Glossary
Ancillary services (SDL)
Also known as: Systemdienstleistungen, SDL, Systemdienstleistung, Ancillary Services, System services
Systemdienstleistungen (ancillary services, SDL) are the services Swissgrid buys as transmission system operator to run the Swiss electricity grid securely: control reserve in three tiers (primary, secondary and tertiary), voltage support, black-start capability and the provision of imbalance energy. The costs are passed on to end consumers through the SDL tariff. For battery storage operators, SDL is the umbrella term for revenue from the balancing energy market, which site studies examine as a third revenue lever alongside peak shaving and self-consumption optimisation.
The largest share of ancillary services is balancing energy. Swissgrid procures it in tenders and in 2025 held around 70 MW of primary control reserve, around 360 MW of secondary control reserve and around 500 MW of tertiary control reserve on annual average (ElCom).
In Ampere Dynamic’s site studies, SDL stands for the revenue from this marketing. The evaluation of 29 site studies, as of 2026, shows: storage systems with SDL as the main application and self-consumption as the secondary application reach a mean IRR of 17.3% with a payback of 5.5 years, against 14.5% and 6.6 years with the priorities reversed. The combination with peak shaving and self-consumption makes the difference.
What the market paid in 2025 and how entry through a pool works is explained in the article Balancing energy with battery storage.