Laboratory Experiment on Concentrating Solar Power

NAME:________________________________ ID:____________________________________ Abstract:In the last 12 years, solar photovoltaics was the fastest growing renewable power technology worldwide. At the end of 2011, the cumulative installed capacity of solar photovoltaics had reached 65 GigaWatts of power up from only 1.5 GigaWatts in 2000. Germany and Italy are responsible for over half the global cumulative capacity, followed by Japan, Spain, the United States, and China. In California, photovoltaics installations have reached an installed solar capacity of 1 GigaWatt. In this laboratory experiment, students will explore the uses and benefits of concentrating solar power. They will build a solar concentrating device, determine its efficiency, define losses, and recommend several ways of improving their systems.

Introduction:A solar concentrator is considered one of the cleanest technologies to harvest renewable power. The first recorded use of solar concentrating power occurred around 212 BC when Greek sailors used mirrors to repel a Roman fleet. In 1882, Frenchman, Abel Pifre, demonstrated a solar powered steam engine driving a printing press. The boiler had a capacity of 42 Liters and the mirror array was 3.5 meters in diameter. Figures 1 and 2 shows drawings of such technologies.

Figure 1: Roman fleet being set on fire. Figure 2: Solar powered steam engine. [1]

In the modern applications of solar concentrating devices, the useful form of energy is considered heat. With heat, the temperature of the water is raised to the boiling point and steam is generated. The steam rotates the turbine connected to a shaft with a series of magnets and conducting materials. It is the movement of magnets that generates electrical current and therefore electricity. Overall, in this process, the thermal energy is in the form of heat is transferred to the mechanical energy in the form of rotating turbines, which is transferred into the electrical energy in the form of electricity.

There are several ways of concentrating solar power. The most popular methods are through using one or the combination of one of the following; parabolic trough, central receiver or parabolic dish concentrator. Figure 3 demonstrates sketches of such systems.

Figure 3: Various types of solar concentrators [2]

A parabolic trough concentrator is a solar thermal energy collector. It is constructed as a long parabolic mirror with a tube running its length at the focal point. The sunlight is reflected by the mirror and concentrated on the tube. It usually rotates to track the sun that moves across the sky.

A central receiver concentrator also known as central tower concentrator is also a solar thermal energy collector. In such design, a tower is used to received the focused sunlight from an array of flat, movable heliostats (or mirrors).

A parabolic dish concentrator is also a solar thermal energy collector. In this design, one or more parabolic dishes are used to concentrate solar energy on a single focal point. It is considered one of the most powerful type of collector.

For the purpose of this experiment, we will focus our attention on central tower concentrator system. Due to the recent need in pollution free technologies, the central tower concentrators have received more interest than ever before. Typically, such systems are deployed on large scale covering several square kilometers. In such systems, thousands of heliostats, or mirrors, are used to concentrate solar power on a single tower which usually holds a boiler. In the United States, several of power plants of this kind are in production in Mojave Desert. The first prototype was completed in 1980s, it is capable of generating 10 MW of power. Figure 4a demonstrates a photograph of this power plant. At the same time, internationally, PS10 and PS20 solar power towers were completed in 2006 and 2009, generating 11 and 20 MW of power respectively, providing energy for over 10,000 homes in the city of Seville, Spain. Figure 4b shows a photograph of the PS20 power tower.

Figure 4a: Barstow central receiver system. Figure 4b: SP20 central power tower in Seville, Spain.[3]In this laboratory experiment, students will design and build a central receiver concentrator from 24 telescoping mirrors. In part I of the experiment, they will use a steel cup filled with water to determine energy conversion efficiency. In part II, they will use pre-assembled Stirling engine to determine the same type of efficiency. The overall goal is for students is to build an energy harvesting device with the highest efficiency possible. After students calculate efficiencies of their systems, they will be asked to define losses and recommend ways of improving their system.

