Solar cells
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Left: one solar panel, note clear glass edges; Center: a panel with the edges taped up; Right: black tray.

I hooked up a solar panel to a voltmeter, and it reads ~2.47V. The voltage appears to be almost independent of orientation (wrt the sun). Also, it is almost impossible to reduce the output voltage to zero. I made a black paper tray to shield the back and sides, made almost no difference. I then taped the edges, but still the voltage did not go down to zero when placed in the tray, and covered.

What appears to be happening is that, if no current flows, *any* amount light raises the voltage to a set level (likely the bandgap voltage).

Single cell 2.47V, 3 in series 7.12V (drifting down, with temperature?), normal to Sun
At 90° still 6.54V
Covered still ~1V

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What about if there is current?

So I hooked up 3 cells the little pump that comes with the kit. Strong dependence on angle!
0.28A normal
0.15A ~45°
0.03A 90°

So the measurements have to be done under load, and by measuring current, not voltage.

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Would this work indoors, or when the Sun is not shining? Growlights might provide enough light, but they are too expensive, see for example Grow lights at Home Depot

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Improvise a switch: wrap 2 traces around the edge of the cardboard, and use a metal paperclip.

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In simple schematics [A] you usually draw a simple circuit, with the current going around.

In a house [B], there are pairs of wires running from the power supply (breaker box), a pair from the light, and a pair from the switch, coming together in a junction box.

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Test the circuit with the audio circuit

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The solar cells light up an LED with very little light.

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The roof can remain loose if you wish.

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Here is a test circuit:

  • 9V battery
  • connector with bare wires
  • 1000 Ohm (ik) resistor
  • various LEDs
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Battery and resistor hooked up

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Important:

The 9V battery is too powerful to hook up directly to an LED. So we lower the current by having a resistor in the circuit.
This is a 1000 Ohm resistor. 1000 Ohms = 1 kOhms, or 1k. Color code here

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3 LEDs in parallel

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Note the greens are not on! Why not?

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4 LEDs in series

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Here I use a paperclip as a switch, to connect across a gap in the copper tape.

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Another way to improvise a switch, using a paperclip

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If you need to mount the switch (I don't have one here) to the roof, tape all 4 sides, try to tuck the tape as close as possible.