Seen here is a TI proof of concept application of a solar/light powered keyboard.  A common off-the-shelf wireless keyboard was modified by removing the its AAA batteries and replacing them with the bq25504, a small rechargeable Li-Ion battery and a small, flexible photovoltaic solar panel optimized for indoor lighting.  Now, the user will no longer be required to replace the AAA batteries, which normally need replacement every 3 to 6 months, but operate over the lifetime of the small coin cell Li-Ion battery, which is typically 3 to 5 years. Depending on the keyboard design, the energy storage device wouldn’t have to be a rechargeable Lithium battery. It could be a thin film rechargeable battery, super-capacitor, or possibly standard capacitor. The removal of the large AAA or AA batteries allows a much thinner and size-optimized design for standard wireless PC keyboards, industrial and medical keyboards and a variety of other applications.