ELEG 620 Solar Electric Power Systems April 22, 2010 Systems and SunPower ELEG 620 Electrical and...
33
ELEG 620 Solar Electric Power Systems April 22, 2010 Systems and SunPower Systems and SunPower ELEG 620 Electrical and Computer Engineering University of Delaware April 22, 2010
ELEG 620 Solar Electric Power Systems April 22, 2010 Systems and SunPower ELEG 620 Electrical and Computer Engineering University of Delaware April 22,
ELEG 620 Solar Electric Power Systems April 22, 2010 Systems
and SunPower ELEG 620 Electrical and Computer Engineering
University of Delaware April 22, 2010
Slide 2
ELEG 620 Solar Electric Power Systems April 22, 2010 ELEG 620
April 22 1.Richard Corkish, UNSW, April 23, 3 pm, 103 Gore 2.
Michael Mackay, What Does Solar Energy Mean? 006 Kirkbride, April
29, 4 pm 3. System design 4. Design, construction and test of a
solar power system 5. SunPower and other solar cells
Slide 3
ELEG 620 Solar Electric Power Systems April 22, 2010
Slide 4
ELEG 620 Outcomes 1.Understanding the nature of Solar Radiation
2. Design of a solar cell from first principles 3. Design of a top
contact system 4. Design, construction and test of a solar power
system
Slide 5
ELEG 620 Solar Electric Power Systems April 22, 2010
Slide 6
Typical Solar System XHighest reliability premium power
solution XUnlimited backup time XNo fuel, no maintenance DC Output
+ Photons In + Storage Battery DC AC AC Output
Slide 7
Village System ELEG 620 Solar Electric Power Systems April 22,
2010
Slide 8
Pick Your Load (1-2 pages) 1.Pick a load. Available PV Power is
50W-800W (non full time graduate students can go as low as as 1W)
2.Identify what you will measure, starting with the oad. 3.Identify
time intervals over which you will measure i.e: # of days 4.Draw a
diagram to show the energy flow and the components in the system
for your specific load. 5.List the input, the output and the
methods for your design part. (What information do you need, what
information do you want, and how are you going to relate the two?)
6.List the methods and the tools you will use for your system test.
(How to test whether the system is working as expected? How to
identify the problems if its not?) ELEG 620 Solar Electric Power
Systems April 22, 2010
Slide 9
Photovoltaic Systems System Design: To make a successful system
need to: Well-designed system. Reliable, appropriate and
well-matched components. Suitable maintenance regimes. Conforming
to legal, social, etc expectations, including relevant standards
Ensure that expectations and maintenance is realistic through
education. Well designed system: Appropriate choice of basic system
topologies. Choice of array size, tilt angle, battery size and
other components to give best performance ELEG 620 Solar Electric
Power Systems April 22, 2010
Slide 10
Photovoltaic Systems Parameters to judge system performance
Availability: fraction of time that energy is available compared to
time load is required. Utilization of incident solar energy: Solar
fraction: fraction of available solar energy which is utilized by
the system. Array-to-load ratio: Has units of Wp /Wh per day. If
the (Wh per day) is from the load, then this is the hybrid
indicator. If the (Wh per day) is the net available to the load, it
is a measure of the system location. ELEG 620 Solar Electric Power
Systems April 22, 2010
Slide 11
Photovoltaic Systems Types of Systems Direct-coupled PV system
DC PV system with storage DC-AC PV systems Hybrid PV systems
Grid-connected PV systems Increasing components in a system
decreases reliability, decreases efficiency Adding additional power
sources increases the availability (usually) and increases fraction
of solar power used. Increasing components increases cost of
systems, but not for same availability. ELEG 620 Solar Electric
Power Systems April 22, 2010
Slide 12
Photovoltaic Systems Impact of variability in solar resource A
key element in renewable energy systems is the design of one
component that has inherent variation (the solar resource) to drive
another component (the load) in which the variation should be
minimized as much as possible. The larger the variation in the
resource compared to the load, the more difficult the trade-offs.
