Small unmounted silicon solar cells are cheap and easily available on line. In this activity students design a panel for a desired volatage, connect cells, and then encapsulate the panel. Each cell when wired in series adds about .55 volts to the circuit.
This can also be done as 1 hour workshop building a single cell panel using copper tape instead of soldering to the cells.
1) Understand the role that photovoltaics can play in our energy future
2) Experiment with solar cells and meters to discover and construct circuit rules
3) Use terminology of electricity volts, amps, watts in context
4) Use series and parallel circuits to design an arrangement
5) Gain experience with the engineering design cycle
6) Practice skills of soldering and work carefully to build a working device
1) Introductory Slide Show- (refer to sections after completing each activity- let students discover design principles by experimentation if possible.)
2) Solar Cell Exploration-
- Measure the voltage of a variety of solar cells, under a light bulb, in the sun, try covering parts of the cell in one direction and then the other,
- Tilting the cells with respect to light source while measuring angle and voltage. Discuss what you have learned about the cells. Record observations on the data sheet.
- Series and parallel circuits- use the encased mini cells to try different circuits- measure voltage and current
- Try unequal size cells in series and parallel = (parallel tracks must have same area)
- Measure current from cell with a diode placed in different orientations
3) Discussion of results and continue presentation presenting rules.
4) Power calculations- Discuss definition of power and generate example of power requirements of different common devices. Calculate the power of sample cells and panels using the formula- P=I X V. Estimate number of cells
5) Panel Design- Define the use you intend to make of the panel. Select the cells and draw a schematic of how the cells will be arranged. Use the worksheet to calculate the voltage and current that you expect your panel to generate in full sun
6) Soldering- layout the pieces, cut the ribbon wire, practice on scraps and then carefully build a panel. Tab the top side of each cell first. Flip the over and use tape to hold the cells in position while soldering down free tabs to the connection spot on the back side. Test connections as you go and test the whole thing before housing it. Add diode to circuit in the right direction. The striped end of the diode is the cathode, the other end is the anode. The anode should be connected to positive side of the cell (the back).
7) Housing- use hot glue to secure the cell array at a few spots. Solder to the flat ribbon to regular insulated wire with an extra bend and extra glue so it can’t pull loose. Use a dab of hot glue at each corner then gentile press the top plate down without crushing the cells. Apply clear packing tape to the edges to seal the unit.
8) Try it out.
Simple Solar Panel
It is possible to connect one or more solar cells with 1/4″ adhesive conductive copper foil tape instead of solder. This cuts down on the frustration with soldering solar cells.
- Place the cell flat on a hard smooth surface.
- Cut a piece of foil tape 1″ longer than the width of the cell. Remove the adhesive backing an position the foil 1/2 ” from one edge of the cell and extending beyond the opposite edge. Carefully smooth it down for maximum contact with the cell conducting grid.
- Flip the cell over and position another tape to touch the contact points on the back and run if off the edge making sure it doesn’t touch the copper strip on the top.
- Position the cell on a piece of plastic or rigid polystyrene.
- Cut a clip lead in two, skin the end, and solder one lead to each extending copper lead. Or press a loop of the wire on the exposed copper strip and seal it with another piece of copper tape.
- Place a piece of clear laminating plastic over the cell and smooth it down being careful to smooth out air bubbles and using the plastic to secure several inches of the clip lead to the cell.
Series scraps cell panel
This variation scraps of cells are arranged and connected directly top to bottom at the edge using double adhesive copper tape, or wire glue**.
- Collect a bunch of solar cell scraps approximately the same area. If possible pick ones in which there are still wider collector grid manifolds on the top of the cell.
- Attach an adhesive copper tape to the back of the first cell. Place it face up on the end of a piece of backing material such as plexiglass rigid plyboard. Orient the top conductor toward the edge where the next cell will sit.
- Apply a short length of double sided copper tape along the edge at the opposite end of the cell, or apply a bead of conductive wire glue.
- Place the next cell on top of the adhesive so there is 1/8” of overlap, gently press this to get a good contact. Be careful not to press any unsupported part of the cell for it will surely crack.
- Repeat for each cell, looping back to the beginning if there is room.
- Attach a copper tape to the top of the last cell.
- The series arrangement may a higher voltage but low amperage. This is ideal for lighting a LED or flashing LED.
** Wire glue is a thick paste that contains conductive carbon in a water soluble binder. You can apply drops of the wire glue at each interface point. This makes a good contact and decreases the chance of shattering cells as you press down.
Solar cell- a single wafer having the characteristic voltage of the basic material
Solar panel- an array of many solar cells, wired in series and parallel and usually encapsulated in a durable container to protect the cells
Diode- and electronic device which allows current to flow in only one direction. This is a necessary part of a battery charging circuit to prevent the battery from discharging into the solar panel at night.
Semiconductor- a type of material which conducts electricity under some conditions but not others
Power- the rate of total energy flow – equal to volts x amps- measured in watts
Voltage- the potential difference or electromotive force- measured in volts
Current- the flow of electrons over time measured in amps
Kilowatt hour- an amount of energy equivalent to 1000 watts expended for one hour.
Parallel circuit- an arrangement in which electricity can flow through more than one path to the same destination
Series circuit- an arrangement in which all electricity must flow through the same single path.
Soldering solar cells
Materials and tools
Flat rigid surface
weights for holding down ribbon
wire glue conductive adhesive can connect cells that are sandwiched in series.
40 watt soldering iron $8.95
diodes- 3 am 20 pack $8.99
Encased practice solar cells for exploration- Pitsco
solar cells- 1.8W $36 for 36
solar cells – 40 for $21 52x78mm good size for smaller panel
186 soldering flux $3.50
tab wire, pre-tinned 200 fit roll $12.95
Small electric motor- 10 for $15- with leads
Adhesive conducting copper tape 1/4″ $12
Styrene sheet panel backer
Or get a set with multiple cells, ribbon, flux in a kit .. search Amazon or Ebay for Solar Cells.