Not sure which model Gooserider has got but if it's a 65 or 165 it would definitely interfere.
Solar Panel Technology Comparisons
- Thread starter chem geek
- Start date
Well, some of the stuff I've seen on evac tubes vs. flat plate seemed to suggest that even though the tubes had higher efficiency in theory, the flat plates tended to come out ahead in the "real world" - it was actually a case of the tubes getting hurt by being TOO efficient! In essence a glazed flat plate does leak a certain amount of heat, but a tube doesn't. Thus if you get much snow or frost on the collectors overnight (which I suspect that we would) the plates melt it off and self clean almost as soon as the sun starts to hit them, probably before they'd even start really producing, and get to work very early in the day. The tubes take a lot longer to self clean, so they may work like gangbusters once they turn on, but often that doesn't happen until mid afternoon - not enough time for them to catch up with the flat panels that had been producing all morning.
As to the solar cover, I have a Polaris 380 (pressure side w/ booster pump) and as I recall the instructions when I put it in, Polaris said not to use a solar cover with it, and to remove any floating pool toys and such to keep them from getting tangled in the hose. I know the cleaner does bat our chlorine floater (I was using tabs - may keep doing so until they are used up) all over the pool. Since we leave the Polaris in the pool all the time, I haven't been willing to experiment with buying an expensive cover that we might not end up being able to use. (Not to mention the challenge of doing a cover with a pool shaped like ours.)
Gooserider
As to the solar cover, I have a Polaris 380 (pressure side w/ booster pump) and as I recall the instructions when I put it in, Polaris said not to use a solar cover with it, and to remove any floating pool toys and such to keep them from getting tangled in the hose. I know the cleaner does bat our chlorine floater (I was using tabs - may keep doing so until they are used up) all over the pool. Since we leave the Polaris in the pool all the time, I haven't been willing to experiment with buying an expensive cover that we might not end up being able to use. (Not to mention the challenge of doing a cover with a pool shaped like ours.)
Gooserider
- May 3, 2007
- 16,839
- Pool Size
- 20000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Hayward Aqua Rite (T-15)
If your interested in solar panel efficiency, check out this site:
Hot Water Ratings
Pool Ratings
Glass tubes tend to have a lower efficiency than the glass panels. However, this testing was done at high temperature so it might not be as relevant to winter time performance.
Hot Water Ratings
Pool Ratings
Glass tubes tend to have a lower efficiency than the glass panels. However, this testing was done at high temperature so it might not be as relevant to winter time performance.
This report [EDIT] (that link was broken -- use this link instead) [END-EDIT] talks about the effect you refer to where the evacuated tubes are "too good" so don't allow for faster melting of frost, hence reducing their efficiency. However, even ignoring that, you have to be careful about the efficiency claims with evacuated tubes since the quoted efficiency numbers are often quoted relative to the collector (black absorber) area inside the tube and not to the gross area of the installation that includes the non-collecting air space between the tubes and inside the tubes to the side of the collector. It is this gross area that is relevant since that is how much space it actually will take up on your roof and is what determines how many panels you need to achieve a certain rate of temperature rise. The charts I made in my post at the start of this thread are all relative to gross area.Gooserider said:
Richard
It's interesting to note that these reports show that the evacuated tube efficiencies are not as low as my table would imply. Either these manufacturers have higher efficiency tube designs (less gaps between the tubes) or the tubes are better at capturing sunlight throughout the day, possibly due to their curved reflective backs.mas985 said:
The best black plastic mat panels are around 1000-1060 BTU/sq.ft. and these are all for pools. For domestic hot water, the best flat glass enclosed panels were around 850-960 BTU/sq.ft. while the best evacuated tube panels were 650-740 BTU/sq.ft. This makes the best case relative efficiency to black plastic mat panels: 100% to 91% to 70%. My original table at the start of this thread has implied relative efficiencies of 100% to 93% to 51%. This discrepancy in the evacuated tube numbers is explained by my use of a Navitron brand rather than the most efficient evacuated tube such as from Sunda Solar here which has a gross area base efficiency of 54% compared to the Navitron of 41%. The relative efficiency for this better evacuated tube is 68% so more consistent.
