Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
isochronic Guru Joined: 21/01/2012 Location: AustraliaPosts: 689
Posted: 02:34am 13 Jul 2019
Copy link to clipboard
Print this post
Does it harm PV cells to operate in short-circuit , ie max current out ? I guess they would be operating as an enhanced radiation absorber. If the panel was water-cooled, it would heat the water .. and could be switched back to electricity production when needed.
Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138
Posted: 04:28am 13 Jul 2019
Copy link to clipboard
Print this post
According to Mr Google, no, it does no harm, panels are rated for short circuit as they are current limiting devices.
Have often though about circulating water under a PV panel to cool it and possibly use the heated water for some other purpose; water would have to run in some sort of sealed tubing (silicon) that was sandwiched to the back somehow; dunno seems a difficult exercise.
Mike
Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904
Posted: 09:13am 13 Jul 2019
Copy link to clipboard
Print this post
You could perhaps try that by re using the condenser from an expired refrigerator. Somehow clamping this to the back of the panel, making sure the copper pipe does not touch the aluminium frame. It would be a quick way to find out if water heating/cooling is feasible?Klaus
isochronic Guru Joined: 21/01/2012 Location: AustraliaPosts: 689
Posted: 09:58am 13 Jul 2019
Copy link to clipboard
Print this post
Thinking about a cell/panel in the sun. The temperature is hotter than ambient as it absorbs the radiation. When current is generated, does the temperature increase or decrease ? I can think of it increasing (from resistive heating) or decreasing (as less overall energy is dissipated locally in the panel) ???
Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138
Posted: 10:30am 13 Jul 2019
Copy link to clipboard
Print this post
The panels temp must decrease when it supplies power to an external load, else it would contravene the laws of thermodynamics.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 03:10pm 13 Jul 2019
Copy link to clipboard
Print this post
Panels for what it it is worth get cooler when operating under load.
I think the rating system of panels is garbage. The standard temp is 25 oc For the panel. I tested some the other week on an 18oC day and got temps well above 40. I can only imagine what the panel temp is on a 35o day but suffice to say, it's a long way above the test temp.
I have looked into using panels to heat water before with people on other forums. Conclusion was like everything else with solar, Not worth trying to get more efficiency.
There are already panels with provision for heating water on the market. Price is high, results are low. Thing with heating water is the higher the water temp the more inefficient the panel becomes.
I also looked at using them for space heating. The idea was to box them in and blow air underneath and into the home. Thing is, when you would want heat, solar radiation in low as is the the amount of energy that could be gained. Panel temps Might be up but sustaining that temp with forced air blowing underneath is something else as would be recovering enough heat to make the exercise worthwhile.
If one were looking to heat water, my suggestion would be to use an air to water heat exchanger (Car Radiator or heater core) and Draw air through that. Would minimise plumbing and risk, be the cheapest option and may aid the panels in keeping them slightly cooler. Would only be worthwhile in summer though.
I was watching some Vids tonight and got another stupid idea.... Went on fleabay and ordered some carbon Gouging rods. I want to see how much light and heat I can generate when hooking them up to some panels. May even be able to use them TIG welding fashion to heat up material and weld or cut with it. Be interesting to see.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 10:18pm 13 Jul 2019
Copy link to clipboard
Print this post
Probably the most efficient way to do it might be to use the electrical output from the panels to drive a conventional heat pump.Cheers, Tony.
isochronic Guru Joined: 21/01/2012 Location: AustraliaPosts: 689
Posted: 01:55am 14 Jul 2019
Copy link to clipboard
Print this post
It suggests that, a panel that is used for current output will have lower temperatures and therefore last longer, than a similar panel that is not active.
Maybe if I use power more, the power utilities can pay me for helping maintain their panels !! (I won't depend on it )
Seriously in terms of panel life, it might be worth building in a current-dumping arrangement with a cheap external resistor and leaving them always active. At least for larger installations.
BenandAmber Guru Joined: 16/02/2019 Location: United StatesPosts: 961
Posted: 02:24am 14 Jul 2019
Copy link to clipboard
Print this post
The heat pump idea sounds the best to me
You could run dump load to heat pump
make your panels last longer
And get some hot water to boot or cold water for the summertimeEdited by BenandAmber 2019-07-15be warned i am good parrot but Dumber than a box of rocks
plover Guru Joined: 18/04/2013 Location: AustraliaPosts: 302
Posted: 09:42am 14 Jul 2019
Copy link to clipboard
Print this post
Just happen to come past this topic, I am thinking similar possibility. My idea is to gain some practical hands on experience collecting energy and delaying the re-use.
