LISBON, Dec 19 (Reuters) - Portugal's Galp Energia anticipates to start producing biodiesel and biojet fuel from waste in an system it is constructing at its Sines refinery in 2026, the company, which is mostly an oil producer and refiner, said on Thursday.

In 2015 Galp participated in a 75%-25% joint venture with Japan's Mitsui to invest 400 million euros ($415 million) in the Hydrogenated Vegetable Oil (HVO) plant, which will have a production capability of 270,000 metric heaps each year.

It will transform waste products, such as used cooking oils, into eco-friendly biodiesel and biojet fuel, likewise called sustainable aviation fuel (SAF), utilizing green hydrogen produced by an electrolyser powered by wind or solar power.

Galp stated in a declaration it received on Wednesday the three reactors to process biofuels, which will enable the HVO unit to "produce SAF and biodiesel in 2026 ... positioning Galp at the forefront of developing low-carbon options necessary for the energy shift".

Galp is also investing 250 million euros in a 100 megawatt (MW) electrolyser system to produce green hydrogen to power the refinery in Sines. ($1 = 0.9637 euros) (Reporting by Sergio Goncalves