our reporter, wolfgang bernert, travelled to arandas in mexico and discovered more about a start-up that's helping other companies harness solar thermal energy. reporter: the lÁcteos mojica cheese dairy is a family business. every week it produces 40 tons of cheese for the mexican market. and every week, the company uses 40,000 liters of hot water. it has to be at a temperature of least 70 degrees celsius to kill off germs. and to heat it, the cheesemaker uses nearly 100,000 liters of liquid gas. the tanks are kept up on the roof, along with his new solar technology, which is already saving him money. rigoberto: up to now we were paying 80,000 mexican pesos a month for gas. now it's 30% less. reporter: but the technology itself didn't come cheap. the solar heating facility on the roof measures 120 square meters and cost the equivalent of 75,000 euros. now the water is warmed directly by the sun. but there's still room for improvement, which is why the head of technology at inventive power is here. they manufacture the solar collector. aldo: the bibiggest challenge s toto integrate the heat