( ( ( The ( energy ( payback time ) ) ) ( of ( a ( power ( generating system ) ) ) ) ) ( ( is ( ( the time ) ( required ( to ( ( generate ( as ( much energy ) ) ) ( as ( was ( consumed ( during ( production ( of ( the system ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN energy) (NN payback) (NN time)) (PP (IN of) (NP (DT a) (NN power) (VBG generating) (NN system)))) (VP (VBZ is) (NP (NP (DT the) (NN time)) (VP (VBN required) (S (VP (TO to) (VP (VB generate) (PP (IN as) (NP (JJ much) (NN energy))) (SBAR (IN as) (S (VP (VBD was) (VP (VBN consumed) (PP (IN during) (NP (NP (NN production)) (PP (IN of) (NP (DT the) (NN system))))))))))))))) (. .)))
The energy payback time of a power generating system is the time required to generate as much energy as was consumed during production of the system.
(ROOT (S (NP (NP (JJ Electrical) (NN energy)) (VP (VBN consumed))) (VP (MD can) (VP (VB be) (VP (VBN expressed) (PP (IN as) (NP (NP (DT the) (NN product)) (PP (IN of) (NP (NP (NN power)) (VP (VBN multiplied) (PP (IN by) (NP (NN time))))))))))) (. .)))