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Climate change

Airborne_Again wrote:

I thought that energy – in the correct sense of the word – is power over time.

No, it’s power multiplied by time. E = P * t (were E is energy in joules, P is in watts and t is in seconds).

Andreas IOM

alioth wrote:

No, it’s power multiplied by time. E = P * t (were E is energy in joules, P is in watts and t is in seconds).

Yes, that’s what I meant. I now realise that “over” could be understood as division. I meant “over” in the sense of the expression “over time” – something that happens over a period of time. Or if we want to be super precise, the time integral of power.

ESKC (Uppsala/Sundbro), Sweden

Peter wrote:

We did this in the climate change thread, but the more wind turbines, the more gas you need to buy to run gas turbines when the wind isn’t blowing

That doesn’t make sense. The UK for example non-renewables are today pretty much just nuclear and gas, so the gas is already being used (and there’s enough of it already to provide 100% of demand, especially in the summer when slack winds are most likely). Every wind turbine installed reduces the total amount of gas you have to burn over a given year.

What the UK needs is to restore its gas storage which was foolishly removed. If you have a couple of weeks gas storage, and fill it duing the periods of low demand, if a week of light winds coincides with high gas prices you can burn the cheaper stored gas.

Andreas IOM

alioth wrote:

What the UK needs is to restore its gas storage which was foolishly removed. If you have a couple of weeks gas storage, and fill it duing the periods of low demand, if a week of light winds coincides with high gas prices you can burn the cheaper stored gas.

alioth, or to use the energy stored in the water reservoirs (like British Energy does at the moment).

EGTR

That doesn’t make sense

It does make sense but to varying degrees according to country. AIUI, the UK does need to burn gas with wind power.

It is a gradually improving situation, due to more wind turbines etc.

Administrator
Shoreham EGKA, United Kingdom

Airborne_Again wrote:

I thought that energy – in the correct sense of the word – is power over time.

Edited for accuracy (E = P*t) – yes of course it is (in a physical sense). On the grid, the energy (or power to be precise here ) is in the form of three phase 50 Hz AC. AC has both active power (the real part) and reactive power (the imaginary part). Only active power does any work, but the reactive part is needed to control the voltage and to push/pull the active power down the lines. Since the reactive power doesn’t do any work, it represent a (necessary) loss. I’m no electrical engineer, but this is how they have explained it to me. You need to control the frequency and the voltage. When you plug something into the socket, you expect (and all appliances you use demand) that it is 50 Hz, 230 V AC, and nothing else. The frequency is related to active power, and the voltage is related to reactive power. Both needs to be controlled with tight margins regardless of consumption, or the grid will collapse.

Simplified you can say that the output from a turbine is mechanical power and mechanical frequency (RPM). This power and frequency is input to the generator in the form of RPM and torque on the shaft. The generator transforms this mechanical power and frequency to electric power and electric frequency (50 Hz AC). To be able to push that power down the lines of the grid, you need voltage and reactive power, which is also supplied by the generator and other electrical stuff. The electric power floating in our grids, is something we take for granted, but it is a very specific and highly refined form of power.

But where does the turbine take it’s power from? Traditionally it doesn’t. It converts stored energy (from a magazine or fuel, nuclear or chemical) to mechanical power on demand. It has a huge amount of E that is stored, and (within specs according to type of plant) can convert this to perfect quality electric power to be pushed down the grid on demand. The grid itself is incapable of storing energy. It is exclusively a transmission line for electric power. To be able to transfer that (active and usable) power, it needs 50 Hz, it needs the correct voltage, and it needs reactive power. As the seconds passes along, it modulates the produced power P so the energy demand precisely equals the conversion from E to P (minus losses). Think of E as a big tank with a tap. The P produced is proportional to how much you open the tap. You have full control (and full control of the frequency etc). This conversion also includes a conversion from stored energy to mechanical energy usable for the turbine, before the turbine, but that’s beside the point here. What is done is a conversion from stored energy to electrical power on the grid.

