Thermax Ltd plans to made an additional investment of up to Rs 6 crore ($900,000) in First Energy Pvt Ltd , alternative energy solutions company in which it had acquired 33 per cent stake last year. First Energy’s brand Oorja, a combination of a ‘micro- gasification’ stove and biomass-based pellet fuel, is adopted by several customers as a substitute to fossil fuels such as LPG and diesel.