Questions to Ask when buying a Solar Thermal Evacuated Tube System

This information was orginallly compiled for visitors at a recent home show and is designed for consumers comparing manufacturers of solar tube systems. Please contact us if you would like more information on industry standards and preferred methods/materials.

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1. Is this system SRCC & Hail rated (or TUV, SolarKeyMark)? This is necessary to receive incentives
2. Is the installer state certified? Also necessary if you intend to take advantage of government-sponsored incentives.
3. What is the frame made of?
4. How long should it last?
5. What is the rated wind load?
6. When attaching it to the roof:
   1. How many roof penetrations are necessary, what do you do to seal them?
   2. What types of bolts do you use? (stainless is best)
   3. Where on the roof will you place the collectors (does it leave room for future expansion or PV installation)?
7. How many tubes are you installing, how much space do they need?
8. Verify seasonal shading is not an issue from trees or roof lines.
9. Are the collectors located where snow blows and builds up?
10. Will snow slide down collector and build up at the bottom when it hits shingles?
11. What is the output per tube in Maine? Make sure you compare like months. Since all reputable systems do well in summer, use December, the most difficult month. This is especially important when using solar thermal for heating.
12. What type glass are your tubes made of? Will their performance derogate over time? Borosilicate looses 20% over 5 years, Soda/Lime is stable
13. How long is the warranty on the tubes, what does it cover?
14. What is the cost of a single tube (in case of damage) and what is necessary to change a broken tube?
15. How long has this model been sold/installed, is lifetime performance data available?
16. Does the tube have a hail rating certification?
17. What is the glass strength?
18. How long is the warranty on the tank?
19. What is it’s expected life?
20. What size storage tank are you installing?
21. What is the tank's heat loss per day?
22. Do the math: output x # of tubes, does the tank storage size make sense. If the tank is too big, the water does not get really hot.
23. Is the tank rated for the use?
24. What type of controller/Pump are you using?
25. How many zones can it handle (is expansion important)?
26. What is the warranty on the Pump/controllers?
27. What is the expected life?
28. What features does it have for monitoring/recording performance?
29. What size pipes are you using from the collector to the tank?
30. If the system is expanded, are the plumbing pipes still big enough?
31. What are the pipes made of?
32. How are the pipes insulated?
33. What will the pipe path to the tank be?
34. Will you use a heat-dump to handle excess heat, what will it be? Allowing the system to dry stagnate (vapor drawback) is not recommended by reputable manufactures and could void the warranty. Plus, excess heat causes the glycol to break down faster and become acidic forcing replacement sooner.
35. How often does the Glycol need to be changed?
36. What is the aprox. cost?
37. How does the owner know it is time to change it?
38. Do you install ball valves at key points to avoid impacting the entire system in case maintenance is necessary? Where/How many?
39. Do you warranty the plumbing lines and work, for how long?

We are always happy to answer questions. We understand that investing a large sum of money is a solar system is a major decision and is best made with good information. One piece of advice we can offer is to get a quote from at least 2 companies. Make sure you explain your needs to each in an even manor. When you get back each proposal ask lots of questions. Then, tell each about the other companies proposal and ask them to find the possible problems with it. That will help you develop a good list of questions to bring back to each vendor for clarification. And remember we have cold winters. Do not be mislead by statistics that are not accurate here in New England. Of course, if you have a seasonal house, you have more flexibility in this matter.

The SRCC is the US rating agency for Solar; they recognize TUV ratings. When comparing products, use rating for Maine, in December!

The TUV is the European agency. They do not recognize the SRCC since the SRCC approves products the TUV will not. www.US.TUV.com

SolarKeyMark

When comparing Flat plate collectors to Evacuated tubes make sure you understand the “Gross area mistake” that throws off the numbers from the SRCC. In brief, the SRCC uses gross collector area. With a flat panel this can accurately be stated as the sq ft panel size. On evacuated tubes you have collectors inside the tubes and space between each tube. You cannot take the sq ft area of the tube set up rack and say it is all “collector”. Much of it is air space. If you use the inflated “collector” area as part of the equation to calculate efficiency of collector per sq ft then you have completely bogus results.

Sadly, we have been to manufacture training classes for flat plates where even the trainers do not understand this issue. Evacuated tubes will always outperform flat plate collectors during cold winter days.