Step 1: How Can They Fly Anyway?
As air gets hot it gets less dense than colder air so it moves upward. Hot air balloons work using hot air to float. Hot air balloons use gas to make hot air.
Solar Balloons use only Sun light to make the air inside the balloon hot. The Solar Balloon is made of dark material that absorbs heat from Sun light and the air inside gets much hotter that the air outside. You can find this for yourself and make a fun educational experiment for your kids.