List of Materials○ 24 telescoping mirrors○ stand○ steel cup○ 6 oz of water - scale to weigh the water○ thermometer○ timer/clock/watch○ Aluminum foil○ Solar power meter (1 per class)○ Ruler○ Stirling engine

Procedure:

Part I: Determining energy efficiency by warming up a cup of water

1. Use the solar power meter determine the solar power density at your location. Point

the solar power meter at the sun and record displayed value in W/m2. Use “W/B” to switch between between W/m2 and Btu/(ft2h).

Power density in= ___________ (kW/m2)= _______(W/m2)

2. Next, with your group partners, discuss possible configurations of harvesting solar power using 24 telescoping mirrors. Your goal is to build an energy harvesting device with the highest efficiency.

3. Choose one mirror configuration that you and your partners agree on would achieve the highest efficiency and discuss it with your teacher assistant.

4. Place the stand in the desired location. Next, position your lab components in the following order;

a. place cup holder with a mounted cupb. pour water into the cupc. cover the cup with aluminum foild. insert thermometer through aluminum foile. arrange telescoping mirrors

Do not touch the cup or thermometer once the first telescoping mirror is in place. Serious burns may occur.

5. Record the temperature of water and time periodically (every minute). Do not spend more than 15 minutes on this task.

6. Using the following relationship, calculate the amount of energy needed to raise given amount of water by a certain number of degrees Celsius.

Q=mc(T2-T1)where, m: mass of water in the cup, in gramsc: specific heat constant, 4.186 Joules/gr °CT2-T1: temperature difference, in °C

Q=mc(T2-T1)Q=_______________________ Joules (Energy)

7. Next, using the following relationship, calculate the amount of power that was put into the system to raise the temperature of water. This will be your power out. Power (Watts) = Energy (Joules) / Time (sec)Power out = _________________ (Watts)

8. Estimate the circular area (in meters2) of the solar concentrator that you built. Each telescoping mirror is 3 inches in diameter. Area = π radius2

Area = ___________________ (m2)

9. Calculate power in from step 1 (using data from step 8), Power in (W) = Power density (W/m2) * Area (m2)Power in=______________ (W)

10. Lastly, calculate the efficiency of your system. The efficiency is defined in the following way, Efficiency = Power out / Power in Efficiency = ______(W) / ________ (W) = __________= __________ %

Part II: Determining energy conversion efficiency using Stirling engine1. Solar energy can also be converted into mechanical energy through the use of

Stirling engine. Stirling engine works a temperature difference in space - a cold area in one place and a hot area in another - to generate movement. It does not need to periodically burn anything, like a gasoline engine, and it does not need to create and release hot gas like a steam engine. It reuses the same gas, periodically heating and cooling it. See Figure 5 for more details.

Figure 5: Work cycle of a Stirling engine. 1) the air at the bottom heats up, creating pressure on the small power piston, which moves up and rotates the flywheel. 2) This moves the big displacer down, shuffling the air upwards, 3) cooling down at the top, which reduces the pressure and allows the power piston to move down. 4) This drags the displacer upwards and moves the air down to the bottom to be heated again, completing the cycle. [4]

2. Modify your design to integrate the Stirling engine into it. You will no longer need the water, aluminum foil or thermometer. You will still need to use the metal cup to collect solar energy. Do not to touch the cup with bare hands, serious burns may occur.

3. Place the Stirling engine on top of the metal cup. Wait for few minutes for the cup to warm up. If the propeller doesn’t start spinning in 5-10 minutes, give it a gently push in the direction indicated on the label for running on “hot”.

4. Measure the time it take for a propeller to go from not moving to constant number of rotations.

Time interval:_________________________ seconds

5. Measure the number of rotations per minute the blade makes.

Number of Rotations Per Minute : ____________________________

6. Disassemble your device by first removing the mirrors, letting the steel cup cool off for several minutes. Next, remove the cupholder with a cup and the Stirling engine.

