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Forum Index : Solar : Solar hot water and frost.
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Coming into the cold season here, and had our first light frost last night. Noticed the solar panels had a nice coating of ice this morning, and I'm a bit concerned how it will go when it starts to really get cold. Its a regular, system, solar panels and tank, with a electronic controller to circulate the water once the panel reaches a certain temperature. Tap water is pumped through the panel, that is, its not a split system when the panel water can contain anti-freeze. Last winter I would throw a tarp over the panels every night, and remove it next morning, to give a little protection. But back then the panels were at ground level, now they are on a stand about 2 meters above ground level, so not easy to cover at night. I've added a function to the controller that goes into action if the panel temperature drops below freezing, it cycles the pump for 1 second, then waits a minute, pumps again, etc. My thinking is this will keep the water moving. I only want to cycle a little warm water into the panel, dont want to have a cold shower next morning. So just wondering what experience others have had with non-antifreeze filled panels in cold climates? Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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Madness Guru  Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
When I lived near Toowoomba I bought a solar tank cheap as the panels had frozen and split. The system I had set up was thermo syphoning with a frost valve that dumped water out of the bottom of the panels if the temperature was low enough. These would be available from any solar supplier. We never ran out of hot water with this system, when you get frost is in clear weather so your tank will get plenty of sun during the day. Do you think 1 second a minute is enough to keep the panels from freezing? What if you ran the pump long enough to put fresh water in the panels and let it do this each time the temperature drops to your threshold. Most Solar systems only circulate water from the bottom 1/3 of the tank so it should not have much effect on the hot water at the top of the tank. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
When i built my picaxe controller for the hot water i also included a short run period every few minutes just to move the water around should it fall below 1C on the panel sensor, so far i dont think i have needed it, but my view was its too late when you find out later it was needed and you have split panels. I still think a coldish shower is better one morning than no shower at all for a week while you repair the panel. Pete. Sometimes it just works |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
This reminded me I should add the code to my Arduino controller to protect against frost. Probably not needed here but it won't hurt to have it any way. I have just set it to turn the pump on at temperatures below 1 at the top of the panels and leave it on until the temperature rises above 2. If it is triggered for frost FR will appear on the LCD until the Arduino is reset. //Madness Solar Hot Water Pump Controller #include <Wire.h> #include <LiquidCrystal.h> LiquidCrystal lcd( 8, 9, 4, 5, 6, 7 ); int relay = 10; //FSS1-102Z DC 5V 2A 250VAC solid state relay int potPin = A2; //LM335Z on hot water tank outlet to pump int potValue1 = 0; int potValue2 = 0; int pot2Pin = A4; //LM335Z on hot water panel outlet int pot2Value1 = 0; int pot2Value2 = 0; void setup() { lcd.begin(16, 2); // lcd rows and columns // initialize the digital pin as an output. pinMode(relay, OUTPUT); lcd.setCursor(4, 0); lcd.print("TANK"); lcd.setCursor(4, 1); lcd.print("PANEL"); analogWrite(3, 128); } void loop() { potValue1 = analogRead(potPin) ; potValue2 = (potValue1 * 0.004882812 * 100) - 273.15; delay(1000); lcd.setCursor(12, 0); lcd.print(potValue2); pot2Value1 = analogRead(pot2Pin) ; pot2Value2 = (pot2Value1 * 0.004882812 * 100) - 273.15; delay(1000); lcd.setCursor(12, 1); lcd.print(pot2Value2); if (pot2Value2 > (potValue2 + 6)) { digitalWrite(relay, HIGH); // turn the pump on lcd.setCursor(9, 0); lcd.print("ON "); } if (pot2Value2 < (potValue2 + 3)) { digitalWrite(relay, LOW); // turn the pump off lcd.setCursor(9, 0); lcd.print("OFF"); } //wait 0.1 seconds delay(1000); if (pot2Value2 < 1) { digitalWrite(relay, HIGH); // turn the pump on to prevent frost damage lcd.setCursor(14, 1); lcd.print("FR "); // FR will be displayed on bottom left //of LCD till Arduino is reset } if (pot2Value2 == 2) { digitalWrite(relay, LOW); // turn the LED on (HIGH is the voltage level) } } There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Thanks for sharing the code Madness. I'll have to grab a copy of the PicAxe code off my laptop and share that too. I've changed the frost pump on period to 5 seconds. See how it goes tonight. Was thinking, instead of circulating the hot water from the tank, what about heating the panels electrically? I'm thinking of fitting a low ohms 10 watt resistor under the glass, at the bottom of the panel. Say 22ohms, so its drawing half an amp and radiating about 6 or so watts ( My controller is 12v ). The air around the resistor would be warmed and rise, circulating the air around under the glass? I have two panels, so about 1 amp total, which isn't much. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
