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PV 101: Basic Exercises

Ohm’s Law: , Amps & E = (V) I = CURRENT (A) R = RESISTANCE (W)

E = I x R I = E ÷ R R = E ÷ I

1. How many ohms of resistance are in a 120- circuit that pulls 5 amps? ______

2. How many amps of current are in a 10-volt circuit that has 2 W of resistance? ______

3. How many volts are in a 10-W circuit that uses 11 amps of current? ______

4. An electrical circuit measures 8 amps at 300 volts. What’s the resistance? ______

5. A 40-volt circuit measures 2 W. How much current will it use? ______

6. If a 120-volt circuit is expected to pull 9 amps, what’s the resistance of the circuit? ______

7. What is the voltage of a 2-W, 80-A circuit? ______

PV 101: Basic Photovoltaics Exercises

Power: Watts, Amps & Volts

P = (W) I = CURRENT (A) E = VOLTAGE (V)

P = I x E I = P ÷ E E = P ÷ I

8. How many watts are consumed if a 115-volt appliance draws 5 amps? ______

9. How many amps are present in a 200-watt circuit running on 25 volts? ______

10. How many watts of power are used in a 110-volt circuit that pulls 15 amps? ______

11. What’s the voltage of a 150-watt circuit with 5 amps of current? ______

12. How many volts would be measured in a 40 W, 2-amp circuit? ______

13. What’s the power used in a 120 V circuit with 0.034 A? ______

14. How much current does a 75 W bulb pull when connected to 115 V? ______

PV 101: Basic Photovoltaics Exercises

Energy: Power & Time (Load Profiles)

Wh = WATT- P = POWER (W) T = TIME (hours) is measured in watt-hours (Wh) or kWh 1 kWh = 1,000 Wh

15. A 75-watt bulb is on for two hours. How many watt-hours does it consume? ______

16. A 15-watt bulb is on for three hours a . How much energy does it consume:

In a day? ______In a week? ______In 30 days? ______In a year? ______

17. A 60 W bulb is on for 5 hours a day and costs $0.123 per kWh. How much energy does it use, and how much does it cost to operate:

In a day? kWh = ______Cost = $ ______In a week? kWh = ______Cost = $ ______In 30 days? kWh = ______Cost = $ ______In a year? kWh = ______Cost = $ ______

18. A 115-volt appliance draws 5 amps for 2.5 hours. How many watt-hours does it use in a day? ______

19. A 110-volt machine that pulls 15 amps runs 12 hours each day.

How many watt-hours does it use in a day? ______How many watt-hours does it use in 30 days? ______How many kWh does it use in a year? ______

PV 101: Basic Photovoltaics Exercises

20. Four 40-W light bulbs are on 24 hours a day.

How many kWh do they use each day? ______

How many kWh do they use in 30 days? ______

How many kWh do they use in a year? ______

If electricity is $0.12 per kWh, how much does it cost to light these bulbs:

Each month (30 days)? $ ______

Each year? $ ______

21. A refrigerator compressor runs 10 hours a day. The voltage is 115 and the current is 6 amps.

What is the wattage of the compressor? ______

How many kWh does the refrigerator use in a day? ______

How many kWh does the refrigerator use in 30 days? ______

How many kWh does the refrigerator use in a year? ______

If electricity costs $0.16 per kWh, how much does it cost to operate this refrigerator:

Each month (30 days)? $ ______

Each year? $ ______

22. A pop (soda) machine runs 12 hours a day at 120 V and 12 A. Electricity is $0.13/kWh.

How much does it cost to run the machine each day? $ ______

How much does is cost to run the machine for 30 days? $ ______

How much does it cost to run the machine for a year? $ ______

PV 101: Basic Photovoltaics Exercises

Phantom Loads

Load Wattage Energy used each kWh used per year Annual energy cost day (24 hours) ($0.15 per kWh) Cell phone charger 2 W Desktop computer 8 W Garage door opener 2.5 W Cable box / DVR 32 W Cable box #2 20 W Wi-Fi router 4 W TV 11 W TV #2 9 W Microwave clock 0.5 W Range clock 0.25 W Night light 0.75 W Ceiling fan 3.5 W TOTALS

System Sizing 1. Find average daily kWh consumption 2. Divide by average hours per day 3. Divide by 0.8 for system losses

Home #1: Married couple, no children, 1,000 square-foot house

January: 440 kWh February: 500 kWh March: 370 kWh April: 460 kWh May: 410 kWh June: 420 kWh July: 620 kWh August: 740 kWh September: 490 kWh October: 350 kWh November: 400 kWh December: 510 kWh

23. Average daily kWh consumption = ______

24. What size system would be appropriate if the site received an average of 4 sun hours per day?

25. What size system would be appropriate if the site received an average of 5 sun hours per day?

26. What size system would be appropriate if the site received an average of 6 sun hours per day?

PV 101: Basic Photovoltaics Exercises

Home #2: Married couple, 4 children, 2,500 square-foot house

January: 975 kWh February: 855 kWh March: 960 kWh April: 899 kWh May: 1,022 kWh June: 1,350 kWh July: 1,570 kWh August: 1,623 kWh September: 1,250 kWh October: 910 kWh November: 1,030 kWh December: 1,290 kWh

