In the modern electricity market model for purchased electricity there is no direct link to the origin of the electricity; When producers submit their generation offers to the exchange and consumption requests to consumers, it is not possible to determine what part of the total supply the consumer has received, moreover, the exchanges do not have detailed information on the energy sources of the offered electricity generation. Accordingly, a mechanism is needed to determine the origin of the electricity supplied to consumers. According to Directive (EU) 2018/2001 on the promotion of the use of energy from renewable sources, the most common mechanism is guarantees of origin issued by the issuing authority. In accordance with the Electricity Market Law, the issuing authority for certificates of origin in Latvia is the Latvian electricity transmission system operator JSC Augstsprieguma tīkls (AST). AST issues European Energy Certificate System (EECS) certificates under an agreement between the transmission system operator and the European Energy Certification System operator for electricity produced from renewable energy sources (RES) or high-efficiency cogeneration.