providing a threshold time period and determining {HEAD ~ the energy} generated by each said renewable power system for {TAIL ~ said threshold time period} 
providing a threshold time period and determining { HEAD ~ the energy } generated by each said renewable power system for { TAIL ~ said threshold time period }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL