Hillig is the founder and managing director of THEnergy, a boutique consultancy established in 2013 focusing on microgrids/mini-grids and off-grid renewable energy. For industrial companies, THEnergy develops energy concepts and shows how to become more sustainable – combining experience from conventional and renewable energy with industry knowledge in consulting. THEnergy also advises investors and energy companies regarding renewable energy opportunities in rapidly changing markets. The initial focus was on commercial and industrial off-grid renewable energy projects, for example in mining, hospitality, telecommunications or on islands. Driven by investor needs, corporate PPAs, rural electrification and energy access have become additional consulting focusses. THEnergy has led several large-scale due diligence processes. Since 2018 hydrogen has been another main consulting focus.