Evacuated Tubes

Solar hot water has come a long way in the last decade, particularly with the introduction of evacuated tube collectors which are rapidly becoming the preferred option over flat plate systems. Dr. Geoff Harding, Carisol evacuated tubes chief scientific consultant in our R&D department was awarded €œHoyt Clarke Hottel Prize€ in 2008 by the American Solar Energy Society (ASES) for his research and development of evacuated glass solar thermal collector technology which is now in widespread use worldwide. Hoyt Clarke Hottel Award€ is the most prestigious prize in the world€™s Solar Industry, his latest research now reveals the…

“3-Hi” Vacuum Tube Technology! The Most Efficient Evacuated Tubes Made!

The Carisol evacuated latest design patented €œ3-Hi€ evacuated tube collectors is the most powerful and long lasting collector ever built. The absorptive coating found on the inner layer determines how efficient the evacuated tube will be during operation, our technological method and raw materials use for this coating also determines the life expectancy of the tubes.

Its predecessor evacuated tubes use a hi-tech reactive sputtering process to coat the inner tube. Most commonly this coating is made from aluminum and aluminum-nitrogen coating (Al-N/Al) which is the primary absorbing coating.

Carisol’s manufacturing international patented interference film coating €œ3 Hi€ evacuated tubes use 3 systems to ensure the most effective heat absorption. This includes a AL-N/AI layer but also a separate aluminum and copper layer. The added layer conduct heat better and also stabilize the coating allowing for a longer lifespan of 25 year or greater.

Besides being the most efficient evacuated tube available on today€™s market in absorbing the suns energy, Carisol evacuated tubes solar collectors have other advantages.

Solar angles (the angle at which the panel meets the sun) plays very little role with solar evacuated tubes as the sun is always striking it at a perpendicular angle right through the day.

However angle plays an important role in the flat panel collection efficiency, with flat panels the solar rays strike the panels at an oblique angle during the early and late parts of the day and are only perpendicular at midday when it is able to absorb more of the sun€™s ray hitting its surface.

Because of the pure vacuum within the evacuated tube, there is virtually 0% heat loss. This is evident by touching a glass vacuum tube which is cold while the liquid inside is boiling. An average of 94% of the suns energy directed to the inside of the tube and is captured when sun strikes its surface. Flat panel collectors will always loose heat through the glass, and become very inefficient at higher temperatures.

Carisol evacuated tubes can operate at a much higher temperature and as such are the preferred choice for home heating applications, solar water heating, solar air heating, solar space heating, solar process heating, solar air conditioning, and commercial solar heating applications. The growth worldwide for evacuated tubes is exponential surpassing that of the flat plate collectors whose growth has now leveled off. Currently Asia used 95% evacuated tubes in solar applications and Europe 86%, quickly adopting vacuum tubes in areas such as home heat and even solar air conditioning.

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

The principle behind solar vacuum tubes is simple. The solar vacuum tube is similar in design to a coffee thermos. It consists of a two layers of glass with a vacuum in between the layers. The outer layer of the solar tube is Borosilicate glass which is very low in iron and allows 98% of light energy to pass through. The 2nd inner layer has a very special coating applied to it.

The Carisol evacuated tube patented 3-Layer process results in a coating that will 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 our solar evacuated tube collectors 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 absorbed solar radiation is then transferred to a heat transfer fluid within the tube (liquid inside the thermos), This liquid quickly heats up and rises to the top. In an open vacuum tube system the potable water is heated directly with in the vacuum tube. Thermo siphon causes the hot water to rise and be replaced by colder water. The hot water is the collected in the top collection chamber and pumped though the system

Heat Pipe Technology – Is 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. 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 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 and should be carefully engineered when use in countries with long sun hours.

Check the specifications below:

Q. The latest is certainly not always the greatest, so which is actually better €“ flat plate solar water heater or evacuated tube solar water heater?

A. Evacuated captures sunlight better as they have a greater surface area exposed to the sun at any time throughout the day.

They are more efficient in transferring heat – up to 163% demonstrated in Caribbean sun hours conditions!

They are durable and if a tube should be broken, it can be easily and cheaply replaced.

They provide excellent performance in overcast conditions and require a smaller roof area than comparable flat plate collectors; also they do not have the same level of corrosion or lime scale problems as flat plate collectors.

The efficiency of the flat vs. the evacuated tube results below will speak for themselves.

The following figures demonstrate efficiencies of collectors when heating water from ambient temperature to 75 degrees Celsius.

Winter: Based upon solar isolation of 426W/m2 and an ambient temperature of 13.1degrees Celsius in the Caribbean, Carisol evacuated tube solar collector is an average of 104% more efficient per m2 of aperture compared to a flat plate solar collector.

Summer: Based upon solar isolation of 840W/m2 and an ambient temperature of 21.3 degrees Celsius in the Caribbean, Carisol evacuated tube solar collector is an average of 50.5% more efficient per m2 of aperture.

Q. What is an evacuated tube collector?

A. Evacuated tube collectors consist of rows of parallel transparent glass tubes, each containing an absorber tube. Newer-technology evacuated tube collectors used to be more expensive than flat-plate collectors but costs have dropped as production increased, especially in Asia. Evacuated tubes are fragile, but they have a number of significant advantages:

  • The collector efficiency remains high in cloudy conditions and low temperatures.
  • The circular tube means that the sun is shining directly on the absorber for most of the day.
  • Evacuated-tube collectors have the ability to heat water to higher temperatures than flat plate collectors.
  • Evacuated-tubes heat pipes can be added or removed as hot-water demand changes.

Q. What is the difference between flat plates and evacuated tubes?

A. Older style flat plates with water tubes attached to the metal were the first active systems. Newer technology evacuated tubes have higher efficiency, no heat loss across a vacuum and quasi-tracking of the sun. As cost is now almost equal, vacuum tubes are supplementing the older style flat plates.

Q. How are solar water heater collectors set up?

A. Solar panels are usually installed on the roof. They can also be wall mounted or free standing. Solar collectors should be orientated facing the equator (south in the northern hemisphere) at a tilt angle of approximately equal to the latitude.

Q. Why use a pressure system when a no-pressure system is cheaper?

A. Flow rate and control. Water flow out of a no pressure system is by gravity, so the collector must be placed above the point of use, and the higher the collector is placed, the more pressure is possible. The tank must be refilled after use, either manually by opening a valve, automatically with a mechanism much like a toilet bowl float valve.

Pressure systems can be installed at any level and are automatically refilled as water is used. Higher flow rates are possible on a pressure system by increasing the pressure.

Q. How would you compare your solar water heater to that of your competitor?

A. Our solar water heater complies with stringent world standards and has achieve over thirty certificates for quality manufacturing and durability from independent labs around the world and given the strength of our company, we can offer some of the best prices in the Caribbean – get a free, no-obligation solar water heater quotation now. Also if you get a better price on comparable system from any competitor, Contact Us.

Q. How long does it takes to install a Carisol system?

A. Installation can be completed within 2 to 3 hours depending on the type of system you are installing.

Q. How many people can a solar hot water systems supply?

A. Typically a single 300 liter system will adequately service a home of 8 people comfortably, however, larger systems are available for very large households or multiple systems can be installed. All systems come with an electric back-up element as standard thus ensuring hot water 24 hours a day, regardless of weather conditions.