Fuels out of Plastic???

Natural oil (petroleum) is a mixture of many components. A well-known component of course is the gas or diesel used in our cars. A less well known component is naphtha. Naphtha is a mixture of hydrocarbon molecules that can be saturated (only single bonds between the carbon atoms) or unsaturated (double or even triple bonds between the carbon atoms. Naphtha is used as a precursor for plastics. For example the plastic poly-ethylene is a plastics that is formed when the naphtha mixture is subjected to a process called cracking (breaking up the larger molecules in smaller ones). This gives in first instance the molecule ethane that can subsequently be polymerized under formation of poly-ethylene, a plastic used in an almost endless variety range of products such as in toys, plastic garbage sacs and electrical isolation of wires. 

 

Because plastic is so widely used it leads at the same time also to a lot of plastic waste (plastic packaging materials, plastic bottles, toys etc). A Swiss company, Innovation Solar/Diesoil, is now doing exactly the opposite as the process described above: they have developed a process that will convert plastic waste materials into diesel fuel. 1000 kilograms of plastic will yield about 850 liter of diesel and all this at a cost price of only 26 Eurocents per liter. Recently a Dutch company (Petrogas) announced a big order to build 15 units that can turn plastic into diesel oil based on this chemical process.  

 

Is this not something? Sounds almost like a perpetual process…….

My question to the reader is: how will the thermodynamic balance (both energy and entropy) be for this reaction: 

Petroleum —> Plastic —>  Diesel oil

 

Solid State Lighting in Europe

Recently the European Commission  (EC) has released a green paper on how to accelerate innovative lighting technologies (http://ec.europa.eu/information_society/digital-agenda/actions/ssl-consultation/index_en.htm). The focus in the entire document is on solid state lighting (SSL) only. About 20% of the world wide total electrical energy generated  is used to generate light. SSL is expected to play a substantial role in an energy efficiency improvement of 20% (EC ambition versus 1990). It is anticipated that SSL (which can be either LED or OLED based technology) can save in combination with smart lighting management systems up to 70% of required electrical energy today. LED’s are expected to convert electrical energy  at an efficiency of about 60%, compare that to incandescent bulbs of only 2% and CFL’s of about 25%.

Looks OK at first sight isn’t ? But it totally overlooks that these new light sources will create new applications and therefore a possible risk that the net result is that we save much less or, even worse, spent even more of our electricity bill on lighting than today. This is comparable to the anticipated reduction in paper use with the arrival of the PC and high quality monitor screens. Well we know how that ended….. look for instance to the amount of junk mail that you find almost daily in your mailbox. Thus we will need to be careful how we apply SSL.

The EC is worried about Europe’s competitive position (quote from the report):

“The USA in 2009 put in place a long-term SSL strategy (from research to commercialisation). China is implementing a municipal showcase programme for LED street lighting involving more than 21 cities; it is granting significant subsidies to LED manufacturing plants and aims to create 1 million related jobs in the next 3 years. South Korea has defined a national LED strategy with the goal to become a top-3 world player in the LED business by 2012”

Two linked objectives are mentioned by the EC: 1) Develop the demand side (European users) and 2) Develop the supply side (role of  the European industry)

One of the problems to overcome is the high price of SSL: a 60W incandescent bulb cost about 1 Euro, a CFL about 5 Euro and a LED about 30 Euro. It is expected that by continuous price erosion in 2015 market share of CFL and SSL will be balanced. Not so far away!

 

Can adding a reliability standard to Energy Star actually hurt LED lighting?

An interesting article in Electronic Design News on SSL and CFL. Follow this link:

http://www.edn.com/blog/PowerSource/39403-Can_adding_a_reliability_standard_to_Energy_Star_actually_hurt_LED_lighting_.php

The article deals about a new proposed energy efficiency standard but has some real interesting quotes about CFL (compact fluorescense lamps). Read also the comments!

See also my earlier blog on CFL’s: https://secondlawoflife.wordpress.com/2010/04/06/reliability-of-compact-fluorescence-lamps/

 

Reliability of Compact Fluorescence Lamps

Some time ago I wrote about the advantages of compact fluorescence lamps (CFL) and a life cycle analysis (LCA) of these devices described in the literature[1]. Basic outcome was that CFL’s indeed do give overall resource savings[2]. In an LCA you have of course to assume an average lifetime of the CFL, typically taken as 5 times[3] that of a regular incandescent lamp (ICL). Because CFL’s are  so much more complex to make than ICL’s,  the resource savings benefit would fall apart if the CFL does deviate substantially from the assumed lifetime.

