Short intro to the solar engine

A solar engine is a little electronic devise that can store energy, delivered by a small solarcell, into a capacitor.
The voltage will increase until a certain level is reached. This is called the trigger level. At this point the energy is released and the motor or coil will react for a short time, normally just parts of a second.
The voltage level decreases and at about 0,7 V the whole process starts over again.
This will be repeated until the light level is too low to reach the trigger level.

Solarcells, for instance a Panasonic 243318 can give 3,4 V with a few mA in full sunlight. That is enough to run a small high efficiency motor. Things get worse when using inside with less light. With a solar engine you can still work in these conditions, it just takes some time to get a trigger voltage.
One of my photovores works with a 40 W light source at a distance of 50 cm (±2 feet), and needs only a few seconds to trigger.
With a coil and a calculator solarcell (much smaller then a panasonic) my libelle will swing its wings with 40 W light source at 70 cm (±3 feet) distance.
In full sunlight I even have to partly cover the solarcell because it gets to much light and the wings stay in the upright position.
There are several possibilities to get a trigger point. I use a flashing LED (FLED). It works fine but needs more light then the trigger components used in America. I couldn’t get them here at the local stores.

In America they use voltage detectors. Several types I’ve found. Most frequently used are TC54 and MN 1380.
You can get them in different trigger voltages. As I mentioned earlier, I use FLEDs and they do the job also.
Even with normal diodes or zener diodes you can get a working solar engine. They’ll just need more light to trigger.
When experimenting with the solar engine start with R= 2K2. Most motors will work with this value. Using a bigger value means less loss of energy but it can happen that the motor has to less torque to turn, so finally nothing will happen.
Use a Voltmeter to measure the increasing voltage, measure points are the two connections of the capacitor.