I would share my code to, but its all a little useless without going into the detail of the circuit and how to build it. Rather than adding extra heating to the panels, i would think it more efficient to simply bring the heater element on to compensate for the added heat losses, using some heating control via the picaxe you can simply warm the water to compensate the losses by using the mains heating element already installed. At the end of the day its the same energy requirement regardless if it a panel heater or a water heater, so i would go with heating the water, and circulating it, as its the pipe work you need to protect and not the full panel. Like i say its better to have a luke warm shower in the morning than the need to repair busted pipes inside panels. Pete. Sometimes it just works |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
If your pump is only circulating the water in the bottom half of your tank you are not going to end up having a cold shower in the morning. The panel temperature only needs to be raised slightly to keep it above freezing. My old system used to dump water a few times on cold mornings but it was only a few litres each time. It certainly never left us short of hot water. The Arduino circuit is dead simple, how to wire the sensors is here and the relay is directly connected to the Arduino output. I have the LCD display on it but it is not really needed and could be left off without changing the code. When I get around to it I plan to put the code into a ATTiny chip, that would bring the build cost down to around $10. I built this controller when the original Rheem controller failed, they wanted over $700 for a new one. This started me on my first Arduino project and within 24 hours I had it working. Gary There are only 10 types of people in the world: those who understand binary, and those who don't. |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
It will be interesting to see how you get on. I agree with Gary, every time a tap is switched on cold water is introduced to the bottom of the tank and the hot layer seems to cope OK so I dont see how a small frost cycle would be any worse. I'm confused, no wait... maybe I'm not... |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
The way my pump works it would be pumping the cold water into the top of the tank, so it would be cooling the warm water instead of gently pooling at the bottom. My thinking is its very hard to detect frost reliably. 2, 1 or even 0 degrees is OK, but -1 and less means trouble. To play it safe, cycle the pump just above 0, but thats a waste of warm water, in winter most nights here get to 1 or 2 degrees, but not freezing. If I use a couple of resistors under the panels, I could turn them on manually at night if there is frost predicted, knowing they would reliably protect the panels. I would later automate it, so they cut in a somewhere around 5 degrees, give or take a error safety margin. In my situation I'm not concerned about the pipes between the panels and tank. They are short runs, a couple of meters at most, and wrapped in insulation. Its the panels that can radiate their heat into the night sky that gets the coat of ice. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
In that case it would be worth looking at the frost valves that just work on temperature and drain water out of the panels. This should not effect your hot water as it would be taking in more water on the cold inlet. The valves would be available from any solar hot water supplier. Or you could make an electronic version and just fit a washing machine type valve to the bottom of the panels. Then you could direct the water coming out back into your tank if the panels are not on your roof. This would also help protect any exposed pipes in your plumbing. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Madness, How can that work with a pressure feed system, as it will just keep draing water to waste, and cost a furtune in pump running costs. It only works with a static system where a punp circulates the water and not a mains pressure loop. Pete. Sometimes it just works |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Sorry but you are wrong, it works on a pressurised system. When the temperature drops the the valve opens and lets out the very cold water until it warms a little and then shuts off. Water is supplied by the pressure pump or mains pressure. It does not drain very much water and the system I used to have drained onto the roof and went back into the rain water tank. If it does not work then why do the manufacturers do it that way? There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
I was wondering the same Pete, makes sense now, thanks Madness. That could work on my system, I would need to relocate a check valve, and it would only be flushing the panel with cold water from the bottom of the tank, and not introducing any cold water into the top of the tank. Yesterday as a experiment I fitted a couple of 22r 10w resistors into the panels. Connected in series, so each resistor was radiating about 1.5 watts, current draw works out at .27 amps. This morning the panels had a thin layer of ice, except for a hand sized area above each resistor, where it was bone dry, and the top 3/4 of each panel was also frost free, but wet with dew. Tonight I'll try the resistors in parallel, so each is radiating about 6.5 watts, current draw about 1.1 amps. My 12v system can spare a amp or two, so its no loss. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Photos of the resistor... 
