Solar panels operate work on a principal called the photovoltaic effect which is the conversion of light into electricity. It was a Frenchman named Alexandre-Edmond Becquerel (24/3/1820 - 11/5/1891) who is credited with the discovery of the photovoltaic effect and as a result of his efforts the first solar cells were made around 1839.
The first solar cells put out miniscule amounts of electricity and the effect was considered novel but useless until it was taken up by photographic industry who were in need of a device to measure light. The first commercially built solar panels were used as light meters in cameras, and this use continues to this day.
The use of a solar panel as a light meter gives us the first important piece of information about solar panels: The output of a solar panel is directly proportional to the amount of light falling on it!
Although solar salesmen may tell you otherwise, there is really no such thing as a solar panel that will work in low light or a solar panel that is shade tolerant. Some solar panels may be slightly better than other solar panels in this respect but a percentage more output than stuff all is still stuff all. The output of a panel is directly proportional to the amount of light falling on it and this means that a solar panel must be in direct sunlight and orientated in the correct direction.