Unit 5Matter-EnergyInterface

PERFORMANCE TASK

738 Unit 5 NEL

The Photovoltaic (Solar) Cell

One of the most important applications of the photoelectric effect is the photovoltaic cell,commonly referred to as the solar cell. The materials used in photovoltaic cells, such as sil-icon and gallium arsenide, convert sunlight into electricity. Introduced in the 1950s and basedon the same solid-state semi-conductor technology used in transistors and computer chips,this expensive technology was originally used for powering satellites (Figure 1). Butimprovements in the technology over the years have significantly reduced the cost so thatit can be applied in many more markets.

Consumer products, such as solar-powered calcula-tors and watches, currently account for about one-thirdof photovoltaic use. Although the average power outputof these cells is in the milliwatt range, consumer prod-ucts have been an important proving ground for pho-tovoltaic technology.

The largest market for photovoltaics is in remotepower applications, areas not served by electric trans-mission grids, such as cottages, cabins, weather stations,and remote communities in North America and com-munities in the developing world (Figure 2).

The third significant market for photovoltaics is insupplying electricity to electrical transmission grids(Figure 3). This can be accomplished either throughvast arrays of photovoltaic modules in a centralized loca-tion—in the same manner as a traditional power plant—or by decentralized arrays of photovoltaic cells on theroofs of houses and buildings. Electricity produced in thisway currently costs over three times that of traditionalsources of electrical energy, but with continual improve-ments in photovoltaic technology, the cost per wattshould decrease.

Process

• Choose appropriate researchtools.

• Carry out the research andsummarize your findingsappropriately.

• Analyze the principles of thephotoelectric effect involvedin the technology.

• Evaluate the societal impacts.

Product

• Demonstrate anunderstanding of the relatedphysics concepts in yourreport.

• Prepare a suitable researchportfolio.

• Use terms, symbols,equations, and SI metric unitscorrectly.

• Produce a finalcommunication, including ademonstration model of anoperating solar cell (Task 1)OR a written report on anapplication of photovoltaiccells in a remote location asdirected (Task 2).

Criteria

Figure 1The International Space Station(ISS) uses solar arrays to collectand then convert solar energyto electricity. When exposed tosolar energy, photovoltaic cellsin the arrays generate smallcurrents of electricity. Thispowers the station and chargesthe batteries, which are usedwhen ISS is not in sunlight.

Figure 3Utility-based, supplemental solar power “farm”

Figure 2This Mongolian nomad stands beside two solarpanels that power lighting and a televisioninside her tent.

Part 1In preparation for your selected task, research the Internet and other sources and pro-vide a report, including diagrams, on the following topics:

(a) How do solar cells use the photoelectric effect to convert solar energy to electricity?

Unit 5

Matter-Energy Interface 739NEL

(b) How efficient are solar cells? Include methods forenhancing the efficiency.

(c) Compare and contrast photovoltaic technology withother forms of electricity generation, including theimpact on the environment.

(d) Briefly summarize the significant advantages and dis-advantages of solar power generation.

In consultation with your instructor, choose one of the fol-lowing tasks.

Task 1: Make a Photovoltaic CellUsing a kit provided by your instructor, you will construct aphotovoltaic cell and test its output. Depending on the kitprovided, discuss any safety issues with your teacher.

1. Follow the instructions provided for making a photo-voltaic cell, keeping a written record of the process.

2. Use your knowledge of the physics of electricity to writeup a procedure for testing and measuring the electricaloutput of the photovoltaic cell. An electrical schematicdiagram will be expected as part of your report.

3. Once the photovoltaic cell is operating, use yourknowledge of the physics of wave optics to propose toyour teacher a way of controlling the intensity and/orcolour of the input light. (Equipment and facilitiesmay limit your options.) Then devise a process formeasuring the relationship between intensity orcolour and the output of your photovoltaic cell.

4. Carry out your procedure, graphing the results ifpossible.

5. Write a formal scientific report of your investigation,including: Materials, Procedure, Analysis, Evaluation,and Synthesis.

Task 2: Using Solar Energy in a RemoteLocationYou will research the technology required to power a retreat(Figure 4) and prepare a written report.

Figure 4

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Data ProvidedA writer is building a retreat on a small mountain onVancouver Island, British Columbia, 10 km up a logging roadfrom the nearest town. There is no electrical power available.Heating and cooking energy needs will be met with propanegas, supplemented by an efficient wood stove. The electricalneeds are the following: a laptop computer, a 19" television,a VCR, a sound system, a mobile telephone, a satellite/Internetreceiver, and one 60-W and three 40-W fluorescent lamps.(The lamps will operate for three hours each evening.)

You must determine:

• the minimum number of hours of sunlight expectedin the darkest months of the year for the location

• the average electrical power requirements in a 24-hperiod

• the size and type of the solar panels needed, the powerof the inverter (DC to 110 VAC), and the number andtype of storage batteries required

• the water turbine that would provide supplementalpower from a nearby mountain stream (vertical fall of50 m) in the winter months

Your report will outline the equipment needed, the cost ofthe materials, excluding any special installation costs, and acommentary on the life of the system and maintenance costs.You should demonstrate knowledge of the physics principlesinvolved in the total system.

AnalysisPart 1Your written report will be evaluated for the following:

• the quantity and accuracy of your research

• the demonstration of the knowledge and under-standing of the physics principles involved

• appropriate referencing and crediting

• the quality of the written communication

• the quality of the diagrams submitted

• the societal relationship of photovoltaic technology

Part 2The evaluation will depend on the optional task selected.

Your Task 1 evaluation will be based on:

• your demonstrated ability to carefully follow instructions

• the viability of your manufactured photovoltaic cell

• the quality of your written report of the investigation

Your Task 2 evaluation will be based on:

• the same criteria as outlined for Part 1