In a fixed tariff, practiced by the majority of the energy supplier, a fixed value is established for the applicable tariff during a defined period (normally one year). These tariffs have the advantage of greater predictability in the energy bill, since in these cases the invoice value varies only according to the energy consumption.
In an indexed tariff, the value of the energy tariff is indexed to the daily market price of electricity (OMIE), which has an hourly variation. Thus, in this type of tariffs, the consumer sees reflected in his bill the changes in the price of electricity, with a commercial margin (spread) for the provision of the service of energy supply, defined by the supplier.
In addition, there are suppliers who, in order to reduce the risk associated with the indexed tariff, define tariffs based on the price of the daily electricity market, establishing, however, a maximum price from which the energy tariff no longer increase. In such a scenario, the client has a more limited exposure to variations in the price of energy in OMIE.