Thursday, April 19, 2018

Computer Memory and Solar Cells.



- 2070  -  Computer Memory and Solar Cells.  Nanowires will be the next jump in solar cell efficiencies.  Atomic level memory storage could radically change our computing devices.
 Both of these solid state devices, photovoltaic and LEDs, are benefiting from the new nano technology.  Where will our needed energy efficiency come from?
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-----------------------------  2070  -  Computer Memory and Solar Cells.  
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-  In the never-ending quest to improve computing technology, engineers have found a way to store data on a single atom.  A hard drive today takes about 100,000 atoms to store a single bit of data -- a 1 or 0.  Today, you can fit your personal music library into a storage device the size of a penny. Using atomic level storage you could fit Apple's entire music catalog of 26 million songs onto the same area.
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-  Atomic-level storage could radically change our computing devices. A smartwatch or ring could carry all your personal data, or businesses could keep potentially useful information that today they can't currently afford to preserve. Storing lots of information is important for artificial intelligence, which has a voracious appetite for data used to train machine-learning systems.
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-   Richard Feynman, said in a 1983 talk about the possibilities of quantum computers that work at atomic scales: "We can in principle make a computing device in which the numbers are represented by a row of atoms, with each atom in either of the two states,"
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-  To make atomic storage practical we would need to make atomic-scale storage economically manufacturable, fast at reading and writing data and stable enough to store data for long periods of time
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-  We can store a bit of data on a single atom, but the scanning tunneling microscope that is needed to read it is vastly larger.  We use a single atom of the element holmium carefully placed on a surface of magnesium oxide.  Then a special-purpose microscope using a tiny amount of electrical current  is used to flip the atom's orientation one way or the other, corresponding to writing a 1 or 0.  We  read the data by measuring the atom's electromagnetic properties.
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-  The last big transformation in storage was the shift from the spinning magnetic platters of hard drives to flash memory, chips that can read and write data faster and that have no moving parts to wear out. Your phone and faster PCs use flash memory that has improved through 3D stacking technology to add new layers to memory chips.
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-  A promising successor to flash could be resistive random-access memory (ReRAM), which could store data more densely than flash by changing how well a tiny metallic filament conducts electricity.
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-  It is not just memory cells we need solar cells to power us into the 25th century.  Looking out to the year 2050 here are the  problems we will be facing:
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            1.  Energy
            2.  Water
            3.  Environment
            4.  Poverty
            5.  Terrorism
            6.  Disease
            7.  Education
            8.  Democracy
            9.  Population
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-  In this list Energy is the number one problem we will face.  Last year the world used 14,500,000,000,000 watts of power.  Most of this energy is generated using gas and oil.  Only 0.5% of our energy comes from solar, wind, or geothermal.
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-  In the year 2050 we will be using somewhere between 30,000,000,000,000 watts and 60,000,000,000,000 watts of electricity.  By that time we will need to be generating 45% of our energy using renewable sources.  The best solution is to get it from the Sun directly.
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-   The Sun gives us 1,360 watts of energy for every square meter of our surface.  The land surface area of Earth is 1.29*10^14 m^2 for a total energy input of 165,000,000,000,000,000 watts, 174,000 terawatts, and we only need 60 terawatts by 2050.  So, there is plenty of energy there for the taking.
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-  The United States gets on average 200 watts per square meter of useable energy.  Photovoltaic cells convert photons into electricity directly.  Today, photovoltaic cells range in efficiency from 5% to 30%.
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-  If we assume that solar cells only give us 10% efficiency the US would still gain 20 watts / m^2 from the Sun using solar cells.  The US uses 3.2 terawatts out of the world’s 14.5 terawatts.  That amounts to 22% of the world’s energy.  The US would need 1.6*10^11 meters^2 of solar cells to generate that 3.2 terawatts of energy.  That is 1.7% of the US land surface, about the size of the state of Washington.
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-  If we had six of these large solar panels placed around the world it would give us a total of 19 terawatts of power, enough for the whole world that is only using 14.5 terawatts.  The US has over 300 million people.  Counting homes and businesses there are probably 400 million roof tops. 