7. Use the following relationship the total rotational kinetic energy of the propeller unit.

Kinetic Energy = ½ I total w2 where, I total: moment of inertia w: angular velocity

Use the following relationship to find the moment of inertia:I total= n (mL2/3)where,n: number of bladesm: mass of the blade, in kgL: length of the blade, in meters

Itotal=_______________________ (kg m2)

Use the answer from part 5 and the following relationship find the angular velocity:w = ( ____ rev/ min) (2 π rad/rev)(1 min / 60 sec)

w = _________________________ rad/ sec

and therefore,

Kinetic Energy = ½ I total w2

Kinetic Energy = _____________________ (J)

8. Use the following relationship to calculate the power.

Power = Kinetic Energy / Time Interval

Power = ________________ (J) / ____________________ (sec) = Power out

9. Lastly, calculate the efficiency of your system. The efficiency is defined in the following way, Efficiency = Power out / Power in Efficiency = ______(W) / ________ (W) = __________= __________ %

Conclusion/Discussion:Please answer the following set of questions,

1. Why do you think the efficiency of your system is so low? Define at least three losses in your system.

2. Taking the losses into consideration, identify at least three ways of improving the efficiency of your system.

3. If you and your partners had another chance at conducting the same experiment, what would you have done differently from the beginning?

4. What effects do the time of day and weather have on this experiment?

5. Brainstorm several direct commercial applications of the solar concentrator.

6. Develop a scheme to generate electricity from a solar concentrator.

Laboratory Experiment on Concentrating Solar PowerPRE Questionnaire

NAME:_________________ MAJOR:_____________ YEAR: _________ MALE / FEMALE E-MAIL:_____________________

1. In the last decade, what was the fastest growing renewable power technology worldwide?a. Wind Turbinesb. Photovoltaicsc. Fuel-Cellsd. Electric Vehiclese. I don’t know

2. How long have solar concentrating devices been around?a. a few yearsb. a few decadesc. a few hundred of yearsd. a few thousand of yearse. I don’t know

3. How much power (over one year) are we capable of harvesting in California using photovoltaic systems alone?

a. a kiloWattb. a MegaWatt

c. a GigaWattd. a TeraWatte. I don’t know

4. What is a heliostat?a. a photovoltaic cellb. a photovoltaic arrayc. a solar dishd. a mirror e. I don’t know

5. If a solar concentrating device has a circular area with radius of 10 cm. What is the area of such device?

a. 20 cm2

b. 60 cm2

c. 100 cm2

d. 300 cm2

e. I don’t know6. In Arizona, on average, 7 kWh/m2 of solar energy density is available a day. If a solar

concentrating device has an area of 2 m2, how much energy is acquired by such device.a. 3.5 kWhb. 7 kWhc. 14 kWhd. 28 kWhe. I don’t know

7. If you have a device that consumes 100 Joules of energy in 10 seconds. How much power does it consume?

a. 10 Wattsb. 100 Wattsc. 1000 Wattsd. 10000 Wattse. I don’t know

8. If a kitchen kettle raises the temperature of 300 gr of water from 20°C to 60°C? How much energy does it consume in doing so? (please neglect all losses) (specific heat constant is 4.186 Joules/gr °C).

a. 1.2 kJb. 2.5 kJc. 25 kJd. 50 kJe. I don’t know

9. If a solar concentrating device is exposed to 1000 Watts of power per day and it harvests 200 Watts of power on daily basis, what is the efficiency of this device?

a. 10%b. 20%c. 50%d. 100%e. I don’t know

10. Select correct statement: Solar energy can also be converted into mechanical

energy through the use of Stirling engine. Stirling engine uses a temperature difference in space to generate movement. It requires;

a. burning gassesb. generating steamc. creating and releasing steamd. heating up and cooling the same amount gase. I don’t know

Laboratory Experiment on Concentrating Solar PowerPOST Questionnaire

NAME:____________________________________________ 11. In the last decade, what was the fastest growing renewable power technology worldwide?

a. Wind Turbinesb. Photovoltaicsc. Fuel-Cellsd. Electric Vehiclese. I still don’t know

