Basics of Electricity

Question 1

The photovoltaic effect produces what type of current?

Answer 1

Direct (DC)

Question 2

Which type of electrical current continually reverses direction as it flows?

Answer 2

Alternating (AC)

Question 3

The unit measure for electrical current in a conductor is the:

Answer 3

Amp

Question 4

What is the abbreviation/symbol for Resistance

Answer 4

ohms Ω

Question 5

What is the abbreviation/symbol for Current

Answer 5

A

Question 6

What is the abbreviation/symbol for Voltage

Answer 6

V

Question 7

What is the abbreviation/symbol for Power

Answer 7

W

Question 8

The unit of force which causes electrons to move in a conductor is the:

Answer 8

Volt

Volts are a unit of electromotive force, also referred to as potential difference and often thought of as electrical pressure.

Question 9

Which type of electrical current only moves in one direction?

Answer 9

Direct (DC)

Question 10

A PV module generates 3 amps at 12 volts. The amount of power produced is ___ ______ .

Answer 10

36; watts

volts x amps = watts

12 volts x 3 amps = 36 watts

Question 11

If a PV array produces 8 amps at 24 volts for 5 hours, the energy produced is

Answer 11

960; watt-hours

8 amps X 24 volts = 192 watts

192 watts X 5 hours = 960 watt-hours

Question 12

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.

Answer 12

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

Question 13

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.

Answer 13

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

Question 14

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:

Answer 14

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

Question 15

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)?

Answer 15

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

Question 16

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)?

Answer 16

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

Question 17

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?

Answer 17

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

Question 18

True or False? A conductor has more resistance than an insulator.

Answer 18

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.

Question 19

What is the power rating of an array that has 24 modules rated at 330 watts each?

Answer 19

7,920 watts

24 modules X 330 watts per module = 7,920 watts or 7.92 kW

Question 20

A graph showing the current and voltage output of a PV module is called:

Answer 20

the I-V curve

Question 21

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?

Answer 21

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.