Term
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Definition
Solar energy arrives at the earth in the form of electromagnetic
radiation covering a wide range of wavelengths and energies
• The quantities which reach the surface are enough to represent the
greatest single potential energy source available on earth
• It is so diffuse and intermittent in nature that its use hinges upon the
development of suitable collection and storage systems
• Today solar energy, in addition to its natural uses evident in the form
of agriculture and commercial forestry, the hydrologic cycle, winds
and ocean currents is used in applications that could replace other
traditional energy supplies, primary fossil fuels |
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Term
| At what rate does sun radiate energy? |
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Definition
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Term
| At the surface of the atmosphere |
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Definition
An average power of 1353 W m-2 is passing through a plane
perpendicular to the direction of the Sun at the top of the Earth’s
atmosphere |
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Term
| Is there solar variation within a year? |
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Definition
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Term
| Is there conservation of energy with solar power? |
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Definition
Yes; The energy produced by nuclear reactions in the interior of the Sun
must equal the amount of energy radiated from the surface
• Stability over a period of nearly 3×109 years is implied by the relative
stability of the temperature at the Earth’s surface
• Conversion of energy contained in the atomic constituents of main
sequence stars such as the Sun from heat of nuclear reactions to
radiation escaping from the surface is largely understood
• The basis for regarding such radiation as a renewable source is that it
may continue essentially unaltered for billions of years |
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Term
Where does Almost all of the radiation from the Sun received at the Earth
originates |
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Definition
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Term
| What is the evidence of photosynthesis on earth? |
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Definition
| In the beginning there was very little oxygen; phytoplankton is the reason oxygen went up |
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Term
| Does light give out a spectrum? |
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Definition
Yes; The depth to which a terrestrial observer can see the Sun lies in the
photosphere
• The photosphere consists of atoms of varying degree of ionization
and free electrons
• A large number of scattering processes take place, leading to a
spectrum similar to the Planck radiation for a black body in
equilibrium with a temperature T ≈ 6000 K
• The figure shows the picture of solar layers, starting from the centre
of the Sun to the left
• The solar radius is defined by the bottom of the visible Sun |
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Term
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Definition
• The solar wind has a density of about 10-20 kg per m3, corresponding
to roughly 107 hydrogen atoms per m3 at the top of the earths
atmosphere
• The ions are sucked into the Earth’s magnetic field at the poles,
giving rise to such phenomena as the aurorae borealis and to
magnetic storms
• Variations in solar activity affect the solar wind, which in turn affects
the flux of cosmic rays reaching the Earth |
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Term
| Is solar very high energy? |
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Definition
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Term
| What is a signature of Big Bang & showing that we are connected to the entire universe? |
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Definition
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Term
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Definition
The solar radiation that approximately corresponds to the radiation
from a black body of temperature 6000 K, meets the Earth–
atmosphere system and interacts with it, producing temperatures
which at the Earth’s surface typically vary in the range 220–320 K
• To understanding the processes involved, one may look at the
radiation flux passing through unit horizontal areas placed either at
the top of the atmosphere or at the Earth’s surface
• The net flux is the sum of the fluxes passing the area from above and
from below. The flux direction towards the centre of the Earth will be
taken as positive, consistent with reckoning the fluxes at the Sun as
positive, if they transport energy away from the solar centre |
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Term
| What does radiation at Earth's surface consist of? |
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Definition
The radiation received at the Earth’s surface consists of direct and
scattered (plus reflected) short-wavelength radiation plus longwavelength
radiation from sky and clouds, originating as thermal
emission or by reflection of thermal radiation from the ground
• The figure on the next slide shows the net radiation flux at the top of
the atmosphere (NCEP-NCAR, 1998) |
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Term
| Radiation at Earth's Surface |
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Definition
| Zero = equator; +90 = North Pole |
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Term
| What is direct radiation? |
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Definition
“Direct radiation is defined as radiation which has not experienced
scattering in the atmosphere, so that it is directionally fixed, coming
from the disc of the Sun |
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Term
| What is scattered radiation? |
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Definition
Scattered radiation is the radiation having experienced scattering
processes in the atmosphere |
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Term
The assessment of the “magnitude” of solar radiation as an energy
source will depend on what? |
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Definition
will depend on the geographical location, including local
conditions such as cloudiness, turbidity, etc.
