The reason why the maximum supply power is different between summer and winter is that {HEAD ~ a periodic test} for the power stations is carried out in winter with {TAIL ~ less power demand} in preparation for summer with more power demand 
is carried out with
The reason why the maximum supply power is different between summer and winter is that { HEAD ~ a periodic test } for the power stations is carried out in winter with { TAIL ~ less power demand } in preparation for summer with more power demand
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH REL REL REL OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH