A switch. When off, they can actually cut your power usage to 0
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Raven, I think you nailed it right there. You meant that as a joke, but it made me think of electronic switches. Switched on timers to turn things off when your not there to flip the switch manually.
Motion sensing switched for lights. Instead of having security lights on all night, they can turn on only when there is movement out there.
More about lights, there are the cfl's. It takes a special circuit to power a florescent light, and a fixture for florescent lights was for a long time a very small investment that would pay for itself eventually. But now that compact florescents have been around a while and are really cheap, and last a long time and fit in the same socket as an incandescent. So, I'm saying that making that circuit small enough to work that way and cheap enough to compete with incandescents makes it a great contribution to sustainability. (It is really move of a savings in consumption that makes out lifestyle more sustainable. You still save more by just turning the lights off.) And they run cooler, too, so in climates where an air conditioner is needed, the savings is double. Less energy lost as heat, and less heat to be removed by the a/c.
Anything having to do with hydroponics. Automatic and efficent lights on timers. Automated flow systems and temperature controls. Being able to grow something in climates where you otherwise would not be able to.
Here's one thing. The "kill a watt". (I though I might design such a thing when I had the electronics skill, but discovered that someone already had, so I bought it instead. ~$20) You plug it into any outlet and it
has an outlet and you plug a device into it and it tells you the amps or watts being consumed. (doesn't work with 220V) It has a timer and can measure cumulative kilowatt hours for devices that get turned on and off. You can enter the cost you pay per kikowatt hour and it makes the simple cost calculation. It doesn't produce anything or convert anything, but provides information. I know which appliances in my home I need to be concerned about and which ones I don't. So, it gives me knowledge for me to make my life more sustainable.
Raven mentioned solar, but any circuit that extract energy from nature, so there's wind and hydro generators, too. Invertors for converting all that to AC to run all your AC stuff.
The list goes on. Do your google work. Mentaly scan all the posts for key words that you can plug into a search engine and plug 'em all in and see what else you can find. (Hey is this homework??)
-tim
Interesting little fun fact, LED's (specifically green LED's) produce about 1.2-1.7 volts when they are in direct sunlight
What?!? No way. Really? I want to know more. Do I need to go out and buy a bunch of green LED's? or can I verify that something happens with just any LED? If you got a link, please post it, but I'm about to go googling anyway. Thanks for that.