its own power plant
... that Grumman Aerospace built its own power plant because it was cheaper than buying electricity from utilities?
... that <a href="./Grumman" id="mwAQM" rel="mw:WikiLink" title="Grumman">Grumman Aerospace</a> built <b id="mwAQQ"><a href="./Bethpage_Energy_Center" id="mwAQU" rel="mw:WikiLink" title="Bethpage Energy Center">its own power plant</a></b> because it was cheaper than buying electricity from utilities?