## Question

A house has the following electrical appliance usage:

• One 18 Watt fluorescent lamp with electronic ballast used 4 hours per day.

• One 60 Watt fan used for 2 hours per day.

• One 75 Watt refrigerator that runs 24 hours per day with compressor run 12 hours and off 12 hours.

• The system will be powered by 12 Vdc, 110 Wp PV module.

• Assume an average of 3.4 peak sunlight hours per day and 3days of autonomy.

Size the PV system including, PV modules, Inverter, Battery, Solar charge controller. State all assupmptions.

Question 2

An offshore wind turbine generator situated at sea level has a rotor blade diameter of 100 metres. The air density is 1.23 kg/m3.

The turbine is rated at 5MW in 30mph (14m/s) winds. Calculate the power generated with a power coefficient of 0.25

Question 3

You need to decide which energy system is more suitable to power the following household requirement. This system will be installed in Perth, Australia. Since the average annual daytime temperatures are quite mild, we need not to worry about temperatures effects on the battery capacity

This exercise is divided into four parts. In part one you will calculate the system requirements. In the second part you will calculate the energy production of a PV system and part three you will calculate the energy production of a wind system. In the final part, You will conclude on the most suitable option after modelling the system.

Please see the instructions for the software “Homer Beta 2.68

Appliance Watts Quantity Total Watts Hours/day Watts/hrs/Day

40W Bulb 40 10 4

100W Bulb 100 2 3

TV 75 2 3

Heater/air con 2000 2 3

Music system 200 1 2

Refrigerator 325 1 6

Freezer 25 1 6

Oven 1200 1 1

Coffee Maker 1000 1 0.5

Total

PART 1: System Requirement

1. Calculate is the total power requirement (Wh) per day.

2. Assuming that peak load occurs when the refrigerator the heater/air con and the TV work simultaneously. Calculate the peak load.

3. Calculate the voltage of your battery bank.

4. Calculate the amp-hour requirement per day.

5. The system is required to work even if there are 3 consecutive cloudy days and the batteries must not run down more than 50%. Calculate the Ah you need to store.

6. Adjust this figure for an inverter efficiency of 93%.

7. Using the lead-acid batteries listed in the appendix, design a battery bank:

- Battery Model?

- Number of batteries in series?

- Number in batteries parallel?

PART 2: PV Power

1. Your PV array needs to point true North. Where is true North in Perth, assuming that your compass points to 000 (magnetic North)?

2. What is the recommended tilt angle for Perth?

3. Assuming that the total sun hours for Perth is 4 hours in June. What is the amperage required from your PV array?

PART 3: Wind Power

1. How many amperes should you be able to supply from the D400 at 7.5m/s?

2. If the wind drops to 1m/s, what will the output current be? What is, theoretically, the maximum current you can obtain from the D400?

3. Let’s say there is a possibility of installing the turbine on top of a 20m high mast instead. Assuming that Zo=0.012, what would you expect the wind speed to be at that height?

## Solution Preview

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PV modules needed:The total consumption per day = 1.092KWhr

Hence the actual supply needed from the PV panels = 1.3 * 1.092KWhr = 1.4196KWhrs.

Watt-peak hours needed = 1.4196/3.43 = 0.414KWhr =414Whr-Peak

The actual rating of the PV modules available = 110Wp

Hence the number of PV modules needed =414/110 ~ 4 PV modules are needed.

Inverter Rating:

Inverter rating should be sum of all the ratings of the appliances = (18+3*60+3*75) = 423W~ 425W

Inorder to account for the surge currents during the starting, the inverter capacity is accounted for three times the motor start up as per the needs of the fan and the refrigerator capacities....