Price regulation in term of feed-in tariff is an introduced instrument in this country. In Bulgaria all of the RES technologies which generate electricity for the public electricity network are supported in similar way (exception are hydro power plants which capacity have to exceed 10MW). However only energy generated in Bulgaria is promoted. The prices are annually adjusted by the regulator authority and it is about 80% of the average energy selling price of the previous year. All technologies are supported during 15 years, beside solar power plants in which case promotion is eligible for 25 years. [54] The RES power plants have priority in grid connection and the grid operators are obligated to purchase for the system operators. Transaction between system operator and distribution grid operator based on contract. Moreover grid operator is obligated to upgrade local electricity network to be able for the RES connection. Costs related with the grid upgrading are covered also by the grid operator. [54] Regulation requirements in Bulgaria are Renewable and Alternative Energy Sources and Biofuels Act (the EEBG), Energy Act and Ordinance on Regulating the Prices of Electric Power (the VE). [54]