While solar energy can cut electricity costs, building constraints and regulatory limits mean it may not work for every estate.    SINGAPORE: When equipment at Grandeur 8 began showing signs of inefficiency, racking up electricity bills of more than S$20,000 (US$15,700) a month, condominium manager Sean Kunnath and his team began looking at ways to bring costs down. The answer for them was solar energy, which they estimated could save the estate S$6,000 in electricity costs a month – if