Transcript solar_basics

Solar Electric Energy Basics
Frank R. Leslie,
BSEE, MS Space Technology
9/19/2001
f.leslie @ieee.org; (321) 768-6629
Roof-top Solar Array Computations
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Find the south-facing roof area;
say 20 ft * 40 ft = 800 ft2
Assume 120 Wp solar modules
are 26 inches by 52 inches; 9.4
ft2/120 watt; 12.78 W/ft2
Assume 90% of area can be
covered, 720 ft2, ~9202 W
and that there are 5.5 effective
hours of sun/day; 51 kWh/day
The south-facing modules are
tilted south to the latitude angle
76 modules would fit the area,
but 44 would provide an
average home with 30 kWh/day
and cost ~$17600 for modules
alone, ~one mile of powerline
Siemens Solar SM110
Maximum power rating, 110 W
Minimum power rating, 100 W
Rated current. 6.3 A
Rated voltage, 17.9 V
Short circuit current, 6.9 A
Open circuit voltage, 21.7 V
Energy Considerations for 2050
• Fossil-fuel energy will
deplete in the future;
millions of years to create
that much fuel
• US oil production peaked
about 1974; world energy
will peak about 2009 or so
• Renewable energy will
become mandatory, and our
lifestyles may change
• Transition to renewable
energy must occur well
before a crisis occurs
PV Cell Basics
• Semiconductor of
transparent positive silicon
and negative silicon backing
• Incoming light (photons)
cause energized electrons to
move to the n-silicon and
out the connector
• Nominal voltage of 0.55 V
requires series connections
to get useful voltage, 16 V
• Short circuit current is
proportional to light intensity
Maximum output when
normal to cell is pointed at
light (cosine of sun offset
angle)
Ref.: FSEC
Energy Usage & Conservation
• The loads supported by the
system must be minimized to
match the available energy
• Load analysis shows the
largest concerns that might
be reduced to cut costs
• Conservation by enhanced
building insulation and
reduced lighting loads
• Increased efficiency of
energy plants will conserve
fossil fuels
Arizona has clearer skies than Florida.
Ref.: Innovative Power Systems
PV System Decomposition into
Functional Components
Collect & Distribute
Energy
Start
Collect Energy
Regulate Energy
Store Energy
Control Energy
Distribute Energy
Use Energy
Each function drives a part of the design, while the interfaces between them will
be defined and agreed upon to ensure follow-on upgrades
PV Systems
• PV modules of 120 W cost
about $400
• Mounting angles to match
sun --- fixed or tracking
• Average module slope angle
is equal to latitude
• Zoning and regulations --Not In My Back Yard
(NIMBYs) problem
• Protection required for
electric line workers due to
“islanding” backfeed
This solar intensity plot for Cocoa FL shows
the cloud effect on what otherwise would
have been a cosine effect
Ref.: FSEC
You are
here!
Zenith
To Sun
Zenith
Angle
To Sun
North
Pole
Declination
Latitude
Equatorial
Plane
Sun’s zenith angle is measured from local vertical
Equator
Zenith Angle of
Sun
Sorensen, p 27. is part of reading assignment for ENS4300
Charge controller
• Limits charge current to
protect battery
• Disconnects battery if
voltage falls too low (10.6 V
is typical)
• Removes charge current if
voltage rises too high (14V is
typical)
• Shifts output of source to a
load (water heater or electric
furnace) if battery is fully
charged
Soltek Mark IV 20 Amp
Regulator
“Big as a breadbox” for a 4 kW
inverter
Energy Storage
• Energy may be stored
chemically, in water behind
high dams, electrically,
flywheels, and compressed
air caverns.
• Hydrogen (like electricity) is
an energy carrier, not a
direct fuel source, but
compressed H2 can also be
stored
• Hydrogen can be made by
electrolysis of water or
“cracking” methane
World's largest storage dam,
Uganda's Owen Falls Dam.
The hydroelectric station at the
dam supplies most of
the electricity requirements of
Uganda, and parts of Kenya.
(Photo:Faculty of Engineering,
Kasetsart University, Thailand)
Storage Battery
• Lead-acid (car) batteries
most economical; but should
be deep-cycle
• Critical rating is 20-hour
value
• Charge cycle is ~60-70%
efficient -- rather wasteful
• Requires maintenance to
ensure long life
• A home might have ten of
these batteries
Soltek
Deep-Cycle
Battery
AP-27
12 Vdc,
115 A-hr
20-hour
rate
Inverter
• Inverter converts low voltage
direct current to 120 Vac
• Loads can use low-voltage
directly at higher efficiency
• Synchronous inverters may
be “inter-tied” with power
line to reduce billable energy
• In “net metering” states, the
energy is metered at the
same rate going into and out
of the electrical grid --- no
storage required!
