Saturday, 15 June 2013

Ketika "Hulk" Bicara Energi Hijau

Mark Ruffalo Visits Stanford to Talk Clean Energy

Life imitated art when MARK RUFFALO, the actor who plays scientist Dr. Bruce Banner (aka “The Hulk”) in the blockbuster film The Avengers, came to Stanford University.

The Oscar-nominated actor/director teamed up with Mark Jacobson, a real-life scientist and senior fellow with the Stanford Woods Institute for the Environment and the Precourt Institute for Energy, for an informal discussion with students about a nascent initiative to convert the world to renewable energy.

The talk was part of a series of planned dialogues Ruffalo and Jacobson had with Stanford students and staff at companies such as Google, Facebook and Tesla Motors. Joining Ruffalo and Jacobson were clean energy advocates Marco Krapels, executive vice president of Rabobank, and Jon Wank, co-president of Skadaddle Media.

Dr. Bruce Banner: "So he's building another portal. That's what he needs Erik Selvig for."
Thor: "Selvig?"
Dr. Bruce Banner: "He is an astrophysicist." 

Thor: "He is friend"

Mark Alan Ruffalo (born November 22, 1967) is an American actor, director, producer and screenwriter. Known for portraying Marvel Comics character Bruce Banner / The Hulk in Marvel's The Avengers (2012), he has also starred in films such as You Can Count on Me (2000), Collateral (2004), Eternal Sunshine of the Spotless Mind (2004), Just Like Heaven (2005), Zodiac (2007), and Shutter Island (2010).

For his role in The Kids Are All Right (2010), he received an Academy Award nomination for Best Supporting Actor.

“It’s the right time for this,” Ruffalo told the 30 or so audience members, most of them students in the Atmosphere/Energy Program Jacobson heads in the Department of Civil and Environmental Engineering. People are more aware of and more ready than ever to grapple with climate and energy problems, Ruffalo said, adding, “Now we’re able to talk about it without going through a centralized media.”

Ruffalo explained that his interest in creating a roadmap to repower the energy infrastructure with clean energy began when he moved to upstate New York a few years ago and learned about hydrofracking, a polluting natural gas extraction method used in the region. “It sounded more and more like a nightmare,” he said.

Local involvement around the hydrofracking issue led to a broader engagement in the sustainability movement for Ruffalo, who has been speaking out to his social media followers and the blogosphere about the need for clean energy. Ruffalo connected with Jacobson and Josh Fox, the director of the 2010 fracking documentary Gasland, at an event in San Francisco last year.

Apa Itu Energi Hijau?

Definisi energi hijau paling sederhana adalah energi yang dihasilkan dari sumber energi yang lebih ramah lingkungan (atau "hijau") dibandingkan dengan bahan bakar fosil (batubara, minyak, dan gas alam). Karena itulah energi hijau mencakup semua sumber energi terbarukan (surya, angin, panas bumi, biofuel, tenaga air), dan menurut definisi juga harus mencakup energi nuklir meskipun ada banyak penggiat lingkungan yang menentang gagasan mengenai energi nuklir masuk ke dalam energi hijau karena nuklir memiliki masalah limbah, dan efeknya yang berbahaya terhadap lingkungan.

Terminologi energi hijau diciptakan untuk memisahkan bahan basar fosil yang mengakibatkan tingkat polusi yang tinggi dengan bahan bakar lainnya yang mengakibatkan polusi lebih rendah dan ramah lingkungan seperti pada sumber energi terbarukan. Perubahan iklim telah menjadi ancaman global, dan dunia perlu menemukan pilihan energi bersih (lebih sedikit emisi), dan dengan demikian energi hijau penting untuk terus berkembang.

 Para Avengers Berkumpul

The three had an in-depth conversation about Jacobson’s work with Mark DeLucchi at the University of California-Davis to develop a global renewable energy plan. The plan – featured on the cover of Scientific American is a blueprint for building an energy grid based only on clean sources such as solar, wind and hydroelectric. This grid, not subject to price fluctuations, would eliminate energy insecurity, air pollution and global warming.

Following that dinner conversation, Ruffalo, Jacobson, Fox and researchers at Cornell University began reaching out to other scientists, business people and cultural figures to further develop a roadmap for repowering the world. The effort would galvanize support for a clean-energy economy at state, national and, eventually, global levels. Jacobson described it as a “grand vision” involving science, economics, policy, finance, multimedia and activism. Ruffalo and Jacobson wrote about their vision in the Huffington Post earlier this month.

