Generating electricity without steam turbines

Gwynston

Watching The Genius of Invention on BBC2 last night (link) and it struck me that we're still generating electricity using steam turbines that were invented over 125 years ago. Whichever fuel is used in power stations, their purpose is still the same: use heat to boil water and generate steam to drive the turbines.

Has nothing better been invented since the 19th century? Or are steam turbines just the most efficient way to generate electricity from fuel?

corkgsxr

Steam is very powerful and is a great way to converting heat to motion

Arse Biscuits!

Well, hydrogen cells can generate electricity, however only on a small scale and once again there are efficiency problems, nowhere near powerful enough to generate the output of a power plant, I asked one of my professors a similar question to this recently. Technically too you could produce electricity using high voltage electrostatic generators, but once again only on a small scale and there would be only a low current anyway requiring major transformers.

In chemical and fuel terms, generating steam to turn turbines is the most efficient way. There are others but they're not viable on a large-scale. You could generate electricity from an internal combustion engine but then you'd consume so much more fuel, although these are used as emergency backups in plants in case of a turbine malfunction. Steam is a very powerful tool, water in any state can do some pretty amazing things. It has a very high heat capacity so it makes for a great energy transporter.

Non-fuel related, there have been a lot of leaps: Solar cells, Wind/Ocean turbines etc. The problem's are with limits and efficiencies like the betz limit for a wind turbine. Although lately there was a breakthrough in solar cell material, using a non-silicon compound to achieve the same efficiency as current silicon based cells (I believe somewhere between the 18-22% mark) so we may see a drastic reduction in the cost of solar cells in the coming years all going well.

djpbarry

Arse Biscuits! wrote: »

Although lately there was a breakthrough in solar cell material, using a non-silicon compound to achieve the same efficiency as current silicon based cells (I believe somewhere between the 18-22% mark) so we may see a drastic reduction in the cost of solar cells in the coming years all going well.

Forget 18 - 22%, it won't be long before the 50% mark is hit:

http://spectrum.ieee.org/green-tech/solar/powerful-pvs-approach-50-percent-efficiency

Capt'n Midnight

the low efficiency of solar panels has a lot to do with the wide variation in photon energies.

in a panel it's one photon per electron captured (excluding re combinations etc) and a blue photon can have twice as much energy as a red one so straight away there's a loss of 50%

it's a lot more complicated than that


But if you use multi layer panels so the top ones adsorb blue light and the bottoms adsorb red then with a three layer one you can hit 40% efficiency, and that's before you take into account newly developed infra red panels. - multi layer panels are very expensive and so you use them with mirrors , with all that sunlight there is a lot of heat so it's best to water cool them, and yes turbines have been used to extract energy out of the heat


and even still since sunlight is free, the main cost is the land and control electronics and the mounting systems for the panels, if you buy in bulk then you can panels delivered in the US for $1 per watt

ozmo

Gwynston wrote: »

Watching The Genius of Invention on BBC2 last night (link) and it struck me that we're still generating electricity using steam turbines that were invented over 125 years ago. Whichever fuel is used in power stations, their purpose is still the same: use heat to boil water and generate steam to drive the turbines.

Has nothing better been invented since the 19th century? Or are steam turbines just the most efficient way to generate electricity from fuel?

The recent mars rover converts heat (from a radioactive source in this case) to electricity using termocouples...
Same idea as system used on the old voyagers that are still working today. But again only good for small scale use.

Also - if your "fuel" is hydro or wind power you. Can turn the generators dierctly without steam involved of course.

Capt'n Midnight

with steam engines you can get more efficiency if you use the exhaust from a high pressure cylinder to feed a low pressure one. Most steam trains were double expansion, for ships where there was more room you could get tripple expansion engines where you took the energy in three steps.

A turbine is getting closer to an infinite expansion engine so more efficient that way. A turbine has no reciprocating parts so less changes in momentum and friction. big turbines have the steam enter in the middle and left and right are mirror images of each other to balance out the thrust to reduce friction.

large electrical machines like induction motors , transformers and generators are very efficient , 95-99+% under optimum conditions depending on who you believe. And that's since the nineteenth century.


new power stations use the combined cycle gas turbine
a gas turbine is a jet engine , it operates at a much higher temperature than steam so much higher Carnot efficiency.
The waste heat from this is used in a boiler to raise steam and then you have a conventional steam turbine doing it's thing.

2/3rd's of the power comes from the jet engines and 1/3 from steam. The overall efficiency is about 60% using well understood, reliable and scalable technologies. This is about twice the thermal efficiency as a pre war coal fired steam generator. - The gains are largely down to using higher temperatures and nibbling away at other inefficiencies. In the UK Drax spent £100m on updating the turbines for a few % gain in efficiency. (it's now 40% efficient because you can't burn coal in a gas turbine)
http://www.draxgroup.plc.uk/media/press_releases/?id=149025



Fuel cells are a bit hard to nail down with regard to efficiency, figures vary wildly. But they can't match the power output, cost, longevity of thermal generators and they usually need very pure fuel as impurities kill them.

jumpjack

there are big news about thermoelectric generation by seebeck effect; so big that "patent wars" already begun leading a company to bankrupt, and that producing electricty from waste heat of gasoline vehicles became economically feasible.
Look around for "quantum dot" or "qdot" or "nanoparticles" thermoelctric generators!

