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The Energy Opportunity in Wasted Heat

The views expressed are those of the author and are not necessarily those of Scientific American.


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For every one unit of energy that is converted into electricity in power plants today, two units of energy are thrown away. This wasted energy is primarily in the form of heat – or thermal energy – and, there is technology available today that can turn this waste into a usable energy stream.

Combined Heat and Power (CHP) is a technology that combines power generation and usable heat capture equipment to increase the overall efficiency of the power plant. These two energy streams can then be used locally (for example, in a manufacturing process) or transmitted via power lines and pipes to local communities. This approach allows more energy output from the same amount of fuel input, allowing society to get more from its limited fossil fuel resources.

Today, the majority of electricity generated in the United States comes from power plants fueled by fossil fuels (coal, natural gas, and oil). These plants run with an efficiency in the ballpark of 33%. The remaining 67% is mostly released into the environment in the form of heat. In CHP facilities, the bulk of this heat is recovered and used, leading to real-world efficiencies of more than 75%. Some CHP facilities in the United States have documented overall efficiencies of more than 87%.

CHP technology has been used in the United States for more than 100 years. Today, about 8% of the country’s electricity generation capacity comes from 82 Gigawatts (GW) of installed CHP. By comparing the efficiency of these facilities to typical fossil fuel plants, one can say that these facilities are responsible for reducing the country’s carbon dioxide emissions by 300 million metric tons per year – the equivalent of taking 50 million cars off the road.

Today, most (87%) of the U.S. CHP fleet can be found at manufacturing facilities. From an efficiency standpoint, this is great – one avoids transmission and distribution losses by co-locating supplies and end-users. It is also an advantage to the production facilities themselves, giving them relatively cheap and dependable energy streams that make them more competitive in the marketplace.

In the European Union, 11% of the region’s electricity is generated using CHP technology.  While some countries have very little or no installed CHP (for example in Greece and Cyprus) others generate more than a third of their electricity using this technology. In Denmark, 43% of total electricity generation comes from CHP (co-generation) facilities.

Seeing the significant potential that exists for CHP in the United States, the Obama Administration has set a target to increase the size of the U.S. fleet by 50% by 2020. This means 40 GW of new CHP capacity over the next 8 years.

Some of this new capacity might be found in the upgrading of existing facilities, instead of building new power plants. Historically, CHP infrastructure at manufacturing facilities in the U.S. was sized in proportion to the baseload heat demand at the plant itself. The is different than in some other countries, where CHP facilities are “oversized” in order to supply local heating and cooling needs. The U.S. fleet could be redesigned to meet this outside demand.

According to the U.S. Department of Energy, a lot of potential also exists in commercial buildings around the country.

State governments, seeing this potential, have already begun to give CHP technology increasing policy support. Today, twenty-three states recognize CHP as a part of their renewable portfolio or energy efficiency recourse standards.

But, barriers exist that discourage CHP deployment in the United States. The most significant might be a lack of awareness and widespread willingness to adopt and use heat outside of industrial processes. This relegates CHP to a much smaller market than it could operate in. And, because CHP plants still rely on fossil fuels to generate their heat and power, their environmental footprints are not negligible. This leads to concerns over the potential for new environmental regulations before the end of the facility’s initial payback period.

But, regardless of the barriers, one things is clear – we throw away a lot of energy. But, the technology exists to allow us to recycle this waste, turning it into a valuable energy stream.

Photo Credit:

1. Graphics courtesy of the U.S. Department of Energy.

Melissa C. Lott About the Author: An engineer and researcher who works at the intersection of energy, environment, technology, and policy. Follow on Twitter @mclott.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. twayburn 8:08 pm 11/8/2012

    Let’s look at Table 1: Why must the Annual Energy Savings be given in different units from Annual Useful Heat? Now, what is meant by Annual Useful Heat? Is this the heat that must be removed to cool the total recovered heat stream down to the input temperature or working temperature of the application that employs it? What about the efficiency of that application? Is the saved energy reduced by the heat rejected to the environment by the application? Is that the actual heat rejected or is the application treated as a Carnot engine?

    Isn’t it true that most of the waste occurs during electrical transmission? What would be the efficiency if the I^2R losses were used as inputs to a suitable distributed heat engine? What might the typical savings be if the transmission lines were sheathed in liquid nitrogen carrying outer conduits even in the case where hydrogen is the principal product of a nuclear reactor thus rendering the transmission lines super-conducting?

    Link to this
  2. 2. priddseren 8:51 pm 11/8/2012

    Finally a useful article. Not only should be we using this wasted energy, the heat from power production of any kind, including life on the planet, contributes excess heat to the atmosphere.

    Pushing for local even onsite power production to capture the excess heat, remove transmission lines to remove transmission waste energy and with onsite power production, only the energy needed is produced, no waste on transformers and the fuel usage would be so much less because it is easier to move fuel ready to use over power already produced.

    We need more ideas like this one, this would actually do something like reduce CO2 or global temperatures instead of the insane belief that carbon tax ideas would work.

