Energy


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

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book_cover_big.gifRecently 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!

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/

book_cover_big.gifSome 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


[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

book_cover_big.gifSemiconductors 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.


[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

book_cover_big.gifThe 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, Tbody = 310K) and the heat sink (the environmental temperature, Tsink  = 293K):

  Efficiency = [Tbody – Tsink]/Tbody = [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.

 


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

book_cover_big.gifRecently 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

 


[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

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