# Using Lab Measurements to Determine the Feasibility of a Photovoltaic Panel

#### Summary

This activity is based on the use of a solar module. It can be performed in a lab setting of as a lecture demonstration activity. Using a solar module that we have on hand (18 volts – no load) we determine a practical value of power output. We aim the panel directly at the sun and then take the following measurements using a digital multi meter: (1) no load voltage, (2) loaded voltage, and (3) resistance value of the load resistor. Using these data, and a standard estimation of solar isolation, the students are instructed to compute the output power of the module as well as the efficiency of the module.

## Learning Goals

Ultimately the intention of this activity is to demonstrate to the students the cost effectiveness of photovoltaic systems. Sub – goals are:
(1) the understanding of the meaning of the term insolation,
(2) an understanding of internal resistance as it relates to a source voltage,
(3) the ability to compute the output power from a solar cell/module/array,
(4) the ability to compute the cost of producing electricity using a photovoltaic system.
The students are engaged in data collection and data analysis. Additionally they will be engaged in the synthesis of a concept about the feasibility of exclusively using photovoltaic systems for the production of electricity. The formulation of such a concept relates to sustainability because it helps the students to understand that no single energy source will be sufficient.

## Context for Use

This activity is appropriate for advanced high school students or for lower level college students. Lab equipment: a solar cell, module or array (the computations are simply scaled up when a larger solar device is available), a digital multi meter, a large wattage- low resistance resistor (around 10 ohms will work fine). Lab facilities are not needed but could be used if available. In this activity the teacher collects the data and the students are guide through the computations. For the student to succeed in this activity they must have an understanding of basic electrical properties and a good understanding of linear equations.

## Description and Teaching Materials

Since this class is taught entirely in a distance education format (we use interactive television) lab activities are difficult. Here is an activity that seems to work. The Department has a solar module (36 individual cells, at .5 volts each) which produces 18 volts under no load conditions. I show the students a series of photos showing the solar module. I review the concepts of ohm's law and watt's law and I introduce the concept of internal resistance. On a good clear day, at some point before classtime, I set up the solar module and direct it perfectly toward the sun. Using a digital multi meter I measure the no load output voltage of the solar module, and then I place an appropriately sized load on the module, and again I measure the output voltage. Photos are taken of my assistant, as she/he is taking these measurements.

In class the students are presented with a blank data table and are instructed to "fill out" the table with the appropriate measurements, including the resistance of the load, the no load voltage and the loaded voltage. The students are asked to compute: (1) the load current, and (2) the output power. Furthermore the students are asked to compute the following: (3) the efficiency of the module based on an ideal output rating of 1KW/M2, (4) the output power in KWhr for a day/month/year based on an average day of 5 hours of sunlight. Lastly the students are asked to determine (5) how many solar modules would be needed to provide electricity for a 1,000 square foot home, (6) the cost/KWhr of electricity generated by the solar module.

Solar Panel Drawing (Microsoft Word 2007 (.docx) 56kB Jun14 12)

## Teaching Notes and Tips

The success of this activity depends on student understanding of electricity. In particular the teacher should himself understand the concept of internal resistance as it relates to power output. Additionally the teacher should be aware of basic solar concepts. Lastly this activity cannot be performed unless the teacher has access to a digital multi meter, an assortment of high wattage resistors, and a solar cell, a solar module or a solar array. The cell will work, the module is much better, and the solar array is probably a little unwieldy. In terms of the load resistor you must have a high wattage resistor, 10 watts minimum. We tied two 20 ohm, 10 watt resistors together in parallel to form a 20 watt, 10 resistor.

## Assessment

Following the completion of the activity the students are asked to turn in their lab sheet showing their data table and their calculations. These lab sheets are examined