• The seasonal variation in solar radiation on a horizontal plane is
shown in the following figure |
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Term
| Does solar radiation vary by season? |
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Definition
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Term
| Does solar radiation vary by season? |
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Definition
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Term
| Describe conversion of solar radiation |
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Definition
Heat generation
• Conversion of solar energy to heat requires a light-absorbing
material, a collector. The collector should be able to distribute the
absorbed radiant energy over internal degrees of freedom associated
with kinetic energy of motion at the molecular level (e.g. lattice
vibrations in case of a solid)
• The Earth and its atmosphere are examples of such collectors
Absorption of solar energy will raise the temperature of the collector
or transfer energy to a reservoir
• The collector will also emit radiation and it may lose heat energy by
conduction and convection processes |
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Term
The frequency spectrum of the emitted radiation will correspond
to what? |
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Definition
| the Planck spectrum for the collector temperature |
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Term
| What are the two types of conversion radiation systems? |
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Definition
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Term
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Definition
A “passive system” need not be characterized by the absence of
definite heat flow paths between collectors and load areas, but such
flows should be “natural” |
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Term
| Examples of passive solar heat systems |
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Definition
Examples of passive solar heat systems are ordinary windows in
buildings, which transmit a large fraction of the solar radiation
• The room behind the window may to a large extent act like a black
body, absorb practically all of the radiation transmitted through the
window and re-emit only a small fraction again to the outside |
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Term
| Do passive systems have pumps or electricity generated? |
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Definition
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Term
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Definition
| Winter - heat absorbing wall; air being circulated; The more air flows, the temperature goes up |
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Term
| Another kind of passive energy system: |
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Definition
Another kind of passive solar heat system uses the heat capacity of
walls facing the sun during daytime.
• The walls absorb radiation and accumulate it and at night they lose
heat to their colder surroundings, including the inside area which is
thus heated.
• The wall’s heat capacity also serves to cool the building during at
least the first part of the daytime, if the wall temperature after the
night’s cooling-off is lower than the next day’s ambient temperature
• More elaborate versions of such solar wall systems, directing the
natural convection according to conditions (night/day,
summer/winter) |
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Term
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Definition
| Need lots of solar radiation, even in winter |
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Term
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Definition
The solar pond itself contains water with a high content of dissolved
salts, causing the formation of a salinity and density gradient,
preventing the mixing of surface and bottom water
• The water absorbs some solar radiation, but if the pond is shallow
most of the absorption takes place at the bottom, thereby creating a
stable temperature gradient increasing towards the bottom, because
heat is transferred upwards only by slow processes |
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Term
| Because of the salinity what can happen? |
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Definition
| we can sustain the gradient due to the salt |
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Term
| 2008 Power Installed from Solar |
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Definition
| 15,000 Mega watts (15 giga watts) |
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Term
| What is biggest market for silicon? |
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Definition
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Term
| .28% of electricity comes from Solar. We want this to be 10%. First we need to know what we need to grow by. What do I do? |
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Definition
| Divide what you want by how much you have; 10%/.28% = how much you have to grow = 35.7. How long with it take to do this? double 2; when you double 2 5 times you get 32; 5 doubles; 2 years per double = 10 year; In 10 years then 10% of our electricity could come from solar (This is at a 42% compounded rate; then we will double every 2 years) |
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Term
| Total US solar module production |
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Definition
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Term
| US made what percent of solar modules in 2008? |
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Definition
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Term
| When is the expected convergence of when you reach competitive prices with fossil fuels in solar? |
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Definition
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Term
| Is wind cheaper than solar? |
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Definition
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Term
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Definition
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Term
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Definition
| Inorganic Thin Films (CdTe) |
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Term
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Definition
| future concepts; nanostructures, organic/hybrid/advanced concepts |
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Term
| What are most solar panels ? (90%) |
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Definition
| first generation because it's the oldest technology, lower costs |
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Term
| Materials used in solar cells? |
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Definition
Active Layer Materials
c-Si, a-Si, a-SiGe, CdTe, CIGS,
GaAs
Materials used in Back Contact
Al, Au, Ag, Mo
ZnTe:N, ZnO, In2O3
Materials used in Front contact
ZnO:Al, In2O3, SnO2:F
Window Layer Collector
Materials
CdS, ZnS, InS, doped Si
Light
Materials used for Substrate
Glass, Mo, Stainless Steel,
Kapton |
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Term
| Are solar panel efficiencies going up? |
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Definition
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Term
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Definition
Slow but steadily improving PV efficiencies
• Production increasing 30-40% per year
• Price reductions follow 80% learning curve
• Grid-connected applications now dominate
• Thin-film technologies hold promise for cost reductions, but
still fraction of market (~10%)
• c-Si, a-Si:H, a-SiGe, CuIn(Ga)Se2, CdTe in production |
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Term
What are the reasons The majority of solar cells fabricated to date have been based on
silicon in mono-crystalline or large-grained polycrystalline form? |
|
Definition
Silicon is an elemental semiconductor with good stability and a wellbalanced
set of electronic, physical and chemical properties.
