Thursday, October 29, 2009

Guest Lecture - Ronald Roedel

The important part of the lecture was about structure of the solar cells and its operation. The main thing was about optical radiation which got absorb by the solar cells and the result creates active charged particle then particles will transferred by the solar.

Basically photons get collected by sunlight which we can call it "packets" of the sun energy. When solar cells were hit by photons the huge mass are get absorbed or reflected the quantity of high-energy photons will blow right away but most of the time they are get absorbed or reflected. While absorbing happened to a photon its energy is transported to a semiconductor. When an adequate amount of energy is transported the atom can run away from its regular position to the different position. Meanwhile the electron makes a hole to shape. Each photon with sufficient energy will usually give a way one electron plus one hole.

Each solar cell has three different and energetic layers. First “a top junction layer (made of the N-type semiconductor) second an absorber layer (which called the P-N junction) and third a back junction layer (made of the P-type semiconductor)”. But what is the P-N junction? In the P-N junction the cell includes its individual built-in electric field. This electric field offers the voltage which is necessarily to power electrons and holes by light absorption to run in their own instructions. In fact, it will direct the electrons to the N-type area, and the holes to the P-type area. Whether we offer an outer current path, electrons will run from side to side this pathway to their original area to join with holes the electric field send there. The electron surge offers the current and the electric field make a voltage. With both current path and voltage we can produce power.

Part of the lecture was about The Doping Model, The Fermi level (the chemical potential) and power and efficiency in the solar cell. About efficiency based on my research on the internet triple-junction compound solar cell can gain more efficiency than other product-around 35.8%. It is not similar to other silicon-based solar cells which normally used in solar panels for the home or office buildings. This product made from compounds “including indium and gallium”. Compound solar cells usually used on space satellites and they are costly to make.

Solar cells have three different generations. First Generation is “Silicon, second generation is Thin Film Structures which included Amorphous Silicon, III-V Solar Cells, II-VI Solar Cells, I-III-VI2 Solar Cells and organic Solar Cells and the third generation is Structures that exceed the single PN-junction thermodynamic conversion limit”.

The conclusion of the lecture was more concentrated on the Silicon. It is clear that the Silicon is the best and it will be the best for ever. Also second generation of solar cells provide a miniature competition to Silicon however this is momentary and third Generation of the solar cells are hardly challenging to make itself to the better position but technologically it is not possible.

Different Types of Solar Thermal Power Production

- Parabolic troughs systems
Parabolic trough system use a bended trough which reflects the direct solar radiation onto a pipe containing a fluid which is called a receiver, absorber or collector running the length of the trough above the reflectors. The trough is parabolic in one direction and straight in the other direction. For change of position of the sun perpendicular to the receiver the trough tilts so that the direct radiation remains focused on the receiver. One advantage of parabolic trough systems is their potential for storing solar thermal energy to use during non-solar periods and to dispatch when it's needed most.

- Paraboloid or dish systems
The advantage of a dish system is that it can achieve much higher temperatures due to the higher concentration of light. Higher temperatures lead to better conversion to electricity and the dish system is very efficient on this point. However, there are also some disadvantages. Heat to electricity conversion requires moving parts and those results in maintenance. In general, a centralized approach for this conversion is better than the decentralized concept in the dish design. Second the heavy engine is part of the moving structure which requires a rigid frame and strong tracking system. Furthermore, parabolic mirrors are used instead of flat mirrors and tracking must be dual-axis.

- Power tower systems
The advantage of this design above the parabolic trough design is the higher temperature as well. Thermal energy at higher temperatures can be converted to electricity more efficiently and can be more cheaply stored for later use. in addition, there is less need to flatten the ground area. In principle a power tower can be built on a hillside. Mirrors can be flat and plumbing is concentrated in the tower. The disadvantage is that each mirror must have its own dual-axis control while in the parabolic trough design one axis can be shared for a large array of mirrors.

