EnergyDeck):
As a kid I used to love all the exhibits at the Science Museum in London where I could push buttons and pull levers. I'm hoping to put together some very simple exhibits for King Athelstan and other local schools to use where kids can cover/uncover solar cells and watch meters twitch and motors whirr. Hardly likely to greenwash the children. But they may generate a little interest along with the watts. I remember that my dad got me hooked on electronics with stuff not very much more complex!
2012-06-16: I'm putting together a very simple device with a small solar cell/panel (~4Voc, 0.25W) wired to a simple analogue meter (Maplin LB08B 65Ω, 250µA FSD). There is a series resistor to protect the meter in bright sunlight.
The cell and meter are in a clear plastic box stuck to opposite sides. Covering the cell with a hand has the meter drop back to zero. To get FSD (full-scale deflection) at (say) V=2.5V implies a 10kΩ series resistor. The meter can probably stand 100% overcurrent for a while. So a resistor value close to this or a little higher is probably fine. It will allow decent needle movement even if not in bright sun.
I have put a 3.3V white LED upstream of the meter, as a voltage limiter, with a further 470Ω to the solar positive. So if the light is really bright then the LED comes on and limits the meter to FSD.
Even though generating is good, avoiding waste is often more effective. Particularly in terms of the amount of CO2 saved per £ spent. In SWLEN's 2017-09 report Wasted Energy: how money and carbon dioxide could be saved in schools: it is noted at the end that [KA] reminded to turn the heating to a frost setting over the Xmas / New Year holiday period saved around £500.
All for about 10 minutes' work!
Thank you SWLEN!