What is the most efficient medium for solar water heating?

What is the most efficient medium for solar water heating? Can oils be used in solar heating systems?

Water is the most efficient liquid for transferring heat from one place to another such as in a solar hot water system. Water has a specific heat of 1 btu/lb °F

Specific heat or thermal capacity can be thought of as the ability of a substance to absorb or maintain heat.

A solar hot water system is most efficient when the heat transfer medium is 100% water. However, in most of the country this isn't possible because of the possibility of freezing. Typically we add propylene glycol to water so that it won't freeze. Propylene glycol has a specific heat of .60 btu/lb °F.

So when we add glycol to the system's water we lower the efficiency of the system. The specific heat of a 50/50 mixture of glycol and water is .85 btu/lb at 80°F. So it holds 15% less heat than pure water. So we would need 15% more storage capacity to store the same amount of heat than if we were using 100% water as our heat transfer medium.

Oils have specific heat ratios in the neighborhood of .40 - .50 btu/lb °F. Oil actually helps engines run cooler. They are not very efficient at retaining heat. They are also very viscous which makes them harder to pump, which uses more energy. They would not make a good fit for solar heating.

The only other liquid that has a higher specific heat than water is ammonia. Ammonia however, wouldn't make a good solar heat transfer fluid since it boils at -27°F.

http://www.engineeringtoolbox.com/specific-heat-fluids-d_151.html

Solar Hot Water Entry Level Course and Exam

After months of applications and confirmations we are proud to report that we finally gained approval for the  North American Board of Certified Energy Practitioners Entry Level Solar Heating course and testing site at Central Georgia Technical College.

This has been in the works for some time and we are glad that we can finally officially announce the news! Les Dell being one of only four NABCEP certified Solar Hot Water installers in Georgia, was approached by Central Georgia Tech back in April to consider becoming an instructor for the course that will be taught beginning in the fall at CGTC's campus.

It's been an arduous few months for everyone involved, especially Dr. Sheila Stille, Becky Lee, the Vice President of Economic Development for CGTC and Jack Laster of CGTC.

Dr. Stille prepared the course curriculum for NABCEP approval which I reviewed for final draft. Jack Laster is the primary instructor for CGTC. The college has contracted with Metro Solar and I will be assisting Jack with the teaching duties. At the end of the course the students will be able to take NABCEP's Solar Heating Entry Level exam to gain the entry level certification. This will be a very comprehensive and hands on course which will prepare the student for work in the green economy.

We are really looking forward to this new challenge and hopefully we can become a positive influence for promoting more green jobs in the State of Georgia and throughout the South.

Anyone interested in enrolling in the course please contact Central Georgia Technical College.

Metro Solar

Unexpected scenarios

Recently, a house that we had previously installed a closed loop glycol system on experienced some foundation damage. The homeowner contacted us so that we could confirm the system's integrity. 

In a situation such as this where there is the possibility of damage to the system the first thing you would want to check would be the system pressure.


We consulted the records for the system in question and found what the system pressure had been set to on the last inspection.

The system is comprised of two collectors mounted on the roof attached to flexible aluminum lines running through the attic and down in a closet and then into the basement where the tanks are located. Visually from the ground, the collectors did not look to be disturbed. We then went to the basement to check the pressure level on the pressure gauge at the pump station. If we had seen a drop in the pressure this would have told us that the foundation problem might have caused a leak in the system piping or either at a fitting.

The flexible aluminum piping is very robust and can take a good amount of movement from the structure. We did not find any loss of pressure and everything was in good working order. But perhaps the moral of the story is that the need to support all fluid piping properly is extremely important because you never know what kind of situation might arise. We never planned on the foundation of the house being damaged but since we supported all of the piping correctly there weren't any issues.

The maximum span between supports for 3/4" hard copper piping is 5.9 ft. Maximum span between supports for 3/4" soft copper is 5.6 ft.

Big News Coming Soon

We are happy to report that some exciting collaborations will be coming soon for Metro Solar! As soon as the partnership is finalized we will make an announcement. This partnership has been in the works since April and is nearing it's fruition. Stay tuned for the formal unveiling!

What gives?

Recently, we conducted a site visit on a previously installed system. The edge of the collector looked as if someone had taken a rasp to it. As best as we can tell it must be animal teeth marks, either a squirrel or racoon, we are not sure.

The Alternative Fuel Vehicle Road Show

A Fisker Karma at the Alternative Fuel Vehicle show at Suniva in Norcross, Georgia.

Besides the Fisker, there was also a Nissan Leaf or two, CODA, Mitsubishi MiEV, Chevy Volt, and a Tesla Roadster

 This Ford is runs on Natural Gas. The road show traveled all across Georgia showing off many different EV and natural gas powered cars.

Nissan Leaf

Atlanta PV installation

 Atlanta home with almost 6kw of PV and solar thermal!

Torquing the lag bolts

 Mounting rails installed

10 module array

14 module array