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Forum Index : Solar : Micromite powered solar hot water
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Just a couple of photos of my solar water heater based on a Micromite. 
The system consists of a couple of solar panels and a 300 liter hot water tank, all second hand, totaling about $300 from memory. The controller is based on a Micromite, has 3 outputs and reads from 4 temp sensors. The controlled is aware of the time, and uses one output to switch on a night light ( 12v fluro under the house ). It also uses the time to trigger certain events, for example, the heating cycle only happens between 7 am and 5pm. The heating cycle runs the pump for a couple of seconds every 2 minutes, just to push a little hot water past the panel temperature sensor. It then compares the panel temperature against the tank temperatures ( Tank Top and Tank Bottom ). If more than 10c above tank temperature, the pump runs for 20 seconds, which will force all hot water from the panel into the tank. Once the tank temperature is hot ( 60c at top, 40c at bottom ), the heating cycle stops for the day. Generally the tank is hot by 10am on a clear day, and 300 liters of hot water will last 3 to 4 days if its overcast. After that, I have a on demand gas hot water system I can turn on, I dont like cold showers! It also has a defrost cycle. If the air temperature drops below 4c, it turns on some heaters in the panels to protect them. If the temp drops below 1c, it will start cycling warm water into the panel. The only problem at this stage is a drift in the time, which was a problem with the early Micromites. It gains about 3 minutes a day, but at the moment I can live with that, I just reset the time once a week. The LCD displays the 4 temperatures, supply voltage, time, and other status infomation. Two buttons give me access to a menu system where I can set time, temperatures, pump duration, etc. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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Zonker Guru  Joined: 18/08/2012 Location: United StatesPosts: 761 |
WOW.. Nice "working" project Giz..! Now, is that the hot water tank behind the panel in green..? Man... Now that's what I call a hot water tank..!  Looks like an awesome design and seems to be working out well for you... I do love it when one can actually finish a project..! I seem to have several NOT currently there yet... I like the "see-through" box you got... It has the water tight ring seal I think.. Anyway, I was wondering if you used thermo probes, (like type "J") and what type of "front-end" interface circuits you used..? I have tried several different kinds... (just wondering)...
Nice control system..!  |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hi Zonker Nah thats a 22,000 liter rain water tank. The hot water tank is under the house, next to the controller. I didn't upload a picture as its covered in insulation and a ugly looking monstrosity. I used LS18B20 probes. Bought a pack of 5 off eBay for about $10, water proof. They interface well with the Micromite, and give a reading in degrees celsius, so there is no need to calibrate or convert the figures. The previous controller was a much simpler device, used a PicAxe chip and 3 thermocouples, it worked, but was a bugger to set up. For me the big feature of this new controller is I can see just how warm the tank is without putting my hand on a uninsulated outlet pipe. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
That looks great Gizmo. One of those things on my long to do list. :) How do you prevent the water carrying salmonella? Is it just a chlorine tablet ones in a while or do you use another process? Here in Thailand solar power is underused. At the makerspace we would like to startup some solar projects and the hot water seems cheap enough to make and easy enough for people to replicate. The salmonella thing is me maybe worrying to much, i have no experience other then using an electric boiler that keeps water above 60c all the time, which is a waste of energy. Water tanks are common here and so are the chlorine tablets. I was just wondering if keeping the water at a higher temperature will change the amounts needed. Microblocks. Build with logic. |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6098 |
I am not sure of the actual requirements, but if you heat the water to above ~60 degrees for a few hours a day, the risk is minimal. The usual method is to switch a mains powered heater on at the end of the day so that the sun has had a chance to do it's thing. Solar hot water is something on my 'to do' list also. Jim VK7JH MMedit MMBasic Help |
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| plasma Guru Joined: 08/04/2012 Location: GermanyPosts: 437 |
This is a cool project . I like the way using this little pic and MMbasic. Btw use a cheap gps receiver and you can forget your weekly reset. |
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| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2817 |
Nice use of the MicroMite there Gizmo
I was going to suggest a GPS receiver to resolve your time issue but I see Plasma just beat me to it. On ebay you will get one for $20ish; or go for a branded one for around max AU$50. Sorry if I missed it, but are the Light & pump battery driven (recharged from solar panels) OR are they mains powered? WW For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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| ajkw Senior Member  Joined: 29/06/2011 Location: AustraliaPosts: 290 |
Good work. If the time error is fairly constant then perhaps you can code in a routine to correct the time daily. Eg*. Option explicit Dim flag Dim timetext$ Dim oldtt$ Time$ = "00:00:00" Do timetext$ = Time$ If timetext$ <> oldtt$ Then Print timetext$ oldtt$ = timetext$ If flag = 0 And Timetext$ = "00:00:10" Then Time$ = "00:00:00" flag = 1 : Print "flag 1" EndIf If flag = 1 And Timetext$ = "00:00:11" Then flag = 0 : Print "flag 0" EndIf If timetext$ = "00:00:15" Then Time$ = "23:59:55":Print "Jump" Loop * Example Code Only. May not be fit for your purpose. |
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palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1873 |
TZAdvantage wrote I don't know what the water in Thailand is like but the water in Australia is maybe the best in the world. We never have a problem with our tap water. I have had solar hot water for about 35 years. I live in Nth. Queensland and our water comes from a dam up in the mountains not far from here. When we recently filled our swimming pool the water from the tap was crystal clear. The water suppliers filter the water and add the necessary amounts of chlorine and in most places also add fluoride to stop tooth decay. Paul. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| plasma Guru Joined: 08/04/2012 Location: GermanyPosts: 437 |
