abstract
alternative
atom
blue
business
clean
concept
conservation
construction
design
drop
eco
ecology
efficiency
electricity
element
energy
environment
environmental
fresh
graphic
green
hydro
hydroelectric
hydropower
icon
illustration
industry
light
line
liquid
natural
nature
outline
plant
power
rain
renewable
resource
shape
sign
single
stroke
supply
symbol
thin
ui
water
wet