... .lifetime:15 years , guarantee:5 years compact non pressure solar systemWorking principle:The non-pressure thermosiphon systems rely on the nature circulation of ... 7. hail resistance: 25mm8. Optional: heat exchanger (red copper), electric heater (1.5kw, 2kw, 2.5kw, 3kw), assistant tank( 5L, 8L ... .3. Simple system, easy installation and low price. compact non pressure solar system