A neat solar engine!

Solar engine

A simple circuit, designed to gather energy from light, store the energy, and then release that energy in bursts to drive a motor, coil, or some other circuit . These are variously called Solar Engines, solarengines, and SEs; in strict electronic terms, they are called relaxation oscillators. The whole purpose of a solar engine is to act like a power "savings account" -- a small trickle of incoming energy is saved up until a useable amount is stored. This stored energy is then released in a burst, in order to drive some useful (if only sporadic and incremental) work.

Various solar engine designs "trigger" (release their stored energy) based any of a number of criteria.

Solar engines have a number of advantages:

* With a solar engine, a solar-powered robot can be made to work (if only sporadically) in even low light levels.

* Solar engines allow solar cell size to be minimized
o Saves money
o Saves weight
o Allows room for the solar cell to be ruggedized.

Four types of solar engines have been defined and built to date, categorized by their trigger mechanism:

* Type 1 - voltage controlled trigger. This is by far the predominant form of solar engine, since they are "efficient enough" for most uses, and pretty simple to build.

* Type 2 - time controlled trigger. These aren't terribly efficient, but are handy for 'bots that need activity at specific times.

* Type 3 - charge curve differentiated, i.e., it triggers when the charge rate of the capacitor(s) slows down. These are (theoretically at least) the most efficient.

* Nocturnal -- These solar engines charge up when it's light, and discharge (i.e., power a load) when it's dark.

For more information, and a whole slew of solar engine designs, see the Solar Engine section of the BEAM Reference Library's BEAM Circuits collection.