- Solar chimneys
Solar chimney often referred to as a thermal chimney. It is a new method of improving the natural ventilation of buildings by using convection of air heated by passive solar energy. A simple description of a solar chimney is that of a vertical shaft utilizing solar energy to enhance the natural stack ventilation through a building. The solar chimney can work better by adding a tremble wall. The advantage of this design is that the system may be reversed during the cold season, providing solar heating instead. Another advantage is the collector can use all solar radiation, both direct and diffused. Also Due to the heat storage system the solar chimney will operate 24h on pure solar energy. Consider that the building materials needed for solar chimneys, mainly concrete and glass and they are available everywhere.

Different Types of Solar Thermal Collectors

Flat plate collectors
Flat-plate solar collector is one type of the solar collectors. The other major types are evacuated tube collectors and batch solar heaters. It is the most familiar solar collectors to use in solar water-heating systems and mostly use for homes and small office buildings for solar space heating. It is basically included of “an insulated metal box with a glass or plastic cover (the glazing) and a dark-colored absorber plate.”

- Tubular collectors
Different principals of evacuated tubular calculator are heat pipe evacuated tubular calculator and all glass evacuated tubular calculator. The simplest modules are made of two connected tube. The selective surface on the outer side of the inner tube is vacuumed incased. The fluid to extract heat must be passed in and out at the same end of the inner tube. One major of disadvantage of this collector compare to others is the necessity of using cylindrical shape.

- Compound parabolic collectors
If we want to stay away from the need of keeping the collector aperture pointed to the sun we are able to simply use compound parabolic collector. We can collect and concentrate solar energy from multiple directions to the one point. By using this technique when the sun moves across the sky we can accept and concentrate the solar thermal energy all day.

- Parabolic concentrators
Increasing solar energy capture can be reached by employing longer curved reflectors to take larger areas for sunshine and redirect that solar energy to a smaller center. The parabolic collectors can produce more solar energies at the focal plane or focal line. Because of the geometry and aperture of the collector it must directly face the sun to avoid loss of collection efficiency and maintain the location so the collector need complex and expensive mechanical tracking devices to keep it pointed to the sun all the time.

- Dish concentrators
Dish concentrators using parabolic dish formed mirrors to focus the received solar radiation onto a receiver that is situated at the focal point of the dish. The fluid in the receiver is heated to very high temperatures and then used to generate electricity in a small sterling engine which is attached to the receiver. Parabolic dish systems are the most efficient of all solar technologies “at approximately 25% efficient compare to around 20% for other solar thermal technologies.”

- Heliostat fields
The middle receiver solar power plant is composed to the lots of independently stirred mirrors which is called heliostat. They are focusing the solar radiation onto a tower mounted receiver. The amount of the energy which is received all depends on three different things. “First the characteristic angles of individual heliostats, second the incidence angle of the sun rays striking individual heliostats and the third the blocking and shading effect of each heliostat.”

Subsidizing Corn‐Based Ethanol

It is clear that scientists think the corn based ethanol is a very unfortunate policy because first, it offers a small amount of net energy after we consider the amount of the energy for production. As a fact, more energy we loss to make ethanol from grain than the combustion of ethanol produces. Second, using corn for fuel will raise food costs in the community. Third, ethanol has a negative balance power. “Ethanol from corn and wood biomass requires 29%, 50%, and 57% more energy” to create the ethanol than the energy restricted within the fuel. “Adding up the energy costs of corn production and its conversion to ethanol, 131,000 Btu are needed to make one gallon of ethanol. One gallon of ethanol has an energy value of only 77,000 Btu”

Unfortunately federal and state are disagreed and claimed that in Brazil people productively use sugar cane based ethanol. But the fact is sugar cane ethanol is more efficient -produces more net energy- and it made of waste left over after the extraction of sugar and also would not affect the food prices in society. The whole discussion about corn based ethanol brings two questions in the public minds. How federal and state public policies are -regarding to the issue- connected to the farming sector? And then how farmers assisted state and federal election campaigns to gain this?

