How long have people been using solar energy?

Answer 1

It depends what you mean by "solar energy." Humans have always used solar energy in some sense: to warm themselves, to grow food, etc. However, I'm assuming that's not really what you mean (although it is important to realize that all energy on earth, with the exception of nuclear fission and geothermal, is ultimately driven by the sun's energy -- even fossil fuels, which after all were plants that grew with sunlight millions of years ago).

Solar power has been used directly in various forms for over 100 years. See the link to below this answer for a nice review of the history of solar power, starting from the beginning. Early on, focused sunlight was used to heat water, which was converted to steam and used to turn a turbine. (This is still very commonly used today and known as "solar thermal" energy although instead of water a fancy high temperature molten salt is used instead to reach very high temperatures).

If you are referring to the type of solar panels that you commonly see on rooftops of homes, etc., those are called photovoltaic solar cells. Those panels take sunlight and directly make electricity using semiconductors. Those are a relatively modern invention.

In 1839, Becquerel observed photoelectrochemical processes for the first time, but wasn't until 1954 that the first silicon-based photovoltaic solar cell was made by Bell Labs with an conversion efficiency of 6%. I'm not sure when the first commercial photovoltaic solar panels were available for sale. It was probably sometime in the mid- to late-1960's solar panels started to become commercially available. It wasn't until the 1970's with the oil embargo and energy crisis that they were sold on any significant scale.