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Forum Index : Solar : Heating With PV Panels
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| Davo99 Guru  Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Inspired by Rogers Thread on heating with Evacuated tubes, I decided to give something a go that came up in the discussion, harvesting the heat from PV panels. Seemed to me after all I learned from that thread that a and ordinary solar electric panel was just a big flat plate collector and it was shown they are also only around 20% efficient at making power so must be some good heat to be had. I Pondered what to use for a backing which would not loose the heat from the panel and give accurate measurements of the heat generated. Being the exacting and scientific type that always like to do things to the highest standards possible, I spotted the cardboard box lying on the pile waiting for Council Clean up and thought Ripper, that's big enough so grabbed that. Cut it to size with a stanley knife and without any skill or dexterity what so ever, Duckt Taped ( Note precision spelling!) to the back of a new 270W panel that was handily within reach. With Infinite wisdom, For once, I remembered to cut a little hole and pull the leads through before I taped the thing down and had to work out which end and where they were. I then cut 5 Slots near the cable end of about 1 Cm wide and 10 or so cm long as inlets. I grabbed the also handy ( where I had been playing with it before and hadn't put away in 3 weeks) 12 V Bilge blower. It's a TMC that is rated at 90 CFM or for metric Minded, about 2.5 Cubic meters a minute. I managed much to my surprise to hack a neat hole near the other end of the panel and secured it with a good push fit being careful to leave some space for the air to pull in.  Sorry for the crappy pic, that's what happens when you go all modern and use a phine instead of the proper tool for the job. All I did was put some cardboard on the back of a panel with slots on the bottom and a bilge blower sucking through the top. The voltage converter can be seen in the lower left of the poor quality Pic. The slots are in the shadow at the bottom of the pic. I carefully worked them out with great detail and precision using complicated formulas in eyeballing them then hacking them out with a half sharp box cutter knife. given the temp I was getting and the fact it didn't fall off, I think they may have been pretty close to the mark by some dumb luck. I stood the panel up on another experiment I had finished with and yet to put away and felt the panel which was dead cold from lying face down on the grass. Didn't seem to be warming up real fast in the 2Pm fading sun so I though not going to see much out of this. I jammed the wires from the blower into the panel leads and the thing ran like it was getting 30V so I disconnected it and went and got my little 20A 24>12V converter. Took me 5 or so minutes to get some leads and a screwdriver etc and hook it all up. By this time the panel had gained some surprising heat. The temp gun said about 68oC. I thought yeah, that's all good and well, that will soon cool off when the blower starts. Fired it up and could tell straight away the heat coming out was significant. I ran it a few minutes and the heat didn't seem to be dropping off so I ran off like an excited little girl and brought back my thermometer. The ambient air temp in the shade was 19 oC. The air coming out of the blower was 34. Confirmed this with the heat gun. Ran the thing for a good 10 Min and it did not drop. I measured the panel angle and found I had the thing standing at 76o and was off on the orientation to the sun a bit. I re aligned it and changed the angle to 62 o which I thought close enough and to my amazement, the temp went up to 38 C coming out the blower. Got to say, I didn't see this happening! Right up till the time I started the blower I thought this is going to amount to nothing but, I have certainly changed my mind. The panel face was sitting at around 67o and didn't really drop nor did the temp of the output. The cardboard backing was around 44O for some time but then fell to around 38 also. After about 30 Min I went and got a 12V 55W Light bulb and put that across the converter output and it lit full bright without the fan speed dropping. I measured the Voltage and got 11.78 so I would say the fan was doing close to rated output. I don't know the Precise CFM I was getting or how much energy that equated to but it was certainly enough for me to think that it was significant enough to do a proper build with this. I would by guesstimate say the airflow was similar to that of a fan heater on high although the temp was obviously less. By about 3 pm the big tree in the back yard was starting to cast shadows on the panel. Thinking of my good friend Roger, I thought I'll watch this and see how this goes with the fall off in fan speed with the converter. It audibly did fall off although the temp remained the same. I thought I'll speed this up a bit and cover some of the panel. It slowed the fan noticeably but to my surprise yet again, the temp went up to 41. Considering the amount of panel I had shaded, even with the lower airflow I was not expecting that either. This is the opposite of what I would have thought in the fan would over power the panel. Seems the efficiency of the panel ( and Tubes) to make heat is way ahead of a panel to make power. Maybe that should have been obvious given their relative efficiency's but when one is powering a 36W fan with a 270W panel.... I would have thought there was plenty of margin to push the equation the other way. Seems not and I can see why Roger had much the same result with his tubes making heat before the fan kicked in. I can say I am quite surprised by the results