spontaniously built solar panel

[mikey ny]

hello everyone,

    I just removed a 4 ft. by 4 ft. 6 inch picture, vintage 1960"s Anderson window co. It is double pane, no low e glass, no argon, wood frame, a bit heavy but clean and unbroken. This will be my first attempt at building a solar panel to heat water for heat or hot water. I have 4 domestic hw coils from some old salvaged boilers that i straightened out, swedged the ends to recieve half inch fittings and connected together. I have about 100 ft of copper coils with small finns on them. tommorrow I will build a wood box around the window, line the bottom with 2 inches of styrofoam insulation with black aluminum over it and install the pipe coils over it in a circulat pattern. I will install the picture window over it and pipe it to either a radiator or a hot water heater to preheat the water. Believe me, it ain't easy to straighten out domestic hw coils, a pair of gloves and some patience and a little profanity works pretty well. I am pretty sure it will make some hot water for something. I will follow up in the near future with a progress report.

            My goal is to make some hot water for something without cutting splittng and burning woood, even it is just for the fall and spring. this year it has gotten to the point to where we are trying to be more conservative with our wood pile since we have thrown our natural gas boiler into the scrap pile since it may be worth more at the scap yard than it is in the basement. We cut some tree's down to allow for more sun onthe south side and we are diving into the solar world of free heat. I hope it works.

                                                            Mr. MIKEY

[ghurd]

Mr. Mikey

Look into what high-E means.

The sun power isn't really getting through that well.

[MountainMan]

This thread got me curious, so I just did some micro-research on "low-e" glass.

It seems there are different kinds of energy efficient glass for different climates, and unfortunately the marketing people who advertise the stuff didn't bother to learn what "low-e" means before turning "low-e" into a buz word for "energy efficient".  The smart thing to do would be to label these types of glass as either "low solor loss" or "low solar gain" glass.

It seems to boil down to two different transmissivity percentages, one for visible light, and another for infrared light (heat).  When the sun shines in the window, most of the heat it brings is from absorption of visible spectrum light.  This heats up the room, and the heat then tries to radiate back out through the windows as IR.

Energy efficient glass for northern climes was first to show up on the market, and its "low-e" is in the sense that it has "normal" transmissivity to visible light, but low transmissivity to IR light.  The sun shines in and warms up the room, and the glass then blocks a decent amount of the IR light that would otherwise leak out through the windows.  This is high solar gain, low solar loss glass.

For southern climates where energy efficiency means blocking the solar gain, there is "low e glass" that blocks significantly more of the visible light than normal glass does.  This reduces the amount of solar gain through the windows.  It also tends to have a low IR transmissivity, thus blocking the IR that is bouncing off of the ground and other surfaces outside the house.  This glass looks slightly gray to the naked eye.

So, it would seem that for a solar water heating project, the best glass to have would be "northern climate low-e glass".  Next in line would be normal glass, and worst for this project would be "southern climate low-e glass", as it is specifically designed to block the stuff you're trying to soak up.

jp

[mikey ny]

excellant info,

        That is great info Mountainman. Since i have regular glass it will work pretty good. I dont know what effect the double pane will have on the project though. I am thinking it might help to keep the heat in because of the air gap between the panes. In the future i can keep an eye out for low-e glass, for some reason i thought it would be bad to use low e but now I know it is good.

                                                         Mike

[hotwired]

Am also building a solar heat panel 4by 8 ft i would like to find out from members what would be the best distance from the glass to the back of panel for best results also i have 1/8 1/4 1/2 thickness glass which is best any other information would be appreciated. Thanks.

[mikey ny]

almost done,

      For my solar panel I ended up useing EPDM rubber left over from a rubber roofing job i just finished. I lined the wood box with faom insulation on the bottom and the sides, then laid in the EPDM .060 rubber.(it is a bit thicker than bycicle tube rubber. I ran about 50 ft. of the hot water coil around in a circular pattern over the rubber. Then i took 3 inch strips of rubber and glued it directly over the pipe and adhered it to the rubber on the bottom. The pipe is now completely covered and attached to the rubber base sheet. Next I folded over the other half of the rubber over the pipe and glued to the rubber where i could , making a sandwitch. The 50 ft of pipe holds just under a half gallon of water ( not very much). In direct sun it makes hot water in a few minutes. I figure if I control a pump with a snap disc at 110 minus 20 it will have to cycle every 6 minutes to make 40 gal in 8 hrs. I have not yet had time to test this cycle theory, but it seems like it would work if the sun shines. The next panel i build i will use black onx pipe from in floor radiant heat systems in place of the copper coils and i could easily get 100 or more feet of pipe into the present 5 by 5 ft box and make twice as much hot water much faster. The only problem is i would have to pay for the pipe.

