* Harmony Gold H1 profit slumps 94 pct * Firm in talks to build solar power plant (Recasts with solar power plans) By Tanisha Heiberg JOHANNESBURG, Feb 12 (Reuters) South African miner Harmony Gold is in talks to build a 30 megawatt solar power plant in the Free State province to supply power to some of its operations to try to reduce power costs and dependence on struggling utility Eskom.