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Forum Index : Solar : Hot Water Boost.
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| Phil23 Guru  Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Just wondering how this concept sits with others. My mental gears started turning after reading this thread. (And I did get a chuckle Mad, Re certain suggestions). Wondered what sort of gain I'd get by circulating the water from my HWS thru one of these during the day. At 3000W I could possibly PWM drive it at a level that would keep the inverter against the stops & utilise the panels to their maximum capacity. First catch is it wouldn't help with the evening usage, as the ripple timer off-peak would still cut in & reheat after 10pm. But if I had it circulating & heating a primary feed tank & could at least be topping the OP HWS up with something that's a bit warmer than what it already gets. OR, should I just consider PWM controlling a standard element in the spare tank I have? (Centre element unfortunately). Right now my Off Peak usage is heading thru the roof. Gone from about 5kWh a day up to 12-15 range & still climbing. All due to the change in our supply temp. The HWS runs at 85°C, before the tempering valve, but the cold supply has dropped from around 23° in January to 9° now. Phil. |
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| windlight Guru Joined: 03/03/2007 Location: AustraliaPosts: 331 |
If you use one check the earth, Chinese equipment is not known for having earths connected. Allan "I like this place and willingly could waste my time in it" - (Act II, Scene IV). |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
I used one of these in my caravan for the sink, and they aren't 'that' bad, but the temp was barely warm unless you were literally running a trickle through it, then it could get quite hot Most dubious thing about them I found was that many only come with a 10A lead and plug- that lead used to get HOT, I opened mine up and fitted a good heavy 15A power cable and hardwired it into the wiring, I wouldnt suggest using the factory wires especially if its going to be running all day... In fact I would suggest rewiring everything inside, the cables were extremely thin for the load it pulled |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Safety is a big issue with those devices, I have spent quite a bit of time in Thailand and those shower heaters are quite common there. Also what is common is people dying due to being electrocuted by them. There are the cheap ones and others made by better-known manufacturers such as Sharp and Panasonic that have RCD's built in. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
First thing is how much solar power do you have to throw at the water heater? If it's like 500W, you are not going to get a lot of gain if your water useage is high. My suggestion would be to connect the spare tank as a feeder for the main tank you don't touch anything on the main tank other than the water supply. On the spare tank, have a PWM controller feeding that the power you can dedicate. I presume that is an amount of power you usually backfeed to the grid? I have this set up but with a Voltage monitoring relay connected. It senses when the line voltage goes high from the solar feed and switches on through the PWM. This way the heater is not sucking through the night when there is no solar, only when there is enough power from the GTI to not only indicate solar generation, but enough generation I have measured to give me the 1500W I have dialled into the PWM plus some headway for other intermittent loads like the fridge. If I turn on the kettle, the Monitoring relay will give it 10 sec then if the voltage is still below threshold, It will turn off the heater till it comes back up again. Preheating the water will save you preheating on the off peak on the main tank. If you only raise the feed tank from 9 to 23o, you know how many KW that's going to save you alone. This way you are assured of hot water all the time because your off peak will kick in to make sure the main tank is always up to temp. I have mine with no off peak. Runs entirely though the PWM triggered by the voltage relay. I have had to manually over ride 3 times so far since feb. One of those was a false alarm. Asbestos hands wife complained the water wasn't hot enough for washing up. I over rode the relay and straight away checked the water temp and burnt my hand. No way in hell you could have showered in that without diluting it with cold but to the mrs, it wasn't hot enough. Told her next time, just boil the kettle and put that in the sink! The benefit we have seen with the solar heating is ( generally) the water is hotter than before. The women noticed that and pointed it out to me. I think the reason is our useage pattern. Off peak is 11pm to 5 am. We shower at night, generally late, 10-11 PM so the water may have been sitting in the tank 18+ hours since the off peak stopped. With the solar in summer, It might have been heating up to 3-4 hours before we used it. I have read that a normal HWS can drop 9o in that time which is significant. I'm pretty sure the adjusted heating time has been an advantage in being hotter when we use it. You could also do this with Direct DC straight to the main heater and have the off