I got. Not what I would have thought at all. As I said, No idea what the actual energy generation was but the result of my test left me feeling that it was certainly something worth while and that there was more energy to be had. There is still plenty of electrical energy that could be converted to heat if that is the primary goal or a lot of heat as a bonus for making power. The thing that dawned on me when I came back in and gazed out at my Ground mount solar array is that this heating arrangement could be set up with no detriment to the power produced by the panels but a significant amount of additional energy is there for the taking. It may be low grade heat but Multiply that by even 5 (Panels)and it's significant enough. The other thing is that this is likely to help electrical production by lowering panel temp. Panels are rated at 1000W M2 radiation and at 25O. It's a pretty Bogus rating though as they do the rating test using flash lights and record the electrical pulse. This means that the panels never heat up as they do in the sun or real world use. As I have seen before and was reiterated again today, pretty much unless the panels are in a snow environment, any sun hitting them is going to push them way over the rated temp and cause a fall off in output. I have looked into cooling panels before and it's yet another of those " Not worth the effort for the gains" exercise but in this application, any gains through cooling are a triple Bonus and one is already getting something for free. Roger, I know you have also been looking at PV and would strongly suggest you do a back to back setup with this to compare to your tubes. I realise you have put a lot of time and effort into those but It just may be that you could well kill 2 Birds with one stone and may be possibly easier for you to get the heating you want at the same time as making power with a PV heat harvesting setup. Took me about 10 Min with my dodgy configuration to set up but I think would be very simple and straightforward for a permanent arrangement. At very least would be good to compare to your tube setup so whichever way you went you knew the advantages and disadvantages of each setup. But apart from all that, I just really want to know how the panels and the tubes Compare for my own selfish reasons! :0) Given all the drawbacks of solar anything in winter I am well aware of, I'm very motivated to construct this into something practical and Durable. Even though it was a nice clear day here today, the solar generation was crap but the heat coming off that one single panel,..... well suffice to say that was an eye opener and something I probably would not have been fully convinced of had I not done it myself and seen the results!  Measuring output temp.  Blower I bought a few years back for $20. 90 CFM, 12V, 3A. It's a flange mount but I glued the white spigot on a few weeks back to use for providing combustion air to an Oil burner. The flanges are for std PVC pipe so could be used on the back of each panel and connected together with T pieces and pipe and one fan ( although maybe larger) used. |
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Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 580 |
Good on yer Davo, I like to see this kind of experiment. I suppose the backing could be insulating foam with some sturdier panel on top. Something cheap enough but durable in all weather - no fun having to re do duct tape all the time  .The alu frames would lose some heat but there's not much one can do other than sticking foam strips on the channel insides. Collecting the heat from several panels would be the tricky part, some kind of manifold to collect the hot air from all the panels so modified. I still think pushing cold air in at the bottom is kinder to the fan blades & motor besides, colder, denser air is easier pushed than hot air sucked. I got 20 panels on my garage roof that could be so modified and its a relatively short ducting run from there into the house. I will think about it when my present hot air collector is in working order. And, as to say, cooler solar panels give more output so the fan thing could be run in Summer too with the hot air vented away from the solar panels. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
It's been on my mind since last week when it came up in Rogers Thread. One of those theroys I had wanted to follow up on. I was in 3 Minds about it, the numbers said one thing but my mind said something else. Yeah, was hard enough getting the duct tape on in a reasonable fashion the first time as the cardboard has been sitting out in the weather and wasn't exactly flat and straight anymore. I was thinking earlier, all this really meeds for a proper roof array is some gal or ally sheet on the back. I don't know what the heat losses would be with Plain metal but I'm kinda thinking not that much really. The other thing I was thinking was styrofoam sheet. That stuff is amazing for insulation. I got one of those insulated boxes they use for Veggies and seafood the other night and Filled it with hot water. Warmed up what I wanted and unsure If I'd need it again I put the lid on. I went out in the cold Hours later and the water was still VERY warm. I was surprised how well it kept the heat in especially since it was about 4o outside. A sheet of this would be nice and light weight, easy to work and loose no heat of significance at all. I was wondering where I could get some? Could easily be glued to the panel frame. Yeah, I really don't think it would be worth worrying about. The heat is low value and the temp differential not that much so I think if one did a test on 2 Panels, one with the insulation and one without, the net difference would be lucky to be within testing error margin anyway. Funny, I was thinking otherwise. If