Eidsiva Energi owns 100 percent of Elvia that is Norway's largest grid company with 940,000 customers.

Elvia builds, operates, maintains and renews power grid in Innlandet, Viken and Oslo.

[5] Construction started already in 1896,[6] and the power plant was fully built in 1899 with installed capacity of 5200 kW.

Contracting services was later a part of the listed company Infratek ASA, whereas the security sercives and telecommunication business was sold out.

During spring 2017, the two largest shareholders, Oslo municipality and Fortum, agreed to delist Hafslund and restructure the company.

The district heating company Hafslund varme and the waste incineration plant at Klemetsrud became one company, Fortum Oslo Varme, with ownership shared between Oslo municipality (50 percent) and Fortum (50 percent).

On 20 June 2018, the city counsil of Oslo decided to merge Hafslund AS and E-CO Energi AS in a new fully owned company.

Hafslund Produksjon Holding was not included in the transaction, as the company's power plants were built before the hydropower license regulation was established in Norway.

The acquisition of Hafslund Oslo Celsio received attention since an important premise for the transaction was that it would invest in carbon capture (CCS) at Klemetsrud, the largest waste facility that the company owns and operates.