Using the more efficient Sunda Solar as the evacuated tube example would change the table values in the 800 W/m2 case going from 54% to 42% while in the 300 W/m2 case it would go from 54% to 21%, so basically if you just add 13% to all values in the evacuated tube columns in my table, then you will get appropriate comparisons when using one of the best evacuated tube panels.
Richard
chem geek said:
That link is no good - gets me a "404" error... However I agree that you need to be careful comparing the different technologies... What was interesting was that the Florida gov't ratings site that was linked to earlier in the thread seemed to show the flat plates actually did better in terms of BTUs / sq ft / day.
Right now my plans are mostly all inside my head, but I'm thinking more or less in terms of doing a thermal storage tank in the basement with coils in it to be heated by a solar setup and a wood gasification boiler, and feeding DHW, radiant floor heating and the pool (and possibly adding a hot tub). Seems from everything I've been reading that this should be quite efficient and make optimal use of the available solar. It would also appear that the temperatures that most people run their thermal storage tanks at (as they discuss it in the "boiler room" area over on Hearth.com) is reasonably consistent with the glazed flat plate units.
Gooserider
- May 3, 2007
- 16,839
- Pool Size
- 20000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Hayward Aqua Rite (T-15)
Yes, but they were testing in what would be considered warm ambient temperatures. In colder weather, the evac tubes might actually perform better since they have some insulating qualities that are less likely to lose the heat .
mas985 said:
True, but this is what I was talking about earlier about the tubes being "too good" - they insulate so well that they don't self clear any snow or ice that gets on them, which effectively shuts them off for extended periods. OTOH that small percentage of re-radiated heat (which is supposedly not very much with the better built panels that use the selective coatings on the glass) is just enough to quickly burn off any snow or ice, getting the panel back into service quickly. Some setups will even have functions to automatically turn on the circs if the light is bright enough that the panel SHOULD be producing but isn't, just to start that burn-off process.
Gooserider
This link seems to work (for now). Sorry about the other link -- it used to work, but links go bad as people move things around on their servers or shut down their websites completely.
chem geek said:
No problem on the link, this kind of thing happens... At any rate, it is the same report I've seen and was talking about, seems pretty convincing to me, and the more I read it the worse the tubes look - it appears they lost in every month when looking at the energy collected per gross area. I don't think it's all that interesting if the tubes do slightly better on an aperture area basis, since I have to find room on the roof for the gross area, not just the aperture...
I look at the frost and snow concerns as significant issues, as we get frequent frosts in this area, not to mention our snows - We may only get a few "blowable" depth snows per year, but we get frequent "coating" storms, which is all you need to put a collector out of action till it clears.
Gooserider
I have an update to the efficiency comparison of different panel types. Actual panel efficiencies were measured for black flat mat panels for pool applications here and for flat glass-enclosed and evacuated tube panels for hot water here where the best black flat mat panels had around 1000-1060 BTU/sq.ft. while the best flat glass-enclosed panels were around 850-960 BTU/sq.ft. while the best evacuated tube panels were 650-740 BTU/sq.ft. This makes the best case relative efficiency to black plastic mat panels: 100% to 91% to 70%. My original table at the start of this thread has implied relative efficiencies of 100% to 93% to 51%. This difference is probably because the best evacuated tubes are better than the Navitron I used for the table. A high efficiency tube from Sunda Solar with 739 BTU/sq.ft. is described here with a gross area efficiency of around 54% (compared to 41% for the Navitron) for a relative efficiency of 68% which is much more consistent. The above links to BTU/sq.ft. data are with actual field measurements in strong Florida sun.
Using the more efficient Sunda Solar as the evacuated tube example would change my table values in the 800 W/m2 case going from 54% to 42% while in the 300 W/m2 case it would go from 54% to 21%, so basically if you just add 13% to all values in the evacuated tube columns in my table, then you will get appropriate comparisons when using one of the best evacuated tube panels. The main points in my charts that show how evacuated tubes get better when the temperature difference is larger, as with hot water heating and cold days, and also are better on cloudier days still applies as does the relative performance of the three panels.
