Thirsty clean energy may add to water stressed world

Jul 19, 2013 Full story: New Scientist 20

As the world gets hotter and drier thanks to our predilection for burning fossil fuels, the technologies we need to reduce emissions could be too thirsty to be sustainable.

Full Story
LessHypeMoreFact

Toronto, Canada

#1 Jul 19, 2013
Water per MWH
Hydropower ----15,000 to 68,000 liters
Solar (conc)--3,000
Nuclear powr --2,650
Coal power ----1,900
Natural Gas ---750
Wind Farms ----negligeable
Photovoltaic --negligeable

This clearly illustrates that the necessary change to green energy should focus on photovoltaic and wind power with the 'storage' going to pumped water storage (can also be diverted to irrigation) or reducing hydro power loads (100% efficient 'pumped storage'. The conversion to green energy can IMPROVE the water situation, if used with a BRAIN. While coal and nuclear will NEVER lower their demand for water.. and it is all 'one way'.

Since: Mar 13

Alexandria, VA

#2 Jul 19, 2013
Clearly you don't read much. Solar takes quite a bit of water for washing the panels or mirrors.

As an interesting addition to your list, Liquid Fluoride Thorium Reactors don't need any water, indeed they can MAKE fresh water from seawater quite well.

Once again, the winner is...(envelope please)

LFTRs!!!

Since: Mar 13

Alexandria, VA

#3 Jul 19, 2013
This is a ludicrous lead in. The following is extracted from the article:
The biggest users of water in the US are power plants, particularly the fossil fuel and nuclear plants that together generate almost 90 per cent of the nation's energy. Nearly half the water the US consumes is used to cool these plants and drive their turbines.
Since it is well known that agriculture consumes about 70% of all water, the quoted statement is bunk. Doesn't bode well for the veracity of the rest of the article.
LessHypeMoreFact

Toronto, Canada

#4 Jul 20, 2013
KitemanSA wrote:
Clearly you don't read much. Solar takes quite a bit of water for washing the panels or mirrors.
Not. http://tinyurl.com/msh8j8a

"Adapted from the semiconductor industry, the multiple shrinking mask etching technique could make glass and polymer films anti-fog or self-cleaning, water-repellent and glare-free."

You don't have to take EVERY opportunity to demonstrate your stupidity you know.
KitemanSA wrote:
As an interesting addition to your list, Liquid Fluoride Thorium Reactors don't need any water, indeed they can MAKE fresh water from seawater quite well.
I have nuclear down. ANY nuclear reactor can divert it's power output to desalination but the thermal efficiency still requires a large supply of cooling water for power generation. It is still a STEAM driven turbine.

The amount of cooling water needed is somewhat more than coal because the steam is a secondary loop and lower temperature than the coal power plant, thus losing overall thermal efficiency. The cheap fuel is the advantage.
KitemanSA wrote:
Once again, the winner is...(envelope please)
LFTRs!!!
I agree with liquid salt thorium power, but at the same time don't worship it. It ends the plutonium stockpiles, dangers of proliferation and is much safer than a light water power plant (not as good as the CANDU heavy water though).

But it should be sited where there is enough water. The wind and solar can be sited where power is more plentiful than water, using 'excess power' to run desalination instead of spilling the wind when demand is lower than supply.

Wind is rapidly overcoming the issue anyway as it integrates short term grid scale storage.

http://cleantechnica.com/2013/05/04/for-some-...

Since: Mar 13

Alexandria, VA

#5 Jul 20, 2013
LessHypeMoreFact wrote:
I have nuclear down. ANY nuclear reactor can divert it's power output to desalination but the thermal efficiency still requires a large supply of cooling water for power generation. It is still a STEAM driven turbine.
The amount of cooling water needed is somewhat more than coal because the steam is a secondary loop and lower temperature than the coal power plant, thus losing overall thermal efficiency. The cheap fuel is the advantage.
It appears that you don't have nuclear as "down" as you think. Liquid Fluoride Thorium Rectors produce much higher temperatures than conventional water cooled reactors and thus are typically designed using Brayton cycles,(gas like He or N2) not Rankine cycles (steam). And the Brayton Cycle outputs much higher temperatures than Rankine without significant loss of efficiency. The output temperature of a Brayton will run a distillation unit with no problem.

Since: Mar 13

Alexandria, VA

#6 Jul 20, 2013
Dang this inability to edit... Reactors, not Rectors. Phoo!
LessHypeMoreFact

Toronto, Canada

#7 Jul 21, 2013
KitemanSA wrote:
<quoted text> The output temperature of a Brayton will run a distillation unit with no problem.
You can run distillation from an OTEC plant. It has nothing to do with the need for water, which is from COOLING requirements. Desalination is a USE of the power, not a 'freebie'.