they were rack mounted, even on a roof, They would be stable and there should be sufficient clearance for a 4" PVC Duct and then just use a spigot like I have on the blower to vent the air into the duct. I'll have to see if there is a 2" to 4" T piece which I have an Idea there is but even a 4" Flange as long as it was short to go into a T should be OK. Should be possible to Control the flow into the duct by the size of holes into the panel backing. That said, also occoured to me today that all that is really needed is maybe a 10MM gap at the end of the panel to let the air in ( if drawing through.) rather than even cutting holes. Should give good airflow across the width of the panel and make the whole setup easier. I don't think 40 o air would make much difference. These fans are designed to pull hot air from engine bays and everything I see tends to be drawn rather than Blown air. It will be something to ask My mate in AC when I see him next. One thing with Pushing would be the fan would be on the outside and therefore quieter. This one is OK but small but larger ones can make a racket. Then again whether you had a fan that was outdoor/ weather rated would be another consideration. Might be cooler pushing the air though but cooking in summer. If it were pushing summer air, could easily be as hot as drawing the heated air through in winter! With 20 panels, even if each one is only doing 200W heat output, that's 4KW. From memory you are up northerly so you would have to be closer to that 4-500w Number so that is serious Heating. Yes, I thought of that too. I was wondering what you could do with all that heat in summer? Drying fruit or meats? Slow roasting? Baking bread??? Certainly pump it though a tumble dryer in a commercial Laundry! Would be perfect! :0) I was also thinking of Rogers case as well. With a swimming pool, one could heat the pool in that crossover time where you don't need to heat the house but heating the pool to get some extra swimming time in would be a nice spin off. I think it would be dead easy to do using a car air to Liquid intercooler. They have many tens of KW heat transfer capacity so would walk in that job. If you had say 10Kw on tap, would work well for you to store the heat for the night. I have been looking on YT searching using PV panels for heating but I can't find anything really. Lots of the drink can heaters and the flyscreens that have been mentioned before but nothing on using panels which surprises me. I know it's all in the search terms but considering the weird, wacky and interesting range of things I have found, surely would have thought something on using regular panels would have fallen into the results. Given what I saw today, I'm amazed every DIY solar energy nut building these heaters aren't all over this and it's a common, run of the mill thing in those circles that we would have all heard of before. Maybe I'm just out of the loop but again, plenty of these other types come up in my searches. |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1122 |
Cool experiment there, would be wary of using Styrofoam, it has a very low melting point, we never use it in solar air panels, unless you want a sticky mess everywhere. Polyurethane foam would be ok, but its expensive, have used the 6mm corflute in the past for backing boards, its really inexpensive, sign writers have it; my DIY solar food dryer has a 2M^2 hot air panel with corflute backing covered inside by sheets kitchen tin foil, been sitting outside past 5 years, no deterioration at all. You will loose 40% of the heat out through the front glass of the panel, as the silicon cells and eva liner are bonded to it with no air gap. Cheers Mike |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 792 |
This is awesome Dave, really pleased to see you try it out. And it brings home the fact that you can just throw something together with cardboard and duct tape to prove (or disprove) an idea or theory. Often not even having to spend any money, just use what we already have lying around. Haha, I think you missed your calling Dave ... you'd make a great technical writer. That's the sort of thing that really excites me about this. I know it won't be all the time ... but in good conditions the fact that you have a sustainable heat source is definitely worthwhile. Then it's a matter of finetuning and working points to get the absolute maximum from it. Haha, my first convert. I gotta say I have often wondered if I was kidding myself over my results ... but I only have to look back over the charts I have recorded to see that there is significant heat gain at times. The early days were mixed with a number of dud days ... but I've seen significantly more good than bad already ... though winter will likely be worse. When you first talked about this, was it your suggestion to have the whole panel in a box of it's own with a seperate glass/clear front? That would allow you to collect the heat from the front as well ... and also capture some of the reflected energy that would normally be lost ... ... but of course that would all depend on whether the additional glass front would reduce the output by more than you'd gain. I think this is the secret to the best useable output from my system as well ... where you vary the airspeed to extract the maximum amount of heat without the temperature dropping too low ... ... and of course if the output drops too low from lack of sun ... you slow down the fan to allow the device time to build up to the temperature you require. So this is the bit about the solar thermal output being up to three times greater than the solar photovoltaic output over time I assume. Haha, yeah ... but what if this idea works better than my evac tubes system ... and I've wasted all this time with them ... ahhhhhh ... can't bear the thought.  