    Link to this
  3. 3. dwbd 9:54 pm 11/8/2012

    Curious the author fails to mention Nuclear Energy, an excellent candidate for CHP. Small Modular Reactors would be excellent for steam & power in the Tar Sands and other industrial process applications. And zero emissions. And Nuclear Power plants waste heat is excellent for desalination. Unlike Fossil Fuel waste heat, nuclear is ZERO EMISSIONS, and the trivial, one-millionth level of waste is contained, and not dumped into the atmosphere, land & water for us to breath, drink & eat. And Nuclear is not limited by the difficult fuel transport problem that afflicts Oil, Coal, Biomass & NG. Particularly bad for Biomass & NG. You can easily locate Nuclear power plants far from fuel sources like in the Arctic, under the sea, in Earth orbit or on other planets and our moon. Nuclear CHP is commonly used in Russia and a few European countries, like Switzerland.

    Other than that, electricity transmission waste energy is only 7% of total, not very significant. And CHP can make a small impact on World Energy consumption, in particular in Northern Areas.

    Some of the hype is misleading however, calling CHP 85% efficient and comparing that to a 35% efficient power plant. Remember an NG furnace is 95% efficient so by that criteria an NG Furnace is better than CHP. Electricity is high value energy, low grade heat is the lowest in value energy – comparing the two on equal terms is bogus. For instance you can turn 35% efficient electricity into 500% efficient low grade heat with a heat pump. The Energy Expert, David Mackay has done an analysis of CHP and concludes that large Central Power stations and Heat Pumps are a better method in his “Sustainable Energy without the Hot Air”, pgs 145-154:

    http://www.inference.phy.cam.ac.uk/sustainable/book/tex/sewtha.pdf

    There are also problems like peak domestic power consumption in evening dumps sufficient waste heat in the household to supply building heat, which will also lead to maximum waste power source heat – which is not used or must be stored at great expense. The district heating installations are horrendously expensive much more than NG or Electricity infrastructure. In summer in Northern Areas you don’t need the waste heat – so the waste heat is not consumed – efficiency drops greatly and the expensive infrastructure is not being used. Many EU countries such as Holland & Britain HAVE NOT embraced CHP.

    As for home CHP systems, unfortunately are outrageously expensive, I know I was seriously interested in one for my home, here is the typical response I got:

    “.. The cost of the ____ system is $35,000 to $45,000 (us dollars) per unit installed. The component and installation costs vary because of the facility size and other variables associated with the existing plumbing and electrical codes. Also, depending on what region of the country one lives in, labor costs will vary. A certified technician is required to install the system..”

    So the real analysis shows CHP is certainly useful in certain locations & industries, but is consistently hyped beyond its real potential. Biggest and best use would be building heat in Northern regions with Small Modular Reactors and Nuclear Desalination in coastal areas with few potable water sources – as Saudi Arabia intends to do.

    Link to this
  4. 4. phalaris 2:45 am 11/9/2012

    What twayburn #1 is touching on is correct. You can’t beat the second law, and this applies to “waste” heat utilisation as well.

    There’s not much new in these concepts, they resurface time-and-again. In Germany it’s pretty well-developed in some cities: the apartment where I’m writing this right now is heated from “waste” heat.

    Buthe naive idea that it’s pure utilisation of waste heat must be countered that electricity demand varies a lot, and what happens when the generators would otherwise be throttled due to low demand? So there’s an overlap with district heating, but to what extent is very opaque.

    Infrastructure costs must also be considerable: the road outside’s been up with large excavations for much of the last year.

    McKay gives a good overview of pros and cons. and is largely con: http://www.withouthotair.com/ (page 145)

    The economics (including the carbon cost) are not so straight-forward, and it’s difficult to get hard facts, which Mckay notes as well This makes me suspicious.

    Link to this
  5. 5. phalaris 3:17 am 11/9/2012

    On the “nothing-new-under-the-sun” meme: http://en.wikipedia.org/wiki/New_York_City_steam_system

    You see from that article that some of the steam in New York is nowadays produced by cogeneration, so you have CHP, but also district heating.

    If this concept is going to make sense anywhere, it would be in a large population concentration like New York.

    Link to this
  6. 6. Dr. Strangelove 3:55 am 11/9/2012

    Melissa, the barrier is not lack of awareness. CHP is useful if you need heat rather than electricity. Not always the case. If you need electric, combined cycle will do. BTW the car’s engine loses 70% of its energy heat loss. Electric cars don’t waste that much energy.

    Link to this
  7. 7. MoEnergySci 5:41 am 11/9/2012

    Dr. Strangelove –

    In electric cars you might not waste your energy at the car itself. However, the car got its power from a powerplant. I believe that it is fair to assume that the powerplant uses fossil fuels and loses a lot of its usable energy to heat losses.

    I agree that there are many opportunities to increase efficiency in cars and trucks and such. I would be interested in seeing how the numbers run for that one – gasoline and diesel vehicles compared to electric vehicles that run on different fuels (in terms of where the electricity comes from).

    Link to this
  8. 8. G. Karst 11:47 am 11/9/2012

    Most of the heat (energy) loss in power stations derive from the latent heat of vaporization, as steam exits the turbine and is condensed (back to liquid) at the condensers. This heat is then rejected via cooling towers (atmosphere) or to a body of water.