The next step will focus on informing policymakers about viable options for converting to a clean-energy economy, Jacobson told the Stanford audience. Beyond that crucial component, the way forward will not have to depend on good intentions alone, he added. “This will be driven a lot by people who want to make money,” he said of developers interested in building renewable energy infrastructure. Krapels echoed that sentiment, saying that Rabobank, the world’s largest agricultural bank, is interested in how renewable energy can save money for its clients. “We’ve been looking at this very much from a business perspective.”

During a question-and-answer session, students offered suggestions for connecting with college students, ranging from campus advocates to conferences.

One student’s suggestions of imitating a Stanford/NASA teacher-training partnership elicited particular interest from the speakers.

 "The Iron Man and The Hulk Together"

Energi hijau masih tidak cukup kuat untuk bersaing dengan bahan bakar fosil. Hal ini terutama karena energi hijau masih menjadi pilihan energi yang secara signifikan lebih mahal dibandingkan dengan bahan bakar fosil, dan dengan demikian banyak negara, terutama negara berkembang, tetap menggunakan bahan bakar fosil yang lebih murah seperti batubara.

Istilah energi hijau tidak hanya mencakup sumber energi terbarukan tetapi dapat diperluas untuk mencakup konservasi energi (contohnya energi hijau juga dipakai untuk menyebut bangunan yang dibangun dengan cara agar tetap dingin di siang hari dan tetap panas di malam hari melalui desain arsitektur yang tidak mengandalkan AC atau sistem pemanas ruangan).

Promosi energi hijau tidak hanya dengan menggunakan sumber energi terbarukan di tahun-tahun mendatang, tetapi juga untuk membuat dominasi teknologi bahan bakar fosil saat ini menjadi lebih hijau dan mengurangi tingkat polusi (seperti teknologi batubara bersih).

Istilah energi hijau kadang-kadang diidentifikasikan dengan istilah energi berkelanjutan, tetapi hal ini tidak sepenuhnya benar karena energi yang berkelanjutan juga mencakup teknologi untuk meningkatkan efisiensi energi. Energi hijau tidak mengacu pada efisiensi sumber energi terbarukan tetapi hanya menekankan pada dampak positif mereka terhadap lingkungan (dibandingkan dengan bahan bakar fosil).

Mari kita kembangkan Energi Hijau, kalau "Hulk" saja peduli, apa lagi kita?

Semoga Bermanfaat


1. Stanford University
2. The Avengers 
3. Indonesia Energi
[Masyarakat Energi Terbarukan Indonesia]

Solar Power Satellite VI

Percobaan yang dikenal dengan nama Suaineadh (yang artinya ‘memutar’ dalam bahasa Gaelic skotlandia) merupakan langkah maju yang penting dalam desain konstruksi luar angkasa dan menunjukkan bahwa struktur yang lebih besar dapat dibangun di atas sebuah jaring ringan yang berputar.

Hal tersebut akan membuka jalan untuk tahap berikutnya dalam proyek tenaga surya luar angkasa.
Dr. Vasile menambahkan:
“Keberhasilan Suaineadh memungkinkan proyek kami  bergerak maju pada tahap berikutnya, dimana akan melibatkan reflektor yang diperlukan untuk mengumpulkan tenaga surya."

“Proyek yang diberi nama SAM (Self-inflating Adaptable Membrane) ini akan menguji peluncuran struktur selular sangat ringan yang dapat berubah bentuk pada saat diluncurkan."
Struktur terbuat dari sel-sel yang dapat menggembungkan diri dalam ruang hampa udara dan dapat mengubah volumenya sendiri melalui nanopumps (pompa nano).
“Struktur tersebut meniru struktur selular alami yang ada pada semua makhluk hidup. Kontrol independen dari sel akan memungkinkan kita untuk merubah struktur menjadi konsentrator surya yang akan mengumpulkan sinar matahari dan memproyeksikannya pada rangkaian sel surya surya. Struktur yang sama dapat digunakan untuk membangun sistem ruang angkasa yang besar dengan merakit ribuan unit individu kecil.”

Lofstrom launch loop

Lofstrom loop could conceivably provide the launch capacity needed to make a solar power satellite practical. This is a high capacity launch system capable of reaching a geosynchronous transfer orbit at low cost (Lofstrom estimates a large system could go as low as $3/kg to LEO for example). The Lofstrom loop is expected to cost less than a conventional space elevator to develop and construct, and to provide lower launch costs. Unlike the conventional space elevator, it is believed that a launch loop could be built with today’s materials.