And my solar panels are supposed to go on the shed. Going to be hard to get all that hot air up to the house. I have to admit, I have thought I should build a basic flywire collector to compare with mine in case I'm wasting all this time for nothing. I shall work out the best way to compare this and maybe give it a try. Again, great to hear. Can't wait for the next installment. Cheers, Roger |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Fascinating stuff guys..... From my past experience with solar thermal water heating projects, insulation will be necessary, although the temperatures with direct air heating will be lower. One problem that needs serious consideration is rain water getting into the insulation. So whatever you decide to use for insulation needs to be waterproof. The stuff used for cool room insulation would be ideal, they have a similar water soaking problem, but from condensation. Another random thought. When solar electric panels are running very hot, as they always do in mid summer, that reduces the electrical output. Forced air cooling from behind should increase the output slightly, maybe by more than the power required to drive a cooling blower ?? I have no idea if that would be practical or worth the trouble. But if the blower and ducting is already there for winter heating, it may also offer an advantage running the blower for cooling the panels in mid summer. Cheers, Tony. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
May have been the most satisfying part of this. I have so many half arsed projects lying round because I need something to finish them which I either can't find or get or have been too lazy to travel half way across the city to get. Temporary/ testing setups just don't normally go so well with me with everything I need being on hand. And yes, I have WAAAAY too much crap lying round. Kinda why I was out there, walking round thinking what can I get rid of and trying to give myself a reality check in what I am accumulating again. Yes, I was surprised how much heat it was giving although.... I could see straight off it was going to be short lived. Because of the suns low angle at this time of year, the house takes out a lot of real estate for anything solar in the mornings and then the one tree I have of significance takes out the rest of the yard by 2-3 Pm depending on position. The ground mount array I put up at the back of the house does not get full sun till 10 and then the shadows are starting to creep onto it from the tree by 2 Pm. None the less, Driving round I am thankful of the good clearance I have from trees and shading. Some places I see with solar I wonder what they were thinking or how the salesman stitched them up into getting it when they would be lucky to have a couple of hours clear window at at time of the year. Yes it was but being cheap and simple, I was looking for the easiest and most efficient way to utilise these panels. Reading Mikes comment that 40% of the heat will be lost is sobering though and certainly takes the gloss off. -IF- as I am still working on the number of 400W M2 (As I have no other number to work from atm) which is 640W total from a panel and 40% is lost, that brings it back to only 384W for a std 1x1.7m panel. That's going to take an array of 5 to make any significant heating. If one then has to cover the panel, the the cost, time to set that up and the electrical losses also take the shine off this quite a bit. I was thinking slap a backing on them and you are good to go but should have realised never going to be that easy. His comment about the styro was helpful, I had no idea it would melt at such low temps so I'll look for some coreflute. I figured that was going on seeing how hot the front of the panel ran but again comes back to the time, effort and cost to do that and then the practicality. when I enclose it all, how do I mount it all on the roof? Permanent ground mount is not an option and temporary I think would be too much of a pain and probably still not practical once we get the landscaping organised. The old solar Conundrum of chasing efficiency. It never fails and rarely so far in my experience, works out. And as usual, we are chasing percentages of declined outputs. In summer if this was around 1600W per panel potential, 40% of that would be worth chasing. When it's winter and we are chasing less than half of the potential to begin with, then the question of try and get the much less amount or let it go comes into play again. And with my experience in PV, it's never worth worrying about. In this case, getting the heat may decline the already depleted electric..... Sigh.... Why do I pursue these endeavours and frustrate my mind with such things? I should take up painting or stamp collecting and be done with it. Yep, simple thermostat should take care of that. I am reminded of the other side of this not even 24 hrs later. Completely overcast, dull and cold this morning. My 5kw inverter that did 20kwh yesterday will be lucky to do 3 today. OTOH any heating in the cooler parts of the house the diesel does not warm will use 10X that. Solar heater would be totally Zero. I can see the panels on the ground mount I put up are still running with dew. This time yesterday they were drying themselves off although still partially shaded. Only one thing wrong with all these Solar/ Renewable energy ideas.... the weather! Yes but the power output of the panel was about 7.5 times the draw of the blower. I know the panel output is far from perfect but I thought they might line up a bit better! :0) Put it all on gum tree and sell it. Write the key words in an ad and you'd probably sell it for a fortune! Ever see what those catch powers and other "Money saving" and environmentally friendly ideas go for despite actually being worth