Some loads have a match to solar resources, but often higher loads
are encountered in months with lower solar insolation. Large
variation in solar radiation means that in order to get higher
availability, the system has: a lower solar fraction a substantial
storage component. Higher cost. ELEG 620 Solar Electric Power
Systems April 22, 2010
Slide 13
Photovoltaic Systems System Design: Goal is to produce a system
within specified cost and power specifications that has the highest
availability and reliability In addition to availability, cost and
reliability, the fraction of solar used and the system losses are
used to guide to the design process. Key issues and trade-offs
Theoretically, power from array over year = load over year + losses
Needed availability = battery capacity to power load during periods
without solar irradiance Not valid because storage cant be large
enough, so need to over design in one portion of year No way around
problem of unused capacity, but can introduce a secondary system
that is either more predictable, lower cost or well-matched to
complement solar resource. ELEG 620 Solar Electric Power Systems
April 22, 2010
Slide 14
Photovoltaic Systems Types of design procedures: Several
different types of design procedures, depending on availability of
radiation data and time period over which calculations are
performed. 1.Determine feasibility/select system topology: rough
calculations, no specific location dependant parameters, and
usually no comparison, iteration or checking 2.Indicative analysis:
look at key trade-offs (tilt, battery size, array size) determine
suitability system topology: location and load dependant
parameters, usually averaged over a month. Different methods have
different methods for choosing battery storage. ELEG 620 Solar
Electric Power Systems April 22, 2010
Slide 15
Screen-Printed Silicon Solar Cell This device structure is used
by most manufacturers today The front contact is usually formed by
POCl 3 diffusion The rear contact is formed by firing
screen-printed Al to form a back-surface field The cell
efficiencies for screen-printed multicrystalline silicon cells are
typically in the range of 14 16% ELEG 620 Solar Electric Power
Systems April 22, 2010
Slide 16
Fabrication Process of Screen Printing Silicon Solar Cells POCl
3 DiffusionPECVD SiN x ARAl Screen-printingAg Screen-printing Belt
Co-firing Texturing P-Si Senergen Devices February 26, 2009
Slide 17
ELEG 620 Solar Electric Power Systems April 22, 2010 Issues for
High Efficiency SP Solar Cells Screen printed front contact - Broad
and low conductivity Ag - High contact resistance Emitter diffusion
- High Joe and low Jsc due to high surface concentration for low
contact resistance Bulk : Conventional Multi-Si and CZ - Low
lifetime New Structure (Back Contact Cell) Screen printed Al rear
contact - High surface recombination velocity - Low reflectivity
Senergen Devices February 26, 2009
Slide 18
ELEG 620 Solar Electric Power Systems April 22, 2010
High-Efficiency Cell Designs p-type FZ Si Al-BSF Al Contact n-type
a-Si ITO Grid intrinsic a-Si SiN/SiO 2 p-Si Ag gridlines Al/Ag rear
contact SiN/SiO 2 n + emitter SiN/SiO 2 p-Si rear contacts p+p+
n+n+ n + emitter ~100 / p-Si Ag gridlines Al rear contact Al-BSF
High-sheet-resistance emitter cell Interdigitated back contact cell
Gridded back contact cell Si heterojunction cell (in collaboration
with NREL)
Slide 19
BP Solar Saturn Solar Cell The BP Solar Saturn solar cell
utilizes a laser-grooved, buried front contact The aluminum back
contact is heated to form a back surface field, which reduces
surface recombination Best lab efficiency = 20.1% ELEG 620 Solar
Electric Power Systems April 22, 2010
Slide 20
Localized Emitter Cell Using Semiconducting Fingers This type
of cell was developed at the University of New South Wales Suntech
may start production in the near future ELEG 620 Solar Electric
Power Systems April 22, 2010
Slide 21
