▁power ed ▁solar ▁controller ▁uses ▁solar ▁electric ity ▁produced ▁on - site ▁to ▁run ▁the ▁p ump ▁that ▁del ivers ▁the ▁solar - he ated ▁transfer ▁fluid ▁to ▁the ▁hot ▁water ▁store . ▁ ▁One ▁claimed ▁advantage ▁of ▁P V ▁power ▁is ▁that ▁it ▁reduces ▁the ▁overall ▁carbon ▁em issions ▁associated ▁with ▁operating ▁the ▁system ▁since ▁it ▁avoid s ▁the ▁need ▁to ▁supply ▁this ▁energy ▁from ▁foss il ▁sources . ▁However , ▁the ▁energy ▁required ▁to ▁operate ▁the ▁system ▁is ▁very ▁small ▁in ▁comparison ▁to ▁the ▁energy ▁produced ▁by ▁the ▁system ▁and ▁the ▁carbon ▁em issions ▁reduction ▁of ▁adding ▁P V ▁power ▁fraction al . ▁ ▁The ▁most ▁practical ▁benefit ▁of ▁a ▁P V ▁power ed ▁controller ▁is ▁the ▁result ant ▁simplicity ▁of ▁the ▁overall ▁system . ▁R ather ▁than ▁using ▁complex ▁algorithms ▁based ▁on ▁store ▁and ▁panel ▁temper atures , ▁the ▁p ump ▁is ▁driven ▁directly ▁by ▁the ▁P V ▁panel : ▁when ▁the ▁sun ▁sh ines , ▁the ▁p ump ▁runs . ▁In ▁practice ▁this ▁is ▁nearly ▁( 9 0 - 9 9 %) ▁as ▁efficient ▁a ▁practical ▁control ▁algorithm ▁as ▁most ▁others ▁achieve ▁and ▁has ▁obvious ▁advantages ▁for ▁reduced ▁system ▁complexity . ▁ ▁A ▁dis adv antage ▁to ▁the ▁P V ▁power ed ▁approach ▁is ▁that ▁the ▁p ump ▁stops ▁immediately ▁after ▁the ▁sun ▁is ▁occ l ud ed . ▁With ▁vac u um ▁t ube ▁and ▁heat ▁pipe ▁solar ▁pan els , ▁these ▁can ▁have ▁an ▁appreci able ▁amount ▁of ▁energy ▁stored ▁in ▁each ▁t ube ▁at ▁the ▁moment