Most efficient way of making electricity

[BigFly]

well I am not sure if this is the right thread because I am new, but i wanted to know. what are the most efficient ways of making electricity besides nuclear? Is there a way to create a lot of electricity from a relatively small source? Is there any new research or development of this topic?

 

[Defennder]

What do you mean by "small source"?

 

[russ_watters]

Efficiency is typically measured thermodynamically and using thermodynamics, nuclear power is the least efficient of the standard methods of power generation. A good combined-cycle gas turbine can be 60% efficient at converting the energy of the fuel to electricity. Nuclear power plant thermodynamic efficiency is on the order of 35%.

But perhaps that isn't what you were asking...?

 

[BigFly]

well is there a way to create a lot of electricity from a small source? Like a really powerful fuel cell? or a super battery lol? as an example, would it be possible to power an entire house with something as small as a shoebox?

 

[russ_watters]

So you're looking for an amount of power per a size. Sort of a power density. No, there isn't anything that exists or is on the horizon that would have a power density high enough to power a house from a shoebox-sized device.

Why would this be important?

 

[BigFly]

i just thought it would be interesting to know that's all. thanks for the post

 

[Pumblechook]

Efficiency is rather academic.. Cost is the important thing.

A fuel could have a high calorific energy content but the conversion to electricity is wasteful.

Another fuel could have a low calorific energy content but the conversion to electricity is not so wasteful.

Either is possible but the one which wins is the one where the overall cost is lower.

 

[TheCoolBrian]

What I would like to know is what has the best Cost to operate and build to energy output ratio

 

[russ_watters]

Welcome to PF. That's two separate questions you asked there. The cheapest to build is a gas-turbine (jet engine) plant. The cheapest to operate is any kind of fuel-less power plant (wind, solar, hydro).

 

[Mech_Engineer]

I would also say the best power-per-volume (or power per weight for that matter) power systems are gas turbines. Multiple-megawatt gas turbines are surprisingly small, some of their support equipment can take up 10 times the space that the turbine itself requires...

 

[Emicro]

I would like to know why waste to energy plants are not more popular. During the early 90's I toured a powerplant just outside of Spokane, Washington that uses refuse exclusively as a fuel source, instead of sending it to a landfill. This seems like a better idea that dumping all that garbage in a big hole and hope that there aren't any pollutants in there.

 

[mgb_phys]

This seems like a better idea that dumping all that garbage in a big hole and hope that there aren't any pollutants in there.

NIMBY (not in my backyard) - it takes about as long to get planning permission for an incinerator as it does to build the pyramids.

To ensure that all the toxins are completely destroyed you have to run the burn at a very high temerature, so you have to add a lot of fuel. Unless the costs of waste disposal is very high, or the waste is presorted to be mainly paper/card/compostable etc it's not worth it.

It is worthwhile to burn garbage/waste oil etc in a cement kiln - these already run at a temeprature high enough to destroy dioxins. But then they get classified as incinerators and the planning problem starts.

Extracting methane from old capped off landfill and burning that in a gas turbine isgenerally worthwhile.

 

[theallknower]

well,a battery made of matter-antimatter could do the trick...the only problem is,for every gram of antimatter you would need about 1 tone of electromagnets,so it isn't that volume eficient,unless you want all the energy consumed in 1 moment,not to mention,to produce 1 gram of antimatter is an incredebley hard job,would take years,mabey,but as a simple concept,this should do...
here,have a quote from a book from reader's digest-the misteries of terra:
"the amount of antimatter that the scientists have is enough to light a 100W light for 1 hour,and the antimatter left in the universe is enough for the light to function 100 hours"
so to produce antimater as we know to produce is very ineficient!

 

[kman92]

actually the plant in Spokane from earlier in the post is a RESCO plant and the only time that they use and fuel (natural gas) is after they clean a burner and turn it back on. Other than that the heat of the burning trash keeps the the fire burning. The burning ash heats water to steam to turn a turbine to make electricity and at least for the Baltimore one it also provides steam to the heat district for building warmth. The steam is then condensed back into liquid water circulated over the steam pipes using water from the surrounding waters. Then the ash is finally taken to a landfill. all the off gasses are "cleaned" with scrubbers, and electromagnets (for the mercury) and other filtration systems. they still let off lots of CO2 so its not the best system but it works and ash takes up much less room in the landfill.

origanaly posted mgb_phys by
NIMBY (not in my backyard) - it takes about as long to get planning permission for an incinerator as it does to build the pyramids.

To ensure that all the toxins are completely destroyed you have to run the burn at a very high temerature, so you have to add a lot of fuel. Unless the costs of waste disposal is very high, or the waste is presorted to be mainly paper/card/compostable etc it's not worth it.