Indeed, it's hilarious even a state-of-the-art 2013 power plant is still steam-powered!!! :eek:

jumpjack

reference:
www.bizjournals.com/albany/stories/2010/04/12/story6.html?page=all

keywords:
Evident Technologies
Invitrogen corp.
thermoelectric
qdot

But this is "old news" from 2011, don't know what happened then.

Capt'n Midnight

jumpjack wrote: »

there are big news about thermoelectric generation by seebeck effect; so big that "patent wars" already begun leading a company to bankrupt, and that producing electricty from waste heat of gasoline vehicles became economically feasible.
Look around for "quantum dot" or "qdot" or "nanoparticles" thermoelctric generators!

As long as they are Carnot engines waste heat will have very low thermal efficiency

Indeed, it's hilarious even a state-of-the-art 2013 power plant is still steam-powered!!! :eek:

It's like saying it's crazy that we are still using Otto cycle engines in cars, when we know there are much better alternatives, and still using Lead-Acid batteries to start them.
Or that nuclear power is really steam power, or that we are still investing in nuclear R&D when there has been no major break through in the last half century.
Or that we are still talking about the internal combustion Hydrogen cars even though they've been around since 1807.
Or that most jet airliners today still have the same layout (and for some the same fuselage sections) as the 1957 Boeing 707.
Or that we've stopped using PAL for broadcast television. (about 70 days before Tanzania did)



It's the whole concept of a Mature Technology.


For thermal plant you have to compare thermal efficiency with the ideal Carnot efficiency.


Is there some 'steampunk' based on someone using thermocouples instead of steam engines as both were about 3% efficient when first discovered ?

jumpjack

i'm looking around for efficiency data, but till now I only found that new thrmoelectric device can reach 90% Carnot efficiency rather than 10%.

But I don't understand difference between thermal efficiency and Carnot efficiency, isn't Carnot efficiency based on temperature difference??

Gwynston

Interesting discussion - thanks for the replies!

So my suspicions were correct - steam turbines are just very efficient. As Capt'n called it - Mature Technology.

Capt'n Midnight

jumpjack wrote: »

i'm looking around for efficiency data, but till now I only found that new thrmoelectric device can reach 90% Carnot efficiency rather than 10%.

But I don't understand difference between thermal efficiency and Carnot efficiency, isn't Carnot efficiency based on temperature difference??

yes


neta is efficiency
TH TC are hot and cold temps (in Kelvin)
W the work you get out for heat input of Q

so using round numbers of 800K input temperature and 400K output temp you get 0.5 (ie. 50% efficiency)

400K would be 127C (~ steam exit temp - would be lower if you use condenser )
800K would be 527C - which means the pipes are starting to glow a dull red colour




Also written as

μC = (Ti - To) / Ti

μC = efficiency of the Carnot cycle
Ti = temperature at the engine inlet (K)
To = temperature at engine exhaust (K)



If you bypass the Carnot cycle by using electrical / magnetic / chemical processes you can get higher efficiencies

But remember all energy degrades to heat so in a lot of cases you are stuck with the Carnot cycle.


Other asides
you can see that higher temperatures are far more efficient - for power generation , in an industrial process you might find that heat is reused each time, with the very highest temperatures for chemical processing or electrical generation, then producing high pressure steam (for various nefarious purposes) then low pressure steam (usually for water boiling or drying stuff) then for heating offices

CHP is where you use the waste heat from electrical generation to heat buildings and stuff. And you start hitting efficiencies of 85% because you save on heating bills.


when you burn fuel you are limited as to the temperature you can reach because air is 4/5th's inert gas that also has to be heated. So you start hitting diminishing returns fairly quickly , you need to move to oxygen and even then the heat is spread between the products of combustion and whatever it is you want to heat. (one of the reasons Thermite gets very hot because no gas to carry away heat) Electric (and solar) furnaces don't have this limitation so can get hotter, they can use low grade heat to reach very high temperatures, not efficiently because of thermodynamics, but may be more efficiently than combustion, and there is also the benefit of more control over the process.

Squeaky the Squirrel

Researchers Say Liquid Metal Could Be The Key To Dramatically Cheaper Silicon - And Electronics

Squeaky the Squirrel

Norwegians trap sunlight with microbeads, produce solar cells that are 20 times thinner, cheaper

Researchers from the University of Oslo have used a bunch of “wonderful tricks” to produce silicon solar cells that are twenty times thinner than commercial solar cells. This breakthrough means that solar cells can be produced using 95% less silicon, reducing production costs considerably — both increasing profits (which are almost nonexistent at the moment), and reducing the cost of solar power installations.

The first trick is using microbeads — very small plastic spheres, uniform in size, that create an almost perfect periodic pattern on the silicon. These beads force the sunlight to “move sideways,” increasing the apparent thickness of the silicon by 25 times.

Was this not blindingly obvious before??

Another few years and you should be able to pick up your super thin sand direct to silicon solar panels in Tesco with your weekly shop.:P

Capt'n Midnight

http://www.mpoweruk.com/amtec.htm

The AMTEC is an electrochemical device for the direct conversion of heat to electrical power. It uses a recirculating alkali metal (Sodium or Potassium) working fluid passing through a solid electrolyte in a closed circuit to produce an electron flow in an external load