Recently, and discussed on hacker news, the opposite happened in Europe: Not enough power was available on the net because of political circumstances. All the generators had to push a little harder, so they all slowed down a tiny bit. Result was the 50HZ of the european grid went a very tiny bit down to 49.999...Hz, and some clocks lost 6 minutes of time as a result.

severine 8y ago
> Recently, and discussed on hacker news, the opposite happened in Europe This news had an interesting discussion recently: Continuing frequency deviation in the Continental European Power System (entsoe.eu) 478 points by Aissen 80 days ago | 323 comments https://news.ycombinator.com/item?id=16535067 https://news.ycombinator.com/item?id=16535067 https://www.entsoe.eu/news-events/announcements/announcements-archive/Pages/News/2018-03-06-press-release-continuing-frequency-deviation-in-the-continental-european-power-system.aspx https://www.entsoe.eu/news-events/announcements/announcement...
- hyperman1 8y ago
  Thanks, that's the one
- morsch 8y ago
  For what it's worth, the clocks are back in sync. https://arstechnica.com/tech-policy/2018/04/european-grid-dispute-resolved-lost-6-minutes-returned-to-oven-clocks/ https://arstechnica.com/tech-policy/2018/04/european-grid-di...

rafd 8y ago

On a simple network, the extra energy is "absorbed" by the remaining hardware components (think: wired getting hotter, etc.), eventually resulting in failure due to operating at higher voltages or currents than designed for. Most electricity networks have a "system operator" whose job is to keep electricity generated track electricity consumed very closely. (An organization, with many automated systems, not a single person). In practice, on a large network, the most noticeable side effect would be AC frequency fluctuations. In a severe case of imbalance, sensors/switches on the network would disconnect part of the network to protect the underlying equipment (probably causing blackouts, if not cascading blackouts). The operator predicts demand and tells each of the many electricity generators how much electricity to generate. Some types of generation are easier to ramp-up o or throttle-down: for example, hydro and natural gas are very easy, while nuclear is not. Residential roof-based solar makes things complicated because it is now a new part of the system that is no longer under the operators control. Some networks also have access to sinks of energy, the most common being pumped storage (usually in connection to a hydro facility), or even, industrial consumers who are willing to "ramp up" on demand. On top of all this is usually a market layer (depending if the electricity generation is privatized or not). For example, in Ontario, the IESO (independent electricity system operator) asks for bids every 5 minutes from all the providers, and based on a modified dutch-auction, selects which providers are allowed to produce and sends them the corresponding instructions. Of course, taking into account various other technical requirements to decide who gets to power or not. In this kind of market, nuclear power, because it cannot throttle up or down, typically bids 0 or negative (because the actual price set is based on the last most expensive bid to get in). During some hours of the year, the market price of electricity is sometimes negative, because nuclear is the only bidder. In Ontario, the government phased out all coal production (yay, no more smog!), but... had to build a lot of new natural gas plants to be able to do the fast ramp-up/throttling the network requires on some days of the year. Most of the year, these plants sit idle.

TobiasA 8y ago

The short answer is that they sell it to other countries/nations that can't produce energy that efficiently.

onetimemanytime 8y ago
Yeah, but I asked what happens in a closed system. Germany, for example, doesn't sell electricity to USA, so there are limits.