Legionella is a problem all over the world , i fear. But if you have over 60 grad celsius on day per week its ok. |
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| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
Plasma, I got my bacterias confused. Little buggers. It is indeed Legionella. I actually worry about this because the temperatures are often between 25 and 45 degrees celcius, the ideal temperature for Legionalla to grow. I made a little solar heater a while ago just to test it, even in winter time i got it to heat up to almost 80 degrees celsius. The holding tank however did never go higher then 50-55. (I could have better result with good insulation, i used none at the time). The one i want to built will use oil and use copper tubing as an heat exchanger to heat up the water. With oil i probably have to make sure it does not get too hot as i will then create steam. When all works well there isn't any water in the system, only ones the tap is opened will water flow through it. The theory here is that the oil will be hot enough to keep the tubing clean of bacteria. Microblocks. Build with logic. |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
I had the building inspector over yesterday doing the final building inspection. We talked about the solar hot water system, and he said chances are it wont pass the plumbing inspection because its not set up correctly. So before I get the final plumbing inspection done, I'll remove the tank and only run the on demand gas water heater. As mentioned above, the tank needs to go over 60c to kill the bacteria. Problem is in winter the system will struggle to do that, because its a big tank and I'm not using the booster element. Plus, I need to plumb in a diverter so the temperature at the tap cant exceed 50c. So to pass, tank needs to reach 60c, but then the water needs to be cooled to 50c before it leaves the tap. So as I mentioned, its easier to take the tank out of circuit for now, and look at some changes once the plumbing final inspection has been passed. What I may do is electrically heat the tank to over 60c once a week. Usually in winter my batteries are charged by midday, so after that I can spare power to heat up the water tank. I'll have to get a lower wattage heater element so I dont drain the batteries. In summer its not a problem, the tank reaches 60c by late morning. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
Similar issue here. The regime I am using is tank to 60C once a week and the top half at 60C once a day or before showering. Fortunately. I have a wet-back to boost it when required. Check with your own local regulations. Dave |
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VK6MRG Guru Joined: 08/06/2011 Location: AustraliaPosts: 347 |
Just wondering, Could you have solar boosted instant gas hot water? Have a small tank with solar circulation pump to pre heat the water before the instant gas system? Not sure if the gas unit will like hot water or not. Has anyone got a system setup like this? And does it work well? Also, It's been a while but the maximite i have around here somewhere (haven't played with it for a year or so) has a real time clock that I added. Could you do that with the micromite? Just a thought. Its easier to ask forgiveness than to seek permission! ............VK6MRG.............VK3MGR............ |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Trying to develop something similar myself. In the process of learn how the ParkAssist code works & hoping to use it as my interface. Have it display 4 different temperatures:- Air Temp, Water Temp, Panel Input Temp & Panel Output Temp. And use the touch screen to input my operating parameters. Think it's probably 25-30 years since I've looked at any Basic code, so a little rusty & the learning curve will be steep, so could have my hand up for help on numerous occasions. Cheers Phil |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Hi Glenn & Others, Have a handful of DS18B20's on the way. My initial thought was that they would each have their own pin on the MicroMite. Is the idea of daisy chaining them all off one pin & using ONEWIRE READ to read them all just way to complicated to consider Vs the little bit of simplicity I would gain in the physical running of wires to sensors from the controller. New & Green to this & don't want to create nightmares. Cheers. |
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| isochronic Guru Joined: 21/01/2012 Location: AustraliaPosts: 689 |
I guess a super-deluxo megabuck version would have a holding tank for the solar heated water (or oil etc), with a heat exchanger to preheat the domestic use water, as well as a electric or gas top-up to cook the bugs. With enough preheat the electricity would not be required at all. Expensive to set up though. I am wondering if "coolth" can be stored instead of heat ? In the country the temperature plummets overnight, maybe freezing, and then air-con is wanted during the days heat. eg ordinary brine would chill down in a radiator overnight, then used for daytime cooling (?) |
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| Lightrock Newbie  Joined: 19/05/2014 Location: AustraliaPosts: 26 |
The second paragraph of Measuring Temperature on page 24 of the Micromite User Manual V5.1 states '--- Multiple sensors can be used but a separate I/O pin and pullup resistor is required for each one.' |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Page 24 is referring to the use of the TEMP() function, which is 1 sensor per input pin. What I'm wondering about is the ONE WIRE communications mentioned on page 90. Wanting to know if that method would be way too complicated. |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Hi Greg, Are you using time a the string returned by Time$ or is it being converted to an numeric format. Considering using the clock to dictate that for my spa controller, but also thinking of a Solar panel as a "Sunlight Present" indicator. Even so, I'll still want a time based variable to dictate That the heat pump can be turned on after say 5pm is the water is not up to temp. Is just using time$ the way to go, or is there another variable that can be derived? Ie 0 to 1440 minutes, or 0 to 84600 seconds. I will need some sort of timing between cycling the heat pump off & on again to avoid compressor lockup. Cheers. |
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