about $2? Best/ worst one I ever saw was this water turbine Generator thing. It was portable pocket sized ( which says a lot about a generating devise to start with!) and you put it in a creek or stream and it charged your phone or other usb devise. The thing won endless awards and accolades and they couldn't make the things fast enough to keep up with buyer demand. Forget the fact you needed an unlikely fast running body of water to get the thing putting out power, don't worry the thing put out about 2W and would take all day to charge your phone, don't worry it cost $200 or so, It was a brilliant idea ( apparently) and made the inventors literally millions plus had them heralded as geniuses and flown all round the world at other peoples expense to celebrate their world saving invention. I get Nauseous every time I think about it. Least your tube setup actually provides worthwhile energy as it is supposed to. Maybe that would be it's failing in these modern times? Yes but how far away is the pool? Like I said, simple water to air Intercooler and your Kids are going to be taking a cake of soap in the pool with them thinking its a bath it will be so warm! Still haven't found anyone using PV panels on the net for air heating. I did see one Vid that struck me as completely ironic though. these guys built a box and lined it black and covered it and had a little solar panel at the top to power the little computer fan pushing the air through. I looked at it and thought all you had to do was put a regular panel in the box you built and you had exactly the same thing and proper power output to boot. Far as I can see, any of these collectors are a black surface.... just like a panel. I reckon these things could be built really easy if there were some extrusions made for the job. Slide the panel in the 35mm Center Channel with the stops 20mm from the end. Put the top sheet of glass/ acrylic/ whatever in the top 5MM Slot. Put on the end and slide the backing down the rear which has the outlet pre punched. Put on the other end so it's all framed up like a panel itself and Bingo, job done. Could fit any std size panel, be quick to assemble and ducting could be pre measured and cut so it all went together easy enough for the typical unskilled Backpacker solar installer to put it together. For DIY, could probably be done with some board that had the channels routed in to make it go together the same way. Just paint the thing ( Black?) and put it together. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
I saw piece on panels that had water heating pipes built in. Apparently they are available commercialy. Never seen them offered here. I was wondering what sort of material could be used to fill the back of a panel that had PVC or similar piping laid into it? An amount of Insulation would be requited on the back and would probably want to be a drain back system to stop cooling at night. Corflute as Mike mentioned would be a good material here, Might just need to tape over or seal the ends to stop water getting in the middle. Hot piece of bar to melt and fuse the ends closed would probably do it well. I think that was discussed here a while back. I looked at it and tested water cooling and saw a definite increase in power. My take away memory was while it worked, the power required to drive a pump and then the water use was not worth it. I seem to remember some gain but if you are making a few hundred watts a day and it costs a couple of hundred bucks to set up.... |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Being a day here only good for sorting ones sock and unmentionable drawers, been looking into the idea of covering the panels to stop the 40% heat loss Mike mentioned. There is NO solar energy to be had today. Raining and still only 12C at 11:30 am. One inverter has made 1.4KWh, one has made .65 and the one up the back might have made 1 Kwh if I'm real lucky. Great day for the Daughter to be home and doing her washing and running the dryer, but at least it keeps the house warm. Long story short, once again for THIS application, my conclusion is enclosing the panels is NOT worth it. The premise of idea with the heat from the panels was the thermal energy could be gained at no cost ( Output wise) to the panels and maybe even a gain. The surprises keep coming with this in that I learned that the reduction in light transmission through Acrylic sheet which the sources I found all said was better than glass ( substantially) was 8%. I had no idea glass knocked out that much light transmission! From what I read, window glass seems to have deliberate transmission reduction so as to help stop the sun fading the curtains ( really!) and could be depending on the ( non tinted) glass, be 20% reduced tansmission. From what I could find all glass has a transmission reduction although hard to determine what that is. at best seems to be 4%, some sources quoted 12% as a minimum. Obviously a lot of different glasses and likewise, the glass with the best transmission would also be the most exy. One thing that I also noted is the sources I found often stated Visible light. I'm still not exactly sure what wavelengths of the magnetic spectrum panels are sensitive to. Definitely some of the Visible spectrum but I highly suspect not all of it. From memory glass knocks out a LOT of the UV wavelengths and probably some of the IR as well so in effect, glass ( not sure about acrylic but would probably absorb some of the non visable wave lengths) could be knocking off a lot more of the light panels are sensitive to. I know panels use toughened glass in their construction but I believe that modern panels also use coated or otherwise specific glass for the application. It can't be recycled in with ordinary glass that I know. There is another factor that occurred to