- 3481 - SOLAR ENERGY - is about to Change? A big change is about to happen in solar cell technology. Solar cell costs are coming down dramatically and at the same time electric rates are increasing. The lines are about to cross. A third generation of solar cells will hit the market that will be 4 times more efficient and 1/3 the cost.
--------------------- 3481 - SOLAR ENERGY - is about to Change?
- This review is about two technologies that make this happen: Multiple junction solar cells coupled with telescopic concentration of sunlight in solar arrays.
- Pacific Gas and Electric is increasing its rates, tracking the rising cost of natural gas. California politicians are “preventing” drilling for oil, installing nuclear reactors, burning coal, using gasoline engines all in the name of limiting pollution in our environment.
-
- The limited supply of natural gas is not enough to sustain today’s low prices. Wind, tides, geothermal are all too small to keep up with demand. Solar photovoltaic’s are the most likely alternative to economically and quickly add to our energy supply.
- Today 95% of the solar photovoltaic cells generating electricity are using “single junction silicon“. Costs have come down significantly since 1970 when the integration process was first developed.
-
- Known as MOCVD, “Metal Organic Chemical Vapor Deposition” process. It was in full production in 1980;s Systems are still only 5 to 19% efficient and the cost, at best, is 60 cents per kilowatt-hour.
-
- The total energy to manufacture the cells was more than they would produce over their 25 year lifetime. PG&E electric rates today are from 12 cents to 23 cents per kilowatt-hour depending on how much electricity you use. Things are about to change with triple junction solar cells demonstrating 40% efficiency and 22 cents per kilowatt-hour.
-
- There are over 50 companies around the world working on these next generation products. By using triple junction cells manufacturing integrates three solar cells into one. Each cell is optimized for a different band of wavelengths of light, red light, blue light and yellow light.
-
- A design similar to telescopes is used to concentrate sunlight on a single solar cell increasing the incident light by a factor of 1,000. So, far fewer solar cells are needed. Each 4 inch wafer contains 3,106 of these 1.5 mm solar cells.
-
- Manufacturing efficiencies allow building the telescopes in a single stamp mold of glass and aluminum, with passive cooling, no moving parts and 35 year life expectancies, you have a product for energy change.
-
- The three junction cells are built on top of each other. Sunlight hit’s the first cell of “Gallium Indium Phosphide” that is optimized for 350 to 660 nanometer wavelengths, which is ultraviolet, blue and green color light.
-
- Photons not absorbed pass through to the second layer below that is “Gallium Arsenide” optimized for 660 to 880 nanometer wavelengths, yellow to red color light.
-
- The bottom layer is a “Germanium” cell optimized to 880 to 1,900 nanometers wavelengths, red to infrared light. Actually, the MOCVD integration process requires over 110 individual layers to match transitions between the three cells and to manage current and heat transfers. With the 1,000 times magnification of light on to these cells normal silicon crystals would just melt.
- The light concentration is actually similar to a telescope design called the Cassegrain reflector telescope. There are two basics types of telescopes, reflecting and refracting. Refracting uses lenses but these are not well suited for solar cell arrays because the lens itself reflects and absorbs the light. Plastic lenses get cloudy with age. The reflecting telescope uses mirrors.
-
- The Cassegrain reflectors uses a large primary mirror with a hole in the middle. The parabolic shape of the mirror reflects parallel incident light beams on to a much smaller secondary mirror above it.
-
- The secondary mirror in turn reflects concentrated light back down through the hole and on to the single solar cell that is only 1.5 millimeters square. The solar cell receives 500, to 1,000, to 2,000 times more light depending on the array design.
- Now imagine shrinking this Cassegrain telescope so that it is only 6 millimeters thick. Next imagine that the mirrors are not mounted separately but imbedded in a double sided mold of glass and aluminum. This is a very efficient and durable manufacturing process.
-
- The Sun sends us energy in a light spectrum spreading from 400 to 2,000 nanometers wavelength. When it reaches our atmosphere its intensity is 1,353 watts per square meter. Gases in our atmosphere absorb some of this energy. This is what heats our atmosphere and gives us this temperate climate of 15 C.
