Active systems use electric pumps to pump water or heat-transfer fluid through the collectors. An advantage of this kind of system would be that storage tanks need not be situated as close to the collectors.
- Direct active system
These kind of system uses pumps to pump household water through the collectors. This design is efficient and lowers operating costs, but is not suitable for areas where water is acidic as it will be corrosive to the collector over time or where there are prolonged periods of subzero temperatures.
- Indirect active system
These systems pump a heat-transfer liquid through the collector. Heat exchangers transfer the heat from the fluid to the water in the tanks. This system is popular in areas where there are long periods of subzero temperatures.
Passive systems have no pumps and so are not subject to the availability of power. They are thus operational even during power outages. They are however not as efficient as active systems as water moves slower through the collectors.
- Thermosiphon passive system
This relies on the natural phenomena of convection to circulate the water in the collector.As water warms it rises through the collector and into the tank situated above the collector. Simultaneously cooler water flows downwards. This system is widely used with flat-plate and evacuated tube collectors. Disadvantages to this would be the poor aesthetics of a large tank on the roof, as well as implications of the heavy tank on the roof.
- Batch collectors
Batch collectors are simple systems whereby water storage tanks are placed in an insulated box with a glazed surface facing the sun. Batch heaters are inexpensive, but only perform well in the warm season and are less efficient than Evacuated tube collectors.