[MountainMan]

1. /8 inch too thin, likely to get busted by small hail.  Remember, it won't be verticle like a normal window.
   
1. /2 inch way too heavy to work with and will block a little bit more light than the 1/4 inch.
   
   

I would say Goldilocks glass is probably 1/4 inch in this case.  Just an opinion.

jp

[MountainMan]

Sounds like you're well on your way.

For a control system, what about doing it the reverse of what you've described.  Max use of the sun would be to run the pump continuously while the sun is out.  Maybe one of those cheap 24 hour timers for starters, and then a safety shutoff if the water in the tank gets to max safe temperature for the users of the hot water - perhaps 110 degrees F. (tank temp, not "output of the black hose" temp).

I suggest this simply because your method would be assuming that your tank is 100% perfectly insulated, and the water stays at the temp you heat it to.  I think your method would result in wasted solar power and luke warm water by dinner time.  The "continuous run" method would also allow for water use during the day with max reheating via solar.

If you hook up the pump as a simple recirculating "take it out of the hot side and push it back into the cold side", then you could leave the "regular" heating system in place and just use the conventional heater as a backup for extra water use and/or cloudy days.  For this to work without valves, you would have to make sure the pump is of a variety that doesn't allow backflow when the pump is not energized.  Or just put a check valve in line with it.  Otherwise, the house water pressure would wind up treating your recirculator as a water tank bypass when the pump is off.

Then you need to set up a small PV array to run the pump, so it's really free hot water.  8^)

best,

jp

[RP]

"easily get 100 or more feet of pipe into the present 5 by 5 ft box and make twice as much hot water much faster"

Remember there's only so many BTUs available in a 5X5 box from the sun.  After a point, adding more pipe won't extract any more heat.

[GaryGary]

Hi,

You might be better off to pump the water continuously at a low flow rate, rather than intermittently.  The hotter you let the water in the collector get, the less efficient the collector will be, because a hotter panel means more heat is radiated out the glass and is lost.  

The commerical solar water heaters use a contoller that has a temperature sensor on the collector, and another sensor in the hot water storage tank.  As soon as the collector temperature is a few degrees above the storage tank temperature, the controller turns the circulation pump on.  When the collector temperature drops below the storage tank temperature, it turns the pump off.  Goldline makes the most commonly used on -- just google on Goldline.

The EPDM wrapped pipe is an interesting idea.  Most of the collectors use fins made from copper or alum that is soldered or press bonded to the pipe.  The metal fins are better conductors than EPDM, but not not nearly as thick -- so the EPDM might work out OK.  If you find its not collecting as well as you think it should, you could try measuring the temperature of the EPDM right over a pipe, and then half way between pipes -- there should not be a big difference if your EPDM "fins" are working well.  The easiest way to measure the temperature would be one of those non-contacting IR temperature scanners, but the glass must be off to use this, or you will just get the temperature of the glass.

If you live in a freezing climate, you will need to think about what to do about freeze protection.  

Quite a few ideas on simple DIY solar water heaters here:

http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm

Hope you post the results on your collector after you have used it a while.

Gary

[mikey ny]

I have a few different snap disc controls of different temps i could use. I also have several different  types of double pole or double throw relays I could use to make a temp sensor you described. I don't think it would be too difficult. I could probably use th factory temp sensor on a hot water heater and a snap disc on the panel with a relay between them. Almost seems too simple, maybee i am missing something. Expansion tank, overheat sensor, mixing valve? I am still not sure what to use for a pump, I really don't want to have to buy much of anything. I have several circulators, an old pool pump, a jet pump, and an old drill driven pump. While one of these make work for experimentl purpose I will probably need to buy one eventially. I would like to stick to ac voltage for now since a pv driven pump and panel is a few more bux than i want to spend. I also have some hot water convectors with 3 speed fans on them, they don't hold much water so i may run the hot water through them as an experiment. If i don't use a storage tank, would it work better, less water to heat will heat quicker?