The  positive LCA outcome convinced me to replace many of the ICL’s in my house by CFL’s and accept the high upfront cost (which is easily 5 times as expensive as ICL’s). I bought about 15 lamps. Much to my surprise and frustration within a year I had 3 failures. Note that I bought the CFL’s from a top brand but  that the manufacturer gives no guarantee whatsoever in case of an early failure.

Therefore, I did a quick and dirty web search to see what one can find about reliability of CFL’s. Well not too much. Two interesting leads I found though.

The first one is a study from the Energy Federation Inc., published in 2002[4]. Over the period 1994-2001 four big brand and four little brand manufacturers were tracked for sales and returns. The big brands had a return rate of 1.4%[5]. Much more detail is in this report such as relation between return rate and wattage of the lamp so I recommend you go to their website and read the report [6].

Based on this you can expect on average one early failure out of 70 CFL’s that you will buy[7]. Clearly, my failure rate (3 out of 15) is much higher. And what is most frustrating is that there is no warranty on these lamps. If they fail after 6 months or so what can you prove? Nothing.

But I am not the only on suffering from this problem. See the kiloxray.com blog (http://www.kiloxray.com/blog/?page_id=8). The author is actually logging the number of failures (there are many!!) he is experiencing and has a good tip: note down on the lamp the date that you put the CFL in operation and……. hold on to the original receipt. You may have a chance to get your money back from the manufacturer although don’t have to high expectations on this. If you have similar experiences or recommendations to share please put in a comment.

© Copyright 2010 John Schmitz

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[1] https://secondlawoflife.wordpress.com/2008/10/05/compact-fluorescence-lamps/

[2] Parsons, David. “The Environmental Impact of Compact Fluorescent Lamps and Incandescent Lamps for Australian Conditions”, The Environmental Engineer 7(2): 8-14 (2006).

[3] Actually numbers vary, you can find numbers as high as 10!

[4] Bradley Steele, The Performance and Acceptance of Compact Fluorescent Lighting Products in the Residential Market; Energy Federation, Inc

[5] Little brands were running slightly higher at 1.5%

[6] http://www.lrc.rpi.edu/programs/lightingTransformation/pdf/bradSteele.pdf

[7] This should be a worse case return rate as you may expect that the CFL manufacturers would have improved the reliability of their products since 2002

 

Energy Conversion Efficiency by LED’s used in Solid State Lighting

Semiconductors play an important role in solving the planet’s energy issues. There are two distinct, but related, phenomena: the conversion of (sun) light in electricity and the conversion of electrical power in visible light. The first conversion is known as the photo-voltaic (PV) technology and the second conversion is the one that is used by Light Emitting Diodes (LED’s) used in Solid State Lighting applications. Both conversions enjoy  considerable interest from scientists, governments, energy companies as well as citizens. Clear is that both energy conversions can contribute substantially in solving the availability and distribution of energy around the planet.

A key factor for the successful acceptance (at least in terms of economically feasibility) of both PV and LED’s is the efficiency of these two types of energy conversions since this will directly impact cost per Watt or cost per Lumen. Indeed, the question arises are there fundamental limitations to these energy conversions? For PV cells it has been reported that the upper efficiency of on silicon based cells will run at about 30%. For LED’s there has not been reported so far a fundamental barrier that would keep the LED away from 100% efficiency (however, the fact that the device heats up during operation hints already to a less than 100% efficient light conversion).

On the efficiency of PV cells I will come back in a future contribution, for now I would like to focus on the efficiency of a LED. A LED is typically constructed from a classical p-n junction but in the LED case the p and n material are separated by what is called an active zone that can be either doped or intrinsic. The semiconductor material must be a direct band gap semiconductor in order to have sufficient conversion efficiency[i]. By putting the LED in a forward bias the electrons and holes that arrive in the active zone can recombine in two different ways:

–         Radiative recombination. It is this recombination that fuels the light emission from the LED.

–         Several other non-radiative recombination processes occur as well. These reduce the amount of holes and electrons available for light emission.

There are other loss (non-radiative) mechanisms operating (such as absorption of the photons by the semiconductor) that further reduce the light generation efficiency.

Recently an article in the Journal of Applied Physics[ii] appeared that gives good insight in the different factors that influence the power-light conversion efficiency. An important factor is the so-called wall plug efficiency, defined as follows:

Wall Plug Efficiency = emission power/electrical power

a pretty straightforward definition. In the article all the different recombination and loss mechanisms are mathematically described and then put together in one model for the LED. This model can then calculate the behavior (and thus wall plug efficiency) of the LED device in terms of operating conditions (temperature, current, voltage), material properties (semiconductor material such as GaN or GaAS and doping) and LED structure (thickness of the different layerings, metal contacts and lay out of the active layer). This is of great help when optimizing the LED device for conversion efficiency.