It is worthwhile to burn garbage/waste oil etc in a cement kiln - these already run at a temeprature high enough to destroy dioxins. But then they get classified as incinerators and the planning problem starts.

Extracting methane from old capped off landfill and burning that in a gas turbine isgenerally worthwhile.

 

[latin4hawk]

As others have said, not sure if this is the correct place to post, but new to the site.
I have created a solar panel from scratch, using a DIY manual. I am stuck on the conversion phase, as I follwed the DIY instructions to the letter & my inverter blew up when connected to the AC side of the circuit. The DIY support staff has not returned my requests x 3 weeks, so I guess I am on my own. Suggestions please... The panel produces between 15-18V. Circuit is good up to inverter as I have been able to charge a 12V battery with a direct connection from the panel.

 

[jim hardy]

my inverter blew up when connected to the AC side of the circuit.

hmmmmm how is it synchronized?

Ever drive a stick shift car and hear the gears grind?
That's why newer ones (post 1963) have all forward speeds "synchronized" .
Same thing applies to your inverter - if it's not matched speed and voltage to grid, it'll be violent when switch is closed. That matching procedure is called 'synchronize'.

See this thread, second post.
https://www.physicsforums.com/showthread.php?t=594556

 

[latin4hawk]

Good to know why... can you suggest something synchronized to get my system rolling?
Thanks

 

[sophiecentaur]

As others have said, not sure if this is the correct place to post, but new to the site.
I have created a solar panel from scratch, using a DIY manual. I am stuck on the conversion phase, as I follwed the DIY instructions to the letter & my inverter blew up when connected to the AC side of the circuit. The DIY support staff has not returned my requests x 3 weeks, so I guess I am on my own. Suggestions please... The panel produces between 15-18V. Circuit is good up to inverter as I have been able to charge a 12V battery with a direct connection from the panel.

If you tried to connect directly to your mains supply then your supply company will not be very pleased with you. If you want them to allow you to do that then you will need a lot of experience and 'letters after your name' to prove you are competent. A lot of the cost to the consumer for Feed In Tarif schemes is to pay for that expertise.
If you are just trying to connect an inverter to the DC you have produced, for feeding a local AC load, then that should be less of a problem. Did you connect the inverter correctly and is it for the correct voltage? (Sorry but the question needs to be asked). It would be best to test such a set up with no appreciable load on the inverter.

 

[psparky]

I don't know if it's the most efficient, but many, many years ago someone was boiling water in a tea pot and they noticed steam being forced out of the tea pot.

Most modern electric plants use high pressured steam to turn their generators. They often use 15 story high boilers (big tea pots) to create this massive pressure. They heat the water by nuclear heat or the more common coal.

They now clean the air using scrubbers to clean the coal exhaust. It's a massive system but they essentially crush up limestone and spray it through the coal exhaust. Limestone is a base and it neutralizes the acid. Then, the used limestone gets scraped out and they turn it into drywall. I was lucky enough to visit the electric power plant on the Indiana, Ohio border, just south west of Cincinnati...I forget the name of the plant.

The mighty Titanic ship was powered by coal...that heated steam that turned the propellers of the ship...and powered all the electric on the ship. However, that ship sunk...but that's another story.

 

[DragonPetter]

Efficiency is typically measured thermodynamically and using thermodynamics, nuclear power is the least efficient of the standard methods of power generation. A good combined-cycle gas turbine can be 60% efficient at converting the energy of the fuel to electricity. Nuclear power plant thermodynamic efficiency is on the order of 35%.

But perhaps that isn't what you were asking...?

I never would have guessed nuclear power would be so inefficient. Where are all the losses or why is it the least efficient?

I'm guessing nuclear fuel is one of the most efficient sources we have as energy/kg, but that's a different definition of efficiency.

 

[psparky]

I never would have guessed nuclear power would be so inefficient. Where are all the losses or why is it the least efficient?

I'm guessing nuclear fuel is one of the most efficient sources we have as energy/kg, but that's a different definition of efficiency.

I agree...due to it's E=mc^2 effect.

Does anyone have any evidence to support the amazing statement "nuclear is less efficient"?

 

[DragonPetter]

I agree...due to it's E=mc^2 effect.

Does anyone have any evidence to support the amazing statement "nuclear is less efficient"?

Well, he's referring to the efficiency of nuclear plants, and is using the thermodynamic definition - basically how well they can transfer the energy from the nuclear fuel to electrical. I was just curious where the losses are or why its so low compared to others.

 

[psparky]

Well, he's referring to the efficiency of nuclear plants, and is using the thermodynamic definition - basically how well they can transfer the energy from the nuclear fuel to electrical. I was just curious where the losses are or why its so low compared to others.