Sanyo HIT Solar Cell The HIT cell utilizes amorphous Si
intrinsic layers (~ 5 nm) as super-passivation layers. The cell is
symmetric except for the a-Si p + emitter layer (~ 10 nm) on the
front and the a-Si n + contact layer (~ 15 nm) on the rear. The
transparent electrodes are sputter-deposited indium-tin-oxide (ITO)
Best lab efficiency = 22% (open-circuit voltages ~ 730 mV) ELEG 620
Solar Electric Power Systems April 22, 2010
Slide 22
SunPower Back Contact Solar Cell The SunPower cell has all its
electrical contacts on the rear surface of the cell The diffusion
lengths > twice the cell thickness Best efficiencies ~ 23%
(SunPower is now using CZ-Si) ELEG 620 Solar Electric Power Systems
April 22, 2010
Slide 23
Advent Solar Emitter-Wrap-Through Cell Advent Solar started
selling EWT cells in the first quarter of 2007 They need to laser
drill ~ 45,000 holes per wafer They claim solar cell efficiencies
of ~ 15% ELEG 620 Solar Electric Power Systems April 22, 2010
Slide 24
Metal-Wrap-Through Solar Cell Photovoltech is commercializing
the MWT solar cell; efficiencies ~ 15% ELEG 620 Solar Electric
Power Systems April 22, 2010
Slide 25
The CSG Solar Cell CSG Solar (Germany) is using laser
patterning of thin polycrystalline silicon to construct a
metal-wrap-through type of back-contact cell. Their best cell
efficiencies are ~ 10%. ELEG 620 Solar Electric Power Systems April
22, 2010
Slide 26
The Sliver Solar Cell Origin Energy (Australia) is
commercializing the Sliver Solar Cell They have demonstrated cell
efficiencies > 20%
Slide 27
ELEG 620 Solar Electric Power Systems April 22, 2010 Senergen
Devices February 26, 2009 Solar Cell Technologies Highest
efficiencies are reached by making tandem solar cells, which
consist of multiple solar cells stacked on top of one another. Each
solar cell absorbs light with energy close to its band gap,
allowing overall higher efficiency. Maximum thermodynamic
efficiency is 86.8%, but material limitations give maximum
efficiencies of just over 30%. Used primarily in space markets From
Compound Semiconductor
Slide 28
28 Physics of Solar Cells ELEG 620 Solar Electric Power Systems
April 22, 2010
Slide 29
29 Solar Cell Operation Boron-doped, p-type silicon Phosphorus
doped n-type silicon Top metal contact grid Bottom metal contact
Cell Cross-Section Anti-reflection coating ELEG 620 Solar Electric
Power Systems April 22, 2010
Slide 30
30 Solar Cell Operation (cont.) 1.Photon of sunlight knocks
electron loose P-type silicon attracts holes 2. Free electron goes
to top metal contact 3. Hole (broken bond) left behind goes to
bottom metal contact N-type silicon Attracts electrons Top metal
contact Bottom metal contact ELEG 620 Solar Electric Power Systems
April 22, 2010
Slide 31
31 1.8% 0.4% 1.4% 1.54% 3.8% 2.6% 2.0% 0.4% 0.3% I 2 R Loss
Reflection Loss Conventional Solar Cell Loss Mechanisms
Recombination Losses Back Light Absorption Limit Cell
Efficiency29.0% Total Losses-14.3% Generic Cell
Efficiency14.7%
Slide 32
ELEG 620 Solar Electric Power Systems April 22, 2010 32
High-Efficiency Back-Contact Loss Mechanisms Limit Cell
Efficiency29.0% Total Losses-4.4% Enabled Cell Efficiency24.6% 0.5%
0.2% 0.8% 1.0% 0.2% 0.3% 0.2% I 2 R Loss 0.1%
Slide 33
Pick Your Load (1-2 pages) 1.Pick a load. Available PV Power is
50W-800W (non full time graduate students can go as low as as 1W)
2.Identify what you will measure, starting with the oad. 3.Identify
time intervals over which you will measure i.e: # of days 4.Draw a
diagram to show the energy flow and the components in the system
for your specific load. 5.List the input, the output and the
methods for your design part. (What information do you need, what
information do you want, and how are you going to relate the two?)
6.List the methods and the tools you will use for your system test.
(How to test whether the system is working as expected? How to
identify the problems if its not?) ELEG 620 Solar Electric Power
Systems April 22, 2010