What it shows
Joining cells in series adds voltage, while joining them in parallel adds current. Shading one cell shows why a single shaded cell can cut the power of a whole panel.
The science
Each cell gives a voltage set by its material, and a current set by the light on it and its area. In series the same current flows through all cells, so voltages add but the weakest cell limits the current. In parallel the voltages stay the same and the currents add.
Materials
Cost: under Rs 500. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Three small solar cells (0.5 V to 2 V, from solar garden lights or a kit)
- A multimeter
- Alligator clips or wires
- A small DC motor, or a red LED with a 330 Ω resistor in series
- Cardboard to shade a cell
- A protractor and a wooden board
Safety
For this project: Do not use mains-connected panels. An adult must supervise soldering. Use only low voltage cells, and do not stare at glare from the cells.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Fix the three cells on the board facing the sun at the same tilt.
Measure the open-circuit voltage of one cell, then its short-circuit current with the meter on its mA range, in the same light (this is safe for a small solar cell).
Join the three cells in series and measure voltage and current.
Join them in parallel and measure voltage and current again.
Run the small motor or LED with each arrangement and note how well it works.
Cover one cell completely with card and repeat both measurements.
Cover half of one cell and note how much the readings fall.
Fill a table of voltage and current for each arrangement and shading state.
What you should see
Series gives about three times the voltage of one cell and parallel about three times the current. Shading one cell cuts the series current sharply, which explains bypass diodes in real panels.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01What happens to voltage in series?
It adds up.
02What happens to current in parallel?
It adds up.
03Why does a shaded cell hurt the series string?
The same current must pass through it, so the weakest cell limits it.
04What is a bypass diode?
A part that lets current go around a shaded cell.
Take it further
Plot the current against the shaded fraction of one cell for the series arrangement.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Science projects
Electricity and Magnetism Experiments
Hands-on experiments with cells, wires, bulbs and magnets
Find out more about physics
Free, well-known places to explore the subject further. Ask a grown-up before you sign up for anything or type your name anywhere.