Solar water tanks for use in a residential application are completely different that a regular hot water tank and are a very important part of a properly designed residential solar water heating system. The primary purpose of a residential solar water tank is to provide thermal storage for the solar energy. This is very similar to a battery in a solar PV system.
In the past DIY'ers converted a regular tank to a storage tank by using the drain ports and the T&P valve port as opening and then running an external heat exchanger on the tank. This was primitive and still left lots of issues such as thermos-ports to measure the temperature. Also playing with the position of the T&P valve is against CSA and UL codes making the system potentially dangerous.
Internal heat exchanger:
A proper residential solar water tank has the heat exchanger built internally to give the best possible heat exchange as it is directly inside the potable water. The insulation in a solar storage tank is also better than most standard water tanks as the tank may need to store the energy for days when it is not sunny. Another distinct feature of a solar water tank is direct thermos ports inside the tank. This allows the solar controller to accurately measure the water temperature inside the system. Our SolarStor tanks have both a top and bottom thermo-port for two sensors.
Single coil or double coil?
>If you just plan to do solar domestic hot water then all you will need is a single bottom heat exchanger coil in your residential tank. However if you plan to add a second heating zone in the future then you should plan on a top heat exchanger as well as the bottom. The top heat exchanger does the opposite of the bottom, it removes heat from the hot water and delivers it to a second heating zone as needed such as a hot tub, pool, hydronic floor heat or an air handler in the forced air furnace.
Sizes of residential solar water tanks:
All UL and CSA certified tanks have a maximum listing of 120 gallons for residential applications. That is generally large enough for a family of 8 person and can be added to a 3 collector solar heating system. If you want to go larger the solution is to by a larger commercial solar tanks which generally comes with a hefty price and often will not fit through a standard 32" door way. However to gain more storage you can combine multiple storage tanks to form a larger "bank of batteries" adding them in parallel will give you a cost effective means to doubling the storage capacity for applications requiring more heat energy such as space heating.
Warranty - All our residential tanks come with a 7 year residential warranty
Where to Buy - Visit our online store to buy solar water tanks
Dual Heat Exchanger
Single Heat Exchanger