The Government has eliminated most barriers to lines companies also generating electricity.
The barriers were put in place by the National Government in the 1990s to stop lines companies, which have a captive market, cross-subsidising the sale of electricity.
The separation has been wound back in stages over the past few years and is now almost completely overturned.
The latest change removed almost all controls on lines companies making renewable electricity, but leaves some restrictions on non-renewable energy.
It also lessens controls on lines companies retailing electricity.
Energy Minister David Parker says the risk of unfair cross subsidies are managed by requiring corporate separation and 'arms length' rules between branches of the same company.