Basics of Electricity Flashcards
The photovoltaic effect produces what type of current?
Direct (DC)
Which type of electrical current continually reverses direction as it flows?
Alternating (AC)
The unit measure for electrical current in a conductor is the:
Amp
What is the abbreviation/symbol for Resistance
ohms Ω
What is the abbreviation/symbol for Current
A
What is the abbreviation/symbol for Voltage
V
What is the abbreviation/symbol for Power
W
The unit of force which causes electrons to move in a conductor is the:
Volt
Volts are a unit of electromotive force, also referred to as potential difference and often thought of as electrical pressure.
Which type of electrical current only moves in one direction?
Direct (DC)
A PV module generates 3 amps at 12 volts. The amount of power produced is ___ ______ .
36; watts
volts x amps = watts
12 volts x 3 amps = 36 watts
If a PV array produces 8 amps at 24 volts for 5 hours, the energy produced is
960; watt-hours
8 amps X 24 volts = 192 watts
192 watts X 5 hours = 960 watt-hours
True or False? Assume a 2,400-watt PV array. If the array were re-wired to produce twice the voltage, the current produced would be cut in half.
True
Remember, in electrical circuits voltage and current are inversely proportional. If one goes up, the other goes down; and conversely, if one goes down, the other goes up.
For example, a 2,400-watt array, operating at 200 volts, outputs 12 amps. Operating at 400 volts, the same array would have its current reduced to 6 amps.
2,400 watts ÷ 200 volts = 12 amps
2,400 watts ÷ 400 volts = 6 amps
If a 25-watt light bulb operates at 12 volts, how much current will it draw? Remember to include the proper amount and term in your answer.
2.08 amps
Remember the basic relationship of watts equals amps time volts. Solving for amps, we see that amps = watts divided by volts. For this problem, we know the number of watts and volts in the circuit, and solve for amps:
25 watts ÷ 12 volts = 2.08 amps
Again, remember to include the proper amount and term. If two 60-watt light bulbs are left on for 2.5 hours, they will consume:
300 watt-hours
In this question we are asking for the amount of energy consumed by the two light bulbs:
60 watts/bulb x 2 bulbs = 120 watts
120 watts x 2.5 hours = 300 watt-hours
A 3,000 watt array is exposed to standard test condition sunlight (1,000 W/m2) for 6 hours. How much energy was produced (ignoring efficiency losses)?
18,000 watt-hours or 18 kilowatt-hours
In this question we are asking for the amount of energy produced by the 3 kW PV array, or watts over a certain amount of time:
3,000 watts X 6 hours = 18,000 watt-hours = 18 kilowatt-hours
A 4,000 watt array is exposed to standard test condition sunlight (1,000 W/m2) for an average of 5 hours each day. How much energy is produced per year (ignoring efficiency losses)?
7,300; kilowatt-hours/year
This would be the number of KWhs the 4 kW array produces over an entire year:
4,000 watts X 5 hours per day = 20,000 watt-hours per day = 20 kWh/day
20 kWh/day X 365 days per year = 7,300 kilowatt-hours/year
A 60-watt incandescent light bulb is left on for 5 hours. How many hours will it take for a 15-watt compact fluorescent bulb to consume the same amount of energy?
20
60 watts X 5 hours = 300 watt-hours of energy used by the incandescent bulb
300 watt-hours ÷ 15 watts = 20 hours for the compact fluorescent bulb to use the same amount of energy
True or False? A conductor has more resistance than an insulator.
False
Conductors are materials that readily allow electrons to flow across them, such as wire and metal. Insulators are materials that are resistive to the flow of electrons; examples of insulators include porcelain, wood, plastic, rubber, and paper.
What is the power rating of an array that has 24 modules rated at 330 watts each?
7,920 watts
24 modules X 330 watts per module = 7,920 watts or 7.92 kW
A graph showing the current and voltage output of a PV module is called:
the I-V curve
What is the capacity (in kilowatt-hours) of a battery rated at 2,000 amp-hours at 48 volts, that is powering a light each night for 5 hours?
96 kWh
Amp-hours can be converted to kilowatt-hours by multiplying by the DC system voltage:
2,000 amp-hours x 48 volts = 96,000 watt-hours = 96 kilowatt-hours
Since the question is asking about the battery capacity, the information about the light is not relevant.
