Transcript Power - River View Hotel

The Vocabulary of Electrical
Power
Solar Under The Sun
Solar School
May 2010
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• The purpose of this presentation is to review
electrical terms such as volts, amps, and watts
• And to relate these terms to components in a
solar power system
Picture of
Four 6-volt batteries, Part-au-Prince
Picture of
Four 155 watt solar panels
Archaie, Haiti
Picture of
50 amp and 20 amp circuit breakers
Picture of
Four 125 amp-hour batteries
Archaie, Haiti
DC vs. AC electricity
• Photovoltaic (PV) panels and batteries are
sources of DC power
– In a DC system, current only flows in one direction
• Electric utilities, generators, and inverters are
sources of AC power
– In an AC system, current changes direction tens of
times a second.
Water analogy for DC electricity
• Current is the flow of electrons in a circuit.
– Units of current are amperes or amps
– Think of current as the water flowing through a
hose
• Voltage is the electrical potential
– Units of voltage are volts
– Think of voltage as the water pressure in a hose
Current
• Current can only flow when there is a
current, I
complete loop
– V = I*R,
where R is resistance
– If the load goes
to 0 ohms
resistance, this
is called a
short circuit
+
LOAD
current, I
Voltage
• Voltage exists even if there is no current
current, I = 0
• When the resistance
is infinite, is an
open-circuit
+
12 volts
condition
12 volts
current, I =0
Power
• Power is the rate at which work is done
current, I
• Units of power
are watts
• Power is the product +
LOAD
V
of current and
voltage
• P=V*I
current, I
V
Power Examples
• A solar panel is outputting 4 amps at 25 volts.
How much power is the solar panel
producing?
• P = 4 amps * 25 volts = 100 watts
• A 150 watt solar panel operating at rated
output provides 5 amps of current. What is
the full-output voltage?
• P = V*I, so V = P/I = 150 watts/5 amps = 30
volts
Energy
• A photovoltaic panel converts solar energy
(light) into electrical energy
• A battery stores energy and delivers energy
• Units of energy are watt-hours
• E = P * t, where t is time
Energy examples
• How much energy will a 155-watt PV panel
produce when it operates at rated power for 5
hours?
• E = 155 watts * 5 hours = 775 watt-hours
• We will often refer to Energy in a particular time
period
– How many watt-hours will a solar array generate each
day if it operates at rated output for 5 hours/day?
E/day = 155 watts * 5 hours/ day = 775 watthours/day
How many solar panels?
• In a SUTS solar power system, the PV panels
must provide enough watt-hours of energy
each week to meet the watt-hour needs of the
equipment and to keep the batteries at full
charge.
• This calculation will normally be performed by
a graduate of Solar 2
How many batteries?
• The batteries must be able to provide enough
watt-hours of energy to meet the watt-hour
requirements of the equipment for at least 3
days of no sun, while maintaining at least 50%
of their total charge.
• This calculation will normally be performed by
a graduate of Solar 2
Deep-cycle batteries
• Batteries for solar power systems should be
“deep-cycle”.
• This means they are designed to provide a
steady flow of power for an extended period
of time
• Common sources of deep-cycle batteries are
golf-cart batteries and wheelchair batteries
Batteries
• Batteries are characterized by two numbers
– Their voltage (usually 6 or 12 volts)
– Their amp-hour capacity
• Amp-hours are an indicator of how much
charge a battery can store, and
• Amp-hours are an indicator of how many
hours a battery can supply a given number of
amps
How does this relate to Solar 1?
• Solar 1 graduates and Solar 2 graduates will
complete the Solar Suitability Survey (SSS)
during the partnership development visits
with the operating partners
Solar Suitability Survey
• One component of the survey is determining
what local or regional sources of solar
equipment exist
• Where a network exists (like Haiti) a solar
supplier will have already been identified
Camp Hopewell, CWU circa 2008
The initial system still used to test equipment and ideas
DC Slo-pump replaced with Sun Pumps circulation pump
AC pump tested and DC pumps adopted
Archaie, Haiti
4 x 155-watt panels
Water treatment system with UV
disinfection
Submersible pump
Water fountains at school yard
across the street
Security lighting for water building
July, 2009
Institute Racine, Port-au-Prince,
Haiti March 2010
2 155-watt solar panels
Water treatment system with
ozone disinfection
Lighting for water building
Outlets for charging computers
and cell phones