There are many types of passive solar water heater systems, and each has its benefits and limitations.
Glazes Flat Plate Collectors
These systems are designed within a metal box, which is insulated and weatherproof. The box contains a dark absorber plate under one or more glass or plastic covers. When the sunlight hits the absorber plate, water-filled heating tubes activate, and the water is circulated through to the tank.
Unglazed Flat Plate Collectors
Unglazed flat-plate collectors are similar to Glazed collectors; the only difference is that they don’t heat the water as much as Glazed collectors do. These systems are generally used for swimming pools or car washes due to their lower heating capability.
Evacuated Tube Collectors
Evacuated tube heating systems consist of insulated tubes made from glass. These tubes form a vacuum space that prevents heat loss. When the sun hits the inner tube containing the water, it provides heat via thermal power. This system provides better efficiency and reaches high temperatures ranging from 77 °C to 177 °C.
Batch Solar Heaters
Batch Solar heaters are also known as Integral Collector Storage Systems. These systems consist of one or more water tanks that allow sunlight to pass through. The water absorbs the heat from the sun and rises in temperature. It is the cheapest heating system as it doesn’t require any additional accessories, other than the tanks.
However, it solely depends on the temperature of your residence too. For instance, during winter, it might not be as efficient as it might become too cold for the system to heat the water properly.