Active solar water heater systems are the most popular type of solar water heaters in North America. They utilize a pump to transfer heat from the collectors to the water to be used, which is stored in a remote location away from the collector. This is also commonly known as a split tank system. The best tanks to use in these active systems have built-in copper heat exchanger coils so that the heat can be transferred from the working fluid which passes through the collectors and into the water which is in the tank without the water or working fluid mixing together.
One advantage of active solar water heaters is that they can store the hot water anywhere, even far away from the actual collectors which receive the sunlight. This allows for strategic placing of the tank close to where the water will be used so that it will not take long for hot water flow from the tap.
Unlike passive solar water heaters, the placement of the tank is normally indoors and so heat loss from the water is reduced especially during winter months due to less temperature differential of the water in the tank and the ambient air around the tank.
Passive solar water heaters with attached tanks will lose a lot more heat to the ambient air in the winter, when there is less sun to collect energy from, since the tank is kept outside.
The tanks used to store the hot water may also have backup heating systems in case of cloudy days where there is not enough heat to meet the demands of the user.
In the Duda Solar split tanks, this element is strategically placed in the middle or upper part of the tank so that only some of the water is heated as it is used. This allows a chance for the sun to come back out and heat the cold water in the bottom half of the tank.
Another advantage of the active solar water heater is winterization. Since the working fluid is an intermediate fluid, a non-toxic inhibited propylene glycol can be used to prevent freezing. Although there are less hours of sunlight during the cold winters in the north, there is still a lot of heat which can be collected with a vacuum tube solar water heater.