[GaryGary]

Hi,

I think you could rig something with the snap switches that would work pretty well.  The advantage that the commercial controllers have over a simple snap switch is that they sence both the collector temperature and the storage tank temperature, and can turn on whenever the collector temperature is greater than the tank temperature.  If the storage tank has cooled down some, then the controller can turn the pump on as soon as the collector temperature gets just above the cooled down tank temperature -- it does not have to wait on a fixed setting snap switch.  That said, I think just controlling the pump from a snap switch located on the collector will probably work fine -- you can always go to a fancier setup later.  If you have a 2nd snap switch available, you might want to set it to turn the pump off when the water in the storage tank gets too hot (some use 180F as the upper limit).  

On the pump, something like a Grundfos UP series (the small end) or the equivalent Taco pumps are not too expensive.  They also come up on ebay and other places quite often at good prices -- they are used in radiant heating systems, so they are very common.  24 sqft of panel typically only needs about 1gpm of flow -- so the pump does not need to be very large.  If you look at some of the water heater kits that are out there, you can get an idea what is commonly used -- here is one: www.sunray.com

You might want to take a look at the diagrams in some of the HomePower Magazine articles listed here (these are mostly free downloads):  

http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm

The expansion tank, air bleed valve, reverse flow checkvalve, and pressure relief do some important things (some safety related), and you probably want to either have them or make sure you don't need them.

Gary

[mikey ny]

a little more progress tonite.

           I managed to plumb in an old 40 gal water tank with a small pool pump ( probably too fast) to my solar panel. tommorow i will run the pump for a while and my son will monitor the water temp and time if the pump works ok. I will keep you all posted , thanks a bunch for the guidance. My kids are having quite a time with this project, i have turned them into believers.

[mikey ny]

Melt down!!!

   Duh! Very hot water plus plastic pump plus plastic pipe equals failure. Can't win em all. the sun will shine again tommorow, better pump and pipe to finish this experiment before it goes on the porch roof. "It must be proven to work before I attach it to the house." said the wife. enough said.

[GaryGary]

Hi,

Can you say exactly what failed?  Any idea what temperature it got to?

I wonder if a temperature/pressure relief valve and/or an expansion tank would have made any difference?

I think that adding the reverse flow checkvalve (cheap) would also be a good idea if the collector is going to be above the storage tank.  Otherwise, you may get reverse circulation at night that will circulate cold water from your collector through your storage tank and cool it off.  The collector will lose heat very rapidly on clear nights, as it radiates to the cold sky temperature.

Please keep us posted.

Gary

[mikey ny]

The plastic corrugated pipe 1 inch diamiter (left over from the old pool pump) got too hot ,kinked and melted where it was connected to the collector pipe. The temp gets above 180 f because i have a snapdisc connected to the pipe in the collector and it dones'nt take long for that to snap. The water tank was open on the top with a 12 inch pipe rising out of it. The tank water never really got too hot before the pipe melted. Your advice on the reverse flow check valve is great. I never considered it would actually work backwards on me at nite. Today i have a circulator pump hooked up to it with a flow valve, it is all hard piped so nothing will melt this time. It has a ball valve on it that i throttled down to slow down the flow to a little more than a trickle just for experimental purpose.  Tonite I am sure I will get a good indication as to how much hot water it will make. I will try to find a temp gauge to tie into it tommorow.

[mikey ny]

well here it is,

      No meltdowns today. I headed up to the adarondack mountains today for a weekend fishing with the kids. believe it or not we are on an island with grid power and phone (slow dial up internet). The 40 gal tank got warm but not quite hot enough to do dishes according to the wife, (no temp guage yet).It was a good sunny day. It will certainly help in preheating our hot water quite a bit, but there is room for improvement. I will decrease the volume of water to about 15 gal. and run it through one of my forced air hot water convectors sometime next week and see what potential it has to heat one room in our big old house.

[GaryGary]

Hi,

If you can tell how large the collector is, what direction its pointed, and what angle its tilted at, and roughly where you live (just latitude or nearby big city is OK).  I can tell you about how much water you should be able to heat on a sunny day.

Gary

[mikey ny]

thanks,

   5 ft. by 5 ft. 6 inches. Double pane glass. 3 inch styrofaom on bottom and sides. 7.5 inches deep. epdm liner. app.50 ft. reclaimed and straightened domestic hw coil from old boilers. covered in 2 layers of .060 epdm rubber (black). Coils are app .5 inch id. Hold app 1 half gal water. It presently lays flat on saw horses in the yard in the albany ny area.

