▁the ▁sun ▁goes ▁in . ▁To ▁avoid ▁over he ating ▁the ▁tub es ▁it ▁is ▁necessary ▁to ▁either ▁p ump ▁the ▁circuit ▁for ▁a ▁short ▁time ▁after ▁the ▁sun , ▁or ▁else ▁to ▁provide ▁a ▁large ▁res er voir ▁of ▁fluid ▁in ▁the ▁header ▁above ▁the ▁tub es . ▁Ne ither ▁of ▁these ▁options ▁is ▁really ▁compatible ▁with ▁the ▁simple ▁direct - P V ▁p ump ▁approach ▁and ▁so ▁such ▁systems ▁are ▁limited ▁to ▁using ▁the ▁less ▁efficient ▁flat ▁panel ▁collect ors . ▁ ▁A ▁P V ▁power ed ▁controller ▁may ▁contain ▁a ▁small ▁electric ity ▁store ▁to ▁allow ▁the ▁controller ▁to ▁remain ▁power ed ▁and ▁display ▁temper atures ▁at ▁night ▁when ▁there ▁is ▁no ▁sun light . ▁This ▁electric ity ▁store ▁is ▁usually ▁in ▁the ▁form ▁of ▁super cap ac itors , ▁since ▁these ▁have ▁a ▁much ▁longer ▁life ▁than ▁batter ies . ▁ ▁The ▁benefits ▁of ▁a ▁P V ▁power ed ▁solar ▁controller ▁comes ▁at ▁a ▁cost ▁in ▁reduced ▁system ▁performance ▁in ▁the ▁range ▁of ▁ 1 - 1 0 %. ▁This ▁is ▁due ▁to ▁heat ▁losses ▁at ▁times ▁when ▁the ▁panel ▁may ▁be ▁hot ter ▁than ▁the ▁water ▁store ▁but ▁there ▁is ▁ins u fficient ▁sun light ▁to ▁power ▁the ▁p ump . ▁This ▁happens ▁mainly ▁on ▁hot ▁days ▁when ▁hot ▁water ▁is ▁likely ▁to ▁be ▁in ▁excess ▁so ▁the ▁potential ▁reduction ▁is ▁less ▁significant ▁than ▁it ▁would ▁be ▁at ▁times ▁when ▁the ▁store ▁was ▁cool er . ▁ ▁References ▁ ▁Further ▁reading ▁Martin ▁C , ▁Watson ▁M ▁( 2