-
- Most of the energy still reaches the surface of Earth and even at higher latitudes with the light going through more atmosphere and striking at an angle we get 850 watts / meter^2 in California.
-
- With solar panels that are 40% efficient it could produce 340 watts of electrical power for each square meter. This electric power can be pumped into the PG&E electric grid or stored in batteries when not being consumed in the household. Like Santa’s sleigh alternative energy will soon be arriving on your roof.
-
- One of the reasons we need electric cars is efficiency. Gasoline powered cars are only 8 to 9 % efficient. Oil burned in electric power plants is 42% efficient. That is four times more oil available for other purposes like medicines, plastics, or lubrication.
-
- The world is consuming 85,200,000 barrels of oil per day. By 2030 it will be 115,000,000 per day. Peak oil has passed and the remaining oil will cost us more and more as it is harder to find and harder to produce.
-
- The U S consumes 24% of the world’s oil and produces 8%. The rest we buy from other countries costing us over $700,000,000,000 each year. Money we just burn. Money we need for other purposes.
-
- These solar cells require rare Earth metals that too are in short supply. Won’t these become similar to oil? Not likely. First because we use so little in the integration process. Germanium is the most volume used.
-
- We get most of it from scraping the chimney flues of Aluminum and Coal burning plants. Coal is a good source for Germanium. We want clean coal technology. We should extract the Germanium first before the clean coal goes into the plant to be burned to produce electricity.
-
- Most solar cells, or photovoltaic cells, respond to only a narrow part of the Sun’s spectrum. Our eyes only respond to 700 nanometers to 400 nanometers, from red to blue visible light. The best techniques in solar cells respond from 600 to 900 nanometers.
-
- But things are about to change. The Sun sends us an electromagnetic spectrum extending far below 700 nanometers into the infrared and far above the 400 nanometers into the ultraviolet.
- The frontier of today’s solar cell technology is to layer several different solar cells on top of each other with each cell optimized for its part of the spectrum. Magnification mirrors are often used to concentrate the sunlight on to the small area of the solar cell.
-
- Earlier solar cells had efficiencies from 10 to 14 % , these recent improvements have got them to 20% efficiencies. Military budgets and laboratories have got cells to 40% efficiencies but the trick is to make them cost effective in high volumes. That is what a new polymer might do for us.
- The polymer is “oligothiophene“, doped with molybdenum and tungsten. This polymer will respond to sunlight wavelengths from 300 to 1000 nanometers. Most solar cell materials fluoresce, that is sunlight striking the atoms excites electrons into a higher energy state. The electrons drop back down to their ground level state and release photons with frequencies matching the energy gaps that they just jumped.
-
- (See Review 2709 “How an Atom Works“, Measuring How an Atom Works“ )
-
- Normally you cannot see the solar cells fluoresce because it is mostly in the infrared part of the spectrum and the light is too feeble compared to the bright sunlight.
Some solar cell designs have figured out ways to boost efficiency by reuse of these infrared fluorescence light photons.
-
- The way the solar cell produces electricity is that some of these electrons become excited enough to break free form the nucleus of their host atom and become “free electrons“. Given a potential gradient and these free electrons will migrate producing an electric current.
-
- Usually with fluorescence the electrons only remain free electrons to be captured for a trillionth of a second. They often drop back down into the ground level state before serving a useful purpose as electric current. This is why solar cells are not 100% efficient.
-
- The new polymer material does not fluoresce, it “phosphoresces“. This is like the glow seen in kid’s toys. The electrons phosphorescence hold on their freedom longer, a few microseconds. These longer lived free electrons are going to greatly improve the efficiency of solar cells.
-
- The polymer is still manufactured in a thin film state and it will still take several years to produce working solar cells out of this material. However, with the demand for alternative energy sources you can bet these higher efficiency and much cheaper solar alternatives are on their way to market. We are still waiting.
-
February 26, 2022 SOAR ENERGY - is about to Change? 958 995 3481
----------------------------------------------------------------------------------------
----- Comments appreciated and Pass it on to whomever is interested. ---
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for copies or Index of all reviews
--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
--------------------- --- Saturday, February 26, 2022 ---------------------------
No comments:
Post a Comment