The energy sector has been open to competition for 10 years, even though most people remain with the historic providers, EDF and Engie (formerly GDF).
Many EDF and Engie customers remain on traditional tarifs réglementés, under which prices are regulated by the state. The alternative is an offre de marché (market rate offer), either from an historic provider or an alternative one, with the choice governed by the rules in the contract you sign.
There are many alternative firms – the largest being Direct Energie, which offers a guarantee of always paying less than the tarifs réglementés for those on its offre classique. Some firms offer gas and electricity and others, such as Planète Oui, a specialist in 100% electricity from renewable sources, offer only one energy form.
Changing suppliers is free, you just have to sign a new contract. Cancellation of the existing contract happens automatically and you cannot be billed for it. You will need your point de livraison number (PDL) for an electricity contract and/or your PCE number (point de comptage et d’estimation) for gas. You can find these on your bills.
Official site energie-info.fr has a comparison tool to help you work out if an alternative company might result in savings: http://comparateur.energie-info.fr
You need to know the power of your electricity meter, which will be on bills (3kWh corresponds to a small flat without electric heating, 9kWh a large one with electric heating. The most common is 6kWh).
You should also check if you are currently on a base (basic) tariff, where energy costs the same whenever you use it, or an heures creuses/heures pleines option (HC/HP) with different rates depending on the time of day (to check if you might benefit from changing there is a tool for working out which tariff best suits your lifestyle at calculettes.energie-info.fr/calculettes/meilleure-option-tarifaire).
You should have to hand previous bills so as to work out your annual consumption or the monthly or annual amount of your bill, otherwise you can make a comparison based on average use. The calculator will estimate how much your bills might be with various alternative companies.
As an example, an average metre and energy consumption in Nice with electricity apart from gas cooking, is shown as costing €924/year on EDF and Engie’s regulated tariffs but €834 with cheaper alternatives, Cdiscount énergie and Dyneff Gaz.