Since the ethanol production requires a big quantity of energy and the majority energy in the country is created from coal the small reduction in CO2 and other polluting emissions from burning ethanol versus gasoline will be more than standard by the power needed to produce the ethanol. Also “ethanol produced has a small energy yield per hectare”. Therefore, it needs a large quantity of land to produce a significant amount of ethanol. Consider that the “20% of the whole corn crop was used to create ethanol, and it offset only 1% of US oil use” in 2008.

The majority of economic studies show that the manufacture of the corn to ethanol- if we believe the costs of environmental- it will damages our environment more than we can visualize. For example, soiling in the corn farming is a very difficult work to achieve. It is involved with “nitrogen fertilizer and petroleum-based pesticides”. Another consideration for ethanol is necessitating the farm to water. Water is limited in the country specially places close to the corn farm. As we mentioned before since corn can count as a food, ethanol production is increasing food prices like meat, milk, eggs and other grocery product because is about “70 percent of corn grain is fed to livestock and poultry in the United States”. For sure this change will attack the economy in the Unites States other parts of the world. Finally, although we want to be optimistic and wish that the all transportation services in the United States get the service with hundred percent of ethanol in the reality we will need to grow the corn feedstock all over on our land area and corn will cover nearly the total places in the United States.

But it is a big difference between the algae and corn based ethanol. For example since the country require the enormous oil needs the algae farms would take only about 15,000 square miles to produce sufficient biodiesel to meet our transportation requirements and it is possible in actuality. In fact each algae farm can be just 120 miles by 120 miles with less than 50 algae farms with only 300 square miles each to get the goal reach. Also algae is more economical and renewable as well as it will not going to displace food crop. In addition, algae are truly easier to handle than other resources since it does not require the level of filtering or titrating. In conclusion it is a desire that users learn how to make algae bio diesel for themselves at home or other places. Then they can to be more responsible for their own energy requirements and stop waiting for big energy corporations to deliver energy to them.

Tuesday, October 13, 2009

Guest Lecture Christopher Davey

The lecture started with two important points. First what are the renewable energy resources and what is the Enviro Mission in the 21 century. Renewable energy is energy produced from natural resources like sunlight, wind, rain, soil. “In 2006 around 18% of global final energy consumption came from renewable energy resources plus 13% from traditional biomass (wood-burning). The next largest renewable source is hydroelectricity which presents 3% of global energy consumption and 15% of global electricity generation. The Enviro Mission Global Solar is a tower developer who is established network of global partners and doing projects underway in the southwest. One of their big projects is a solar updraft tower power generating station recognized as “Solar Tower Buronga” in Buronga, New South Wales which started in 2001.” The height of the tower will be approximately twice as the world’s tallest structure.

The renewable energy resources have different benefits included 100% green resources with zero water, zero emission, zero fossil fuel, more reliable cost, more flexibility on hours to operate and site flexibility. Some of the technologies in renewable energy are nuclear, wind, photovoltaic and solar power. But need to consider that on top of the advantage they have disadvantage. Although nuclear power has a very high capital costs it has long development lifecycle and politically sensitive. Wind power doesn’t have a storage capability and really unreliable but the caption cost is moderate on that. Photovoltaic also has an extremely high caption cost with very expensive to install, expensive to storage and it just can operate 4 to 6 hours per day. Finally solar power is not economical in storage with high caption cost and can just operate 6 to 8 hours per day.

The attractive part in the lecture was solar tower section. Solar tower is a projected type of renewable-energy power plant. In fact it is a combination of three old and established technologies like chimney outcome, greenhouse outcome, and wind turbines. The producing skill of the solar tower mainly depends on two different factors. First the size of the tower such as collector size and chimney height and second the volume of air which needs to get warmed to run up to the chimney.

The solar tower has a big advantage over wind powers and other solar producer. The solar tower is based on no wind program and can work 24 hours and 7 days a week. They are also low costs with sustainable energy (zero water and fossil fuel use), it has more than 75 life expectation, integrates with variety of heat forms storage (hot air can be stored inside the collector region to be used to warm the air later on.) and being eco-energy for the 21st century. In addition, in our era solar tower can be a major motivated option in energy projects since it has lots of advantages compare to other developments.

