The Solar Association of New Zealand thinks proposals to centralise electricity sales could make it harder to cut greenhouse gas emissions.
The Labour and Green parties are proposing, if elected, to create a state agency to buy electricity from power generators at a set price and pass on savings to consumers.
Solar Association chief executive Adrian Kerr says if householders were exposed to the same electricity spot market as businesses, price signals would tell them to cut useage when prices - and carbon emissions - are high.
At present, the price of electricity to households is generally fixed for a year, but the association thinks consumers should be exposed to the same electricity spot market as businesses.
It says when electricity prices are high it generally involves power generation that has high greenhouse gas emissions, and getting a single price would disguise the greenhouse gas component of the electricity that people use at any one time.