One should also keep in mind that practical considerations may make a situation where the evacuated tubes should do better than flat glass-enclosed actually turn out to be worse as described in this report. The evacuated tube panels in this case are actually "too good" so they don't melt the frost/snow on the panels as quickly thus preventing as much heating as the flat glass-enclosed panel.
Richard
Using the more efficient Sunda Solar as the evacuated tube example would change my table values in the 800 W/m2 case going from 54% to 42% while in the 300 W/m2 case it would go from 54% to 21%, so basically if you just add 13% to all values in the evacuated tube columns in my table, then you will get appropriate comparisons when using one of the best evacuated tube panels. The main points in my charts that show how evacuated tubes get better when the temperature difference is larger, as with hot water heating and cold days, and also are better on cloudier days still applies as does the relative performance of the three panels.
One should also keep in mind that practical considerations may make a situation where the evacuated tubes should do better than flat glass-enclosed actually turn out to be worse as described in this report. The evacuated tube panels in this case are actually "too good" so they don't melt the frost/snow on the panels as quickly thus preventing as much heating as the flat glass-enclosed panel.
Richard
- Jul 2, 2008
- 37
Has anyone tried a homemade system? A few years back I came upon some irrigation pvc pipe and plumb it with a sump pump and garden hose. It worked really well on the flat roof that I had at the time. At my present house I want to try something similar with my pool pump and plumbed into my present system. :-D
czechscott, it is completely possible to make solar heating panels using simple parts from places like Home Depot. However, the resulting panels won't be nearly as efficient as the commercial panels. In the end, the commercial panels end up being less expensive when comparing systems that produce the same amount of heat, and the commercial panels will require less roof/ground space to lay out the panels.
Richard:
Knowing all you know about this technology, what would you use on your pool for solar heating? It can be hard up north in Canada where June and September get plenty of sun, but the ambient temperature is only around 75. Is it to much to wish for to get a pool above that with Solar Heating?
Also, being a skeptic, I am hard pressed to believe that some of these companies state a 70% to 90% reduction in electricity used for Domestic Hot Water. Do you believe that?
I currently have 3 Fafco (4 X 20) panels on my roof, facing south at an angle of 40 degree pitch. I have no problem during July and August at keeping the pool above 82. My Pool is 392 Sq Ft of surface area. What would you use in my situation, would you in fact put in a Solar Hot Water System, and then use it for pool in summer?
Richard
Knowing all you know about this technology, what would you use on your pool for solar heating? It can be hard up north in Canada where June and September get plenty of sun, but the ambient temperature is only around 75. Is it to much to wish for to get a pool above that with Solar Heating?
Also, being a skeptic, I am hard pressed to believe that some of these companies state a 70% to 90% reduction in electricity used for Domestic Hot Water. Do you believe that?
I currently have 3 Fafco (4 X 20) panels on my roof, facing south at an angle of 40 degree pitch. I have no problem during July and August at keeping the pool above 82. My Pool is 392 Sq Ft of surface area. What would you use in my situation, would you in fact put in a Solar Hot Water System, and then use it for pool in summer?
Richard
Pooladdict - If ALL I wanted to do was heat my pool, and especially if I didn't need to worry about freezing (i.e. I was either running a drainback setup, or was going to drain the panels in freezing weather) I'd go for the basic rubber mat style panels, low cost and do the job quite well.
However if I wanted to get DHW, and especially if I wanted to do home heating, I'd go for the flat glass panels, as I've stated. Obviously you will have the limitation that the further north you are, the less heat you will get in the winter, so the question of payback becomes an issue. Also because NO solar system is probably going to be able to supply 100% of your heating needs, you will still have to have an electric or dino-burner backup of some sort. Up to a point, each incremental increase in the size of the solar system will give a roughly corresponding decrease in the cost of running the backup, but once you reach that point, going beyond it gives a diminishing cost savings, so there is a definite need to do some serious number crunching on how much each incremental size increase will cost vs. the savings it will produce. You might also need to worry more about "tuning" options, such as doing seasonal adjustments of the panel angle to maximize performance - your 40* array is good for summer, but will suffer in the winter (The stuff I've read says the optimum no-adjust position is about equal to your latitude, if you do adjust, you should set for the solar angle at noon, which will mean steeper angles in the winter, and lower ones in the summer)
The claims of the DHW people need to be taken with a large grain of salt - a great deal of the benefits are going to depend on the details of your personal setup and your household's lifestyle choices - How long / often do you shower, do you do it in the evening when your tank is fully charged, or in the morning when things have cooled down so you might need some supplemental heat to bring things back up to temp? How big is your array? How big is your storage tank? and so on down the line... Obviously the company that wants your money is going to pick the best set of options, but they are probably telling the truth in that they have customers that DID save that much. (OTOH, I have seen people that reported their water bills went UP when folks didn't have to worry as much about running out of water so they showered longer...)
