He was able to show and won a Nobel Prize for it. He showed how light can be converted into electricity, which is what solar panels do. That's nearly 100 years!
Big money has to extract every cent out of fossil fuels before they will turn to alternative energy...they are criminals!
Photovoltaic action was first noted in the 1870's and one of the first known photovoltaic arrays was installed in NYC in the mid 1880's. Einstein just came up with the math that explained how it worked in the early 1920's.
But cost and efficiency of the devices kept photovoltaics at the novelty stage until recently. It took more energy to make those early solar cells that they would produce over their lifetimes, they were difficult to manufacture in mass back then and they were highly inefficient when considering watts/square foot output.