Let me summarize a few important conclusions from the article:

–         There is not a fundamental reason why the power-light conversion cannot be 100%. Even stronger, the conversion can be more than 100% (see next point for explanation)! However, the high efficiencies may not always in a practical operating window (for instance at the current densities the LED needs to run because of a certain required light output per surface area semiconductor).

–         The energy of the photon may come not only because from the band gap energy difference but phonons (thermal energy from the lattice) may contribute as well. In that case the LED can act as a heat pump: the device cools actually and can in that way extract heat from the environment and achieve efficiency better than 100% (using the above wall plug efficiency definition).

–         Further improvements will be possible to increase the light output of LED’s.

Thus, we can expect to see in the coming years more developments coming to improve the Solid State Light technology and this will be a very valuable contribution to our energy strategy.

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[i] See for an explanation: http://en.wikipedia.org/wiki/Direct_and_indirect_band_gaps

[ii] O. Heikkila, J. Oksanen, J. Tulki, Ultimate limit and temperature dependency of light-emitting diode efficiency,  Journal of Applied Physics 105, 093119 (2009)

©  Copyright John Schmitz 2010

 

Can the Human Body Be Considered a Heat Engine?

The human body can deliver lots of work. Consider, for instance, the athlete running a marathon, or the cyclist racing in the Tour de France. We also know that human body temperature is normally 37°C and that usually the environment is cooler, say 20°C. From this we could suggest that there is some resemblance between a heat engine, in which the body is the heat source, and the cooler environment could act as a heat sink. So let’s make a few simple calculations to see how closely the body resembles a heat engine. We know that the efficiency of a heat engine is determined by the temperatures of the heat source (the body temperature, T_body = 310K) and the heat sink (the environmental temperature, T_sink  = 293K):

  Efficiency = [T_body – T_sink]/T_body = [310-293]/310 = 5.5%

 Thus, based on this temperature difference, the body would be able to achieve only 5.5% efficiency. Fortunately, scientific studies already have estimated the human body’s efficiency [1] in other ways. One study reasons that for an average man to produce 75 Watts of power, he will need to breathe about one liter of oxygen per minute. That liter of O₂ is combusted in body cells to form carbon dioxide (CO₂). It has also been determined that one liter of oxygen generates in this way about 300 Watts of power. Thus, we can conclude that the efficiency of the human “engine” is 75/300 = 25%. What causes the difference between the 5.5% efficiency as calculated above, and the 25% from the combustion determination? The explanation is that the human body cannot be considered a heat engine. The work is not generated in the same way as a steam engine, which directly transforms heat into work and lower-temperature waste heat. Instead, the human body is more like a fuel cell, where chemical energy is transformed into work (see also Whitt et. al.). For this kind of transformation, one obviously cannot use the efficiency formula of a heat engine.

 

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[1] Whitt, F.R. and Wilson, D.G., Bicycling Science, MIT Press, Cambridge (1976)

 

Energy and the Internet

Recently a Harvard University scientist, Alex Wissner-Gross, was quoted in TimesOnLine  that each computer search of the internet could produce as much as 7 gram of CO2 (the journalists of TimesOnLine compared that to boiling a kettle of water that would produce about 15 gram of CO2).[1] Google responded that the calculation was not right as an average search would only last about 0.2 second and that that would then equate to about 0.2 gram of CO2.[2] Clarifications later on revealed that Google referred to a one time search hit whereas Wissner-Gross referred to a complete search that encompasses several hits. Further more Google pointed out that the company has several environmental footprint reducing initiatives underway.

But it remains of course interesting to know how much energy the ICT infrastructure needs. It has been suggested[3] that this could be up to 2% of the world’s total greenhouse emissions (comparable to the amount produced by air transportation).

Closer to ourselves: who knows how much energy your PC at home takes up? Well I did not know the answer and I have monitored my PC  for a week. I simply hooked up a kWh meter between the outlet and the PC/printer/external HD/scanner assembly. The lucky number is: 6.3 kWh per week. At night I switch the PC off and during day time I put the PC in standby after 20 minutes of idle time. I also compared this figure with my freezer/fridge combination:

1.             PC                                 6.3     kWh/week              327 kWh/year
2.             Freezer/Fridge       38.1   kWh/week           1981  kWh/year

Then also good to know is that the electricity need of an average Belgian family is about 3500kWh per year.[4]

What we conclude from this that indeed PC’s and accessories do require a substantial amount of energy that is not small compared to other household appliances. A critical look at standby regimes and shutting down overnight seems to be wise.