What about solar and wind? There is no storage, hence there is no conversion from energy. It’s a direct conversion from wind or solar power to electrical power. There is no E and there is no tap. How will this work? In all senses of the words – It doesn’t work. You either have to build some storage, or you have to use one of the traditional powerplants to take up the variations. There is one other way though, and that is to modulate the demand. Just cut of increasingly bigger chunks of the grid when the wind stops and the sun doesn’t shine. That will for sure make people happy

Solar isn’t all that bad here. That must be said. Solar panels are DC. To get something useful, this DC is converted in an inverter to AC 50 Hz. Those inverters are fancy pieces of electronics and (usually) also have the ability to produce reactive power. This ability is very useful for the utilities. They will say, OK we will purchase all your surplus power from your solar panels, if you use one of these particular inverters and always stay connected to the grid. What they will not tell you is that they use your inverter to produce reactive power so they don’t have to. This happens when the solar panel produces perhaps less than 90-95 percent of the rated capacity. All the losses in the transmission lines are therefore taken by you, not the utility. Solar panels are indirectly good for the stability of the grid as whole in this respect. But I bet very few households know that they are giving away this very useful commodity for free to their utility company Seen from another angle, solar panels at least make up for some of the bad randomness on the grid. They are indeed useful even when the sun doesn’t shine.

You need a big E and a tap to produce power on demand. Wind and solar have neither. Since traditional thermal power using fossil fuel is out of the question, then the only solution is to store the energy somehow. But the requirement for energy storage to make it work is so large that unless someone by magic invents some super cheap inverse fusion battery, it is not going to happen.

The elephant is the circulation
ENVA ENOP ENMO, Norway

To push electricity into the grid you need to synthesise a corresponding sine waveform but with a small phase shift, or in phase but with a slightly higher voltage. The electronics which do this synthesis is what is called an “inverter”. I used to design this stuff but not for many years now.

If you are running a power station and your power comes from generators (actually what we call alternators because they generate AC) then you do the same. I don’t know the detail but they probably sync the rotation exactly and tweak the field current to achieve just the right excess of voltage to get sufficient power to flow out of it into the grid so as to achieve a some specific torque on the generator.

How did the grid work in the days of only coal or oil fired power stations? Or nuclear plus coal? No magic back then but it worked just fine

Administrator
Shoreham EGKA, United Kingdom

LeSving wrote:

AC has both active power (the real part) and reactive power (the imaginary part). Only active power does any work, but the reactive part is needed to control the voltage and to push/pull the active power down the lines. Since the reactive power doesn’t do any work, it represent a (necessary) loss. I’m no electrical engineer, but this is how they have explained it to me.

Well, I’m no electrical engineer either, but I’m anyway not sure that’s correct. Reactive power isn’t something you really want, but it is unavoidable due to the impedance in both transmission lines and electric motors. Large amounts of reactive power has to be compensated for. E.g. railways with AC traction systems have to use large scale compensation because the traction motors (at least before the advent of power electronics) has lots of impedance.

You either have to build some storage, or you have to use one of the traditional powerplants to take up the variations. There is one other way though, and that is to modulate the demand. Just cut of increasingly bigger chunks of the grid when the wind stops and the sun doesn’t shine.

This is something that opponents to solar and wind power have beaten to death. Sure it’s correct that you need some regulating ability but that does not need to have nearly the total capacity needed. In Norway and Sweden we have lots of hydroelectric power which is perfect for this purpose. Also, the problem gets less the larger the grid. How often does it really happen that “the wind stops and the sun doesn’t shine” over a large area – particularly if you compare with the power outages which are caused by faults. This is always passed over in silence.

we will purchase all your surplus power from your solar panels, if you use one of these particular inverters and always stay connected to the grid. What they will not tell you is that they use your inverter to produce reactive power so they don’t have to.