It's my understanding that nuclear electric power plants simply heat water as well, turning it into high powered steam. It is also my understanding that nuclear power makes massive amounts of heat.

How can a nuclear plant be less efficient. It would appear to be the exact opposite.

Perhaps we aren't comparing apples to apples here?

 

[jim hardy]

How can a nuclear plant be less efficient. It would appear to be the exact opposite.

Power plant guys measure efficiency by output / input.
Input is heat derived from fuel, measured in BTU's stateside (English unit)
Output is kilowatt-hours which is a metric unit, KWH.
Note BOTH are measures of energy and could be converted to ergs or Newton-meters or whatever you like.
Efficiency is called ""Heat Rate" and is BTU/KWH.
A popular conversion factor between BTU and KWH is 3412.7 BTU/KWH, there's others but they are all close.
So 100% efficiency would be a "Heat Rate" of 3412.7 BTU/KWH, which of is course not reachable see below...
The basic limit is as somebody said thermal.

And the steam power plant can be reduced for analysis to a heat engine moving heat energy between a hot reservoir(boiler) and a cold one(condenser),, tapping off some along the way to sell as electricity.
The steam turbine-generator converts heat first into mechanical energy and then electrical energy.

Carnot tells us efficiency of a perfect heat engine is in proportion to difference between hot and cold reservoirs at different temperatures,
efficiency = (1- Tcold/Thot) is the limit of any heat engine.
That is the absolute best any turbine could do.
A real one might do 70% as well.

A coal boiler might make steam at 1,000 degF and reject to a local body of water at 70 degF. Converting to absolute temperature, that's 1460 and 530 absolute degF.
1- (530/1460) = 0.637 or 64%, which tells us a perfect coal plant could yield a heat rate of 3412.7/.64 = 5,333 BTU/KWH .

A real one will be more like 8,000 to 8,500 because the turbine is not perfect and a lot of heat goes out the stack.

As PKruse has posted elsewhere combined cycle plants can achieve heat rate of 6,000 for two reasons
1. They start at higher temperature inside the jet engine
2. They recover jet engine's exhaust heat and use it to power a steam turbine

6,000 BTU/KWH is ~57% efficient.

Nuke plants make steam at lower temperature. My plant's design point was 516 degF. That'd be 976 absolute
yielding max possible efficiency of 1-(530/976) = 0.457, 46% .
or max theoretical heat rate of 7417 BTU/KWH.
We achieved more like 10,500 BTU/KWH ,~32% efficiency, ~70% of ideal carnot limit.
There's no stack, so that 30% less than ideal represents the mechanical inefficiency of turbine plus power used by the pumps that move the water through the reactor and boilers..
We had 18,000 horsepower of reactor coolant pumps and about the same on boiler side.

Digression - mea culpa -
but if you research the subject you are going to encounter term "Heat Rate".
Above i hope explains that as welll as addressing OP's question.

Right now, coal is hard to beat but EPA is strangling that.
A gas fired combined cycle plant is also attractive.
I think you can expect more nukes in your future.

Windmills have no fuel cost but they make electricity by the thimblefull so need sizeable subsidies to get built. They're also maintenance intense.

old jim

 

[the_emi_guy]

Jim,
Great info!
You have me curious why nuke plants boil at a lower temp. Is this a safety thing, needing to keep the water sufficiently separated from nuclear material?

 

[jim hardy]

curious why nuke plants boil at a lower temp. Is this a safety thing, needing to keep the water sufficiently separated from nuclear material?

Like most things, it's a compromise.

PWR design keeps the water in the reactor well below its 'critical point', which is 705 degF and 3206 psi.

So, at full power, water exits reactor at about 600 degF and pressure there is kept about 2250 psi so it won't boil.
That water flows through the steam generator tubes and gives up its heat to the secondary water on other side of those tubes. It leaves steam generator tubes at ~ 545 degF to make another round through pumps and reactor.
Water on other side of tubes will be heated to somewhat less than temperature of reactor side water. That's because a temperature difference across tube wall is necessary else heat wouldn't flow from one side to the other.

So that tube design is a compromise beteween a thick wall that's robust and a thin one that conducts heat well.
They settled on a temperature drop of about 50 deg across the tube walls at full power. That makes steam for the turbine at about 50 degF less than the average of steam generator's reactor side inlet and exit.
Average of 600 and 545 is 572.55 .
Subtract 50 deg across the tubes yields 522.5 degF steam, which is slightly over 800 psi.
here's a saturated steam table.
http://www.engineeringtoolbox.com/saturated-steam-properties-d_273.html

so, in summary it's a compromise between delivering nice high pressure steam to the turbine and keeping the reactor side water in a well behaved liquid form.