© Copyright John Schmitz

 

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[1] http://technology.timesonline.co.uk/tol/news/tech_and_web/article5489134.ece

[2] http://googleblog.blogspot.com/2009_01_01_googleblog_archive.html

[3] Recent Gartner report, see reference 1

[4] http://www.vreg.be/nl/04_prive/05_meteropneming/04_verbruik.asp

 

Green Cars

In an earlier blog I wrote that, short term, the best way to contribute to the planet’s energy issues is by reducing our energy “consumption”. We saw also that road transportation claims about 20% of the total energy bill. In addition we know that a substantial amount (about 70%) of the energy liberated from the car fuel is wasted mainly in the form of heat to the environment.[1] The power required  to move the car is substantially. Let’s take as a quite familiar reference: an incandescent lamp of 100 Watts. Only a small fraction of the 100Watts is actually converted into light (ca 10%) the rest is converted into heat. From experience everybody has a sense of how much heat a 100W bulb generates. After a few minutes the bulb is very hot and you could burn your fingers when you touch it. To compare, cars have engines of say between 50 and 150 horse power (hp). In the table below I have converted the hp’s into kW:

 

            50 hp   =          36 kW

            100 hp =          74 kW

            150 hp =          110 kW

 

Thus a 50 hp car consumes 360 times as much energy as our light bulb! And a 150 hp car even more than 1000 times. It is therefore clear that if we could save only a little bit on this waste, that we are talking immediately about large amounts of energy savings.

On top of the heat waste, cars propelled by internal combustion engines produce per km also an amount of CO₂. And we all know what the impact is of CO₂ on the earth ecosystem. To give you some feeling: one liter of petrol produces 2400 grams of CO₂. At room temperature and one atmosphere that is about 50 liters. A typical car will burn about one liter of petrol per 20 km. Therefore, reducing CO₂ will then directly reduce the energy consumption.

The European Commission and governments have from that point of view put quite strict regulations in place for CO₂ emissions of cars. These regulations have a two prong approach: tax reduction for the buyer of clean cars and penalties for the car producer if the car does not meet minimum emission criteria. The criteria for the car manufacturer are: an average CO₂ emission in 2012 if less than 130 gr/km. The penalty to pay by the car manufacturer is 20 E/gr in 2012 but increasing to 95 E/gr in 2015. On the other hand  car buyers can get an appreciable tax (up to 5000 Euro’s) cut when buying a new car that has a low CO₂ emission rating.

Sensible measures I would say.

 ©  Copyright 2009 John Schmitz

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[1] Actually less than 20% of the energy from the fuel becomes available to deliver mechanical traction of the car! Other losses are fiction, idling, standby, accessories and AC.

 

“Saving” Energy

Can we “save” energy? Of course not. We cannot “save” energy as the first law of thermodynamics explains: energy is conserved no matter what we do. The only thing we can do to help solve the planet’s energy problem is to reduce the speed with which we degrade the quality of the energy sources available to us. And indeed the best way to accomplish that is to “use” as less as possible of this high quality energy. Examples of high quality energy are fossil fuels, nuclear fuel, solar or PV energy, wind energy etc. The common factor in all these different sources is that the energy is concentrated in a relatively small volume. A typical example of low quality energy is heat (most of the times at least). Why? Heat is difficult to maintain and tends to leak away and thus disperses over a large volume. One joule of heat remains one joule of energy regardless whether the volume in which it is contained is one cubic cm or the entire galaxy. So where is the problem? Here is where the Second Law of thermodynamics kicks in. High quality energy conditions have a low entropy value whereas low quality energy has a high entropy value. The entropy law teaches us that with each “use” of energy the entropy increases (and thus the quality is decreasing) and that there is no recovery back from that. In other words quite a fundamental limitation and no technology can help you overcome that Second Law!

There are two ways how we can help ourselves to slow down the ever ongoing energy quality degradation.

1) The quickest one is simple: reduce the need for energy as much as you can! Let’s have a look at the energy ‘consumption” breakdown (IEA 2008):

Category	Relative energy usage (%)
Industry	32
Road transportation	20
Air/sea transportation	6
Agriculture	3
Services	7.8
Buildings	28
Fertilizers	5

For example, as long as the fuel “consumption” in the USA per km is still about 40% higher than that in Europe it is clear where the focus needs to be. Also, note that about 20% of the total energy needs goes into road transportation. Thus if we would start to drive energy efficient cars, it would cut 10% of the US total national energy bill! No needs for new inventions, just take what exist already today!

