Simplify the following text for a Grade 14 native English-speaking person.
Original: Alternative energy such as solar energy , heat pumps , hot water heat recycling , and sometimes geothermal heating , may also be used as available , usually in combination with backup systems supplied by gas , oil or electricity .
Simplified: Alternative energy such as solar energy , heat pumps , hot water heat recycling , and sometimes geothermal power , may also be used as available , usually in combination with gas , oil or electricity .