peak as backup if you want to go straight from the panels or have a dedicated set. Using a DPDT and a Mosfet, you could feed the heater solar through the day and then top off with off peak at night when needed. |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Phil you can drop back the power consumed by the 3.6KW element by putting a motor run capacitor in series with the AC L connection. You will have to play around with values. The following Arduino code works well with my regulator to divert excess power across to the HWS. The resulting PWM output needs to be stepped up to 12V which can easily be done with a 2n2222 transistor on the low side to drive a 25A AC SSR. if (vin > (Setpoint - 0.2)) { hwval = (hwval + 4); } if (vin < (Setpoint - 0.4)) { hwval = (hwval - 14); } hwval = constrain(hwval, 0, 255); analogWrite (PWMHW, hwval);  There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I'd like to find someone who could build me an arduino with either staged or variable PWM so the output to the heater could match the input From the solar. Something that would do a small input in the morning as the sun came up and ramped up the output then tapered off when the input declined. Having a fixed output which I have as pretty low to make sure I don't grid draw can be inefficent but using the monitoring relay sure is better than just a timer. At least when I'm home which is a lot of the time I can turn up the PWM on high output days although the 1500W input seems to do a pretty good job over the course of a day. Very overcast today so I doubt I'll get any heating at all. Not a big deal, only 2 of us here atm with a 400L HWS so won't even worry us till friday if there is no sun. If not, I'll just over ride the thing for a few hours to top it up a bit. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
George are you trying to get a 0 export by diverting all the power to the HWS from your GTI? There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
Ha, Didn't even see your post when I wrote mine mad. No, Not trying to divert it all for 0 export although I do have a practical need for that with something else and I have been trying to find a device to do it. Everything so far seems to control an inverter where I want something that could divert or switch off any source. With the heater, just trying to look for something that is more automated. Today for instance is cloudy and there will be little output but yesterday I could have probably fed 2.5 KW to the heater instead of 1.5. other days may only allow 500W. As well as the water heater, in winter it would be great to have something I could also use to divert varying power to something like a simple bar heater in the house. With such a devise I could use the excess power I have and if I put on the Jug I'd not be drawing from the grid because the devise would sense the lower line voltage and throttle the heater back or shut it off. Seems a simple thing but very hard to find... if they are even made. Seems a lot of things like this that could be applied to solar regulation just don't exist when I'm sure they would be dead easy to make. I was thinking of something that monitored the Line Voltage and kept that at a threshold. The more input the GTI's make the higher the line voltage so if I had something like the Voltage monitor that sensed that and then fed in more power as the line voltage limit allowed, that would be it. Something like what GTI does with loading panels. For the zero backfeed, I have an electronic metered phase in my meter box which I can't back feed. The age of the meter detects that as a reversal and attempt to steal power so registers a charge both ways. I'd like to be able to connect a GTI to that so I can supply the house loads connected without charging myself for the power I supply. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Line voltage will vary from all sorts of things within your property and outside. How much power you want to feed to your HWS is far to vague to write code for with what you have written here. "Today for instance is cloudy and there will be little output but yesterday I could have probably fed 2.5 KW to the heater instead of 1.5. other days may only allow 500W. As well as the water heater, in winter it would be great to have something I could also use to divert varying power to something like a simple bar heater in the house. With such a devise I could use the excess power I have and if I put on the Jug I'd not be drawing from the grid because the devise would sense the lower line voltage and throttle the heater back or shut it off. " What can be done and is available off the shelf is devices that detect when you are exporting power and divert it to your hot water system and aim for 0 export. If you are making more power than the HWS can take either by too much power or the thermostat has turned off it will still export. It would not be difficult to make a device to do this too a set a limit and would all be based on current. It could be setup to try to export 0 or limit to a value. The closest I can think to what you have asked for is to have knob on it that you can set the export limit as you desire. If the other project you are talking about is the one where you want to turn on GTI to meet the power demand of your air compressor or whatever it was I can't help with that. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