My take is use of the simple Solar Mike controller designed for approx 260V panels. The energy is "pumped" into storage via an electrical element of about 120 ohms. The element is meandering through iron special bricks. Some may recognize the Electricair Heat storage units off yesteryear.
For about 6 KW unit I think it is about 18 bricks used, our unit initially had two elements in parallel, now we only use one element to prevent element burnout. The single element last for years now. With two elements et seemed to run a bit too hot. The internal temperature of the core gets very hot.
I am keeping a look out at the local tip shop for more bricks. Then I need to build a high temperature enclosure. I have in mind a crude control to let the heat out by removing "door panels". At the moment a the mechanical design a bit up in the air.
The beauty is delaying the use of the heat from day to night time in the colder/cooler Tasmanian climate. Certainly the idea of using this as background heat in the colder bedrooms out of reach of the sun during most months seems perfect to me. I am guessing 4 KWh per day would be nice but I think the needed number of solar panels may dictate other wise.
Actually, anybody got information on material that can be used to insulate. Probably need to be able to stand 500 deg C or more. The stuff used in our present commercially installed unit now seems to wither away when you try and dismantle the unit for moving. Have heard there is something better these days and hopefully not too expensive.
Clearly I am not close to have a grip on the practicality yet but it is a start.
Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138
Posted: 10:59am 14 Jul 2019
Copy link to clipboard
Print this post
White Rock wool insulation blanket, should be easy enough to get.
Cheers Mike
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 07:49pm 14 Jul 2019
Copy link to clipboard
Print this post
For insulation at very high temperatures, perlite is probably the best low cost readily available material.
Its actually fine fluffy volcanic ash and comes loose in a bag, and I used it to insulate my metal casting furnace. You can buy it from garden suppliers, and being very light and very porous, it holds water well, makes an excellent basis for making up potting mixture.
Being volcanic ash its totally fire proof and will not degrade over time at extremely high temperatures and is an excellent thermal insulator. Some of that with an outer blanket of rock wool would be about the best you can do. Cheers, Tony.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 12:40am 15 Jul 2019
Copy link to clipboard
Print this post
This was my idea too... before winter.
Some random and disjointed thoughts.....
I number crunched a bunch of different materials and the best I came up with for the job was good old water. It has a thermal capacity far above iron, sand, rocks, gravel or anything else that was a common, cheap and easily accessible material.
If you have a target of 4Kwh ( which I don't think would be near enough) 100L of water raised in temp from 20 oC to 80 oC would give 7 Kwh.
The very FIRST thing you need to look at here is your ability to generate the required heat input, in winter, before you think of anything else at all.
The big problem as always with solar is the more you want it the less there is. I have a LOT of solar panels but the amount I'd need extra to get that 5 or 7Kwh extra a day is significant. In Tasmania where the winter radiation in Hobart is 1/3rd lower than Sydney, you'd want 5KW of panels even on a sunny day to get where you want and at ideal tilts and orientation. If the weather becomes cloudy, you are probably going to be lucky to get 3kwh out of them. Ask me how I know?
Long time since I have been to Beautiful and scenic Tassie but the weather is colder there and from memory winter weather is not ideal for solar generation. I have been helping a guy down there with the exact thing you want to do but he has the space and Dedication to throw a LOT of panels at the exercise and it is costing him a great deal more money than what I pay for panels up here. He ended up a few weeks ago shipping a couple of Pallets of panels down there. He got the panels at a good price but the cost ( and frustration) of getting them down there showed he has a deeper dedication than I.
So first thing is work out the amount of panels you'd need. I'd suggest 5 Kw Minimum. More is always better for the less than sunny days. Can you get the panels? (supposedly used) I think you may find a difficulty here. used panels are not easy to come by in Tas. When you do get them, have you the space to erect them either on your roof or on the ground? If on the roof, what direction and angle would they be? Any shading issues? What is the weather like where you are when you will want them most? If you get a lot of cloud, that will knock your generation to impractical and useless levels.
IF you have solar I would suggest just adding panels to your existing system ( many as you can) and run a plug in heater straight out the socket. I have 3 inverters all doubly or near it overclocked with panels and even so,I have not even seen them come up to near full output in the last 2 Months. The array with 3.75 Kw of panels facing North at the correct ( steep) Winter angle and with another 2.25Kw of panels facing west at the " ideal" ( latitude angle is doing the best even though it's on the smallest 3.6Kw inverter. That hit 3.2 Kw for a while yesterday.