CZ - the stuff I've seen suggests that if you put enough effort into building a DIY system, you can get very close to the efficiency outputs of the commercial panels, but the more sophisticated your DIY setup gets, the more it costs, until you really aren't saving anything. In addition the better commercial panels will still do better between the manufacturer's ability to source materials that most of us can't get in home user quantities, and the ability to use manufacturing machines and techniques that aren't possible / cost effective for a home builder. That said, if you can come up with cheap (recycled?) materials, and are willing to give up some efficiency, you might well be able to make a quite workable pool heater. Where things get more challenging is when you are looking at the higher temperatures and efficiencies needed by a DHW or home heating system...
Gooserider
However if I wanted to get DHW, and especially if I wanted to do home heating, I'd go for the flat glass panels, as I've stated. Obviously you will have the limitation that the further north you are, the less heat you will get in the winter, so the question of payback becomes an issue. Also because NO solar system is probably going to be able to supply 100% of your heating needs, you will still have to have an electric or dino-burner backup of some sort. Up to a point, each incremental increase in the size of the solar system will give a roughly corresponding decrease in the cost of running the backup, but once you reach that point, going beyond it gives a diminishing cost savings, so there is a definite need to do some serious number crunching on how much each incremental size increase will cost vs. the savings it will produce. You might also need to worry more about "tuning" options, such as doing seasonal adjustments of the panel angle to maximize performance - your 40* array is good for summer, but will suffer in the winter (The stuff I've read says the optimum no-adjust position is about equal to your latitude, if you do adjust, you should set for the solar angle at noon, which will mean steeper angles in the winter, and lower ones in the summer)
The claims of the DHW people need to be taken with a large grain of salt - a great deal of the benefits are going to depend on the details of your personal setup and your household's lifestyle choices - How long / often do you shower, do you do it in the evening when your tank is fully charged, or in the morning when things have cooled down so you might need some supplemental heat to bring things back up to temp? How big is your array? How big is your storage tank? and so on down the line... Obviously the company that wants your money is going to pick the best set of options, but they are probably telling the truth in that they have customers that DID save that much. (OTOH, I have seen people that reported their water bills went UP when folks didn't have to worry as much about running out of water so they showered longer...)
CZ - the stuff I've seen suggests that if you put enough effort into building a DIY system, you can get very close to the efficiency outputs of the commercial panels, but the more sophisticated your DIY setup gets, the more it costs, until you really aren't saving anything. In addition the better commercial panels will still do better between the manufacturer's ability to source materials that most of us can't get in home user quantities, and the ability to use manufacturing machines and techniques that aren't possible / cost effective for a home builder. That said, if you can come up with cheap (recycled?) materials, and are willing to give up some efficiency, you might well be able to make a quite workable pool heater. Where things get more challenging is when you are looking at the higher temperatures and efficiencies needed by a DHW or home heating system...
Gooserider
I agree with Gooserider. Nevertheless, since we use our pool for swim therapy and keep it warm at around 88F, if I had to do things over and money were no object then I would have purchased glazed (flat glass) panels (at triple the price) so that I would have more heating in the spring and fall and not need to use as much gas assist. If possible, I would have tried to use a brand that allowed pool water without using a heat exchanger. I'm not sure why most do not allow that since the copper they use shouldn't be any different than in household piping and that used to tolerate 1 ppm FC with no CYA when the water was chlorinated (now, monochloramine is used instead). Our municipal water has 300-500 ppm phosphates as a corrosion inhibitor so I'd figure that the panels should be able to tolerate pool water.
