Flat solar thermal panels or evacuated tube?

[Thermal John]

The choice really depends on location. Flat Plates will generally perform better during optimal sunny conditions. The vaccuum that helps an evacuated tubes performance in cold conditions hampers its performance a bit in warm conditions as it cant take adavantage of ambient air temperatures. if you live in a cloudy or windy climate the tubes will be a good choice as long as you dont have extended snowy conditions (no snowmelt ability) otherwise you need a 60 degree tilt to shed snow effectively.

There are a lot of evacuated tubes out there that are closing in on flat plate prices so cost isn't really as much of a factor these days. Stagnation can be an issue, if you are installing a closed loop antifreeze system, but there are glycerin based fluids that are both non toxic and extremely durable with boiling points of 460F or so. This at least helps prevent vapor lock if you lose power to your pump. They also wont turn acidic like propylene glycol can when stressed over and over again (around 260F).

I'm based in the Pacific NW and we can see decent performance for DHW but space heating just doesn't pencil out for decent financial payback, because of our 226 fully cloudy days a year where I'm at. For space heating contribution Evacuated tubes probably make more sense but you still need good winter sunshine to make an actual contribution without oversizing your system to greatly.

I discourage people to go solely by efficiency curves on collectors which can be misleading, as they dont acuratelty represent other factors such as the incidence angle modifier. An identically sized collector with a higher efficiency rating can actually be producing less heat than a lower efficiency collector with a differently shaped absorber surface. You should really check SRCC charts to see what the collectors produce BTU wise rather than their efficiency %.

Keep researching as this isn't a decision you want to make hastily.

John

[russ]

Hi John - Welcome to Solar Panel Talk!

Move east of the Cascades - then no problem with sun. Can be a bit cooler though.

Russ

[Thermal John]

Thanks Russ, good to be here!

I must admit I'm pretty jealous of the sun hours over there. Surprisingly we don't see all that many installers on that side of the mountains, cheap electricity seems to limit interest all over the state no matter how much sun.

John

[russ]

Hi John, I was born in Seattle and grew up in Central OR - some beautiful country in the NW!

The cheap hydro power does tend to make solar less attractive. And, as you pointed out, the abundant cloudy days on the coastal side of the mountains.

I remember that when I lived in Portland we were rather surprised to see the sun between mid December and mid June - a bit of a stretch but not much.

If you ski though - wonderful - you are about the first in the country to hit the slopes.

Russ

[Stone Liu]

We suggest flat panel thermal collectors, because 80% of this style are widely used around the world, except China, in China, 80% use evacuated tube.
We are Solar products manufacturer, Product Range:

Solar Photo-thermal: Solar Flat Panel Thermal Collectors, Air-source Heat Pumps, Solar Water Heating Systems.

Solar Photovoltaic: Solar Panels (Mono/Poly/Thin film), PV Roof Systems, Solar Street Light, Smart Grid (On/Off) Power Generation Plant, Building Integrated/Attached Photovoltaic (BIPV/BAPV), Solar House.

Regards.
Stone Liu

[Stone Liu]

There's a lot of good information contained in this thread. I work for a manufacture where we distribute both flat plates and evacuated tubes.

It all comes down to value - which system produces the most in your area for what you spend. However, there are a few general pros and cons for each technology to consider.

Evacuated tubes produce more on cloudy / overcast days than flat plates. They also produce higher internal temperatures (our manifolds generally stay around 160-170F during the day), and are easier to maintain.

Hope this information helps!

Thanks for your detailed information. I agree with your opinion.
Flat panel collectors are widely used in project than evacuated tubes.

[roscho04]

Just because 80% of flat panel are used around the world is not a good reason to use flat panel.
That would be like you telling to vote for someone because 80% of the people are going to vote for some one.I am not saying that flat panel are no good. sorry had to jump in.

[Stone Liu]

Just because 80% of flat panel are used around the world is not a good reason to use flat panel.
That would be like you telling to vote for someone because 80% of the people are going to vote for some one.I am not saying that flat panel are no good. sorry had to jump in.

