Complex sentence: Unlike its sister site at Watten, there was no on-site power plant; electricity at Wizernes was provided by a connection to the main electric grid, with consumption estimated at between 5,000--6,000 kVA.
Split into simpler sentences: Unlike its sister site at Watten, there was no on-site power plant. Electricity at Wizernes was provided by a connection to the main electric grid, with power consumption estimated at between 5,000--6,000 kVA.