Criticism of the current electricity market, inconsistency and prospective for renewable energies

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Re: Criticism of the current electricity market, inconsistency and prospective for renewables




by Remundo » 04/01/23, 12:29

the vapor molecules are a gas, not far from the behavior of an ideal gas.

there are 2 possible expressions of the entropy in this case depending on whether one works in pressure/volume or volume temperature variables.

A simplified expression for n moles is for example:
S(T,V)=n Cv ln(T) + n R ln(V) + S0

where Cv is the molar heat capacity at constant volume, and R the ideal gas constant.
S0 is a constant that does not matter.

Entropy progresses as the natural logarithm of temperature (in °K)
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Re: Criticism of the current electricity market, inconsistency and prospective for renewables




by SebastianL » 04/01/23, 12:51

While the first principle is a principle of conservation of energy, the second principle is a principle of evolution. It stipulates that any real transformation takes place with an increase in global disorder (system + external environment); disorder being measured by entropy. We also say that there is creation of entropy.

The modern expression of the second principle formalizes this creation of entropy:

ΔS(global) = ΔS(created) = ΔS(system) + ΔS(outside) > 0

In the case of the reversible ideal transformation, there is no creation of entropy:

ΔS(created) = ΔS(system) + ΔS(exterior) = 0.


So when I overheat, I create entropy outside?
I don't understand at all why the overheating is not reversible, I overheat at equal pressure, I increase the volume so I can activate a piston (NRJ), if I want to return to the initial state, I push the piston back with the same NRJ, I return the overheating energy, No?
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Re: Criticism of the current electricity market, inconsistency and prospective for renewables




by Remundo » 04/01/23, 13:21

the entropy balance is a tricky exercise, and not very useful.

in general there is always internal creation entropy. It is necessary to scrupulously define the systems, their limits, etc...
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Re: Criticism of the current electricity market, inconsistency and prospective for renewables




by sicetaitsimple » 04/01/23, 16:13

SebastianL wrote:I only admit a little, I will wait to have a specialist opinion able to calculate the maximum performance at 500°c 78bar (epr), technologically possible.
When we do the rankine cycle 220bar at 620°C, the calculator gives 44.5% the Germans do 47.5%, the road is not so clear.

Regardless of the values ​​you cite, which I'm not going to discuss, the "unclear road" is that all modern steam power plants use a reheat cycle, i.e. the HP steam is superheated, then expands and cools in the HP body, then returns to the boiler to be "reheated" generally to a temperature close to the original temperature, or even slightly higher, before returning to the MP body of the turbine, then the LP bodies.
I don't think your calculator takes this into account, hence the difference.
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Re: Criticism of the current electricity market, inconsistency and prospective for renewables




by Remundo » 04/01/23, 16:18

and above all it does not change the substance of the problem, whether we are at 30-40 or 50% efficiency on the turbine, degrade the electricity by Joule effect for thermal storage which goes back to a machine with an efficiency <50% is a bad idea.
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Re: Criticism of the current electricity market, inconsistency and prospective for renewables




by sicetaitsimple » 04/01/23, 16:27

Remundo wrote:and above all it does not change the substance of the problem, whether we are at 30-40 or 50% efficiency on the turbine, degrade the electricity by Joule effect for thermal storage which goes back to a machine with an efficiency <50% is a bad idea.

Certainly, but I said that from the second message of this thread *, I will not repeat myself! :D

*extract:Which storage would be heated with renewable electricity, to then be reconverted into electricity with a yield of 30 to 40%?
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Re: Criticism of the current electricity market, inconsistency and prospective for renewables




by SebastianL » 05/01/23, 00:38

Entropy is important because we cannot "reheat" to infinity, we must be able to condense the steam to liquefy it (therefore non-turbined pressure), pump it and reheat it again. The most classic rankine calculator will place this high entropy vapor, low pressure and incondensable, in the final condenser loss.
We see it very well, if we do a rankine hirn 500°c at 70bar:0.1bar then at 140bar:0.1bar, we gain 2% minimum.

