Ancillary services (AS) in the electricity supply sector are defined as services delivered by grid operators to customers in addition to the transmission and distribution of electrical energy. This includes the provision and operation of a schedule and congestion management system as well as coordination activities in Switzerland and Europe. By far the greatest share of costs for ancillary services, however, is taken up by control energy. This is a kind of insurance against power outages that Swissgrid takes out with electricity producers and consumers in order to cope with critical grid situations if unforeseen events occur.
This «insurance» is needed because electricity cannot be cost-efficiently stored in large volumes using conventional means. At any given point in time, therefore, the amount of electricity produced must correspond exactly to the amount being used. If this balance is endangered, for instance in the case of failure of a power station or a major consumer, the missing or excess energy must be compensated for immediately using control energy. In such a scenario Swissgrid contacts the ancillary service providers with which it concluded an agreement in advance. These then perform their agreed service, i.e. either increasing or decreasing their energy production. At present, ancillary services are mainly offered by producers such as pumped storage power plants. On the condition that the minimum requirements defined by Swissgrid are met, electricity consumers that can flexibly ramp up or reduce their electricity consumption can now also offer control energy services.
Swissgrid is obliged by law to procure ancillary services in accordance with transparent, non-discriminatory and market-oriented criteria. As the company does not possess any power plants of its own, it invites tenders on the control power market newly created in 2009 and then chooses the most favourable.