Sixpack of Solar: How Many Solar Devices Can You Make from a Plastic Bottle?

How Many Solar Devices Can You Make from a Plastic Bottle?
A clear PET plastic bottle can help disinfect water.
6 hours of sunlight's UV-radiation kills diarrhoea-causing pathogens in water making it safer to drink.
A clear bottle full of water and a little bleach can become a solar skylight, providing the equivalent of a 50w incandescent light to a windowless shack.
Cut the bottom off a clear plastic bottle to make a mini-greenhouse, a hot cap, to protect seedlings from frost.
Surround that bottle hot cap with a circle of other bottles full of water for solar heat storage to extend the growing season.
Here's a bottle inside a bottle inside a bottle to heat water in the innermost bottle
and a variation of this design using a clear bottle, a dark can full of water, and a set of reflectors.
They illustrate the essentials of solar thermal energy:
light reflects
dark gets hot
clear keeps the wind out
With that knowledge you can move, concentrate, and store energy.
This clear plastic water heater is much larger and more practical for household use.  It is made almost entirely from recycled packaging waste.
You can make a window out of plastic bottles, too,
and a south-facing window is already a solar collector.

But that's another story.