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UK wind record
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adam2
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PostPosted: Fri Dec 08, 2017 2:32 pm    Post subject: Reply with quote

PS_RalphW wrote:
I would expect small unmetered wind to have just about stalled, as of 2017, as it is almost impossible politically and without subsidy uneconomic to install more, when offshore wind has ever increasing economies of scale.


Agree, new small wind turbines are largely confined to off grid premises, in which they are not metered, and in any case are typically replacing small FF generators.
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adam2
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PostPosted: Thu Dec 14, 2017 5:33 am    Post subject: Reply with quote

Tonight, electricity from wind is the single largest contributor to the grid.
Coal, natural gas, and nuclear are each below 6GW whilst wind is about 7.5GW.
This has occurred regularly overnight in the last few weeks, but was almost unknown until recently.

With the current concerns regarding gas supplies this is most welcome news.
Every GWH of electricity generated from wind is two or three GWH of natural gas not burnt and therefore still in stock for future needs.
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fuzzy



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PostPosted: Thu Dec 14, 2017 8:30 am    Post subject: Reply with quote

So how fast can a coal plant alter output dramatically? The technology must have changed [or it's fibs], because they used to say it takes 1/2 day to restart coal. This morning says ~7.9GW coal. Iguess you can lower furnace feed. I suppose excess could be mopped up by refilling pumped storage.
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adam2
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PostPosted: Thu Dec 14, 2017 10:17 am    Post subject: Reply with quote

To start a coal plant from cold does indeed take many hours, half a day would be reasonable.
To slightly alter the output of an already running coal plant takes only seconds.
To start a coal plant that is already warmed can take less than an hour.

Historically, frequent starting and stopping of coal plant was avoided as the extra heating/cooling cycles increased risk of metal fatigue and failures.
That is probably less of a concern these days with plant that has a limited remaining life in any case.
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vtsnowedin



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PostPosted: Thu Dec 14, 2017 11:56 am    Post subject: Reply with quote

adam2 wrote:

Every GWH of electricity generated from wind is two or three GWH of natural gas not burnt and therefore still in stock for future needs.

Is not a GWH of gas equal to a GWH of electricity? The volume of gas needed to generate a GWH of electricity should already take into account the efficiency of the turbines used.
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adam2
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PostPosted: Thu Dec 14, 2017 12:42 pm    Post subject: Reply with quote

vtsnowedin wrote:
adam2 wrote:

Every GWH of electricity generated from wind is two or three GWH of natural gas not burnt and therefore still in stock for future needs.

Is not a GWH of gas equal to a GWH of electricity? The volume of gas needed to generate a GWH of electricity should already take into account the efficiency of the turbines used.


A GWH is a measure of energy. To convert energy from one form (such as natural gas) into any other form (electricity in this case) generally entails considerable losses, therefore to produce a GWH of electricity takes a lot more than a GWH of gas. Often about two or three times as much, though the exact figure varies a lot according to the design of the plant and the conditions of use.
This also explains why electricity is almost always a lot more expensive than gas. When you buy a KWH of electricity you are, in effect buying two or three KWH of gas, AND paying a share of the other costs of running a power station.
There are of course exceptions in places with cheap and plentiful coal, hydroelectric, or nuclear power, and expensive imported natural gas.
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BritDownUnder



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PostPosted: Thu Dec 14, 2017 8:13 pm    Post subject: Reply with quote

To add to Adams post I think gas energy content is quoted in GWh as if the gas was burnt and the GWh is the energy transferred as heat released rather than the less efficient process of burning the gas to release energy in the form of heat and then converting thermal energy to mechanical energy and thence to electrical energy all of which have some losses due to Carnot efficiencies, friction, 2nd law of thermodynamics etc.

It is quite possible to just burn the gas directly in many applications such as heating food and heating your house rather than using electricity derived from gas but I think you know that already.
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johnhemming2



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PostPosted: Thu Dec 14, 2017 10:05 pm    Post subject: Reply with quote

The only reliable way of working out the energy value of gas is in energy of oxidation. If part of that energy is used to create electricity then all well and good and the rules on Entropy come into play (2nd law thermodynamics).