And whatever you use for the secondary look (gas or steam) the temperature will be lower than a primary loop such as coal and thus lower thermal efficiency. BUT it doesn't matter for nuclear because the fuel is CHEAP. On the other hand, it DOES raise the need for cooling water.

Since: Mar 13

Alexandria, VA

#8 Jul 21, 2013
LessHypeMoreFact wrote:
<quoted text>
You can run distillation from an OTEC plant. It has nothing to do with the need for water, which is from COOLING requirements. Desalination is a USE of the power, not a 'freebie'.
And whatever you use for the secondary look (gas or steam) the temperature will be lower than a primary loop such as coal and thus lower thermal efficiency. BUT it doesn't matter for nuclear because the fuel is CHEAP. On the other hand, it DOES raise the need for cooling water.
Quit listening to yourself blather and read up on LFTRs. With Brayton cycles they do not need water for cooling, at all. Dry cooling suffices with no signifincant loss of efficiency.

http://en.wikipedia.org/wiki/LFTR
boris

Moscow, Russia

#9 Jul 21, 2013
KitemanSA wrote:
Clearly you don't read much. Solar takes quite a bit of water for washing the panels or mirrors.
As an interesting addition to your list, Liquid Fluoride Thorium Reactors don't need any water, indeed they can MAKE fresh water from seawater quite well.
Once again, the winner is...(envelope please)
LFTRs!!!
Washing the panels or mirrors ?? What a joke.

Since: Mar 13

Alexandria, VA

#10 Jul 21, 2013
boris wrote:
<quoted text>Washing the panels or mirrors ?? What a joke.
Yes, have the panels and mirrors is a joke, one of the reasons is the need to wash them to maintain production. Uses a lot of water.

Since: Mar 13

Alexandria, VA

#11 Jul 21, 2013
Dang, "having the panels" not "have the panels".
LessHypeMoreFact

Toronto, Canada

#12 Jul 22, 2013
KitemanSA wrote:
<quoted text> Quit listening to yourself blather and read up on LFTRs. With Brayton cycles they do not need water for cooling, at all. Dry cooling suffices with no signifincant loss of efficiency.
http://en.wikipedia.org/wiki/LFTR
http://en.wikipedia.org/wiki/Brayton_cycle

Using a gas as the 'heat exchange fluid' has nothing to do with it. The fact is that you have to have TWO circulating loops in order to keep the radiation from the generation loop. This lowers efficiency and thus requires more cooling.

And ANY heat exchange can use water OR air as the 'heat sink'. The only issue is the SIZE of the heat exchanger. Water is cheaper and more compact in most cases, so it is the first choice.

I think you may be an example of 'a little knowledge is a dangerous thing'.
LessHypeMoreFact

Toronto, Canada

#13 Jul 22, 2013
Note also that the article you reference is to the effiency of a SOLAR POWER TOWER which doesn't have the 'secondary loop' issue to contain radiation.

The 'wikipedia' is not a good source for the deeper science. It is closer to a good newspaper but has the problem of being written by enthusiasts. YOU could have written the entry.

Since: Mar 13

Alexandria, VA

#14 Jul 22, 2013
LessHypeMoreFact wrote:
<quoted text>
http://en.wikipedia.org/wiki/Brayton_cycle
Using a gas as the 'heat exchange fluid' has nothing to do with it. The fact is that you have to have TWO circulating loops in order to keep the radiation from the generation loop. This lowers efficiency and thus requires more cooling.
And ANY heat exchange can use water OR air as the 'heat sink'. The only issue is the SIZE of the heat exchanger. Water is cheaper and more compact in most cases, so it is the first choice.
I think you may be an example of 'a little knowledge is a dangerous thing'.
When you start with a very high temperature, the efficiency is not hurt much. LFTRs start at a high enough temperature that the expected overall efficiency with dry cooling will be on the order of 45%. If triple reheat/intercool is used, it may reach ~50%.

The point I made was that Brayton Cycle turbines do not lose efficiency with higher sink temperatures as badly as Rankines do. They are a natural fit for dry cooling, unlike Rankines.