• The success of silicon in microelectronics has created an enormous
industry where the economies of the scale directly benefit the
presently smaller photovoltaics industry |
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Term
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Definition
It is known that the indirect band gap of Si leads to an absorption
coefficient that increases very slowly above the fundamental
absorption edge
• Light trapping schemes have been developed to greatly reduce the
thickness of Si needed to achieve good light absorption
• Light penetration in most cases will substantially exceed the width of
the depletion layer in Si
• So the quality of Silicon chosen needs to achieve the long minority
carrier lifetimes that will support long diffusion lengths |
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Term
| Advantage of thin film pv? |
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Definition
However, the direct-gap semiconductors such as Cu(InGa)Se2
(Copper Indium Gallium Di - selenide - CIGS), CdTe (Cadmium
Telluride), GaAs (Gallium Arsenide) and InP (Indium Phosphide) have
very strong absorption at photon energies essentially immediately
above the band gap
• The thin-film PV materials have major advantages in needing less of
the active semiconductor absorber
• The purpose is to fabricate these in large areas on inexpensive
substrates to take advantage of cost-reductions in the fabrication
process |
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Term
| WHere is the best places in the US for solar power? |
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Definition
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Term
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Definition
| In the middle of the day we are using maximum energy; solar is available when you need it most: during daytime |
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Term
| 3 types of in-organic thin film materials |
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Definition
Amorphous silicon
• Copper Indium (gallium) diselenide (CIGS)
• Cadmium Telluride (CdTe) |
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Term
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Definition
Amorphous silicon (a-Si:H) is deposited most commonly by RF
(13.56MHz) plasma-enhanced-vapor deposition (PECVD)
• Very High Frequency (70MHz) and microwave frequencies or hot
wire deposition are sometimes used
• These excitation modes are to dissociate the precursor gases to
provide more reactive radicals
• These type of solar cells exhibit the well-known Stabler-Wronski
instability related to weakly bound H which terminates some of the
unsatisfied or dangling bonds |
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Term
| Copper-indium-gallium diselenide (CIGS) |
|
Definition
CIGS and CdTe are utWilized in polycrystalline thin film form
• Their abosrber layers are weakly p-type and are used together with
n-CdS forming a heterojunction-type solar cell
• The wider band gap CdS (Eg = 2.4 eV ) is typically used with a
transparent conducting oxide that serves as the electrode and
electron collector
• A major difference between the two types of solar cells is the order
of deposition of the layers
• CIGS is typically deposited on a molybdenum coated substrate with
CdS and TCO deposited last |
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Term
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Definition
CdTe has reached cell efficiencies of 16.5% which is about 3 % lower
than CIGS
• These results were obtained at NREL using borosilicate glass
substrates, a high transparency and high mobility TCO, Cd2SnO4,
together with an intermediate resistance interfacial layer
• The NREL group used chemically bath-deposited CdS and 8-10μm
thick CdTe with deposition temperature near 600°C
• The best cells on soda-lime glass with commercial TCO are 12-14% |
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Term
| Tandem structures in the chalcogenide solar cells |
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Definition
Thin-film a-Si modules regularly use double or triple junction
structures as do high efficiency, III-V solar cells
• It is an objective envisioned for the polycrystalline thin films as well
• Alloys of CdTe with Zn, Mn and Mg are being studied for possible top
junctions and HgCdTe for bottom junctions in the II-VI semiconductor
materials
• Wider gap alloys obtained by substitution of the In with Ga or with
Ga and Al are under active study
• Substituting S for some of the Se will also raise the band gap |
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Term
| Challenge of scale-up to 1m squared module sizes |
|
Definition
Transition from small cells (1 cm2 or less) to large-area modules (~
1m2) fabricated from thin films involves many challenges
• In the case of small cells, the cells can be individually tested before
assembly and rejected
• For thin films, a low density of pinholes or even weak diodes can
seriously degrade the module performance
• It is practically essential to develop methods for removing or isolating
the shunts
• This has taken different forms with different materials |
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Term
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Definition
1. SPain
2. Germany
3. Rest of Europe
4. US |
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Term
|
Definition
1. Japan
2. Europe
3. Rest of World |
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Term
| First solar module production capacity |
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Definition
Ramped the first 25MW module
production line in Perrysburg, Ohio to
its steady state volume in 2005
Added two additional 25MW production
lines in the U.S. in 2006
Annual Capacity = 75MW by end 2006
(raised to 90 MW in 2007 and
192 MW by end 2009) |
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Term
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Definition
Indirect .23
Direct Emissions .025 |
|
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Term
| What is the EROEI of CdTe Solar Panels? |
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Definition
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|
Term
| Which model of solar panels gets you your payback fastest? |
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Definition
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Term
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Definition
solve the Si feedstock shortage
• reduce wafer thickness well below 200 μm or improve thin-Si
growth
• develop rapid and cheap film-Si growth methods (< 20 μm?)
• develop light trapping and thin-film Si methods (~2 μm)
• demonstrate that module costs can continue to drop at 80%
experience curve at volumes x100 greater |
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Term
| Conclusions for thin film PV |
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Definition
• Thin-film technologies hold promise for cost reductions,
but still fraction of market (~10%)
• a-Si:H, CuIn(Ga)Se2, CdTe in production
• magnetron sputtering yields competitive efficiencieswith
high temperature deposition (CSS, VTD)
- high materials, device quality
- deposition rate is much slower than CSS or VTD
• ms affords flexibility for reactive doping, alloying
• controllable dep. rate ® thin absorber layers
• low temp growth:
® good for second cell of tandem
® good for polymer substrates |
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