Water Storage Tanks as Passive Thermal Energy Storage

blue water tubes for solar heat storage

There are numerous examples of water storage tanks being built into home interiors to form a solar thermal energy storage unit. Primary role of such unit is to act a as a buffer to the daily-nightly swings in temperature.

By storing excess solar energy using water filled tanks, it is possible to control indoor air temperature and minimize huge temperature swings in hallways, living rooms or even greenhouses.

Solar water storage tanks placed near the south side window can provide not only a cool, sculptural centerpiece for your home but can also drastically cut down on your heating bills and save both electrical energy and money. Beside their main role, solar tubes often serve as attractive accents or room space dividers. As you can see in the picture, dyes can be used to additionally increase solar gain (efficiency) and to provide a desired color effect.

The most interesting thing about this innovative tube is that passive solar heating & cooling can be implemented without any solar charge controllers, wires or solar panels. Instead, you simply need to take several transparent fiberglass tubes, fill them with water and place them next to the south window or wherever they will get a maximum exposure to sun light so that they can absorb and store energy from the sun to fill your room with heat . And that`s it, once established – the system will work on its own from there.

Passive Thermal Energy Storage – How does it work?

Well, it`s very similar to Trombe walls. Water tubes form a thermal mass machine with no moving parts and a completely maintenance-free solar thermal energy storage system. Basically, the system stores heat during the day and keep warm at night. The sun is a very powerful energy source, yet mankind allows this heat to be wasted or dissipated. Thermal mass provides us with an inexpensive, non-mechanical way of storing the sun’s heat.

It is known that radiant heating and cooling is most comfortable for a man. Water storage tubes represent a low-tech form of radiant system which prevents wide temperature swings by absorbing and diffusing solar energy. The radiant energy of solar storage tanks will naturally regulate home temperature, but it can not be used as a substitute for heating/cooling needs.


When installed to face the south window, solar tubes function as a Direct Gain Water Wall. Water absorb and store solar energy, while allowing natural daylight to pass through. Solar tubes temper both the light and heat from the sun by removing wide temperature fluctuations while also helping to reduce glare from the south facing windows.

Water Storage Tanks as a Thermal Mass – What is it?

By definition, thermal mass is equivalent to thermal capacitance or heat capacity, in other words it is the ability of a body to store thermal energy. If you check the Specific Thermal Capacity value for various materials, you will notice that water has a remarkably high thermal mass. This means it can store more heat for a given volume. For example, water has a volumetric heat capacity more than double comparing to concrete or bricks. Also it naturally absorbs and releases its heat to the surrounding air. Another important factor is that convection currents in water allow heat to travel around more quickly than in a solid object, like concrete or brick. Thus, water is able to add or remove heat from our home without the external supply of electrical energy.

You can easily build your own DIY thermal reservoir and place it in your living room. Water storage tanks (or so called “heat storage tubes”) can range from 4 to 10 feet (1-3 m) in height with 12 to 18 inches (30-45 cm) diameter. That kind of tube holds a lot of water inside, which equals to a lot of free heat. If you plan to construct the tubes yourself, also have in mind that the structure needs to hold and sustain huge amount of water with all the weight and pressure that comes along with such volumes.

It is also possible to install such thermal energy accumulation tubes into a greenhouse. Imagine how much energy and money you could save by utilizing this simple solution.

green house hot water storage tanks for efficient solar thermal energy storage

green house water storage tank for solar thermal energy storage

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