me straight off, Reflection. All glass and all surfaces bar anything matt black, reflects light. That's how you see it. Light falling on glass is going to bounce off to a greater degree with a greater angle. Stands to reason. IF the goal was to harvest max heat, then yes, I can see where covering the absorber surface would be essential. That however was not where I was coming from.... although maybe should be. In reverse to the Co-gen principal, rather than the heat be the main product and the power be the happy by product, I do want it the other way around. The other thing is If I take the "whatever I can get " approach and don't get too caught up on efficiency, the whole exercise becomes far more Doable. Construction is greatly simplified, cost is much reduced and practicality takes a big step in the right direction. If I work on the rounded theoretical number of 400W M2 for winter at Sydney latitude ( anyone able to confirm or correct that number?) then a 10 Panel array becomes quite worthwhile..... Maybe. That's optimal. Most of my roof is east west and the north roof would be the most difficult to institute this. I'd have to be full on serious about it and cut holes in the roof to bring the air in. It's also just a bugger of a roof to work on. I may be able to do something on the east west Verandah roof but not sure what my yields for that would be. 7 Panels each way. If I got say a constant 2Kw out of them, hmmmm, it's borderline at best for the effort. And still comes back to there being nothing when I want it the most like today. Then again, yesterday would have done well I think. For those with a good north roof this could be a very viable option especially if 20 panels could be pressed into service. I was also thinking that if a double rowed array was used where there are one lot of panels above another as is common, perhaps something like just aluminium sheet backing on the upper panels where the air was harvested from would be a Bonus? It the panels were close on the ends and or sealed together. the heat from the lower panels should rise up under the upper string and heat the rear surface as well. At worst, if something more insulating were used, this warm air from the lower row should remove any temp differential between the air in the panels and ambient in that area. While like everything else the idea looks good and is workable on it's face value, the real test comes in at the how practical is it for you to actually do question? Still making my Mind up atm. A small, 2-4 Panel temporary array just for the en-suite may be worthwhile though. Sun exposure would be limited but at least I have the nearby space to place the panels. Might be worth a revisit to Murphy's Idea of the roof space air..... although thinking of that, I thought why my ceiling temps may not be so significant.... because half the damn roof is shaded by Panels!! I feel like I am being pranked by my own endeavours here!! |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1122 |
Hey Dave, placing some sort of sealed boxes behind your panels seems a lot of work. The most efficient cheap solar air heater you can easily make is a timber box made out of rough sawn 6 x 1 fence palings approx 1m x 2.4m. - to fit the corflute size, recess the back with corflute siliconed in around the edges and tinfoil glued inside to that. Extra insulation on the sides doesn't make much difference. Run 3 layers of open mesh aluminum flyscreen door material painted black spaced 15mm apart on a slant, glaze with 1 - 1.5mm clear polycarbonate, >90% light transmission. Black polypropylene garden shade cloth works almost as well here. 150mm air ducts in at the bottom extended near the glazing and out at the top on the other side of the mesh, couple of 120mm computer muffin fans in the inlet driven off a small 12v PV panel. This setup will be >70% efficiency, you will be surprised at the amount of heat that it generates, if the sun is shining.  Cheers Mike Edited 2021-06-03 14:18 by Solar Mike |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Interesting. I now get the use of the flyscreen, the air is drawn though it rather than over it. Clever. I was wondering why the design use screen instead of a solid collector? You diagram cleared that up. Mike you are obviously an expert on this, do you have any links to charts or input as to what the expected output of such a setup might be? I calculate for the area of the collector using 400W as the Sydney winter insolation and the 70% efficiency you state, this should give about 672w of thermal energy. Dies that agree with your thoughts? |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1122 |
I'm no expert, just have built quite a few over the past 30 years. Here is a link to construction and testing with graphs etc, they built and compared quite a few differing styles. Here For glazing they used corrugated clear polycarbonate roofing, I have used it in the past and it gets very brittle over 10y period and will break as it is very thin. Bunnings sell rolls of 1mm clear poly, that's what I use now, you could throw a brick at it and it wont break. There is also a more industrial version 1.5mm thickness this is sold by PSP here in NZ. These work best if you stand them vertically against the wall of your house, picks up the low winter sun and rejects the mid summer when you don't need it. Cheers Mike |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Sun is out again today so I have taken the panel heater setup out in front of the ensuite. Found some non insulated 6" Duct up the back I cobbled onto the blower in every sense of the word and set it up near the window. Almost 11 Am and it's still half shaded. I'm going out shooting shortly for a few hours so I wanted it in place to catch the best of the day. Might get a few decent