If this is true it is really bad. Do you have any sources for your claim?

ESKC (Uppsala/Sundbro), Sweden

Also, the problem gets less the larger the grid. How often does it really happen that “the wind stops and the sun doesn’t shine” over a large area.

That’s also what I thought was behind the idea of interconnection. Would be interesting to find some real data on this.

Private field, Mallorca, Spain

Peter wrote:

How did the grid work in the days of only coal or oil fired power stations

It worked exactly as today. Large synchronous generators produce a steady 50 Hz at a set voltage. Then there are lots of small scale plants of various principles producing random power, and leeching of the grid regarding everything else. The company I work for produce turbines, governors for the turbines, voltage regulators for the generators (among many other things, subsea electrical grid for instance). I’m into the turbine/governor area, but I’m today making systems in the production and optimization of power production.

The basic principle is the turbine governor handles the frequency and the power. This is done by essentially controlling the “tap” from the stored energy. The voltage regulator handles the voltage and the reactive power from the generator by varying the field strength. Solid state “stuff” (frequency converters, phase compensators etc) are today placed around the grid to stabilize and optimize the grid, and of course there are lots of transformers. The solid state stuff is probably the only real difference from earlier days. Before, some of these things were rotating machinery. Those distributed solid state “stuff” enables much better control of the reactive power on the grid. This enables the large generators to only produce active power, thus they can produce more of it without heating up.

The problem with thermal power, is they can only to a limited degree control the “tap”. Not nearly to the degree needed for the grid. Hydropower is exceptionally good at this (it’s the only thing that works really, due to the large power variations needed, several GW within seconds). Therefore a mix of thermal and hydropower have always been the standard. Where no hydropower was available, pumped storage plants do the same thing, and are designed to do exactly that. Pumped storage plants are all over Europe. A misunderstanding (in perception) is perhaps that pumped storage plants are used to store energy. A few are used for this, but the large majority are used exclusively to stabilize the grid. Stabilize in this respect means to keep the frequency at 50Hz by absorbing and producing power as needed. Surplus power on the grid results in increased frequency, while too little power results in decreased frequency.

Where no hydro or pumped storage is available, you have a problem. Then the thermal plants must regulate as much as they can, which results in large decrease in efficiency. If that is not enough, the consumption must be modulated. This can be done by running high power intensity factories at night for instance. Gas power plants are much better than nuclear and coal in this respect.

Onto this very fine tuned and huge systems (the grids are the largest systems mankind has ever built) we now want to inject lots of random power. Germany has done this with success. At times, close to 100% of the electricity is made from wind. How do they control the frequency, voltage, reactive power? The thing is, they don’t! The only reason this is possible is France, Switzerland, Poland, Austria, Norway etc is connected. Some supply and absorb power (Norway, Switzerland and Austria with hydropower), while other supply base load (France, Poland, Czech Republic etc with thermal). The Czech Republic also has a few big pumped hydro stations. I have been at one of them. Germany also has pumped hydro, but not even remotely enough to control 100% wind power.

Airborne_Again wrote:

Sure it’s correct that you need some regulating ability but that does not need to have nearly the total capacity needed

That’s exactly what it means, no matter how you look at it, if you want to prevent black outs at all times. What will skew this to some extent is private households and other entities obtaining storage and generating capacity on their own, while still being connected to the grid. If every household already has storage and generating capacity, then the utility companies for sure won’t double this up for them. But how long can you be disconnected without emptying your reserves? one hour, one day, one week?

These newest zero houses can stay disconnected indefinitely in principle. It’s not cheap. Large parts of the industry cannot be disconnected however, like the metal industry for instance.

I sometimes wonder if the society has gone mad. All this can be translated into math, and 1+1=2, it will never ever equal 5 no matter how much some people “believe”.

I always think about this sketch, it never gets old:



The elephant is the circulation
ENVA ENOP ENMO, Norway
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