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-  Assume the average roof top can hold a 10 x 30 meter solar panel.  That would total 1.2*10^11 m^2 of solar panels on roof tops.  This is close to the 1.6*10^11 m^2 that we need.  If we can increase solar cell efficiency from 10% to 11% that would more than cover energy needs for the US.  Some semiconductor solar cells are already 30% efficient.  The problem is they are so expensive they can only afford to use them on satellites and space craft.
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-  This gets us to the heart of the problem.  Solar cells are too expensive.  It costs $30,000 to put solar panels on the roof of your house.  On 400 million roofs that would be $12 trillion , even bigger than the US National Debt.  Today, other sources of energy are so much cheaper:
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----------------------------------------. Total lifetime cost per kilowatt hour:
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-                       Coal                             1-4 cents
-                       Natural Gas                 2.3 - 5
-                       Oil                               6 - 8
-                       Wind                           5 - 7
-                       Nuclear                        6 - 7
-                       Solar                            25 - 50
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-  In 2004 the US, solar, wind, and geothermal energy only represent 0.5% of the energy generated.  86 % comes from coal and gas (2004:  85.65 / 99.74 total quadrillion BTU)
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-  What about nuclear.  The US has 103 nuclear plants.  Each producing 1,000,000,000 watts of electricity.  A total of 0.1 terawatts.  We need 3.2 terawatts, or 3200 nuclear plants.  We have to build 3,100 more plants.  If we built one nuclear plant each week it would still take us 60 years to build them all.  This is not likely to happen.  Nuclear is providing 8% of electricity we consume (8.23 quadrillion BTU) and is generating 20% of electricity production in the US.
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-  Learning how to make solar cells cheaper seems an obvious way to go.  If we could reduce the production cost by a factor of ten, to 2.5 - 5 cents it would become one of our most practical sources of energy.
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-  If you operate a solar cell backwards it becomes a light emitting diode, put electricity in and get light out.  A lot of the electricity generated in the US is used to produce light, 22%.  LEDs can be 10 times more efficient than incandescent light bulbs:
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-                       Incandescent   ------------------  5  %  Efficiency
-                       Fluorescent  ------------------     25  %
-                       Electric Discharge  --------       30  %
-                       White LED  -------------------  50  %
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-  If we can get LED bulbs produced as cheap as incandescents we can reduce our energy consumption by 20%.
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-  Both of these solid state devices, photovoltaic and LEDs, are benefiting from the new nano technology.  Nanowires that are 1/1000 the diameter of the human hair, 50 nanometers diameter, are grown on the cell substrates.  When photons hit the semiconductor of solar cell the photon is absorbed and an electron is released. 
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-  Using nanowires to traverse the cell the electron flows the length inside this single crystal.  The electron is quickly and efficiently piped to the cathode of the circuit.  Without nanowires impeded the electron would have to bounce and jump from atom to atom throughout the semiconductor before reaching the cathode.  The nanowires offer a significant improvement in light - electricity conversion efficiency.  The same efficiencies happen when in reverse the electron travels through a semiconductor to generate a photon.
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-  The manufacturing process is cheap.  The nanowires are grown as single crystals on the substrates in a wet process like growing grass. None of the traditional expensive semiconductor processes are used. If these processes become perfected we may see solar cells costing 10 fold less than they cost today.
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--------   Footnotes  ---------------------------------------------------
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-  (1) -  Surface area of the Earth = 4*pi*radius^2  =  4*pi*(6.368*10^6 meters)^2  =  5.11*10^14 meters^2.  Assume 25% of the Earth is land then 1.29*10^14 meters^2 * 1,360 watts / m^2 = 173,800 * 10^12 watts.  174,000 terawatts reaches our land mass.
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-  (2)  -  1.6*10^11 m^2  =  61,780 miles^2 and the state of Washington is 66,544 miles^2.  A solar panel 93% the size of Washington State.  So, we would only have to sacrifice one state to provide all the energy needs for the other 49 states.  Just cover the state of Washington with solar cells that are 10% efficient.  Of course, Kansas would probably be a better choice, they get more sunshine year round.
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 -------------------------   Thursday, April 19, 2018   --------------------------------
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