    In addition nuclear power stations have an extra heat loss from the moderator (reflector) created from the attenuation (thermalizing) of fission neutrons. This heat is removed by large amounts of cooling service water.

    There have been many attempts to recover such “waste” heat, by the heating of greenhouses to grow tomatoes etc, or for building heating, with varying degrees of success. Mostly utilities are unimpressed on the financial return and are put off by the additional operational hassle and system complications. This is very low grade heat and such a scheme requires industrial parks to be designed and built close to power stations, which themselves should be designed and built for such purpose. Tremendous wholesale investment and cooperation required. GK

    Link to this
  9. 9. sethdiyal 12:06 pm 11/9/2012

    Note the always unstated goal here at SCIAM of promoting Big Oil by never mentioning nuclear unless FUKU can be brought it and distracting low information readers into thinking Big Oil is taking care of business greening fossils with such as carbon capture, coal to gas conversions, ethanol, wind/solar with gas backup, auto mileage standards, and this – the mythical energy efficiency scam.

    Out in the Tar Sands, Big Oil burns almost 2 billion cu ft gas per day to produce low value low pressure steam to loosen the tar from the sand. That gas could easily be run through a CCGT/Cogen plant on site turning half of it into electricity first. It just doesn’t get any better than this for Cogen and it still isn’t done.

    As I said another Big Oil Scam, confusing the almost 100% illiterate American voter, maintaining their profits and deferring nuclear as long as nitwits will put with Hurricane Sandy’s and droughts every year.

    Link to this
  10. 10. JohnSmith57 12:59 pm 11/9/2012

    “But barriers exist that discourage CHP deployment in the United States. The most significant might be a lack of awareness and widespread willingness to adopt and use heat outside of industrial processes.”

    No, everyone knows how much heat is wasted. And they have known since the days of Sadi Carnot. The problem is that the heat is wasted for a very good reason.

    Getting useful work from heat energy requires that a great deal of it be wasted. And it is very hard to use waste heat. That’s the main reason why it isn’t use. Not lack of awareness.

    Link to this
  11. 11. dwbd 8:28 pm 11/9/2012

    Speaking of a real, practical, CHP endeavor, the Slowpoke III reactor was designed to supply heat and electricity to Northern Communities at about 1/10th the cost of the Oil which supplies >95% of the North’s energy. With ZERO emissions. Oil that has to be trucked in on winter ice roads, or shipped through frozen Arctic seas or even flown in on Hercs. A precarious and difficult supply. And life-threatening supply.

    Canada was ahead of the Rest of the World, with the 10 MWth, 600 KWel reactor. Intrinsically safe based on TRISO (pebble bed) fuel, runs 3 yrs @ 10MWth on one fueling. So safe it was licensed for unattended operation, with remote monitoring. Fuel load can be carried on one plane. Cost $10M or $1k per kwth, way cheaper than Oil, suitable for heat & power for small Northern Communities and Mining Camps which rely on expensive, job killing, smoke belching, terrorist funding Oil for most of their Energy. Also could have been used in fuel guzzling Ocean Shipping. Was earmarked for Canada’s submarines.

    http://www.nuclearfaq.ca/cnf_sectionH.htm#g3

    http://www.nuclearfaq.ca/north.htm

    Unfortunately, the Slowpoke III was blocked by despicable Greenies, who as usual try their damnedest to maintain Big Oil’s Energy Hegemony. Thanks to these paid-by-Oil Greenie Cretins billions of tons of CO2 have been released needlessly into the atmosphere as well as millions of tons of acid rain causing sulfur & nitrogen oxides, heavy metals: mercury, lead, arsenic; carcinogens: PAH’s, Furans, PCB’s, Dioxins. All thanks to the corrupted Greenie Sleazoids – prominent amongst them: the Sierra Club, the WWF, Greenpeace, Union of Concerned non-Scientists, Enemies of the Earth (mistakenly called Friends of the Earth). That Big Oil graft sure makes that Global Warming thing seem unimportant whenever “the N Word” is mentioned.

    Link to this
  12. 12. phalaris 6:56 am 11/10/2012

    As with many a renewable utopia, one of the problems with CHP is back-up.
    Take the situation where the generation facility is completely dependent on the takers of “waste” heat for cooling capacity, and the takers completely dependent on the facility for heating. If the facility has to shut down e.g. for maintenance the takers go cold. In summer, the takers take less, and the facility has to slow down or run at reduced thermal efficiency. So extra heating and cooling capacity, which is not being used for a lot of the time, is needed.

    Many of the commenters have touched on this and other problems.

    If anyone is to be convinced that we’re missing out on something here, what is needed is real-life case studies with hard, verifiable data demonstrating net carbon savings. One looks to SciAm to come up with this, and not, I’m sorry to say, a rather superficial article which ignores the many problems.

    Link to this
  13. 13. techagnostic 10:41 am 11/11/2012

    Yet another obstacle to wider use of CHP or CoGen is the rate structure under which utilities in the U.S. earn their profits. The local utility in the San Francisco Bay Area was able to kill several attempts by regional factories and the like some years ago.

    Link to this

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