27. Average daily kWh consumption = ______

28. What size system would be appropriate if the site received an average of 4 sun hours per day?

29. What size system would be appropriate if the site received an average of 5 sun hours per day?

30. What size system would be appropriate if the site received an average of 6 sun hours per day?

Home #3: Single person, travels frequently, 800 square-foot house

January: 112 kWh February: 96 kWh March: 105 kWh April: 121 kWh May: 140 kWh June: 138 kWh July: 210 kWh August: 189 kwh September: 98 kWh October: 102 kWh November: 88 kWh December: 108 kWh

31. Average daily kWh consumption = ______

32. What size system would be appropriate if the site received an average of 4 sun hours per day?

33. What size system would be appropriate if the site received an average of 5 sun hours per day?

34. What size system would be appropriate if the site received an average of 6 sun hours per day?

PV 101: Basic Photovoltaics Exercises

Series & Parallel Circuits In a series circuit, voltage adds but current remains constant. In a parallel circuit, current adds but voltage remains constant. Each PV module is rated 25 V and 8 A.

PV 101: Basic Photovoltaics Exercises

Answers

Ohm’s Law 1. 120 V ÷ 5 A = 24 W 2. 10 V ÷ 2 W = 5 A 3. 11 A x 10 W = 110 V 4. 300 V ÷ 8 A = 37.5 W 5. 40 V ÷ 2 W = 20 A 6. 120 V ÷ 9 A = 13.3 W 7. 80 A x 2 W = 160 V

Power 8. 5 A x 115 V = 575 W 9. 200 W ÷ 25 V = 8 A 10. 15 A x 110 V = 1,650 W (1.65 kW) 11. 150 W ÷ 5 A = 30 V 12. 40 W ÷ 2 A = 20 V 13. 0.034 A x 120 V = 4.08 W 14. 75 W ÷ 115 V = 0.65 A

Energy 15. 75 W x 2 h = 150 Wh 16. 15 W x 3 h = 45 Wh/day 7 days = 315 kWh 30 days = 1.35 kWh 1 year = 16.425 kWh 17. 60 W x 5 h = 0.3 kWh and $0.04/day 7 days = 2.1 kWh and $0.26 30 days = 9 kWh and $1.11 1 year = 109.5 kWh and $13.47 18. 115 V x 5 A x 2.5 h = 1,437.5 Wh 19. 110 V x 15 A x 12 h = 19.8 kWh/day 30 days = 594 kWh 1 year = 7,227 kWh 20. 4 x 40 W x 24 h = 3.84 kWh/day 30 days = 115.2 kWh and $13.82 1 year = 1,401.6 kWh and $168.19 21. 115 V x 6 A = 690 W 10 h = 6.9 kWh/day 30 days = 207 kWh and $33.12 1 year = 2,518.5 kWh and $402.96

PV 101: Basic Photovoltaics Exercises

22. 120 V x 12 A x 12 h = 17.28 kWh and $2.25/day 30 days = $67.39 1 year = $819.94

Phantom Loads Cell phone charger = 48 Wh/day, 17.52 kWh and $2.63/year Desktop computer = 192 Wh/day, 70.08 kWh and $10.51/year Garage door opener = 60 Wh/day, 21.9 kWh and $3.29/year Cable box / DVR = 768 Wh/day, 280.32 kWh and $42.05/year Cable box #2 = 480 Wh/day, 175.2 kWh and $26.28/year Wi-Fi router = 96 Wh/day, 35.04 kWh and $5.26/year TV = 264 Wh/day, 96.36 kWh and $14.45/year TV #2 = 216 Wh/day, 78.84 kWh and $11.83/year Microwave clock = 12 Wh/day, 4.38 kWh and $0.66/year Range clock = 6 Wh/day, 2.19 kWh and $0.33/year Night light = 18 Wh/day, 6.57 kWh and $0.99/year Ceiling fan = 84 Wh/day, 30.66 kWh and $4.60/year TOTALS = 93.5 W, 2.244 kWh/day, 819.06 kWh and $122.86/year

System Sizing 23. 5,710 kWh ÷ 365 = 15.64 kWh 24. 15.64 kWh ÷ 4 h ÷ 0.8 = 4.9 kW 25. 15.64 kWh ÷ 5 h ÷ 0.8 = 3.91 kW 26. 15.64 kWh ÷ 6 h ÷ 0.8 = 3.26 kW 27. 13,734 kWh ÷ 365 = 37.63 kWh 28. 37.63 kWh ÷ 4 h ÷ 0.8 = 11.76 kW 29. 37.63 kWh ÷ 5 h ÷ 0.8 = 9.41 kW 30. 37.63 kWh ÷ 6 h ÷ 0.8 = 7.84 kW 31. 1,507 kWh ÷ 365 = 4.13 kWh 32. 4.13 kWh ÷ 4 h ÷ 0.8 = 1.29 kW 33. 4.13 kWh ÷ 5 h ÷ 0.8 = 1.03 kW 34. 4.13 kWh ÷ 6 h ÷ 0.8 = 0.86 kW

Series & Parallel Circuits 1. 75 V, 8 A 2. 25 V, 24 A 3. 50 V, 16 A