Space elevators

More recently the SPS concept has been suggested as a use for a space elevator. The elevator would make construction of an SPS considerably less expensive, possibly making them competitive with conventional sources.

However it appears unlikely that even recent advances in materials science, namely carbon nanotubes, can make possible such an elevator, nor to reduce the short term cost of construction of the elevator enough, if an Earth-GSO space elevator is ever practical. A variant to the Earth-GSO elevator concept is the Lunar space elevator, first described by Jerome Pearson in 1979.

Because of the ~20 times shallower (than Earth's) gravitational well for the lunar elevator, this concept would not rely on materials technology beyond the current state of the art, but it would require establishing silicon mining and solar cell manufacturing facilities on the Moon, similar to O'Neill's lunar material proposal, discussed above.


The use of microwave transmission of power has been the most controversial issue in considering any SPS design, but any thought that anything which strays into the beam's path will be incinerated is an extreme misconception. Consider that quite similar microwave relay beams have long been in use by telecommunications companies world wide without such problems.

At the earth's surface, a suggested microwave beam would have a maximum intensity, at its center, of 23 mW/cm2 (less than 1/4 the solar irradiation constant), and an intensity of less than 1 mW/cm2 outside of the rectenna fenceline (10 mW/cm2 is the current United States maximum microwave exposure standard).

In the United States, the workplace exposure limit (10 mW/cm2) is at present, per the Occupational Safety and Health Act (OSHA), expressed in voluntary language and has been ruled unenforceable for Federal OSHA enforcement.

The beam's most intense section (more or less, at its center) is far below dangerous levels even for an exposure which is prolonged indefinitely. Furthermore, exposure to the center of the beam can easily be controlled on the ground (eg, via fencing), and typical aircraft flying through the beam provide passengers with a protective shell metal (ie, a Faraday Cage), which will intercept the microwaves.

Other aircraft (balloonsultra-light, etc) can avoid exposure by observing airflight control spaces, as is currently done for military and other controlled airspace. Over 95% of the beam energy will fall on the rectenna. The remaining microwave energy will be absorbed and dispersed well within standards currently imposed upon microwave emissions around the world.

The microwave beam intensity at ground level in the center of the beam would be designed and physically built into the system; simply, the transmitter would be too far away and too small to be able to increase the intensity to unsafe death ray levels, even in principle.

In addition, a design constraint is that the microwave beam must not be so intense as to injure wildlife, particularly birds. Experiments with deliberate microwave irradiation at reasonable levels have failed to show negative effects even over multiple generations.

Some have suggested locating rectennas offshore, but this presents serious problems, including corrosion, mechanical stresses, and biological contamination.

Phased array transmission was originally developed in 1905 by Nobel Physics Laureate Karl Ferdinand Braun who demonstrated enhanced transmission of radio waves in one direction.
A commonly proposed approach to ensuring fail-safe beam targeting is to use a retrodirective phased array antenna/rectenna. A "pilot" microwave beam emitted from the center of the rectenna on the ground establishes a phase front at the transmitting antenna. There, circuits in each of the antenna's subarrays compare the pilot beam's phase front with an internal clock phase to control the phase of the outgoing signal.

This forces the transmitted beam to be centered precisely on the rectenna and to have a high degree of phase uniformity; if the pilot beam is lost for any reason (if the transmitting antenna is turned away from the rectenna, for example) the phase control value fails and the microwave power beam is automatically defocused Such a system would be physically incapable of focusing its power beam anywhere that did not have a pilot beam transmitter.

It is important for system efficiency that as much of the microwave radiation as possible be focused on the rectenna. Outside of the rectenna, microwave intensities would rapidly decrease, so nearby towns or other human activity should be completely unaffected.

The long-term effects of beaming power through the ionosphere in the form of microwaves has yet to be studied, but nothing has been suggested which might lead to any significant effect.

Kunjungi Juga:

Semoga Bermanfaat.

To Be Continued 

Apa Itu Angka Knudsen?

Didefinisikan sebagai rasio dari rata-rata panjang jalur bebas molekular terhadap suatu skala panjang fisik representatif tertentu. Skala panjang ini dapat berupa radius suatu benda dalam suatu fluida. 