(I am a retired engineer with a BSMechEng, and my major was Power Systems. I am quite conversant with them.)
LessHypeMoreFact

Toronto, Canada

#15 Jul 22, 2013
KitemanSA wrote:
<quoted text> When you start with a very high temperature, the efficiency is not hurt much. LFTRs start at a high enough temperature that the expected overall efficiency with dry cooling will be on the order of 45%. If triple reheat/intercool is used, it may reach ~50%.
And the latest coal power plants have thermal efficiencies of above 47%. That still leaves half the energy to be dissipated on the 'cooling' side. Which is why they tend to use water for cooling. It much reduces the area of the heat exchanger compared to air. And the economics of dissipating this energy is independent of whether it is Rankine or Brayton.
KitemanSA wrote:
<quoted text>
The point I made was that Brayton Cycle turbines do not lose efficiency with higher sink temperatures as badly as Rankines do. They are a natural fit for dry cooling, unlike Rankines.
The lower the 'temperature differential' the lower the efficiency, though you have a point perhaps in the design. Steam cycle has the problem of the heat of evaporation and condensation (thermal energy change without temperature change) and efficiency is based on the temperature differential. But it is a false argument if the overall efficiency of the system is equal (as I pointed out). For the same temperature drop you need about the same heat exchanger design and flow. The basic physics of the heat exchange requires water cooling for economic reasons unless you are willing to drop the overall efficiency of the plant (due to lower temperature differences).
KitemanSA wrote:
<quoted text>
(I am a retired engineer with a BSMechEng, and my major was Power Systems. I am quite conversant with them.)
And you are an enthusiast which tends to bias your viewpoint. You have not countered MY points, and this is just an attempt at 'argument by authority'. But I have seen PHd's with mental health issues and some that have 'lost it' so you do not win on that count. Even an honest engineer can be distracted or blind.
LessHypeMoreFact

Toronto, Canada

#16 Jul 22, 2013
http://aries.ucsd.edu/LIB/REPORT/CONF/ANS00/s...
Note. One relevant discussion might be this paper about a design for a fusion reactor using He as the working fluid. One problem with gas as a working fluid is the high flow rates or pressure needed.

But really the main issue with efficiency is the materials. High temperature means high efficiency but only to the degree that the materials can handle.

There is promise in advanced carbon carbon composites (which can take the temperature) that have no problem in a Helium gas from oxidation, etc. That may improve the overall efficiency up to 60%,but there will STILL be a lot of heat to dissipate and water is a much more effective coolant than air.Precisely because of the high heat of evaporation. The size of an equivalent air interchange is prohibitive.

Since: Mar 13

Alexandria, VA

#17 Jul 22, 2013
LessHypeMoreFact wrote:
<quoted text>
The lower the 'temperature differential' the lower the efficiency, though you have a point perhaps in the design. Steam cycle has the problem of the heat of evaporation and condensation (thermal energy change without temperature change) and efficiency is based on the temperature differential. But it is a false argument if the overall efficiency of the system is equal (as I pointed out). For the same temperature drop you need about the same heat exchanger design and flow. The basic physics of the heat exchange requires water cooling for economic reasons unless you are willing to drop the overall efficiency of the plant (due to lower temperature differences).
Brayton cycle efficiency is calculated by Pressure Differential, not temperature. Due to gas laws, one can convert the equation to temperature, but it is not the max to min like a Carnot cycle but the temperature differential across the compressor (or turbine).

Since: Mar 13

Alexandria, VA

#18 Jul 22, 2013
LessHypeMoreFact wrote:
There is promise in advanced carbon carbon composites (which can take the temperature) that have no problem in a Helium gas from oxidation, etc. That may improve the overall efficiency up to 60%,but there will STILL be a lot of heat to dissipate and water is a much more effective coolant than air.Precisely because of the high heat of evaporation. The size of an equivalent air interchange is prohibitive.
You seem to be employing the "Magic Field". The issue started with me saying that LFTRs could use dry cooling (zero water/MWh) without significant loss of efficiency. Having apparently seen that you are losing that argument, you now magically change the topic to "water is a more effective coolant". Nobody is arguing against that contention, but it is immaterial to the topic at hand, to whit the fact that LFTRs do not need water for cooling.
what

Sumter, SC

#19 Jul 22, 2013
KitemanSA wrote:
<quoted text> Yes, have the panels and mirrors is a joke, one of the reasons is the need to wash them to maintain production. Uses a lot of water.
Rain washes mine.....

Since: Mar 13

Alexandria, VA

#20 Jul 22, 2013
what wrote:
<quoted text>Rain washes mine.....
I suspect you do not live in the desert where the big arrays are placed. And many people wash their home panels.

Enough rain to keep them clean also suggests a low average production.

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