Post on 29-Jan-2016
The Vocabulary of Electrical Power
Solar Under The SunSolar 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 Picture of
Four 6-volt batteries, Part-au-Prince 50 amp and 20 amp circuit breakers
Picture of Picture of
Four 155 watt solar panelsArchaie, Haiti
Four 125 amp-hour batteriesArchaie, 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 complete loop– V = I*R,
where R is resistance– If the load goes
to 0 ohms resistance, thisis called ashort circuit
+
-
LOAD
current, I
current, I
Voltage
• Voltage exists even if there is no current• When the resistance
is infinite, is an open-circuitcondition
+
-
current, I = 0
current, I =0
12 volts12 volts
Power
• Power is the rate at which work is done• Units of power
are watts• Power is the product
of current and voltage
• P = V * I
+
-
LOAD
current, I
current, I
V 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 watt-hours/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 ideasDC Slo-pump replaced with Sun Pumps circulation pumpAC pump tested and DC pumps adopted
Archaie, Haiti July, 2009
4 x 155-watt panels
Water treatment system with UVdisinfection
Submersible pump
Water fountains at school yard across the street
Security lighting for water building
Institute Racine, Port-au-Prince, Haiti March 2010
2 155-watt solar panels
Water treatment system withozone disinfection
Lighting for water building
Outlets for charging computers and cell phones