▁efficiency ▁does ▁not ▁only ▁include ▁the ▁effort ▁to ▁reduce ▁carbon ▁dio x ide ▁em issions . ▁It ▁var ies ▁and ▁depends ▁on ▁the ▁energy ▁being ▁supplied ▁for ▁the ▁particular ▁technology , ▁such ▁as ▁foss il ▁fu els ▁from ▁a ▁coal - f ired ▁plant ▁that ▁produces ▁gas oline ▁for ▁cars . ▁Im pro ved ▁efficiency ▁will ▁cut ▁em issions ▁for ▁foss il ▁fue led ▁techn ologies ▁compared ▁to ▁low ▁carbon ▁sources , ▁such ▁as ▁electric ity ▁which ▁is ▁produced ▁from ▁renew able ▁energy . ▁Non eth eless , ▁impro ving ▁energy ▁efficiency ▁is ▁a ▁key ▁tool ▁for ▁reducing ▁carbon ▁dio x ide ▁em issions ▁and ▁most ▁low ▁carbon ▁sources ▁( which ▁includes ▁renew able ▁energy ▁and ▁carbon ▁capture ▁storage ). ▁ ▁Ren ew able ▁Energy ▁( RE ) ▁▁ ▁Ren ew able ▁energy ▁is ▁generated ▁from ▁natural ▁resources , ▁such ▁as ▁sun light , ▁wind , ▁and ▁rain . ▁Ren ew able ▁techn ologies ▁function ▁from ▁resources ▁that ▁vary ▁from ▁solar ▁power , ▁wind ▁power , ▁to ▁hydro elect ric ity ▁and ▁are ▁constantly ▁renew ed . ▁Ren ew able ▁energy ▁techn ologies ▁have ▁an ▁advantage ▁over ▁conventional ▁energy ▁systems , ▁as ▁they ▁have ▁a ▁much ▁lower ▁impact ▁on ▁the ▁environment ▁and ▁are ▁considered ▁a ▁clean ▁source ▁of ▁energy . ▁A ▁dis adv antage ▁to ▁using ▁renew able ▁energy ▁includes ▁the ▁source ' s ▁un stable ▁market , ▁with ▁uncertain ▁profit ability ▁from ▁the ▁competition ▁of ▁foss il ▁fu els . ▁The ▁energy ▁source ▁therefore ▁is ▁not ▁in ▁a ▁likely ▁position ▁to ▁gain