Consumer rights watchdog Consumentenbond has called for solar energy suppliers to be more transparent about the cost of sending unused power back to the grid.

Homeowners’ costs have increased since the government abolished a concession that allowed them to sell their unused energy back to the supplier, but the rates that companies charge under the new rules vary widely.

Customers have seen the cost of an annual contract increase by an average of 38% since last July, the consumers’ association said.

A household with 12 panels faces an annual bill of €368 if their energy is supplied by Engie, but Oxxio charges around €200 more for an equivalent setup.

The Consumentenbond wants companies to harmonise prices by using a uniform calculation method, making it easier for potential customers to compare tariffs, as they can for gas and electricity.

“They all do it differently,” CEO Sandra Molenaar told Nu.nl. “One charges a set monthly fee while another works with so-called scales or sets a tariff per kilowatt hour. For consumers it is almost impossible to compare suppliers.”