Wednesday, October 7, 2009

Why do people hate wind energy so much?

Public perception to any new product is very important to shape people reaction to that product. Wind power was one of the subjects that bring lots of discussions and arguments to the public. As we know wind turbines are local issues and people have not experience them before so when wind farms started to develop in some areas the residence are affected by other peoples who doesn’t have any knowledge of wind power in action and other resources such as public media.

Some surveys exposed that 85% of the community support the use of general renewable energy and 80% are support of the use of wind power and even 70% would be have a problem to live within 5 miles of a wind power farms. Although it proves that the majority of the public report about wind turbines is positive considering the negative view of the wind power is necessarily.

There are couple reasons that people disgust the wind power. First people think wind turbines are not natural looking. This seems to come from the people who believe nature should be perfect and not spoiled by signs of human activity. Second people think wind turbines are not truly very effective and they are more a public relations trick. This is usually come from engineers who have done the numbers critical in the field. In fact those engineers are not disagreed with the wind generation as much as they are disappointed of the public reaction to the wind power. They try to argue that wind power will not solve all energy problems in the world. The third is wind turbines kill more birds than it should be but by checking the charts and graphs the numbers of the birds killed by glass tower is much bigger than wind turbines. Also in reality the number of the birds who killed by wind turbine is less than 1%. Fourth they are nice to look at but work as a noise factor. In fact wind farms are not really close to the resident area and the noise will not make any problems for dweller. As a result all these people think the wind generation is a dangerous distraction and it will make more problems instead of solving any.

People with negative approach should accept that the wind energy is one of the world's fastest growing sources of energy. Factually hundreds of new wind turbines are developing from fields across the world every year. With such explosive growth the questions about what they should look like or where they must and must not be installed is meaningless. The more important thing is be concerned about our usages in the world and try to conserve our natural resources.
Internal heat gain = electrical equipment and residents of the house give off the heat in the building. Heat gain from electricity is almost equal to the electricity usage in a building or zone. The average use of the electricity in American house is 11,000 kWh/yr. Some examples are microwave, computer laptop, coffee maker, TV and refrigerator. The best ways to manage or reduce internal heat are first change our equipments to more efficient product (energy star product), second reduce the use when it is not necessarily and the third use ceiling fans or indoor air motion in hit days of summer instead of air conditioning.

Conventional heating = since the conventional heating truly can save amount of energy and money for people the best way to reduce the energy consumption is check the existing heating system and ensure that the system works accurate. If not, consider purchasing a high efficiency model since they would help to reduce energy costs as well as conserve our natural resources. As the software recommended us for some area like Los Angeles, design a garage or storage space on the side of the building facing the coldest wind could help insulate.

Passive solar direct gain low mass and high mass = for passive solar gain main thing is help the building to gain more solar power and keep the heat inside. Material of the building would make a big difference in keeping heat. Accurate insulation for the floor and wall can keep the heat inside during the winter. As it is recommended on the program it is better to face most of the glass area south to maximize winter sun contacts but design some overhangs or sun shade to completely shade glass area in the summer time. Also it is better to not be planted trees in front of passive solar windows.

Sun shading = Sun shading is really important for Los Angeles area since they need maximum sun shading for winter and minimum sun shading for summer. So each season has a different approach to it. As mentioned on the top create some overhangs to completely shade glass area in the summer time help the house to keep the energy inside the building. In some windy climate sun shading can protect the house from the wind as well as sun.

Comfort = Comfort in the building deign need to consider as well. By design the Sunny wind-protected outdoor spaces we can reduce the energy waste in colder area. In addition, in some climate area like LA square footage of the building is important. When floor area is smaller the amount of the waste by heating and cooling energy is less as well.

Monday, October 5, 2009

I didn’t know it would be that hard. Well, I wrote about the baby in my notes during my classes when I was pregnant and it turned to be a problem now. Whenever I go through my notes to study I see my writing and the story start again. Tears, tears and tears.

