Our water heating solar system have different capacities to choose. There are two factors for you to choose the capacity. The one is the number of family members, and the other is the need to use domestic water heaters on a regular basis. Normally, one people needs about 50 liters, you can choose the capacity of solar water heater according to the number of households. For example, 150 liter water heating solar system can be used for 2 to 3 members.