I think the ratio to electrical energy is normally something like 2:1 some of the CCGTs actually manage a 55% efficiency.
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vtsnowedin



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PostPosted: Fri Dec 15, 2017 12:55 am    Post subject: Reply with quote

I am having a hard time describing how unsatisfactory your explanations about the value of a GWH of gas is.
If a GWH of gas will not produce a GWH of electricity just what will it produce?
Gas is normally measured by the standard cubic foot or cubic meter. GWHs are a measure of electricity production and are a measure of final output. To say that a quantity of gas is equal to a GWH measures that final production (or at least should in any rational system) .
Are you guys sure you know what you are talking about?
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PS_RalphW



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PostPosted: Fri Dec 15, 2017 1:01 am    Post subject: Reply with quote

Then consider it this way. For each GWh of energy released by burning the gas, half gets turned into electricity and half goes up the chimney as hot exhaust gasses, mostly CO2, heating the atmosphere both directly, and through the greenhouse effect. It is possible to make direct use of some of this heat energy in district heating systems, etc., But that is rare in practice. And yes, we do know about this, I , for example have a degree in chemistry from UK "ivy league" standard university, others here clearly know as much as me.
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johnhemming2



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PostPosted: Fri Dec 15, 2017 8:14 am    Post subject: Reply with quote

vtsnowedin wrote:
Gas is normally measured by the standard cubic foot or cubic meter. GWHs are a measure of electricity production and are a measure of final output.


Giga Watt Hours are a measure of energy. A watt hour is 3,600 Watt Seconds. A Watt Second is a Joule. Hence 1 GWh==3.6TJ

GWh are not measurements of electrical energy, but of energy more generally.

Hence you can measure potential energy from height, chemical energy inherent in propane, or electrical energy with Wh.

Hence you start with say 2GWh of chemical energy and end up potentially with up to 1.1GWh of electrical energy.

Various measurements are used for energy millions of cubic metres are used for gas. Wh for electricity, tonnes of oil or barrells of oil for oil. There are conversions between these because they are all really measurements of energy.

At times tonnes of oil equivalent is used.
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adam2
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PostPosted: Fri Dec 15, 2017 10:11 am    Post subject: Reply with quote

vtsnowedin wrote:
I am having a hard time describing how unsatisfactory your explanations about the value of a GWH of gas is.
If a GWH of gas will not produce a GWH of electricity just what will it produce?
Gas is normally measured by the standard cubic foot or cubic meter. GWHs are a measure of electricity production and are a measure of final output. To say that a quantity of gas is equal to a GWH measures that final production (or at least should in any rational system) .
Are you guys sure you know what you are talking about?


A GWH of natural gas will produce a GWH of heat when burnt under perfect conditions.
If this heat is to be turned into electricity, then very considerable losses result, as with any heat engine, and a lot less than a GWH of electricity will be produced.
The very best CCGT plant operating under ideal conditions can have an efficiency of 55%, though 50% is probably more realistic under average working conditions.
Older or less efficient plant is often in the region of 33% efficient, some OCGT is worse than that.
Therefore as an approximation, it may be said that "two or three GWH of natural gas are required to produce a GWH of electricity"
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PostPosted: Fri Dec 15, 2017 12:41 pm    Post subject: Reply with quote

adam2 wrote:
Therefore as an approximation, it may be said that "two or three GWH of natural gas are required to produce a GWH of electricity"


That was what I took you to mean in the first place. This is why Donald Trump should invest in wind and solar. It's like printing money.
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Potemkin Villager



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PostPosted: Fri Dec 15, 2017 1:32 pm    Post subject: Reply with quote

adam2 wrote:


Historically, frequent starting and stopping of coal plant was avoided as the extra heating/cooling cycles increased risk of metal fatigue and failures.
That is probably less of a concern these days with plant that has a limited remaining life in any case.


Presumably this must apply to all thermal generating plant including those fueled with gas? I have heard it said that CCGT plant in particular is not happy ramping up and down and being stopped and started and that overall energy efficiency drops very significantly at part load.
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adam2
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PostPosted: Fri Dec 15, 2017 1:39 pm    Post subject: Reply with quote

Gas burning plant tolerates load changes and start/stop cycles better than coal, but efficiency and services life are somewhat reduced thus.

CCGT plant can often produce some electricity fairly quickly from the gas turbine, but the steam turbine wont produce anything until steam has been raised.
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