EcoRenovator  

Go Back   EcoRenovator > Improvements > Solar Heating
Advanced Search
 


Blog 60+ Home Energy Saving Tips Recent Posts Search Today's Posts Mark Forums Read


Reply
 
Thread Tools Display Modes
Old 06-14-14, 08:48 AM   #1
osolemio
Hong Kong
 
Join Date: May 2010
Location: Hong Kong
Posts: 102
Thanks: 15
Thanked 17 Times in 13 Posts
Default Best fluid for solar panel

Working on my project (still), now getting closer to getting the solar panels.

As they are focused and user higher than normal temperatures, temperatures could potentially reach 200 C (about 400 F) in worst case scenario. In normal operations, they shouldn't, but in case they do, what fluid is better for the purpose?

Also, in the winter, temperatures could reach down (rarely) to -30 C (about -22 F).

I realise there are many other parameters to consider, but any suggestions? I heard mention of some kind of spirit which is even less dangerous to the environment than glycol.

Most of the system is water based anyway, it is only between the solar panels and down to two heat exchangers, where the anti-freeze and above-boiling scenarios could exist.

Thank you

__________________
Space heating/cooling and water heating by solar, Annual Geo Solar, drainwater heat recovery, Solar PV (to grid), rainwater recovery and more ...
Installing all this in a house from 1980, Copenhagen, Denmark. Living in Hong Kong. Main goal: Developing "Diffuse Light Concentration" technology for solar thermal.
osolemio is offline   Reply With Quote
Old 06-14-14, 09:31 AM   #2
stevehull
Steve Hull
 
Join Date: Dec 2012
Location: hilly, tree covered Arcadia, OK USA
Posts: 829
Thanks: 241
Thanked 165 Times in 123 Posts
Default

Remember that the higher the temperature of the circulating fluid, the lower the efficiency of the collector. This is not trivial.

The efficiency drops rapidly as collector temperatures go over 100 C (212 F). The lower the collector temp, the higher the collector efficiency and the fewer number of panels need to be installed.

This is why I advocate "drain back" collectors. Water (cheap) can be used as a collector fluid and problems with heat exchanger corrosion (and subsequent introduction of toxic materials) become moot.

Drain back collectors are one of the simplest type of collector, yet few consider their utility. They are also the longest lasting of collectors with some in Israel lasting more than 50 years! Those areas have cold winters and hot summers.

Drain back only pump when the collector temps will support water fluid movement; easy to do.

So my suggestion is - just water!

Alcohol based mixtures are my second choice as gycols tend to gum up at high temperatures.


Steve
__________________
consulting on geothermal heating/cooling & rational energy use since 1990
stevehull is offline   Reply With Quote
Old 06-15-14, 01:36 AM   #3
AC_Hacker
Supreme EcoRenovator
 
AC_Hacker's Avatar
 
Join Date: Mar 2009
Location: Portland, OR
Posts: 4,002
Thanks: 303
Thanked 703 Times in 526 Posts
Default

Quote:
Originally Posted by stevehull View Post
...The efficiency drops rapidly as collector temperatures go over 100 C (212 F). The lower the collector temp, the higher the collector efficiency and the fewer number of panels need to be installed...
Steve, this is the perfect place for a diagram of what you are talking about.

Surely, as a consultant in the energy field, you could find a diagram to make your point clear.

Are you going to leave it to us amateurs to explain things properly?

-AC
__________________
I'm not an HVAC technician. In fact, I'm barely even a hacker...
AC_Hacker is offline   Reply With Quote
Old 06-15-14, 03:27 AM   #4
osolemio
Hong Kong
 
Join Date: May 2010
Location: Hong Kong
Posts: 102
Thanks: 15
Thanked 17 Times in 13 Posts
Default

Thank you for your fast replies!

I am aware of the efficiency curve, and indeed, I intend to keep these panels (and the fluid), really cool. And I can do so, as I have extensive heat storage facilities, over 1500 kWh of annual heat storage, as well as over 1000 USG of water storage, and other medium term heat storage possibilities.

The thermal peak power is around 10kW, although I might be able to tweak it even higher, given my extensive cold storage (into the ground).

The panels aren't suitable for drainback, as the way they are designed one cannot be assured they drain properly. I am stuck with some kind of anti-freeze, possibly IPA spirit or similar, trying not to have to use glycol for various reasons.

The curcuit for solar panels will be separate from all the other heat storage, which will all be water based, so the volume of the anti-freeze liquid isn't too much (compared to the 1000+ USG for the rest of the system).
__________________
Space heating/cooling and water heating by solar, Annual Geo Solar, drainwater heat recovery, Solar PV (to grid), rainwater recovery and more ...
Installing all this in a house from 1980, Copenhagen, Denmark. Living in Hong Kong. Main goal: Developing "Diffuse Light Concentration" technology for solar thermal.
osolemio is offline   Reply With Quote
Old 06-15-14, 02:46 PM   #5
greif
a van down by the river
 
Join Date: Jun 2011
Location: Kaukauna,WI
Posts: 108
Thanks: 6
Thanked 5 Times in 5 Posts
Default

It gets that cold in hong Kong?
__________________
Gary R

“If you want total security, go to prison. There you're fed, clothed, given medical care and so on. The only thing lacking... is freedom. ” ― Dwight D. Eisenhower
greif is offline   Reply With Quote
Old 06-15-14, 04:45 PM   #6
stevehull
Steve Hull
 
Join Date: Dec 2012
Location: hilly, tree covered Arcadia, OK USA
Posts: 829
Thanks: 241
Thanked 165 Times in 123 Posts
Default

Quote:
Originally Posted by AC_Hacker View Post
Steve, this is the perfect place for a diagram of what you are talking about.