Secara sederhana, angka Knudsen adalah berapa kali panjang diameter suatu partikel akan bergerak sebelum menabrak partikel lain. 

The Knudsen number (Kn) is a dimensionless number defined as the ratio of the molecular mean free path length to a representative physical length scale. This length scale could be, for example, the radius of the body in a fluid. 

The number is named after Danish physicist Martin Knudsen (1871–1949). Who taught and conducted research at the Technical University of Denmark. He is primarily known for his study of molecular gas flow and the development of the Knudsen cell, which is a primary component of molecular beam epitaxy systems.

The Knudsen number is a dimensionless number defined as:
\mathit{Kn} = \frac {\lambda}{L}
For an ideal gas, the mean free path may be readily calculated so that:
\mathit{Kn} = \frac {k_B T}{\sqrt{2}\pi\sigma^2 p L}
  • k_B is the Boltzmann constant (1.3806504(24) × 10−23 J/K in SI units), [M1 L2 T-2 θ-1]
  • T is the thermodynamic temperature, [θ1]
  • \sigma is the particle hard shell diameter, [L1]
  • p is the total pressure, [M1 L-1 T-2].
For particle dynamics in the atmosphere, and assuming standard temperature and pressure, i.e. 25 °C and 1 atm, we have \lambda ≈ 8 × 10−8 m.

Relationship to Mach and Reynolds numbers in gases

The Knudsen number can be related to the Mach number and the Reynolds number:
Noting the following:
Dynamic viscosity,
\mu =\frac{1}{2}\rho  \bar{c} \lambda.
Average molecule speed (from Maxwell-Boltzmann distribution),
\bar{c} = \sqrt{\frac{8 k_BT}{\pi  m}}
thus the mean free path,
\lambda =\frac{\mu }{\rho }\sqrt{\frac{\pi  m}{2 k_BT}}
dividing through by L (some characteristic length) the Knudsen number is obtained:
\frac{\lambda }{L}=\frac{\mu }{\rho  L}\sqrt{\frac{\pi  m}{2 k_BT}}
The dimensionless Mach number can be written:
\mathit{Ma} = \frac {U_\infty}{c_s}
where the speed of sound is given by
c_s=\sqrt{\frac{\gamma  R T}{M}}=\sqrt{\frac{\gamma  k_BT}{m}}
The dimensionless Reynolds number can be written:
\mathit{Re} = \frac {\rho  U_\infty L}{\mu}.
Dividing the Mach number by the Reynolds number,
\frac{Ma}{Re}=\frac{U_\infty \div  c_s}{\rho  U_\infty L \div  \mu }=\frac{\mu }{\rho  L c_s}=\frac{\mu }{\rho  L \sqrt{\frac{\gamma  k_BT}{m}}}=\frac{\mu }{\rho  L }\sqrt{\frac{m}{\gamma  k_BT}}
and by multiplying by \sqrt{\frac{\gamma  \pi }{2}},
\frac{\mu }{\rho  L }\sqrt{\frac{m}{\gamma  k_BT}}\sqrt{\frac{\gamma  \pi }{2}}=\frac{\mu }{\rho  L }\sqrt{\frac{\pi  m}{2k_BT}} = \mathit{Kn}
yields the Knudsen number.
The Mach, Reynolds and Knudsen numbers are therefore related by:
Kn = \frac{Ma}{Re} \; \sqrt{ \frac{\gamma \pi}{2}}.


The Knudsen number is useful for determining whether statistical mechanics or the continuum mechanics formulation of fluid dynamics should be used: If the Knudsen number is near or greater than one, the mean free path of a molecule is comparable to a length scale of the problem, and the continuum assumption of fluid mechanics is no longer a good approximation. In this case statistical methods must be used.

Problems with high Knudsen numbers include the calculation of the motion of a dust particle through the lower atmosphere, or the motion of a satellite through the exosphere. One of the most widely used applications for the Knudsen number is in microfluidics and MEMS device design. 

The solution of the flow around an aircraft has a low Knudsen number, making it firmly in the realm of continuum mechanics. Using the Knudsen number an adjustment for Stokes' Law can be used in the Cunningham correction factor, this is a drag force correction due to slip in small particles (i.e. dp < 5 µm).

Semoga Bermanfaat. 

Ucapan Terima Kasih:

Bapak dan Ibu Guru Semasa SMA

Guru dan Dosen di Pendidikan Fisika, FPMIPA Universitas Pendidikan Indonesia


Arip Nurahman Notes