Trace
Legend
4 kilowatt
Inverter
Loads
• Household load analysis
estimates the peak and
average power and energy
required
• Some might be reduced or
time-shifted to decrease
system costs
• Incandescent lamps produce
far more heat than light;
CFLs provide ~100 W light
equivalent at 27 W load
27 watt
(100 W
equivalent)
Compact
Fluorescent
Lamp (CFL)
CFL Costs without replacement labor: $21.30
Incandescent Costs with replacement labor: $39.98
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CFL Costs with replacement labor: $23.30
Incandescent Costs with replacement labor: $56.54
Hint: You can buy a CFL at a large local
discount store for $4.68!
Energy Transmission
• Energy transmission lines
may lose 5% en route
• Only three electrical grids for
all Contiguous US (CONUS)
• Mine-head coal plants avoid
coal trains and the power to
drive them
• Hydrogen pipelines could
transport gaseous energy
cheaply and parallel natural
gas lines
Guyed transmission tower with
multiple conductor spreaders
(note at left) to increase current
capacity or reduce loss
Energy in Transportation
• Air and ground
transportation requires
energy-dense fuels (liquids)
• Fixed natural gas plants
compete with CNG for cars
and trucks
• Research is on-going with a
Lear jet fueled with
hydrogen from two large
high-pressure vessels
running lengthwise over the
passenger compartment -- a
dubious location
Compressed natural gas car at FSEC
Generic Trades in Energy
• Energy trade-offs required to
make rational decisions
• PV is expensive ($5 per watt
for hardware + $5 per watt
for shipping and installation
= $10 per watt)
compared to wind energy
($1.5 per watt for
hardware + $5 per watt
for installation = $6 per
watt total)
• Are Compact Fluorescent
Lamps (CFLs) better to use?
Ref.: www.freefoto.com/
pictures/general/
windfarm/index.asp?i=2
Ref.:
http://www.energy.ca.gov/
education/story/storyimages/solar.jpeg
Photo of
FPL’s
Cape
Canaveral
Plant by
F. Leslie,
2001
Conclusion
• Solar electric energy is best
applied where the cost
justifies; remote from the
grid
• Costs of fossil-fuel pollution
and subsidies are not easily
found -- controversies exist
• PV costs are falling, but
fossil-fuel costs will soon
surpass them
• At that time, PV will compete
with wind energy, which is
currently competitive with
fossil fuels
Questions & Answers
Is a Solar Roof Practical?
Sun intensity at surface ~1000 watt / square meter
PV cells about 15% efficient = ~150 watt / square meter
Roof might be about 20 x 40 feet = 800 square feet; 90% coverage = 720
square feet
A 120 watt solar module is about 26 inches x 52 inches = ~ 9.4 sq. ft, thus
peak power production is ~12.78 watt / square ft
720 square feet*(12.8 watt/square feet) = 9202 watts peak power
Optimally, roof array could yield 9202 watts for 5.5 hours/average day = 51
kWh each day on average; average house might need 30 kWh
Storage would provide energy at night and during cloudy weather, but
increases the cost
Current cost estimates are about $5/W & $0.06 to $0.20 per kWh vs. $0.07
from utility
Utility line extension costs about $18,000 to $50,000 per mile
References: Books, etc.
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Brower, Michael. Cool Energy. Cambridge MA: The MIT Press, 1992. 0-262-02349-0,
TJ807.9.U6B76, 333.79’4’0973.
Duffie, John and William A. Beckman. Solar Engineering of Thermal Processes. NY: John
Wiley & Sons, Inc., 920 pp., 1991
Home Power magazine. Ashland OR. www.homepower.com
References: Internet
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http://geothermal.marin.org/ on geothermal energy
http://mailto:[email protected]
http://www.dieoff.org. Site devoted to the decline of energy and effects upon population
http://www.ferc.gov/ Federal Energy Regulatory Commission
http://www.humboldt1.com/~michael.welch/extras/battvoltandsoc.pdf
http://www.siemenssolar.com/sm110_sm100.html PV Array
http://www.soltek.ca/products/solarmod.htm
http://www.soltek.ca/index.htm
http://www.ips-solar.com/yourproject/costanalysis.htm Cost analysis
http://www.ips-solar.com/yourproject/resource.htm Energy analysis
http://www.aep.com/Environmental/solar/power/ch5.htm Renewable energy
http://ens.lycos.com/ens/dec2000/2000L-12-01-01.html