Surely, as a consultant in the energy field, you could find a diagram to make your point clear.

Are you going to leave it to us amateurs to explain things properly?

-AC
AC - feel free to add a diagram. I welcome others that can put into pictures that which I write of.


Steve
__________________
consulting on geothermal heating/cooling & rational energy use since 1990
stevehull is offline   Reply With Quote
Old 06-15-14, 10:29 PM   #7
jeff5may
Supreme EcoRenovator
 
Join Date: Jan 2010
Location: elizabethtown, ky, USA
Posts: 2,353
Thanks: 369
Thanked 593 Times in 496 Posts
Send a message via Yahoo to jeff5may
Default

If your solar collectors are expected to reach 200degC, you had better deal with the possibility of steam generation in your design. Especially if the collector flow may stagnate (purposely or accidentally) during full sun exposure. One high pressure event is all it takes to destroy lots of work.

Actually, a concentrated solar system using alcohol as antifreeze would have a LOWER boiling point than water alone. Like around 80-90 degC, depending on the strength of alcohol. So what you are proposing here is a high-temperature solar still. If designed properly, your setup might not even need much of a pump at high temperatures. Just design your heat exchanger to also function as a condenser.

Last edited by jeff5may; 06-16-14 at 05:05 AM.. Reason: info
jeff5may is offline   Reply With Quote
Old 06-16-14, 10:28 AM   #8
osolemio
Hong Kong
 
Join Date: May 2010
Location: Hong Kong
Posts: 102
Thanks: 15
Thanked 17 Times in 13 Posts
Default

The solar panels are not expected to reach 200 C, on the contrary, they should ideally be kept at 75 C or lower.

In case there is a fault in the thermal transfer system, or anything else that causes the temperature to runaway, the system should survive without substantial damage.

The panels themselves can sustain the 200 C stagnation temperature, although the PV part of them (PV-T focused panels) will degrade faster, and yield less, the higher the temperature is.

It is an experiment into ways of dealing with solar which is a combination of existing and new technologies. Being an experiment, it must be protected against unforeseen circumstances, whether that be freezing, boiling, overpressure and so on.

Since I cannot use the drain back principle, due to the design of the heat absorbers, I need to find the optimum liquid which ideally has a freezing point below -30C, high boiling point (ideally 200 C or more), doesn't gel, doesn't cost a fortune, isn't toxic and doesn't evaporate. I will have to look at characteristics of specific heat capacity vs pump power required as well, though I realise I cannot get everything but have to compromise.

I wasn't sufficiently specific in the first post, sorry about that, but I hope you understand the requirements now.

The project is located in Scandinavia. Had it been in Hong Kong, I wouldn't have had to care about freezing, on the other hand, I wouldn't have a high heating requirement either.
__________________
Space heating/cooling and water heating by solar, Annual Geo Solar, drainwater heat recovery, Solar PV (to grid), rainwater recovery and more ...
Installing all this in a house from 1980, Copenhagen, Denmark. Living in Hong Kong. Main goal: Developing "Diffuse Light Concentration" technology for solar thermal.
osolemio is offline   Reply With Quote
Old 06-16-14, 08:23 PM   #9
jeff5may
Supreme EcoRenovator
 
Join Date: Jan 2010
Location: elizabethtown, ky, USA
Posts: 2,353
Thanks: 369
Thanked 593 Times in 496 Posts
Send a message via Yahoo to jeff5may
Default

Those are some pretty stiff specs. What you are talking about here is hydraulic oil or brake fluid. Neither of which make extremely efficient heat transfer fluids.

By the way, here's a chart of what Steve said:

Last edited by jeff5may; 06-22-14 at 12:23 AM.. Reason: info
jeff5may is offline   Reply With Quote
Old 06-20-14, 04:39 AM   #10
osolemio
Hong Kong
 
Join Date: May 2010
Location: Hong Kong
Posts: 102
Thanks: 15
Thanked 17 Times in 13 Posts
Default

Quote:
Originally Posted by jeff5may View Post
Those are some pretty stiff specs. What you are talking about here is hydraulic oil or brake fluid. Neither of which make extremely efficient heat transfer fluids.
How about oils like this one?

http://s02.static-shell.com/content/...ansfer-oil.pdf

It seems to be made for the purpose, what's the downside? This would be a good "Checklist" for what other properties to look for, in a solar panel fluid: Heat Transfer Fluids for Solar Water Heating Systems | Department of Energy

__________________
Space heating/cooling and water heating by solar, Annual Geo Solar, drainwater heat recovery, Solar PV (to grid), rainwater recovery and more ...
Installing all this in a house from 1980, Copenhagen, Denmark. Living in Hong Kong. Main goal: Developing "Diffuse Light Concentration" technology for solar thermal.
osolemio is offline   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 02:55 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2020, vBulletin Solutions Inc.
Ad Management by RedTyger
Inactive Reminders By Icora Web Design