hours before the thing is shaded again. The outside temp was 14 when I set it up and 14-15 in the ensuite, but feels a lot colder. There is already 17o air blowing in so it is an inprovement. The thing was blowing gently before there was any sun at all on the panel but as there was no difference between inside and outside temps, I wasn't worried. Outside temp is still the same with a bit of wind which isn't helping. I was going to leave the window open beside where the duct goes in to allow for airflow but though more cold might go in than hot come out. THere is an exhaust fan in the roof so that should pass the incoming air pressure. Probably the warmest air but this is about as rudimentry and flawed testing as one can get so if I see any improvement in temps when I get back, I will be happy. Such a change from one day to the other. The little diesel heater was put on at 3pm on Wednesday and I turned it off at 10 am this morning. With a low of 3 here last night and the heater on level 2, the place was warm enough this morning. Only used about 2L of fuel from Midnight and well worth every bit. Be interesting to see what the temps of the walls and fittings in the ensuite are when I get back. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Well so much for that idea! I doubt any more than 20 min after I left, the came over with deep dark clouds. I wasn't far from home and the clouds were as far as could be seen and I had a good view around where I was. Wind came up and there was no solar energy to be had. Bummer. Was looking forward to a nice sunny day and making some needed Kw's of power. The fan was running when I got back, seem to run in very poor lighting conditions with the controller, but I didn't even bother checking the air temp because I knew it could not be any more than ambient. Before I left the last check I did was 19 coming out the panel and the ambient was 16, maybe. The panel was still only 50% in sun if that. I have a dressing room between the bedroom and the ensuite so I closed that off from the bedroom and the bathroom. The ensuite and the dressing room were the same temp when I left. Coming back the dressing room was still the same temp but the ensuite had gone up 1-2o depending where I aimed the temp gun. Too close to make any conclusions but the limited time the sun was shining and the warmed air was blowing in I think was inconsequential. May have got a better result today just blowing outside air in with a bigger fan. Not sure when the next sunny day is supposed to be, I think the weekend weather will be ordinary but Monday is -Supposed- to be sunny. See how it goes next time round. :0( |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Trying again today... with Mrs knowledge and lack of Complaint! Miracle! Maybe she would welcome making in there warmer as well. Initial Temp inside is 13o. Dressing room again the same so presents a reasonable control parameter. Hard to say which one has the greater thermal mass. One has tiles and porcelain, the other is filled with clothes and furniture... containing more clothes. Less density in the fabric but you have to appreciate how many clothes my Mrs has and how densely packed that 4 or so meters of Racking ( which I have literally had to brace up from the floor in multiple places to stop the bolts tearing through the shelving above) which must weigh 300+ Kg all up. Well shaded panel is pushing in 15 O air minutes after start up. If the sun holds out today will be interesting to see what sort of temp rise this gives. Sealed the window pretty good and no wind so far so I think the input from outside air will be minimal as well sun falling on that wall which is absolutely Minimal this time of year.... which is why the damn area is so bloody cold... unlike the hotbox it becomes in summer. Off to Bunnings to look at some suitable panel backing and a 4" to 6" flange to connect the blower to the ducting I have... and maybe some new ducting if it's cheap enough which last time I looked was anything but. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I remember when I was messing around trying out double glazing, a sheet of ordinary window glass left out in direct sun gets as hot as anything else left out in the sun. That suggests to me, that the glass is absorbing IR radiated heat, not transmitting or reflecting it. Although I have not played around with polycarbonate, it may very well not get as hot as window glass, suggesting that it does in fact transmit radiated heat better. I have no idea of how well polycarbonate stands up to UV radiation. A lot of plastics deteriorate quite badly from UV, clear stuff tends to fog or go yellow. Often plastics recommended for outdoor use are "UV stabilsed" whatever that means. I am not a plastics guy, its something I know nothing about, but if they say polycarbonate works, it probably does. Cheers, Tony. |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1122 |
