a) In large cities instead of transporting the  rubbish to the garbage dump, the waste disposal vehicles bring them to a sorting area. The biomass is separated and taken to special factories. There is used as fuel, instead of oil and coal, in a power station in other words it is burned to produce electricity and/or heat for "district heating", especially for the case of small units when electricity production is not feasible economically. In such cases the heat generated is transported in the form of hot water 

b) Vegetable oils and grease from various restaurants can be gathered and processed to produce bio-fuels.

c) In rural areas, where various agricultural activities lead to production of sufficient biomass (pruning, leftovers after the olives are pressed to get out the oil, leaves, etc.) special boilers can be used, where they are burned and heat up the water for the electric heater. When finished oil is used in the boiler.