Photovoltaics
Spring 2013
Physics 12
UCSD
Physics 12
UCSD
Passive: cheap, efficient design;
block summer rays; allow winter
Solar Thermal: ~30% efficient;
cost-competitive; requires direct sun;
heats fluid in pipes that then boils
water to drive steam turbine
Solar hot water: up to 50% efficient; several $k to
install; usually keep conventional backup; freeze
protection vital (even in S.D.!!)
Photovoltaic (PV): direct electricity; 15% efficient;
$5 per Watt to install without rebates/incentives;
small fraction of roof covers demand of typ. home
Spring 2013
Physics 12
UCSD
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Biofuels, algae, etc. also harvest solar energy, at few % eff.
Physics 12
UCSD
current flow
photon of light
electric field
Si doped with
boron, e.g.
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Lecture 12
n-type silicon
Si doped with
phosphorous, e.g.
p-type silicon
liberated electron
3
external load
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Photovoltaics
Spring 2013
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Spring 2013
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Lecture 12
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Photovoltaics
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0.58 V
Physics 12
UCSD
+0.58 V +0.58 V +0.58 V +0.58 V +0.58 V
3.5 volts
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UCSD
Spring 2013
Lecture 12
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3×Q
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5×Q
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Photovoltaics
Spring 2013
Physics 12
UCSD
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Physics 12
UCSD
MPPT charge
controller, system A
breaker box and shunts
for current measurement
system
monitor
Physics 12
UCSD
Spring 2013
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Physics 12
UCSD
400 W inverters for
systems A & B
green: battery % full
extension cords go
inside to appliances
charge controller,
system B
black: battery voltage
(right hand scale)
red: solar input, Watts
unused MPPT charge
controller
cyan: load usage;
baseline for inverter,
intermittent TV use
ground wire (to pipe)
class-T fuse (110 A)
Spring 2013
Lecture 12
numbers at top are
total solar yield (red)
and total system usage
(cyan) for that day,
in Watt-hours
class-T fuse (110 A)
12 V lead-acid
golf-cart battery for
system A: holds
1.8 kWh
identical12 V battery
for system B
conduit carrying
PV input wires
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Home PV monitor for three late-October days in 2007: first very cloudy,
second sunny; third cloudy
Spring 2013
see http://www.physics.ucsd.edu/~tmurphy/pv_for_pt.html for more examples
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Photovoltaics
Spring 2013
Physics 12
UCSD
Physics 12
UCSD
With three panels, I
could tackle something
more worthy, like the
refrigerator…
Can see cyclic behavior
as fridge turns on and off
Once battery reaches
absorb stage voltage
(~29.5 V), can relax
current to battery (falling
red envelope)
When fridge pops on,
need full juice again
Some TV later in day
extensions on mounts allow tilts to 50°
portion shown here only gets 10° and 20°
Spring 2013
UCSD
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Physics 12
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Physics 12
UCSD
A smart inverter can
shut off when battery
gets low, using grid power
to supply to loads
“Kyocera Skyline”
Inverter comes back on
when battery voltage hits
a certain level
Note consistency of
energy supplied (red
numbers) and energy
used (cyan numbers)
Infer 2107/2358 = 89%
efficiency across first
four days (efficiency of
sending solar juice to
inverter, including battery)
“Solar Quilt”
Using solar for fridge 75% of time; otherwise grid (4 panel setup)
getting most out of system, without wasting solar potential
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Spring 2013
grid-tie system delivering up to 11 kW
typ. home system less than 1/4 this size
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Photovoltaics
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Physics 12
UCSD
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flat: 918.4 kWh in 30 days → 30.6 kWh/day; tilted: 974.5 kWh → 32.5 kWh/day
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Physics 12
UCSD
30.78, 32.90
Numbers indicate kWh produced
for flat, tilted arrays, respectively
41.99, 45.00
37.87, 40.07
37.59, 40.75
40.95, 43.64
35.02, 36.96
Similar yields on cloudy days
10.60, 10.60
13.35,13.28
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Photovoltaics
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UCSD
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At present, UCSD has installed 1 MW of solar PV, online since Dec. 2008.
UCSD uses 30 MW, 25 MW generated on campus (gas turbines, mainly)
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