The commercial flat 1 - 1.5mm poly has one side that is UV stabilized, it has a plastic tear off film that must be removed. Corrugate roofing version also has an UP stabilized surface, Twin wall version with hollow sections also works well in this application. My polycarbonate panels on the solar drier get mildly warm, it is more transmissive that plain window glass. > 15 years outside still clear no fogging. Cheers Mike Edited 2021-06-05 16:54 by Solar Mike |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Came back about 3 Pm after a fruitless search for Reducers at Bunnings and the local Legend Plumbing/ irrigation place. Went to walk in the front door and a guy comes to the warehouse man door and says Come in this way Mate, I have locked that door up. I said oh, sorry, I won't annoy you if you are closed. He said no that's fine, come in. Told him what I wanted and seems they make everything bar 50 to 100MM and 100 to 150MM reducers in DWV. Didn't have both in pressure either. Bugger! Did get some copper fitting and pipe at a bargain price for the Diesel exhaust/ heat exchanger. Nicest, friendliest, happiest best customer service guy ever. Last time I went there they were flat out and the older guy I spoke to was helpful and apologetic as could be as well. Don't know why I have bothered with Bunnings, NEVER have what I want in any Plumbing fitting, relatively expensive despite what they advertise and never any fker around to help you when you need to ask something. Didn't have any Duct I wanted either. be one thing if they didn't sell it but they do and again as always, No stock. I can well see why online shops are giving places like that a hard time. When I got home I went straight in the dressing room and shot some temps. The change room had come up 2o on average. The en-suite had come up 5-6 o despite where I shot the temp. Funny enough, the tiles and sink were not where I got the lower readings. It was on the outside facing wall where there was now a bit of sun. I went to take the temp of the incoming air and found there was none but could hear the blower. Knew straight away the duct had come off. Thought I had taped it on OK but also knew it was still very makeshift hence trying to find some better fittings or duct work. I surmise it probably let go when the panel was outputting the highest temps of the day. Going outside confirmed this. The blower was running pretty good despite the panel being half shaded again. Re connected the duct, went back inside and got 21o air coming out pretty quick. Mostly everything inside was at 19 so there still was potential for temp rise at that time and I fully believe could have got the room warmer still had the duct stayed on. As soon as I walked in there from the dressing room I could feel it was warmer and far more pleasant. Also warmer than what it is normally which is still an icebox at any time. I can't think there was very many KW of heat that went in if even a single one BUT, it was enough to make a noticeable and pleasant difference. Checking just now with the sun behind the trees and hill a good hour, the ensuite has lost 2o and the Dressing room is the same. It only has a small wall exposure with half of that of course being another big full height window. The ensuite is still cool at 17 But it does not give that immediate cold feeling it Normally has. Today was a flat out perfect day. Bright sun, no clouds, no wind, about as good as a winters day is going to get. None the less, I am of the belief that 2 panels would make a big difference to that room and maybe put enough heat into it for it to retain some and be far more pleasant to be in. The big trick will be the setup and the duct. That wall is west facing so is shaded buy the house close in till 11 am I have room to move the panels out further but then I'll have a long length of duct laying round exposed to the elements, the dog who takes that path when I throw the ball over the house from back to front which is her favourite game and the wind. I have panels on the roof Immediately above which faces west so I am unsure how bad that would decline heat generation but I assume fairly significantly. I could tilt a couple of panels but the degree required to make a difference and how that would look lessens my enthusiasm for the idea. I could use 90/100mm DWV pipe for the duct, it's cheap enough but what would the heat loss be ( could paint it black which may improve things) and insulating it would probably be more than I would want to spend on the exercise. I also looked at Bunnings today for some sort of roll foam material for backing the panels and found nothing. Sure I have seen some foil backed foam material that should have been suitable for the job before but saw nothing today. There was some tar impregnated material that looked excellent as collector material but probably too flimsy as a backing on it's own. was REALLY cheap, I think they may have made a pricing mistake on that. Might go back and get some tomorrow. If I do I'll never use it, If I don't, in a fortnight I'll be thinking it would have been perfect for the next hair brained Idea I come up with and the price will be 20X what they have it for now. Might just have to look at some plywood, paint it for weather protection and maybe foil line it on the inside if that will help any? Open to other suggestions for easy to obtain, economical materials suitable for the purpose. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Several of the suppliers/ manufacturers when I was researching this stuff guarantee it never to yellow or degrade in light transmission. Something I found a little surprising, but none the less. Seems this is something they are well aware of and a common objection/ belief they want to overcome. In my understanding, usually means they don't break down. Like electrical Conduit. If it's exposed you have to get the UV stabilised one which is usually great where as the orange stuff is general not exposure rated.... far as I know. I know plastic Drums can break down over time, some more quickly that others. The clear ones break down quicker, the blue ones will whiten a bit but never seen one go brittle or crack like the clear ones including IBC's will. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Mike what do you pay for a sheet of this in Nuzelund and what size is it or what do you use? Everywhere I can find here the stuff is a Bomb. There don't seem to be that many places here doing it I can find on the net either. Do you have any recommendation for a reasonably rigid material for use as a panel backing? Edited 2021-06-05 17:45 by Davo99 |
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