If you connect them into your system then you will have the benefit of them in summer too. Depending on your concern for rules and regulations, You can just hook a GTI into the socket providing it does not exceed it's rating and if you have the old Spinny meters they will turn backwards when power is being fed in above what you are using. If you have a system already and an electronic meter, plugging in another GTI will give you more FIT.
I looked at those older heat storage heaters and a tank of water was much cheaper, much easier to set up and I rather have a tank of 80o water in the house than a pile of bricks sitting at temps that could cause ignition of anything they touched in the event of problems. That said, you do not need to have the thermal mass at a particularly high temp at all. Increasing the amount of thermal mass would mean you could sink in the same amount of energy but have a lower temp rise. As heat seeks cold, the lower the temp of your storage the less aggressive the temp loss as it always works on the differential temps between the hot and cold. 5 Kwh sunk into 200Kg of thermal mass is still the same amount of energy as 5Kw sunk into 50 kg of material, just the temp of one will be lower than the other. Much like the relationship of Volts, amps and watts.
The difference will be how much space to you have for the thermal mass? I wouldn't even be looking to insulate it myself. I'd be going for a large mass that slowly radiated the heat day and night. If the place is warm through eh day the temp differential will be less and the heat transfer from the mass to the air will be slower or even stop if the 2 reach equilibrium. As the temp drops at night, the radiation from the mass will naturally increase.
If you have the space, I'd be doing a bit of number crunching on equating the energy input with the temp you want to the amount of thermal mass and not insulating at all. For the numbers you are suggesting, which again I think would be on the low side although I spose every bit helps, You may not need all that large a heat sink at all even if you do just construct it from Normal bricks or pavers. You could easily insert a small heating element out of a bar radiator into the brick/ thermal mass pile ( paying attention to Silicone/ heat proof leads) and let it go like that. Would be very safe with no flammable material and the heat would saturate the pile and radiate out into the home. If you wanted thermal control, throw a blanket or 2 over it and remove them at night. I think you would find however but the time the heat was radiating youd want it anyway.
I have seen things on the net where people build Lounges and " Furniture" Out of bricks or mud and have that as thermal storage in their house. I imagine sitting on a lounge that is radiating a gentle heat through the Cushions and coverings would be a very comfortable and satisfying experience indeed. The Russians and others build their beds out of mud and have the flue of their fireplaces running right through it so it is a thermal mass and radiates gentle heat to keep them warm both in bed and to heat the house after capturing other wise wasted heat up the flue.
That may not be practical for you as it probably is not for my place which is why I favoured the water barrel. To get round my concern of potential leaks, I would just " Double bag" the tank. I got onto some plastic 120L tanks that fit easily inside 200/ 240L drums. If the inner tank did leak, it would be contained in the outer tank. I find the chances of leakage from a Moulded tank with no outlets to be infinitesimal however.
I floated this idea else where and people had a fit and ridiculed me over using plastic tanks with heating elements. I was sure this would not be a problem so I set a problem up. I put several elements in the tank making as much contact with it as I could. Even a 3600W element has too low a power saturation to melt the plastic and the water even when boiling still carries the heat away too quickly to even make surface impressions in the plastic. I'd rather go with the thick plastic drums than risk metal rusting or leaking at the seams. In any case, you run them one season then remove, inspect and replace with new ones if you want. The biggest danger I see is UV break down which would not be a problem indoors.
Practice has shown over the last couple of months that even with an element lying right on the bottom of the tank, there has been no effect at all.
Because Voltage rise is an issue here, I have the element in the water tank connected to a Thermostat and a voltage activated switch that turns the heater on when the voltage goes high and the inverter would throttle back or shut down. That's working well on all fronts. Have the same on the hot water system for the house on another circuit with another array. The heater does not always get the water up to full temp especially on the cloudy days so I either go with what I have ( mainly the case) or check it in the afternoons and kick it in manually.
My conclusion is that for MY house, generating sufficient heat to warm the place in winter this way is not practical or effective. I can't even keep up with the demand of my reverse Cycle AC with the 20+ Kw of panels I have. I'm going back to my idea of a waste oil heater or a small Diesel heater from an RV. A constant 5 KW my be enough for what I need and if it is not, it will be cheaper heat than buying in the power over what I am making and may allow the panels I have to keep up with the AC making up the shortfall from the diesel heater.
Anyway, I hope all that gives you some food for thought on how this might work for you and give you some heads up and ideas. :0)
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
Print this post
)