DIY Solar Heat Storage Systems

 

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Home made solar heat storage systems are practical and cost effective alternatives to the conventional, closed loop solar hot water system above. Did you know that standard, commercial, 100-gallon, solar hot water tanks retail for more than more $1000? Don't even ask how much it would cost to heat a house with these tanks.  

If you’re handy with tools a homemade heat storage vault could save you thousands of dollars., but before picking up a hammer consider the alternatives. The rising cost of energy and the increasing threat of global warming are good reasons to go green, conserve energy, recycle, and become more energy independent. You may decide to install your own PV system for $5/ watt, but you may need an electrician to sign off on a grid hook up.

Solar thermal applications offer another alternative with a price tag as low as $0.50 per Watt and a payback period of less than 3 years. Of course a watt of electricity is worth more than a watt of heat but not that much more. Only you can decide what applications are suitable for your needs and your talents.

 

Solar heat storage systems may simply use the thermal mass like this adobe located in the sunbelt area of New Mexico. It works by storing solar heat energy during the day and by releasing gradually at night. This is how extreme temperature fluctuations in desert areas may be moderated. Cold climates require glazing materials to trap heat. Standard Trombe Walls and Modified Trombe Walls use glazing materials, but a Modified Trombe Walls has the additional benefit of allowing solar heated air to flow into the house either by convection or fan.

 





This modified Trombe Wall could use a concrete wall to store heat, but a better idea would involve using an insulated outside wall to prevent heat loss. The interior walls of the house as well as the furniture could then be used to store heat.

Notice how the roof extends way over the top of the glazing. This extended roof blocks summer sunlight radiation and allows in winter radiation. The flaps open to allow rising hot air to enter the house, but when the Trombe Wall cavity cools down the convection currents reverse and prevent heat from escaping.

Gary Reysa uses a black screen inside the Trombe Wall cavity to facilitate the process of converting light into heat. Click on the illustration to see the details of Gary's work.



 

A close relative of the Trombe Wall is the Solar Greenhouse:

This passive solar greenhouse uses an out flap and an in flap to trap solar heat. The out flap only allows cold household air to enter the greenhouse space. The in flap only allows solar heated air to enter the living space inside the house. At night when there is no heat coming from the sun the convection currents  reverse and both flaps close.

The funneling effect of the glazing concentrates heated air near the top of the glazing and facilities the process of separating hot air from cold air. in this way heat from the sun is transferred into the furniture and walls of the house.

This is an example of a simple passive solar heated house with a little greenhouse that may be used to get seedlings off to an early start. Some heat will naturally be stored in the plant beds but most of the heat inside the greenhouse will be lost through the glazing. Separating the area of heat gain from the area of heat storage is a basic solar thermal concept that becomes increasingly important as the temperature drops and as the quantity and quality of sunlight diminish. Now that we understand how pneumatic solar heating systems store heat let's take a look at some hydronic systems.


A batch heater may be made from a recycled hot water tank, some aluminum flashing and an old patio door. it's easy to build and it may provide a suitable pre heat hot water supply is a sunny area.

HOWEVER in cold climates where freezing is a concern the year round use of the batch heater is not advised.

Another problem with this method of storing heat has to do with the proximity of the storage tank to the glazing. 90 % 0f the heat loss takes place through the glazing material. Thermo pane is good but not good enough for most areas. insulating the heat storage area from the heat collection area is very important in cold climates.

Both of these closed loop solar hot water storage systems were built in Plattsburgh, NY. 

The one on the left was built in 1980 from a recycled, sealed 100 gallon holding tank and some 3/8" copper tube.  The copper tube is bonded to the outside of the tank with chicken wire and cement. This is an external heat exchange system. 

The multiple, 55 gallon, open tank heat storage system on the right was built in 2005. Heat is exchanged through copper coils inside the tanks. The heat is then extracted from the tanks as needed to preheat water for DHW. This system uses internal heat exchange.

Multiple tanks can improve heat stratification and improve collector efficiency, but a heat storage tank may also be framed in plywood wood and lined with EDPM. See how Gary Reysa built his own heat storage tank

Some people only use a concrete slab to store solar heat, but unfortunately it's impossible to regulate temperature from the same place that heat is stored.






There are numerous ways to store and distribute the the suns heat energy and I'm sure you'll soon discover them. I like to use water to store heat not only because it's readily available but also because it has the highest heat capacity of any common substance. This unique ability of water has to do with it's molecular OH stretching frequency. Water is also safe to work with and easy to transport with the help of a circulator or pump. 

Water may also be heated directly by employing the drainback or trickle down solar heating system. This eliminates the need for heat exchange tubes in or on the storage tanks. Of course there must still be a heat exchange method used for pressurized hot water, but it is possible to have solar heated water flow directly through drums.

This multi tank heat storage method may be used to hold and distribute heat through a radiant floor heating system. Domestic hot water may also be made with the same series of tanks by extracting heat from a cement platform on which the tanks rest.

If you have an illustrated article about heat storage system that you'd like to publish on my web send it in and I'll find a place for it.








 

 

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