The sun's energy is one of the most overlooked contributors to the high energy costs that homeowner's face every month. Solar heat gain is used to refer to heat from the sun that enters your home through windows and skylights even when they are closed.  This heat must be removed by your air conditioning making it work harder and costing you more money.  A very cost effective way to control this heat and help keep your energy bills down is to use residential low E window films.