12. How long have solar concentrating devices been around?a. a few yearsb. a few decadesc. a few hundred of yearsd. a few thousand of yearse. I still don’t know

13. How much power (over one year) are we capable of harvesting in California using photovoltaic systems alone?

a. a kiloWattb. a MegaWattc. a GigaWatt

d. a TeraWatte. I still don’t know

14. What is a heliostat?a. a photovoltaic cellb. a photovoltaic arrayc. a solar dishd. a mirror e. I still don’t know

15. If a solar concentrating device has a circular area with radius of 10 cm. What is the area of such device?

a. 20 cm2

b. 60 cm2

c. 100 cm2

d. 300 cm2

e. I still don’t know16. In Arizona, on average, 7 kWh/m2 of solar energy density is available a day. If a solar

concentrating device has an area of 2 m2, how much energy is acquired by such device.a. 3.5 kWhb. 7 kWhc. 14 kWhd. 28 kWhe. I still don’t know

17. If you have a device that consumes 100 Joules of energy in 10 seconds. How much power does it consume?

a. 10 Wattsb. 100 Wattsc. 1000 Wattsd. 10000 Wattse. I still don’t know

18. If a kitchen kettle raises the temperature of 300 gr of water from 20°C to 60°C? How much energy does it consume in doing so? (please neglect all losses) (specific heat constant is 4.186 Joules/gr °C).

a. 1.2 kJb. 2.5 kJc. 25 kJd. 50 kJe. I still don’t know

19. If a solar concentrating device is exposed to 1000 Watts of power per day and it harvests 200 Watts of power on daily basis, what is the efficiency of this device?

a. 10%b. 20%c. 50%d. 100%e. I still don’t know

20. Select correct statement: Solar energy can also be converted into mechanical energy through the use of Stirling engine. Stirling engine uses a temperature difference in space to generate movement. It requires;

a. burning gassesb. generating steam

c. creating and releasing steamd. heating up and cooling the same amount gase. I still don’t know

ADDITIONAL QUESTIONS

Was this experiment too long, too short or just right? Circle one: Too long Too Short Just right

Was this experiment at the appropriate level of this class?Circle one: Yes Maybe No

How would you rate the introduction to the lab?Circle one: Outstanding Good Fair Poor

How would you rate the lab’s clarity and understandability?Circle one: Outstanding Good Fair Poor

How would you rate the quality of the lab activities?Circle one: Outstanding Good Fair Poor

What is your overall assessment of the value of the lab?Circle one: Outstanding Good Fair Poor Please comment on how we can improve this laboratory experiment. Something you liked or disliked about it. Something you prefer for us to change?

Laboratory Experiment on Concentrating Solar PowerPre & Post Questionnaires Answers

ANSWERS1. In the last decade, what was the fastest growing renewable power technology worldwide?

b. Photovoltaics2. How long have solar concentrating devices been around?

d. a few thousand of years3. How much power (over one year) are we capable of harvesting in California using photovoltaic systems alone?

c. a GigaWatt4. What is a heliostat?

d. a mirror 5. If a solar concentrating device has a circular area with radius of 10 cm. What is the area of such device?

d. 300 cm2

6. In Arizona, on average, 7 kWh/m2 of solar energy density is available a day. If a solar concentrating device has an area of 2 m2, how much energy is acquired by such device.

c. 14 kWh7. If you have a device that consumes 100 Joules of energy in 10 seconds. How much power does it consume?

a. 10 Watts8. If a kitchen kettle raises the temperature of 300 gr of water from 20°C to 60°C? How much energy

does it consume in doing so? (please neglect all losses) (specific heat constant is 4.186 Joules/gr °C). d. 50 kJ

9. If a solar concentrating device is exposed to 1000 Watts of power per day and it harvests 200 Watts of power on daily basis, what is the efficiency of this device?

b. 20%10. Select correct statement: Solar energy can also be converted into mechanical energy through the use of Stirling engine. Stirling engine uses a temperature difference in space to generate movement. It requires;

d. heating up and cooling the same amount gas