Hi Mad, What's your opinion on a simple energy monitor for measuring available solar for feedback to control micros. For example, on my Spa Controller; essentially a solar water heater, I have a little solar panel from a garden light with about a 10 ohm resistor across it. I then read the Vout from a divider I have across it to get it in the mV range I want. It's not totally linear, but the follows the pyranometer on my weather station with a usable error/variation. Surely with a bit better type of load circuit than a simple resistor, a reasonable reading of w/m² could be derived, & used in your code. AND, multiples could be used of course, so they had the same orientation as the panels. Phil. |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
I realise that is impractical so I have been trying to take another direction with that. Instead of turning the GTI on and off, it could be running all the time. It could be going to say a HWS or another dump load when the AC was not wanting current. When the AC wants power, it is switched from the HWS but only to what the AC wants to achieve Zero or very minimal backfeed. If I have to Feed back 100W while Pulling 2.5KW, good deal and I'm still ahead. Surprised the Chinese haven't come up with devices like these. Maybe we just have a lot more solar than anywhere else in the world and the million unit demand isn't there? |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Phil I am more inclined to think it is better to measure what you are exporting and base it on that, I have seen one type of solar power to HWS diverter that uses your idea though. You could use a sensor like this, depends on what your goal is though. Do you want to get the spa heated as cheaply as possible or just divert excess power to where it is useful? A heat pump would be a more efficient way to do it also. Was it you that was talking about the heat pump HWS that had failed controllers but good working compressors. An inverter type unit that you vary the speed with to suit the available power would give more heating for the same energy input. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
George Australia has the highest uptake per capita of PV in the world, there is lots of solar in China but I think a lot of it is big commercial installations. If you had your HWS, AC and GTI on the same circuit you could detect if there is any export from that circuit and vary the HWS so there is no export from that circuit. If done the legal way and the GTI is connected to the switchboard you could compare the export and import of 2 circuits and control the HWS to get 0 export. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308 |
Nothing stopping me setting it up anyway I like. The array I would put in if I could do this would be over the switchboard and easy to wire up. I'm having a guy come in to put in some HD circuits and was going to have one ran to that area just in case I ever want to put more panels there. I was running the numbers yesterday. having the panels facing west is a virtual waste of time for winter generation which is what I need to prioritize. Tilting them even 15 Degrees north adds about 30+% efficiency. Hooking everything into the one PHASE would be no problem at all. Not sure hooking 3.6 KW of heater and another about the same for the AC on the same circuit would be the best idea but Putting them on the same phase which nothing else is on atm wouldn't be an issue at all. AC is 3 phase where heater is single so could only partially put them on the one circuit anyway. All 3 circuits would tie back to the same phase which I would think would be workable would it not? |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
What you need is a point where the current can be sensed that is only showing the GTI, HWS and the AC. If that is reasonably close to the HWS even better. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
I am sure I saw some 'current shunts' suitable for AC work in one of my old mine electronics suppliers cattledogs, that read current as a voltage output.... one on panels, one on hws, one on grid and a small pic style computer (micromite?) to measure currents and switch on/off as required? eta A mate in Columbia just installed a solar system, and their grid tie/ islanding inverters can be set to export/not export/battery charge- all sorts of stuff ours seem incapable of doing grrr |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1664 |
The Spa is a completely different system; should have clarified that. It has 3 water heating panels, built from Corrugated iron sheets & irrigation pipe. Most of the detail is covered back here in a post 2 years ago. It has evolved a bit, has a heat pump incorporated, robbed from a Rheem HWS. On a slight tangent, I saw mention of Catch Power in a quoted post above. That company is about 60km's down the road from us. About 40 minutes in the bush... Cheers Phil |
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renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Probably just different software for the same inverter. Might be able to upload similar software to yours?? Cheers Caveman Mark Off grid eastern Melb |
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