And the panel early this morning. You can see where the resistor sits under the glass. 
Only the bottom corner had any frost on it, which makes sense. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Madness, Now i undertand what you meant as "dump water" i had thought you meant it dumped or drained the panels as often used in a country with below zero temps,and could not see how that would work in this case. Glenn, As Madness has pointed out a simple return drain soleniod would do the same job, and use a fraction of the power with a good result. Even using a garden irrigation solenoid with flow control adjustment would work well. Pete. Sometimes it just works |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Yeah may look into it. The heater resistors are working well, and I can spare the amps. I cant spare the water, so would need to feed the dumped water back into a tank. Priced a frost valve, not cheap, so the garden irrigation solenoid and controller ( or add on for my existing controller ) would need to be built. Honestly, the heater resistors are a simple fix. Silent, no water used or heated water lost. They are connected to my night light controller, so cut in at dusk and off as the sun comes up. I do have a couple of spare panels if it goes pear shaped. The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Gizmo et al I wish I understood electronics, but alas, I've a cave-man mentality in that area. What I do understand is mechanics and thermodynamics. On my own solar water-heating system, I utilize a set of ball valves, which allow me to shut off the incoming water supply to the panel, isolate it from the receiver (storage tank), open a vent at the top of the system and dump the contents of the water trapped inside the section exposed to sunlight. Yes, it does waste about a quart or maybe a little more of water, but that flows onto my garden below, so it's not really wasted. With NO water inside the pipes, they, as well as the brass fittings connecting everything, cannot freeze. I used "Pex" (polyethylene) pipe in the entire system. The pipe won't crack even when it freezes, BUT the fittings, if allowed to freeze containing water WILL crack, therefore the vent-and-drain application. It works like a champ. The only drawback is you have to remember to go outside and do it BEFORE everything turns to ice. If I'm away, I'll usually leave it drained and when we are in the middle of ice storms and freezing weather in the Winter here, I just leave the solar application drained and off. I mounted my solar panel BELOW my storage tank and utilize "thermo-syphoning" as an effective "pump" to circulate cold water from the bottom of the receiver, through the panel, then to the top of the receiver, where it mixes with the rest of the water in the tank. This arrangement provides me with 50 gallons of boiling-hot water all late Spring through early Autumn and it's just 4 little valves; very simple. . . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Mac, I was in the same situation however there is a possible solution. Try spending some time learning about the Arduino which is a very cheap micro controller. There is a huge amount of circuits and code online to cover an incredible range of projects. Also there is a vast range of sensors, servos etc available at little cost on ebay and many retailers in the US. With a little persistence it will allow you to greatly expand what you can build. Gary There are only 10 types of people in the world: those who understand binary, and those who don't. |
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rustyrod Senior Member  Joined: 08/11/2014 Location: AustraliaPosts: 121 |
With 240 available look at these from 1 metre to 18 meters http://www.ebay.com.au/itm/Water-pipes-heating-cables-heater -Anti-Freeze-Frost-Protection-Various-Length-/141087257751?p t=AU_Building_Materials&var=&hash=item20d974b497 I might get one and have it wired to the night rate, so the power company can switch it on and off for me  Always Thinking |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi All I had the freezing problem when I lived in Victoria years ago and I used a thermostat control to pump the hot water back into the collector it switched the circulation pump on at 3 C and of at 6 C it only ran for several minutes to do this and the hot water loss was not a lot over the night, better than frozen collector and pipe damage, it survived quite a few -10 C nights like that, I put the thermo sensor in the panel as I found it was warmer in there than outside and that was where the water was. It was a bit crude but effective, a better system would have been to have a tank with internal coil and use antifreeze but the tank I had was an old copper storage tank with a capacity of 100 gallons mounted up in the ceiling. It also had a electric element in the tank that could be turned on in the event of no solar energy which happens a bit in the cold southern country. All the best Bob Foolin Around |
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