In your situation, the easiest and least expensive thing to do would be to increase the number of panels for your pool. Right now, you've got 61% of your pool's surface area. For greater heating, you'd want 80% or more panel area and you'd want a pool cover that was very insulating -- ideally, a bubble-type cover that passes infrared and visible light through. This assumes that you've got direct sunlight in the spring and fall. However, if your days are mostly cloudy or there is wind and cool air, then the glazed (flat glass) panels would work better (at higher cost). Just remember that on cloudy days with flat black mat panels, you will lose heat and the temperature of the pool will drop making it harder to catch up when the sun does come out.
As Gooserider noted, the domestic hot water system isn't going to save you that much energy in the winter compared to the summer (the maximum energy with the sun so low and the days so short is simply less during the winter) so trying to share the two uses (i.e. domestic hot water vs. pool) is questionable. Also, domestic hot water typically uses a much smaller number of panels since the volume of water is much smaller. I suppose that during the winter, using many panels would boost the heating so perhaps it would be of some benefit if you weren't using the pool anyway. That is, if you were to get the glazed panels for more efficient pool heating, then certainly they could be switched to be used for domestic hot water during the winter. I think the economics, however, would get justified by the pool heating, not by the domestic hot water heating. You'd have to compare this economics against something like a heat pump that is more energy and cost efficient compared to gas heat (though takes far longer to heat up quickly if that becomes necessary).
Our pool is around 500 square feet in surface area and we have 10 7.5'x4' panels (300 square feet or 60%) and 2 9.5'x4' panels (76 square feet or 15%) though these latter panels only get partial sun most of the time (due to a Sycamore tree). We have an opaque electric pool cover so don't get heating directly into the pool during the day and we lose about twice as much heat at night compared to a better-insulating bubble-type cover. During June, July and August, we are able to heat the pool to 88F with solar alone except for a few days in June and August that get cloudy. September needs more gas assist. May and October require much more gas heating to get to 88F, though if we just needed 80-82F then solar alone would probably work. Our average day/night temps for each month are as follows:
Apr 68º/45º 5.91 kWh/m2/d
May 74º/48º 6.77 kWh/m2/d
Jun 78º/52º 6.95 kWh/m2/d
Jul 81º/54º 6.13 kWh/m2/d
Aug 81º/54º 5.49 kWh/m2/d
Sep 80º/54º 4.85 kWh/m2/d
Oct 75º/50º 3.77 kWh/m2/d
Nov 64º/46º 2.71 kWh/m2/d
This link will tell you the solar insolation at the Earth's surface for any location and time of year. [EDIT] (This link gives a more practical solar insolation map for the U.S. using different kinds of tilted and tracking panels and using real-life data accounting for weather and minimum, average and maximum for each month.) [END-EDIT] This is the best case amount of solar energy since clouds and weather will significantly lower this amount. I show above the daily solar insolation for each month (I'm at a 38 degree North latitude). These are for a flat surface while normally you angle your panels towards the south (if in the northern hemisphere) for more heating during the summer so actual solar insolation is a little higher than shown above. For Canada at around 50 degree North latitude, the numbers are somewhat lower.
Richard
In your situation, the easiest and least expensive thing to do would be to increase the number of panels for your pool. Right now, you've got 61% of your pool's surface area. For greater heating, you'd want 80% or more panel area and you'd want a pool cover that was very insulating -- ideally, a bubble-type cover that passes infrared and visible light through. This assumes that you've got direct sunlight in the spring and fall. However, if your days are mostly cloudy or there is wind and cool air, then the glazed (flat glass) panels would work better (at higher cost). Just remember that on cloudy days with flat black mat panels, you will lose heat and the temperature of the pool will drop making it harder to catch up when the sun does come out.
As Gooserider noted, the domestic hot water system isn't going to save you that much energy in the winter compared to the summer (the maximum energy with the sun so low and the days so short is simply less during the winter) so trying to share the two uses (i.e. domestic hot water vs. pool) is questionable. Also, domestic hot water typically uses a much smaller number of panels since the volume of water is much smaller. I suppose that during the winter, using many panels would boost the heating so perhaps it would be of some benefit if you weren't using the pool anyway. That is, if you were to get the glazed panels for more efficient pool heating, then certainly they could be switched to be used for domestic hot water during the winter. I think the economics, however, would get justified by the pool heating, not by the domestic hot water heating. You'd have to compare this economics against something like a heat pump that is more energy and cost efficient compared to gas heat (though takes far longer to heat up quickly if that becomes necessary).