Basically the entropy increases at overheating because it is physically impossible to heat a water molecule, at constant pressure, without performing a "lost" expansion which degrades the "saturated vapor" binding energy and switches this energy for the PV equilibrium of an ideal gas

My strategy error is therefore to want to inject the energy of the thermal storage via a simple, entropically ineffective overheating!
the optimum would be to use HT storage to create supercritical steam at very high pressure 1000Bar, 1000°C, therefore with low entropy at the start, to make a "special" quasi-isentropic expansion with fixed fins only and to use the work corresponding to these successive dynamic depressions up to 70bars 500°c, to suck up liquid water (1236.6kj/kg) and steam (2711kj/kg) already heated to 285°c, which would reduce the share of heat coming from HT storage. The liquid water flow is then adjusted so that the steam comes out of the expansion at 500°C 70bar.
All the water injected by suction corresponds to an energy supply from our heat pump using the expansion work of 1000bar => 70bar 500°c.
COP Carnot = Tc + 273 / (Tc - Tf). between 500°c and 285°c = 773/215=3.69
The expansion work from 1000Bar 1000°c to 70Bar 500°c = (4373.0kj/kg - 3411KJ/kg) / 4373.0kj/kg = 0.22
The superheat contribution, necessary, of the steam at 285°c to 500°c is always the same 638KJ/kg to gain the 3% yield at the level of the power station.
In these 638KJ/kg that we want to supply at 500°c, 22% were useful energy to capture 81.1% of the energy at 285°c towards 500°c and there remains the 78% of energy not usefulness of the trigger, i.e. a total of 181.1%. We can then deduce that the true energy share of HV storage is 100/181=55%, i.e. 379.5MW instead of 690MW.

The plant would normally have produced 3GW x 0.37 = 1.11GW
HV storage efficiency 1476MW-1110MW/379.5MW=96.44% : Cheesy: : Cheesy: : Cheesy:

Ahah the dream continues! It was my last idea for this gasworks, hold on!
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Re: Criticism of the current electricity market, inconsistency and prospective for renewables




by SebastianL » 05/01/23, 01:14

Sorry, I forgot that there was a little less primary power

Power of the reactor 3.69GW x 81.3% = 3GW (fixed by the nuclear reactor)
Superheat power 3.69GWGW x 18.7% x 55%= 0.3795GW (heat flow from HT storage)
Useful power at 3.3795GW x 40% = 1.351GW
The plant would normally have produced 3GW x 0.37 = 1.11GW
HV storage efficiency 1351MW-1110MW/379.5MW=63.7% :frown: snif the dream is already gone : Cheesy:
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Re: Criticism of the current electricity market, inconsistency and prospective for renewables




by SebastianL » 05/01/23, 01:49

Re-edit, ignore previous post!

Power of the reactor 3.3439GW x (1-(0.187x0.55)) = 3GW (set by the nuclear reactor)
Superheat power 3.3439GW x 18.7% x 55%= 0.3439GW (heat flow from HT storage)
Useful power at 3.3439GW x 40% = 1.3375GW
The plant would normally have produced 3GW x 0.37 = 1.11GW
HV storage efficiency 1375MW-1110MW/343.9MW=77% :frown: snif the dream is already gone : Cheesy:

The maximum discharge speed of the HT storage becomes not terrible, only 344MW!
On the other hand, the storage allows a formidable erasure on the network, with 16 resistors well arranged the erasure precision can be 15KW on an erasure capacity of 1GW
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Re: Criticism of the current electricity market, inconsistency and prospective for renewables




by Obamot » 05/01/23, 02:35

Honestly, does coming out of formulas with contested elements advance the debate?

Couldn't you focus on elements that have a consensus instead (if there are any and it becomes clearer)

And this to focus more simply on the simplified process, as you see it...
And see if other avenues are possible?
The stumbling blocks that can be admitted/settled "apart, honestly"

Because if there are impossibilities, we should not hesitate to go on other hypotheses?
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