filmor 8y ago

As others have said, if nothing is done about the energy excess, it goes into an increase of the frequency. In Germany, there are 3 different steps to handle this (I guess it's pretty much the same in other countries too). 1. The primary reserve power is short-term fine-grained capacity that takes effect automatically (is not requested by the TSO[1] explicitly) if the frequency leaves the +-0.01 Hz band around 50 Hz. The capacity is then provided proportionally to the distance, full capacity is supposed to be provided when the frequency goes under 49.8 or over 50.2 Hz. The tricky part is that the capacity needs to be supplied in both directions which can for example be done by modulating the frequency differences on a power plant running slightly under its full capacity. In Europe, this capacity is provided jointly spread over the whole grid and totals roughly 3 GW in both directions (e.g. simultaneous full outages of two large power plants). Broadly speaking, primary reserve power is supposed to stabilise the grid, i.e. to stop a frequency in/decrease. 2. Secondary reserve power is supposed to kick in after 5min, latest 15min of primary reserve power usage. This is done automatically by the individual TSOs (in Germany we have 4 because we can :)) if the reason for the deviation is in their grid, and sends a request to a controller in the providing power plants, which have to provide 1MW 1min after the request and full (sold) capacity after 5min. It's not as immediate as primary power as the to-be-produced capacity is not directly calculated from the frequency, but the request messages still change quite frequently, usually a few times per second. This part is supposed to move the frequency back to 50 Hz. 3. At last, if secondary reserve is drawn for too long, minute reserve power is activated. This is just a straight "you have 15min to provide 50 MW, 30min onwards after you start". It's essentially just an economical optimisation on the process, since due to the higher lead time, conventional power plants can actually start up to provide it, while for both secondary and primary reserve power they need to react so quickly, that a full ramp-up wouldn't be efficient. Back to your main question, on how negative reserve power is provided then concretely, this could be: - Downmodulating running power plants (primary, secondary and minute reserve) - Charging batteries (likely just primary and secondary reserve since minute reserve would exceed capacity) - Starting up additional consumers (minute reserve) - Running turbines without actually producing any power (worst case minute reserve) - Shutting of wind turbines by turning their rotor blades (likely just secondary, can't be provided guaranteed for long due to changes in the wind, would be fast enough for primary reserve but can only work in one direction) [1]: Transmission System Operator

Someone 8y ago

On top of what others say, the spot price of electricity decreases in the hope that that induces demand. Sometimes, it even goes negative.

Angostura 8y ago

In the UK, there is a sophisticated siren system that when sounded requires citizens to make a cup of tea with our electric kettles.

trebligdivad 8y ago
You're joking but see: https://www.nationalgrid.com/uk/electricity/balancing-services/reserve-services/demand-turn https://www.nationalgrid.com/uk/electricity/balancing-servic... that lets get people get paid for taking load in exactly these situations! You should probably apply to get paid for operating that emergency siren system.
madez 8y ago
I think that would be awesome, if correctly dosed. It would create a sense of belonging and working together.

cesarb 8y ago

The power generation system uses a closed-loop control. It's easier to visualize if you think of a single traditional rotating generator connected to resistive loads like incandescent bulbs. The electrical power being used by the lamps acts as a "brake" on the generator: it takes energy from its rotation, so you need more mechanical power to spin the generator shaft at the same RPM. Now suppose some of these incandescent lamps are turned off. The power being consumed is reduced, so the power being taken from the shaft rotation is reduced, so you need less effort to spin the shaft. If the mechanical input is the same, the shaft will spin faster. And here is the trick: there's a mechanism which senses the shaft increasing its speed, and reduces the mechanical input, for instance by partially closing a water gate, until the speed returns to normal. The same happens in the opposite direction: if more of the incandescent lamps are turned on, the shaft slows its speed, the mechanism senses this and opens the water a little more, until it's back to the correct speed. What we have on modern continent-wide power networks is basically a scaling up of that principle. So the answer to your question is: the extra power is not produced, the production automatically reduces until only 95 units of energy are being produced, matching generation and demand. What happens if that's not the case? Simple, if production and demand are not within a few percent of each other, protective relays cut the generators and/or loads until it matches, to prevent damage to the generators, power distribution devices, and loads.

tofflos 8y ago

You've already received a lot of good answers and some of them go into the underlying mechanics. Here is a simplistic ("business") explanation to go with them: If too much power is being produced the system will eventually fail and everything will go dark. The entity responsible for the system, the system operator, will pay someone to produce less in order to prevent that from happening. As you can imagine most producers are happy to receive more money for producing less!

onetimemanytime 8y ago
I understand the business side. Burning coal or spending water to produce something that is not selling or has a negative value (we pay you to use it) is not a good strategy, but I didn't know that it can be done in real time...given the speed of light.
- tofflos 8y ago
  Ah, then you're into mechanics. Excess power is continuously converted into increased rotational speed of a very large turbine at a hydro power plant. But the increase in speed takes some time due to inertia. The hydro plant operator has a device attached to the turbine, a regulator, that reduces the flow of water running through the turbines in real-time - lowering the amount of power going into the system which in turn slows down the turbine. This service is the foundation of a working power system and is called "automatic" or "primary" regulation. Usually the system operator pays ahead of time for this service to be available followed by an additional payment afterwards for actual use. A single hydro plant can only do so much though - it can not reduce the flow of water below zero and the system will fail if it ever runs out of primary regulation reserves. The system operator will then have to pay an additional party to produce less in order to prevent that from happening. This is called "secondary" or "tertiary" regulation and is not real-time.