The cooperative announced the project earmarked for the roof of its shopping centre in the town of Neuendorf on Friday.
Migros said it had received a building permit for the solar system to provide enoguh electricity to power 1,000 single-family homes.
The coop said the photovoltaic panels will be delivered in the spring and mounted on an area equivalent to almost seven football fields.
The solar power system is expected to be connected to the public power grid by the summer of 2013.
The retailer already has 24 rooftop solar systems in operation.
With the new plant Migros said it was renewing its commitment to renewable energy sources which it launched earlier with its “Generation M” sustainability programme.
“The solar panels provide about one-sixth of the total electricity demand of the Neuendorf shopping centre,” Hans Kuhn, the centre’s director, said in a statement.
Although Migros is calling the project the biggest of its kind in Switzerland it may get an argument from the canton of Geneva.
Last month the canton unveiled what it touted as the largest solar system in the country on the roof of a building at the Palexpo exhibition centre.
With 15,000 panels, the photovoltaic system produces enough electricity for 1,350 households, according to Services Industriels de Genève (SIG), the state-owned utility.