   My ideal use for this will be to heat one or two rooms by running the hot water through a forced air hw convector (McQuay) without useing a holding tank. The whole system will hold about 4 gal. of water or anti-freeze. I am pretty sure it will work well for that during the day, of course. I will post some pics if i can figure out how.

[GaryGary]

Hi,

Albany is near 40 deg latitude.  On a clear day this time of year for a horizontal collector, 1 sqft of receives about 2240 BTU for the full day.  I'm guessing the actual collection area for your collector might be 85% of its 27.5 sqft area, or 22 sqft.  If your panel is 50% efficient (about typical of a decent collector), then it will collect this much heat on a full sunny day this time of year:

    Heat Output = (22sqft)(2240 BTU/sqft)(0.5 efic) = 25,000 BTU

This should heat your 45 gallon tank about:

    Temperature Increase = (25000 BTU)/(45 gal)(8.2lb/gal) (1 BTU/lb-F) = 67F

So, if it started at 60F, it might get to 60+67 = 127F.

This does not include losses from your tank or pipes between tank and collector (these losses might be significant if the tank is poorly insulated).

If its heating up a lot less than this, then your panel may not be collecting too efficiently, and you might think about making some changes to it.

Bear in mind that the numbers above are for a sunny day -- cloudy and partly cloudy days will collect less.

If you are going to use it for space heating, then you want to tilt it up to collect the most heat in the winter.  For Albany, your best winter tilt would be Latitude +15deg, or about 55 degrees.  It should ideally face due south.  You can don't have to hit these exactly -- within 30 degs of south is OK, and and within 15 degs of the tilt is OK (even vertical (e.g. mounted on a wall) works well for winter time collection).

Gary

[mikey ny]

Thanks Gary,

   We lugged all the parts for the panel to the porch roof tonite and assembled it. (we built it to be modular). I leaned it against the 2nd floor wall at about 55 degrees. Tommorow I will fasten it to the wall. I will run pipe to one convector using some left over black onx pipe. I plan to tee in a 2 inch riser pipe about 18 inches tall above the top of the panel instead of using an expnsion tank.I am assuming this will give room for expansion and also relieve the system of any air or high pressure. I will install a taco circ pump at the convector. I think I will use a 110 minus 20 snap disc in the collector to control the pump, and install a flow valve after the pump. Sounds pretty simple, I think it will work. I will insulate all of the pipe as much as possible, including the riser pipe. I will finish in about a week and leave well enough alone for now, I figure i will start out small and add to it slow but sure. I need time to finish the modifications on my wood boiler. I will have many comments and questions about that system in another post. Thanks again.

                                                      Mike

[mikey ny]

finnaly done,

    everything is done I will post the actual working results when it gets cooler around here, maybee the end of sept. thanks for all the support.

                                             Mike

[mikey ny]

boil over problems,

   I am having a problem with the water in the solar panel boiling out of the riser tube, I think maybee i should build it as a closed system with an expansion tank and pressure relief valve. Also the other day at about noon I turned on the system and when the pump started, the cool water went into the solar panel and the inside pane of glass snapped. The glass i s very thick, maybee 3/16 inch. I think it was from the shock of quick contraction from the cold water. Any thoughts on this???

[GaryGary]

Hi,

A closed system with an expansion tannk might help to solve your problem, but it should also work as an open system like you have.  Drainback systems (which are quite common) just allow the fluid to drain back down to a drainback tank when it not hot enough to be pumping.  So, if they work, it seems like yours should work.  I have heard that when a drainback system comes on and the collector is already hot, that there is a lot of hissing and banging as the collector fills with water.  You might confirm that your pump has enough head capability to get the water up to the panel on startup, and that its flow rate is high enough.  2 or 3 gpm should be plenty.

I'm a bit surprised that the glass cracked.  I gather that there is a bit of space between the collector pipes and EPDM and the inner glass, and no water leaks?

A lot of the commercial collectors use a single pane of tempered glass -- maybe you have discovered why.  If you need to replace the glass, one alternative would be to use polycarbonate sheet.  The Polycarbonate is good to temperatures up to 270F, and is tough (its the football helmet stuff).  Home Depot carries SunTuf corrugated Polycarbonate sheet that is 2 ft wide by 8 or 12 ft long at $1 per sqft.  It needs to be well supported.

Gary