Saturday, October 3, 2009

اینجا نشستم و با خودم حرف میزنم، از متیو میپرسم یعنی فکر میکنی من آخر داستان خوب میشم؟؟؟ میگه جسمی آره ولی مغزی مطمئن نیستم

Thursday, October 1, 2009


من سالها بود كه خدا را باور نداشتم چون همیشه فکر میکردم خدای كه نتونه جهانه بی نقص خلق کنه خدا نیست. خدای كه جنگ را برای لذت خلق کنه خدا نیست. خدای كه از درد کشیدن دیگران اخم نکنه خدا نیست. روزی كه این کوچولو ته دلم جوونه زد، داشتم شک میکردم به اعتقادم. كه شاید واقعا خدایی هم باشه كه بتونه شادی بیاره. حالا کاملا گم شدم
دلم قرص فراموشی میخواد. باید یادم بره. میخوام كه یادم بره. درد از روح ام آغاز شده و تمام جسمم را در از بین میبره. روز دوشنبه کوچولوی ۲ ماهه و نیمه ام را از دست دادم. دردش تمام بدنم را داره داغون میکنه

از چهارشنبه پیش شروع شد. صبح چهارشنبه وقتی كه رفتیم مطب دکتر ازم خواست كه برم برای اولترا سند. خیلی درد داشتم. چند روزی میشد كه از درد نتونسته بودم راحت بخوابم. ولی توی اتاق اولترا سند همه چی از یادم رفت. وقتی كه عکسش روی صفحه مانیتور ظاهر شد مثل اینکه همه دنیا دوره سرم میچرخید. داشت دست و پا میزد مثل ماهی قرمزی كه توی تنگ آب شنا میکنه. صدای ضربان قلبش آرامم کرد. اونجا بود. خیالم راحت شده بود از اینکه جاش راحته. تنها چیزی كه نگرانم میکرد این بود كه درد داشتم. دکتر باهام حرف زد و گفت كه همه چی خوبه ولی اگر بچه حس کنه كه نمیتونه کامل رشد کنه خودش جلوی رشد خودش را میگیره

جمعه درد بیشتر شد و بدن ام شروع کرد به خونریزی. وقتی كه زنگ زدم به بیمارستان گفتند كه اگه مقدار خونریزی کم است هیچ خطری نیست و بیخود نگران نباشم. این داستان تا یکشنبه شب ادامه پیدا کرد تا اینکه وقتی ساعت ۲ نیمه شب دیدم كه دیگه فاصله درد و خون را از هم تشخیص نمیدم فهمیدم كه دارم از دستش میدم. صبح روز دوشنبه توی مطب دکتر تا قبل از اینکه دستگاه اولترا سند را روشن کنه هنوز ته دلم امید داشتم كه حالش خوبه. وقتی دستگاه را روشن کرد خشک ام زد. بچه مثل ماهی قرمز های شب عید كه چند روز بعد از عید میمیرن مرده بود
I am so sorry sweetie هیچی نمیشنیدم. فقط صدای دکتر از ۱۰۰۰ کیلومتر اونطرف تر آمد كه گفت
و بعد دستی كه بغلم کرد و سعی کرد جلوی هق هق گریه ام را بگیره. بعدش را یادم نیست. فکر کنم چند ساعت را توی اتاق بودم تا حالم جا بیاد. دکتر میخواست بدونه كه تصمیم دارم چه کنم؟ میخوام برم برای جراحی یا اینکه صبر کنم كه بدن ام خودش بچه را پس بده. گیج بودم و نمیتونستم تصمیم بگیرم
سعی کرد جای هر دوتامون تصمیم بگیره Med
گفت كه جراحی میکنیم و قرار جراحی را گذاشت برای چهارشنبه صبح. ولی همون شب خونریزی بدتر شد و قبل از اینکه بفهمم زیر سرم مرفین بدن ام بچه را پس داد. بعد از آن فقط درد دارم و درد و درد. روحی بیشتر از جسمی