Transcript Lesson 1 - River View Hotel

Introduction
• Hi, y’all,
– I’m leaving in the morning, so I didn’t get to spend
as much time on this as I would have liked
– Please let me know if you find it useful
– Suggestions for improvement are welcome
Lesson 1
• Before beginning this lesson, please read
“Electrical Needs Assessment” with the
glossary, and “The Vocabulary of Electrical
Power
Contents
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Review of terms and relationships
Sample Problems
Skill building problems
Answers to skill building problems
Review of terms and relationships
• Current is the flow of charges
– Measured in amps (short for amperes)
• Voltage is the electrical potential
– Measured in volts
• Power is the rate at which energy is used
– Measured in watts
– 1 watt = 1 amp * 1 volt
Mechanical Power vs.
Electrical Power
• A gasoline engine’s power is measured in
horsepower
– 1 horsepower = 746 watts
Energy
• Energy is what a photovoltaic cell captures
• Energy is what a pump, motor, or light uses
• Energy = Power * time
– Measured in watt-hours
AC vs. DC
• The power produced by batteries and PV
panels is DC (for Direct Current)
• DC current flows in one direction
• AC current changes direction tens of times a
second
AC vs. DC power
• In a solar power system, DC power goes in to
an inverter; and AC power comes out of an
inverter.
• The inverter has electrical losses.
– When you know the AC watts, add 15% to find
how many DC watts will have to be supplied
Sample Problem 1
• A 23 watt CFL (compact fluorescent light) puts
out as much light as a 100 watt incandescent
bulb. How much energy does each bulb use if
it burns for 8 hours a night?
Answer to Sample Problem 1
• A 23 watt CFL (compact fluorescent light) puts
out as much light as a 100 watt incandescent
bulb. Both bulbs use 120 volt AC power, how
much energy does each bulb use if it burns for
8 hours a night?
• This is a straight “plug in the numbers”
problem
• CFL: 23 watts * 8 hours = 184 watt-hours
• Inc: 100 watts * 8 hours = 800 watt-hours
Sample Problem 2
• A CFL bulb uses 184 watt-hours a night
• An incandescent bulb uses 800 watt-hours a
night
• How many hours of sunlight are needed on a
300 watt PV array to provide the energy to
light the bulbs for a night?
Answer to sample problem 2
• PV panel watts are DC, the lights are AC
– CFL: 184 watt-hours AC * 1.15 = 212 watt-hours DC
– Inc: 800 watt-hours AC* 1.15 = 920 watt-hours DC
• (* 1.15 adds 15 %)
• Since Energy = Power * time,
time = Energy/Power
• CFL: 212 watt-hours/300 watts = 0.71 hour, or 42
minutes
• Inc: 920 watt-hours/300 watts = 3.1 hours, or 3
hours and 4 minutes
More on problem 2
• It takes 42 minutes for a 300 watt panel to
gather enough energy to run a 23-watt CFL
bulb for 8 hours
• It takes 3 hours and 4 minutes for a 300 watt
panel to gather enough energy to run a 100watt incandescent bulb for 8 hours.
• Solar 1 grads will work with the OP’s to reduce
their energy demands while meeting the OP’s
needs.
Sample problem 3
• A CFL bulb uses 184 watt-hours a night
• An incandescent bulb uses 800 watt-hours a
night
• How many amp-hours will each bulb draw
from a 24-volt, 225 amp-hour battery in one
night?
Answer to sample problem 3
• From sample problem 2, the CFL needs 212 watthours DC and
• The incandescent bulb needs 920 watt-hours DC
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Since watts = volts*amps, amps= watts/volts
CFL: 212 watt-hours/24 volts = 8.8 amp-hours
Inc: 920 watt-hours/24 volts = 38.3 amp-hours
Another reason to use CFL’s!
Skill Building Problem 1
• If a 310 watt PV panel array puts out 5.5
amps, what voltage is the PV panel providing?
SBP 2
• An AC air conditioner uses 1,500 watts. If a
site gets 5 hours of sunlight a day, how big
should the PV array be to run the air
conditioner for 3 hours?
SBP 3
• Conduct an “electrical needs assessment” in 1
room in your home
– That is, find the number of watt-hours of energy
per week that is used in one room in your home
Answer to SBP 1
• If a 310 watt PV panel array puts out 5.5
amps, what voltage is the PV panel providing?
• Since watts = volts * amps, volts = watts/amps
• 310 watts/ 5.5 amps = 56 volts
Answer to SBP 2
• An AC air conditioner uses 1,500 watts. If a
site gets 5 hours of sunlight a day, how big
should the PV array be to run the air
conditioner for 3 hours?
• 1500 watts AC * 1.15 = 1725 watts DC
• 1725 watts * 3 hours = 5175 watt-hours
• 5175 watt-hours/ 5 hours = 1035 watts