Does solar work on cloudy days?

Short answer, Yes!

Solar Photovoltaics (PV), does work on cloudy days, but at a reduced performance.

A measure of the amount of sun reaching the Solar modules is called irradiance. Irradiance is the power of electromagnetic radiation from the sun incident per unit area. In solar we often measure this as Watts per square meter and tells us how much energy is available to the solar modules at any given time. Irradiance may be reduced by clouds, particles in the atmosphere, lower elevations (more atmosphere), shading from obstacles (such as trees), and incidence angle (angle of module towards the sun).

Solar modules can operate off of both Direct Normal Irradiance and Diffused Horizontal Irradiance. In otherwords, direct energy from the sun, as well as the scattered inderict energy from the sun that has reflected off clouds, etc.



On a very clear, sunny day, you may have an irradiance level of 1000 W/m2. On a cloudy day you may only be reciving 500 W/m2. If everything else is equal, your system will be producing half as much energy on the 500 W/m2 day. A very cloudy day can be as low as a couple hundered W/m2, down to below 100W/m2, significantly reducing your systems output during that time.

Solar thermal systems such as Solar Hot Water and Solar Hot air systems operate off a slightly different principal and take advantage of infared energy. These systems also continue to operate on cloudy days though their performance may not be rduced as significantly as solar PV.

 

To really get your dollars worth you do need direct sun to reach peak performance. With that said, the modules can produce at a reduced rate without any direct sunlight on a cloud covered day