 Because of the high fuel prices there have been proposals from politicians and governments to reduce taxes on fuels. This is precisely the wrong measure to implement. What should be done is to lower the tax or subsidize more measures that will result in less energy needs such as home insulation, fuel efficient cars and fuel efficient heating units. The best way to solve the energy problems of the planet in short term is reducing the need for energy in the first place!

 2) The other way to mitigate the energy problems of the planet, but then more long term, is the use of renewable energy sources, basically all based on the solar energy that reaches the earth. The sun is such a rich source. Realize that the energy influx is many times higher than the world energy need. There are massive problems to overcome such as costs price and, more importantly, the capacity of our power grid that can accommodate these variable energy sources. This will ask for clever storage means that must come along with the renewable sources.

© Copyright 2009 John Schmitz

 

Wasting Energy? Why?

There are many instances that we can see that in our attempts to transform energy into as much as possible usable work, we are always left with this “rest” amount of heat that we can not use anymore to generate even more work¹. Clear examples of these imperfect transformations are the coolant radiators in our cars and the cooling towers of many factories or power plants. In power plants that use fossil fuels we can have an efficiency as poor as 50% or often even lower, meaning that only 50% of the energy enclosed in the fuel is converted into electrical power, by means of burning fuel, heat generation that leads to steam and steam that will drive then turbines and generators. 50% or less is that not a shame? Of course the question arises why that is the case?

Why can we not convert for the full 100% the energy enclosed in the fuel into utile work? Well it is here that the Second Law of thermodynamics kicks in, also known as the entropy law. But before we go deeper into this entropy law first a bit more about the First Law of thermodynamics. The First Law is nothing more than the law of conservation of energy. Energy can be present in many forms (chemical, heat, work, electrical, nuclear etc etc) and the total amount of all this energy in the universe is constant. The First Law will not object to convert a given amount of energy fully into work. Unfortunately we never observe this attractive situation. The answer why that is so can be found from an analysis of the entropy law.

What is entropy? Entropy is a concept discovered while people were answering “simple” questions such as why heat only streams from warm to cold places. Another question that came up around 1800 was caused by the growing popularity of steam engines. Steam engines can also be called heat engines because they convert heat into work. Another example of a heat engines is a car engine. Steam engines where used in England to pump water out of the coal mines, a job that was done by many workers day and night before steam engines became available. To keep the steam engine running, fuel (such as wood or coal) was burned to generate the steam. While the steam engine was gaining ground, many improvements (for instance James Watt was able to improve efficiency with about 25%) were done that increased the efficiency of the steam engines considerably. Therefore much more work could be obtained from a given amount of fuel.

While this went on there was a young French military engineer, Sadi Carnot, who asked himself the question whether there was perhaps an upper limit to this efficiency. To answer that question he carried out a careful analysis around 1825 using a simplified model of a steam engine². The result of his analysis was that the upper limit of the efficiency was only determined by two factors: the temperature of the heat source (the steam) and the temperature of the heat sink (the location where the steam was condensed, for all practical matters the outside air). More precisely he found that the amount of heat, Q_h, taken from the heat source at temperature , T_h, is related to the amount of heat given up at the heat sink, Q_c, at temperature T_c, as: Q_h/T_h = Q_c/T_c. Although he did not coined the factor Q/T as entropy (that was done by Rudolph Clausius around 1850) he clearly laid the foundation for scientists such as Clausius who came to the conclusion that “something was missing” and was needed in addition to the First Law . That something became later the Second Law of thermodynamics.

The best possible efficiency of the steam engine was then shown by Carnot to be equal to (T_h-T_c)/T_h (an atmospheric steam engine efficiency is therefore limited to about (373-272)/373 = 25% efficiency).

The work of Carnot showed very clearly that in order for a heat engine to work you MUST have a heat source at high temperature and a heat sink at colder temperature and that the heat disposed at the heat sink can NEVER generate any work anymore unless you have another heat sink available at an even lower temperature. Also, from the fact that Q_h/T_h = Q_c/T_c, it becomes clear that in an heat engine you MUST give up an amount of heat, Q_c, to the cold sink no escape. That is the fundamental reason for having the efficiency of the heat engines less than 100%! We can also see now that the efficiency of heat engines will increase if we make the temperature difference between the heat source and heat sink as large as possible.

See for more background on this topic:

https://secondlawoflife.wordpress.com/2007/08/28/carnot-efficiencies/

https://secondlawoflife.wordpress.com/2007/05/25/can-we-recycle-energy-or-the-role-of-law-of-entropy/

 

© 2008 John Schmitz

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1. With work we mean here the ability to lift weights, or to to turn wheels which in turn can rotate shafts.

2. This model is well known as the Carnot cycle.