The separation you mentioned between water and fuel is done by the metal tubes enclosing the fuel.

nucleartourist dot org is an industry site for anybody interested. Check it out.


old jim

 

[psparky]

Wow Jim Hardy...your brain is light years ahead of mine...and most other peoples' for that matter.

I'm a simple guy...you answered everything but my question. You did actually answer it, but I'm not smart enought to figure it out.

So...if you would please...answer this question either YES or NO.

Is nuclear less effecient in regards to the topic at hand?

 

[sophiecentaur]

Wow Jim Hardy...your brain is light years ahead of mine...and most other peoples' for that matter.

I'm a simple guy...you answered everything but my question. You did actually answer it, but I'm not smart enought to figure it out.

So...if you would please...answer this question either YES or NO.

Is nuclear less effecient in regards to the topic at hand?

You would have to define what you mean by efficiency. How far back in the chain of events do you look? You can obviously get a lot of energy in a shovelfull of nuclear fuel. Does that count as 'efficiency'? Not in conventional terms.
If nuclear reactors use lower steam temperatures then they are less thermodynamically efficient. Does that matter if you can get cheap and safe nuclear fuel?

Sadly, there is only one 'measure' you can compare fuels with and that is Joules per Dollar / GBPound / etc.. But that doesn't involve a valid value for the cost. Long term / short term / cost to indigenous populations / cost to our health / cost of accidents etc etc.

You are on really shaky ground to try to evaluate this. In the end it's down to tree huggers vs 'deniers' (Swampy vs Nigel Lawson) and just where you place yourself on the continuum between the two.

 

[jim hardy]

Thanks Sophie that is a concise statement of the question.

Wow Jim Hardy...your brain is light years ahead of mine...and most other peoples' for that matter.

Sparky, actually the opposite is true. i answered the 'question' from a physics perspective.
And I'm kind of a geek when it comes to social skills.
Present day Nuclear plants are generally less efficient than fossil because of the temperatures available. There are exceptions, a General Atomic plant near Lyons Colorado ( Ft St Vrain ) would have made steam 1000 degF at 2400 psi , equalling most fossil plants. But bureaucracy and business decisions shut it down. I think there's an integrated reactor under development in Idaho that also offers fossil-like thermodynamic efficiency.


From a business perspective efficiency i guess would be revenue divided by cost.
This is where economy of scale kicks in . Plants get bigger spreading the cost of labor over more energy . So your joules per dollar goes up as labor cost is diluted.. and joules translate into revenue 3,600,000 of them make one KWH.
Interest payments on capital to build the thing also affect business-perspective efficiency. That's a big part of the trouble with windmills. They're expensive to build so it's green tax credits funding that industry.

Lastly , op asked " Is there a way to create a lot of electricity from a relatively small source? "

So far as i know the steam turbine is still the best we have. And they're getting huge, here's an 1100 mw unit in Japan 'with its hood up'...
http://www.power-hitachi.com/products/ffp/st/images/fornpp_08.jpg
http://www.power-hitachi.com/products/ffp/st/fornpp.html

it's the equivalent of probably a thousand windmills plus it can run 24 hours a day eighteen months at a stretch.

if you're thinking of a football sized device that makes megawatts i don't know of one.

But i do speculate a lot about residential electric load. Small scale devices that a home handyman could maintain i think might prove cost effective. E.G. solar water heating in flat plate collectors worked great in Florida when i was a kid. When electricity got down to 2cents/kwh most people went "all electric" and their solar panels went away with next roof repair..


old jim

 

[sophiecentaur]

Jim
The great thing about this forum is that the whole is greater than the sum of its parts. You just injected a load of extra info into my memory and it's already making connections with what's already there. I haven't had a bath in power generation matters for years and it's really done me good. Many others too, I bet.

 

[jim hardy]

thanks guys, i hope it helped.
Indeed i too relish the synergy here and learn an awful lot.

@ Mr L'hawk -

can you suggest something synchronized to get my system rolling?

what you are after is a "Grid Tie Inverter"
i can't recommend one because I've never worked on one.
but a search on that term shows plenty of them.

Sola and Tripp-Lite are two well established and competent manufacturers, i'd look at their offerings as a start.

old jim

 

[sophiecentaur]

I suggest (again) that, for a start, you contact y our electricity supplier. 'Buying' your electrical energy from them and then 'paying them' with your own energy may not be the deal as far as they're concerned. Your equipment must be squeaky clean for them to allow a connection. If you have a fault that ends up costing them money could land you in court. You are allowed to kill yourself but you have to protect everyone else involved. This gear isn't cheap and you need to be sure that you can actually use it 'live'.