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How Solar Hot Water System Works

1.Solar Collectors: Heat Pipes & Evacuated Tube Technology

The operation of the solar collector is as follows:

1. Solar Absorption: Solar thermal energy is absorbed within the evacuated tubes and is converted into usable concentrated heat.

2. Solar Thermal Transfer: Copper heat pipes transfer the thermal energy from within the solar tube into the copper header.

3. Solar Thermal Storage: A thermal transfer solution (water or glycol mixture) is pumped through the copper header. As the solution circulates through the copper header the temperature is raised by 5-10 C / 9-18 F.

Evacuated Tubes:

The solar evacuated tube is similar in design to a cofee thermos.  It consists of a two layers of glass with a vacuum in between the layers.  The outer layer of the solar tube is Borsoillicate glass which is very low in iron and allows 98% of light energy to pass through.  The inner layer has a very special coating applied to it. The solar evacuated tubes we supply  use  a patented 3-Layer  process that results in a coating that can absorb more of the sun's energy while being able to withstand temperatures in excess of 300 degrees (575 F) without deteriorating.  This coating is what makes these solar heat colllectors superior to any other collector on the market.   The special selective coating change the short wave solar radiation into long wave heat radiation and is almost 94% efficient meaning only 6% of the suns energy is lost!

The inner and outer layer are fused at high temperatures at the end leaving an empty space between the inner and outer layers. All air is pumped out of the space between the two layers (evacuation process) creating the thermos effect which stops conductive and convective transfer of heat which might otherwise escape into the atmosphere. Heat loss is further reduced by the low-emissivity nature of the type of glass that is used.

The solar collector is the engine of any hot water system.  Solar vacuum tubes have always been the most efficient solar power production systems but were more expensive than other flat panel system.  However the growing demand of solar and modern manufacturing techniques has driven down the cost such that vacuum tube technology provides the greatest return on investment versus any other solar system. 

Heat Pipe Technology

Inside the glass tube is the copper heat pipe. It is a sealed hollow copper tube that contains a small amount of proprietary liquid, which under low pressure boils at a very low temperature. In fact the liquid contained in the heat pipe boils at only 86F (30 C). The header is enclosed in the manifold (above).

s the most efficient heat transfer technology available for solar system on the market today.   Instead of water flowing  in the center of the vacuum tubes, a hollow copper tube is inserted through the length of the tube.  This special tube contains a small amount of  special liquid that acts as heat transfer medium.  The hollow chamber is made under vacuum conditions which cause the fluid to vaporize at  lower temperatures (30 C or 86 F) as a result of the low pressure.   The vapor  rises to a condenser bulb (heat dissipater) where it is cooled back to a liquid and gravity returns it to the base of the heat pipe so that the process is continually repeated.  

Copper heat pipes are used because they can absorb and transfer heat very efficiently with virtually no energy loss.  This technology allows the energy to be transferred indirectly to the hot water system.  It is used extensively in systems that require a heat exchanger such as a close loop system.   Any hot water system being designed in freezing conditions will need to use heat pipes as antifreeze must be used and the therefore the water needs to be separated from the heating system via a heat exchanger.  Heat pipe systems are more efficient than open vacuum tubes but also come at a significantly higher price with the added copper materials.




Because the evacuated tubes are round, they serve as a passive tracking solar collector maximizing their performance.


2. Solar Heat Exchanger Tanks

Brass valves and components
Includes temperature and pressure relief valve
Collector feed and return fittings located at
front of tank for convenient installation
Highly efficient tank design
Highly efficient heating element
Prolonged tank life due to specially designed
inner tank lining that resists corrosion
Copper tube heat exchanger
Bottom inlet for cold water to prevent mixing
with hot water
Easily accessible inlets, outlets, valves and
anode rod to quick install.
Automated temperature control valve
Temperature overheat protection

The solar heat exchanger tank stores 60 to 120 gallons of solar heated water depending on model selected. Typically the heat exchanger tank sits between the city/well water supply and the customers existing tank.

When hot water is drawn from the existing tank, it is replaced by water from the solar tank that is already hot, meaning that the heating elements or gas burner of the existing tank do not have to operate.


3. Solar Pumping Station, Pumps & Controllers


Tying the collectors and the tank together is a system that consists of valves, a controller, and a pump.

Options are available to configure the system using a pre-configure pump-station (left), or design it with best-of-breed components (right).

Our installers use both methods, depending on the application.






For maximal reliability and virtually free maintenance, we use the closed-loop antifreeze system rather than the inferior drain back system which is still widely used due to its lower system cost. The major disadvantages of the drain back system are: (1) All pipes need to slope downward, which is difficult to achieve everywhere. (2) If main water is used as heat-transfer fluid in an un-pressurized system, collector tubes will scale and require frequent maintenance or will malfunction; water used in a closed, un-pressurized loop will quickly breed bacteria and pollute the potable water. (3) Some drain-back installers try to counter these problems by using a closed-loop propylene glycol drain-back system. If the propylene glycol is not pressurized and is exposed to oxygen, it will degrade quickly. Also, every time the system drains back, a thin film of antifreeze is left inside the collector, which dries and leaves a small residue. Eventually the film will build up enough to degrade the collector and diminish its efficiency.

Use Solar Energy to Heat a Building

There are a number of options for taking the heat out of a water tank and delivering it to the building on demand. For new construction, it is better to use a primary loop-secondary loop plumbing configuration. Do not mingle the fluid in the solar storage tank or solar loop with the fluid in the hydronic heating system. The best way to integrate a solar system into a hydronic system is to use a large storage tank with a heat exchanger mounted inside the tank to extract the heat. This exchanger shares fluid with the hydronic heating system (inside the exchanger) so the fluids never mingle.

When you integrate a solar heating system into a traditional heating system you have two heat sources to choose from. This can be done automatically by using two thermostats in the building, one for the solar heating system and one for the back-up. Set the solar thermostat slightly higher than the one for the back-up system. As the temperature falls in the building, the first thermostat to call for heat will be the solar thermostat, extracting heat from the solar storage system and deliver that heat to the house.

You can integrate a solar heating system with a forced-air heating system. A liquid-to-air heat exchanger is placed in the duckwork near the furnace. It is always preferable to install the heating coil in the hot air duct above the furnace. If an air conditioning coil is already installed in the ductwork, it will probably be ins the hot air duct just above the furnace. If there is room, try to place the heating coil above it. Hot water from the solar storage system is circulated through the liquid-to-air heat exchanger and the furnace fan moves the warm air through the ductwork.

Other options for delivering the solar heat into the building include a separate radiant floor system, one or more fan convectors, or baseboard units. With all these options, hot fluid is taken from the solar storage tank and circulated through the heat distribution device where the heat is delivered into the building.

Radiant floor heating is the most comfortable and most economical to operate.

SolarPlusGreen LLC, 1104 Hendersonville Rd, Asheville, NC 28803; see location map.
Ph: 828-301-2021, Fax: 828-277-1240;