# What affects the output of a solar panel?

##### Class practical

This activity explores factors which affect the power output of a solar panel, and may lead to an investigation of quantitative aspects of some factors.

#### Apparatus and materials

Each group will need

Solar panel unit

Small motor unit

Desk lamp (40 or 60 W tungsten lamp)

Digital multimeter (or voltmeter)

Plug-plug 4 mm leads (red), 2

Plug-plug 4 mm leads (black), 2

Metre rule

Piece of cardboard

Translucent sheets (e.g. tracing paper) cut a suitable size to cover the solar panel

Coloured filters

Clamp stand

#### Health & Safety and Technical notes

Desk lamps with metal shades can get very hot. Take care when moving them.
Place the colour filters far enough away from the lamp so they don’t burn.
Be careful if considering other types of lamp such as halogen lamp and fluorescents because they can emit significant UV.

The activity works best if done in a room with blackout or low light levels. Otherwise ambient light may overwhelm the variations in light levels being controlled.

If students are to measure the distance of the lamp from the panel, make a reference mark on the lamp casing level with the centre of the light bulb.

You can obtain solar panels and a small motor unit from Middlesex University Teaching Resources

• SEP 050 Solar panel unit
• SEP 051 Large solar panel unit
• SEP 052 Small solar panel unit
• SEP 054 Small motor unit

#### Procedure

a Connect a solar panel to an electric motor. Shine a desk lamp on the panel so that the motor turns.

b Connect a voltmeter across the solar panel.

The voltmeter can be used to get an idea about the output of the solar panel. A voltmeter does not measure power (power = voltage x current), but the voltage can be used to make comparisons.

c Explore the effects of:

• moving the lamp closer and further away
• partially covering and uncovering the solar panel
• tilting the panel backwards and forwards
• putting a translucent sheet between the lamp and the panel
• putting different coloured filters between the lamp and the panel.

#### Teaching notes

1 A solar power system for a house is not always going to give the same power
output. It will depend on the time of day, the season, the weather, and so on.

In this activity, students use a range of investigative skills, including the identification of different kinds of variable, the tabulation of data and drawing different kinds of graphs and charts.

This can be done in small groups as a qualitative activity to get a feel for the factors that affect the output of a solar panel, in which case the activity may only take up part of a lesson.

2 Students should find that the maximum output is given with a high light intensity and the biggest surface area, and with no tilt in relation to the light source. The translucent sheet and coloured filters reduce the power output.

3 Student could go on to a quantitative investigation of particular factors, done in pairs and taking longer. Different groups could each look at a different factor, and then report back to the whole class. Possible relationships to investigate:

• how does the distance of the lamp affect the voltage across the panel? A suitable range of distances is from 10 to 25 cm (if using just the motor); with the voltmeter, a suitable range of distances would be from 10 to 50 cm.
• How does the area of the panel exposed affect the output voltage?
• How do different filters affect the output voltage? for example: glass, clear plastic sheet, white paper

4 Ask students to explain how their results relate to real conditions with the Sun. You could have students take their panel outside and look at the effect of tilting it, of partially covering it or of using different kinds of filters.

This experiment is copyright of Gatsby Science Enhancement Programme, and is reproduced with permission.

#### User feedback

Rick Marshall : Fri 19 June 2009: This task involves a solar cell and not a panel - solar panels transfer insolation into thermal energy (usually heated water or air)
Editor: Students doing web searches will come across various terminology in use (solar panel, solar cell, photovoltaic cell, PV cell). Just as the terms 'electric cell' and 'battery' are often used interchangeably, so the terms 'solar cell' and 'solar panel' are often used in different places to mean different things. In the SEP booklet, a number of solar cells joined together has been referred to as a solar panel.