Our pool is around 500 square feet in surface area and we have 10 7.5'x4' panels (300 square feet or 60%) and 2 9.5'x4' panels (76 square feet or 15%) though these latter panels only get partial sun most of the time (due to a Sycamore tree). We have an opaque electric pool cover so don't get heating directly into the pool during the day and we lose about twice as much heat at night compared to a better-insulating bubble-type cover. During June, July and August, we are able to heat the pool to 88F with solar alone except for a few days in June and August that get cloudy. September needs more gas assist. May and October require much more gas heating to get to 88F, though if we just needed 80-82F then solar alone would probably work. Our average day/night temps for each month are as follows:
Apr 68º/45º 5.91 kWh/m2/d
May 74º/48º 6.77 kWh/m2/d
Jun 78º/52º 6.95 kWh/m2/d
Jul 81º/54º 6.13 kWh/m2/d
Aug 81º/54º 5.49 kWh/m2/d
Sep 80º/54º 4.85 kWh/m2/d
Oct 75º/50º 3.77 kWh/m2/d
Nov 64º/46º 2.71 kWh/m2/d
This link will tell you the solar insolation at the Earth's surface for any location and time of year. [EDIT] (This link gives a more practical solar insolation map for the U.S. using different kinds of tilted and tracking panels and using real-life data accounting for weather and minimum, average and maximum for each month.) [END-EDIT] This is the best case amount of solar energy since clouds and weather will significantly lower this amount. I show above the daily solar insolation for each month (I'm at a 38 degree North latitude). These are for a flat surface while normally you angle your panels towards the south (if in the northern hemisphere) for more heating during the summer so actual solar insolation is a little higher than shown above. For Canada at around 50 degree North latitude, the numbers are somewhat lower.
Richard
launboy
0
Anyone ever thought of making their own glazed panels out of flat black pool heater panels? I've been considering trying it out this fall. During the summer the normal panels do fin for our pool, and hopefully will work for the hottub too.
I'm more worried about the fall and winter. I don't think the panels will do much during our cold snowy Wis. winters, but during the spring and fall I think a home-made box around a mat would help quite a bit. What do you all think?
Thanks,
Adam
I'm more worried about the fall and winter. I don't think the panels will do much during our cold snowy Wis. winters, but during the spring and fall I think a home-made box around a mat would help quite a bit. What do you all think?
Thanks,
Adam
launboy said:
It might work, but I'd be worried about what the peak temperatures might get to - the mats are designed for a fairly low operating temperature, and even if you stagnate them, are going to radiate any excess heat picked up if they are used as designed. If you enclose them, then you prevent them from radiating excess heat, and greatly raise their operating temperature - this may exceed their safe operating temperature, especially if you stagnate them for any reason.
IIRC the mats are generally intended to work around 100*F, with a maximum stagnation temp around 130*F or so. Glazed plates can run in the 120-140*F range, and can easily get over boiling if stagnated, which is higher than most mat material can take as I understand it. For instance EPDM is usually only good to about 180*F or so...
There is a reason why most glazed panels are made with metalic guts, and are normally installed with copper plumbing rather than PEX or other plastics.
Gooserider
launboy
0
Hmm.. very interesting point. I never even thought of that. Not sure if it will really be an issue for me though. This past summer I only turned the panels off once while the sun was out. The pool hit like 94* because I wasn't home to shut them off earlier.
This summer that will (most likely) never happen. This is because instead of just heating the pool to 86-88*, I will also be (attempting) to heat the spa to 102* ish. Spa will take first priority and I will switch to pool when it hits temp. Still figuring out how I'm going to automate that part though.
Thanks,
Adam
This summer that will (most likely) never happen. This is because instead of just heating the pool to 86-88*, I will also be (attempting) to heat the spa to 102* ish. Spa will take first priority and I will switch to pool when it hits temp. Still figuring out how I'm going to automate that part though.
Thanks,
Adam