You don't have an enumeration. You have two enumerations. There is an outer enumeration:
Anlage und Dauer
And for the first item you have a list of properties that form an inner enumeration:
Technologie und Größe (der Anlage)
If you put them together, you get encapsulated enumerations. For each of them you need an »und« between the penultimate and the ultimate item of the enumeration. This is equal in English:
The amount of funding depends on the technology and size of the facility and the duration already funded.
Outer enumeration:
facility and duration
Inner enumeration:
technology and size (of the facility)
If you want to use only one and/und you must get rid of the encapsulated enumerations. This means you have to bring them on the same level:
The amount of funding depends on the technology of the facility, the size of the facility and the duration already funded.
Now you have technology, size and duration at one level, which means, you now can put a comma between the first and the second item.
Same in German:
Die Höhe der Förderung ist abhängig von der Technologie der Anlage, der Größe der Anlage und der bereits geförderten Dauer.
Another trick is what πάντα ῥεῖ mentioned in his answer: Use a synonym
In English:
The amount of funding depends on the technology and size of the facility as well as the duration already funded.
In German:
Die Höhe der Förderung ist abhängig von der Technologie und Größe der Anlage sowie der bereits geförderten Dauer.