Hi, glad to talk to you, how about your suggestion of using flat panel collector or using evacuated tube?
I promote flat panel collector mainly reason is besause of there is no risk of vacuum tubes fried and easily breakable.
I am looking forward to hearing from you.
regards.
Stone

[roscho04]

Hello Stone hope all is well:
I really don

[russ]

Like Roscho04 says - depends on your location and requirements.

Both types of collectors can collect similar amounts of heat - flat plates are better for low temperature applications (such as household use hot water) in temperate climates while evacuated tube types do better when higher temperature water is required, in cloudy situations and during the winter in cold areas.

I have the flat plate type - mild climate here. A neighbor has a big bank of evacuated tube types and keeps a good portion covered all summer.

Roscho04 is just the reverse of my situation - for his location the evacuated tube type is better.

[Naptown]

[QUOTE=roscho04;33026]Hello Stone hope all is well:
I really don

[Peter69_56]

Hot tubes

I don't think there is really a right answer because there are different factors.

1. tubes are more efficient, but cost a lot more. The lower efficiency of panels isn't necessarily a problem, since the sun is effectively unlimited, so you can put up more panels (unless you have limited space). So you need to know the specific costs of each compared to the amount of water they heat; this varies with suppliers, but in many cases, tubes will be cheaper.

2. how robust they are. Tubes can be a little fragile, where as you can usually jump on a panel without damaging it. So are you likely to get anyone throwing rocks?

3. how accessible they are; tubes can get extremely hot. You don't want children or animals touching them.

This is not correct, unless the vacuum has been lost in the tubes. If the tubes are working they are like a thermos, hot inside and cool outside. With the vacuum lost they can then be hot on the outside and will not function as designed then. If you have hot tubes, have them replaced.

[Peter69_56]

Array tilt

re evacuated tubes and radiant floor and my prior post. my 75 tube array shares a boiler loop with a backup boiler. on this loop is a radiant loop for 450 sq ft, a heat exchanger for a 2700 gallon endless pool (indoors) and heat exchanger for dhw. the tubes run during the day. the boiler runs after the sun sets to catch up if there is a need. I only let the pool take boiler heat for an hour max via a wiring setup and relay i have with the pool circ pump.

the boiler turns off at 8am and cools to prevent thermal shock from the tubes that start circulating about 10 am this time of year.

the solar gain(south facing, mostly glass) in this room along with the floor heat keep this room at 66. i have turned off the boiler on a really cold night (-20) to see what happened and the room temp fell to 59 so the floor holds alot of heat .(The floor has a 2" "mudpack" base under ceramic tile.)

i am running glycol as this is a closed system, not a drainback.

once the loop is warmed, even now when the sun is low the panel loop will continuously run about 120-125, and heats the pool and the floor as long as they are calling for heat.

although i have run the array at 170, it does not run that hot continuously except in the long days of the summer. I find that i can harvest the most heat running it with a differential setpoint controller set at 135/115.

i am still working on the dhw as i have a standalone hw heater for now. it has been problematic getting the aquastat to call correctly as there is no port for it on the conventional tanks. this may have to wait for the how water heater to be replaced.

finally, i have my array at 70 degrees to maximize the low winter sun. the array runs less efficiently in the summer. I rarely dump heat even in the summer with this setup.

What is your latitude? I am at 38 degrees 08 minutes South (Melbourne Australia), and am considering tilting my array to 55 degrees for more winter bias and less summer heating so I have more overall heating but still have unboosted hot water from spring to autumn.

[Peter69_56]

Hotter Water Not Total Heat

Perfect Solution Mountain!

Your temperature loss problem can be solved by insulation.

The quantity of water you need to recirculate you are not going to get from solar panels unless you have a lot of them.

Vacuum tube only has the capability to produce hotter water - not more total heat. Your location - winter time you are never going to get 200 liters per panel per day from solar panels.

I am not sure what you are saying here. Surley if one adds more tubes the temperature will rise, and if one then puts more tubes in parrallel, say 3 parallel banks of 30, then one will have both heat and temperaure. In series for temperature increase, and parallel for volume of heat?

[Naptown]

Just had an issue today.A competitor called with-an ET problem. Seems they have a 120Gallon Rheem tank with wraparound heat exchanger. 50 tubes. Tank temp 110 F manifold temp 250 F What do you think is wrong? i know the answer but throwing it out for comment. We are at 39 north latitude.