Helen is the City of Helsinki's energy company, founded in 1909 as the city's electricity works, which supplies electricity, district heating and district cooling. Through its nuclear subsidiary Helen Nuclear (Helen Ydinvoima Oy), incorporated in January 2026, it is studying a small nuclear plant for district heating, with options for combined heat and power. It published the environmental impact assessment programme on 5 November 2026, with the assessment report due in 2028.