I am in the initial phase of p lanning for the installation of solar panels (have not decided on type: flat panel OR evacuated tubes) My roof has a 3/12 pitch and slopes in an east-west direction. Furthermore, I am not to keen on a rooftop installation. Idea: I have a 48 foot (6x8 foot sections) freestanding triangular type antenna. It is very solid. My plan is to install 2 x 24 foot towers on the north side of my house approx. 8 feet apart. They would be anchored on cement bases and would ride up alongside my house. They would extend 10 feet higher than the roofline. I would then hang my panels using these towers. Any comments/ideas regarding this installation plan? Regards, Eric

Seems kinda high-profile expensive & complicated...

What's your latidude, and what kind of factors force you to hang 'em so high in the sky? (Ground based, just seems a lot simpler & cheaper to design build & maintain...)

Thhanks for your reply. -High profile is not an issue. -I live in the woods .... limited ground installation possibilities due to shading. -The proposed area is right above my utility room .... minimize pipe length. -latitude: 45 degrees (Ottawa, Canada) One advantage with going with evacuated tubes in this kind of instalation is minimizing wind issues and weight. Comments? Eric

Evacuated tubes are likely to get you higher winter performance in Ottawa too. And should you damage a tube, you're out the one tube, not the whole array.

Space heating, or domestic hot water (or combined?)

While you get better annual return by facing them more toward the sky (latitude minus 15 degrees), with evacuated tubes in snowy cold areas they can collect snow that never melts KILLING winter performance, whereas flat panels have sufficient heat loss out the glazing that snow rarely survives noon on the first sunny day. To ensure gravitational show shedding, set 'em up as latitude+15 (60degrees). This will maximize winter performance at the expense of summer, but that's not necessarily a bad thing- larger arrays need active heat-dumping in the summer if set up for maximal summertime gain.

Flat panels can often provide their own heat-dump- when the tank is at max temp, running the pumps at night lets them radiate to the cooler sky. That trick doesn't work with evacuated tubes though. If season overheating become a problem you can rotate individual tubes 90 degrees to take their solar gain down by half or more- just be sure to spin 'em back before winter sets in. :-)

I agree that evacuated tubes are both lower mass, and less of a sail than flat-panels. Any pole-mounted system needs to take this into account, and do the math (or have a pro engineer it for you.) Last thing you want is a heavy snow load and a Polar Express dropping the thing through your roof at the least-most convenient moment.

evacuated tubes are better

Not necessarily. They have drawbacks like snow and ice do not melt off them as fast as it does on a flat plate. This has been proven by the NREL people and my own experience as an installer.

I'm not sure which is better, but DEFINITELY take into account the thrust force involved if an ice storm turns your array into a big sail.

I just installed 40 tubes of the Narva evacuated tubes. These tubes pass water in and out of them, much like at flat plat collector. We finished the insullation of the piping yesterday. This made a big differense in system performance. I will be interested to see how well snow sticks to my system. It is mounted on my roof which is at a 45 degree angle.

http://isuglobal.com/docs/s-power_Collector_Brochure%5B1%5D.pdf

I am heating 2 120 gallion tanks of water for heat and hot water. So far the system has operated for 11 hours and the tanks are at 118 and 106 deg f.

Hello gobuck,

I would love to discuss your installation .... can you contact me directly at: enleclair @ sympatico .ca

Cheers!

Eric