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Forum Index : Solar : Simplified Solar Hot Water
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| Davo99 Guru  Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
To a degree I understand that. I have had a learning curve with solar as well. It's different to most other forms of power. With other things if you have say 250W, You have 250W. With solar you bog it down and you have 57W... maybe. Some of the convertors and related advise are pretty misleading even by informed people. There are vids saying you can heat how water with a ew hundred w and a controller. then you find the water they are heating is barely enough for a very quick shower and that's going to take a lot of time on a sunny day. On a cloudy day, You are SOL. I have also found a lot of solar ideas are all low voltage and basicly tiddly winks unless you go grid tied. I have got a couple of KW of panels and hooked that to elements and it works well but finding any sort of pre built controller is impossible. Direct solar heating isn't all bad either if you use the brute force method. May not be efficient but for those like me that don't have the smarts to build a controller, having something rather than nothing is still a bonus. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
The idea is pretty simple, and it can be done with very few parts. As you say, bogging down the panel with excessive loading on really evil grey days is a definite no no. So its just a case of keeping the panel operating voltage working around the sweet spot, and you don't need a fancy mppt software tracker to do that. It just requires reading the rating sticker on the panels, and from that (and knowing the number of series connected panels) working out a suitable voltage operating range where the efficiency does not fall away too much at either the high voltage end or the low voltage end. And its not as critical as many people would have you believe. People think of the peak power operating point as being needle sharp, and if its not exactly at the 100% power point its going to work like crap. Its not a power "peak" but a bloody wide flat hump. And something pretty basic will recover at least 90% and more likely 95% of all that there is there to get. If you want that extra 10%, just fit one extra panel its much more sensible than trying to squeeze the last .001% with an expensive and exotic control system. Cheers, Tony. |
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mackoffgrid Guru Joined: 13/03/2017 Location: AustraliaPosts: 460 |
I agree that MPPT is kind of over rated or emphasised. As an offgrid site, you have to / should install far more capacity of solar power - because its cheaper than batteries. On my hot water inverter I did incorporate a hill climbing MPPT algorithm, I wasn't going to, but I did because I could  |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
I found this calculator which is handy for those that struggle with Ohms law. Didn't know this part of it that well myself but the calculator actually allowed me to understand it so I can work it out myself now. It's near the top of this mans site. https://www.davidpoz.com/ I have modded a saved copy of the sheet to work with the specific panels I have. Just makes the tooing and froing much quicker. Spot on. The other thing I found with solar that's pretty flexible is tilt. The " Ideal" Tilt actually isn't. It's a general all round that really gives the best performance maybe a month in total for the year and the rest is sub standard. Direction has a bit more effect but my south facing panels on the shed can still contribute a useful amount of power in summer. Garbage in winter but in summer, gives me power I wouldn't have otherwise. I like to set up for winter optimisation where I can because the longer hours of sun in summer and the higher radiation levels mean the summer output takes care of itself. IMHO peak power is also greatly over rated. On a normal system where the panels are only up to 30% overclocking the inverter, peak power is still rather fleeting. For me, the real money is to be made in the ramp up and trailing off periods. The goal should be to get the inverter working as hard as you can as long as you can. For that there is no substitute for square inches. More panels you have the faster the inverter will light up and the later it will shut down with a better output for longer in the day. Was it you Tony that came up with the 60O east west panel configuration to deliver the most consistent output for battery charging? Again flying in the face of convention but perfect for the practical goal of most consistent output for the longest period. This is my rule of solar inefficiency. It's always cheaper and more productive to just add more panels and forget about the efficiency than to try and make the ones you have work harder. This is especially true for bad weather. More panels you have, the greater the output when the efficiency improvements add up to basically a few watts that don't make a difference of any meaning to the days total anyway....within reason. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
No not me, someone else invented the "passive tracker" but it sure works very well. Here's mine, 60 degree elevation facing due east/west on the garage roof.  Its only 1.2Kw + 1.2Kw but it gets going a good half hour earlier than the big north facing system, and hangs on for another half hour late in the afternoon (in summer). The power comes up pretty fast at sunrise, remains almost constant all day long, then drops away rapidly at dusk. In fact this might be more useful where there is no battery, or for grid tie where the max power that can be fed back into the grid is limited. For battery charging or heating water, easterly facing panels might be best, where you want big power for bulk battery charging, or rapid heat recovery early in the day. For airconditioning, westerly facing panels should give their max power in the afternoon and early evening. Its best to think the whole thing right through, as different solar applications can benefit in different ways from most suitable panel orientation. Cheers, Tony. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Exactly why I have put up an array on the west roof of my house. Although not wonderfully insulated, The place does not get hot till 2 pm or later even on 40+ days. Once the heat permeates the walls and insulation though and gets low enough to come in the windows, watch out! I suggested growing some seasonal Vines on the back west wall of the house the other day to provide summer shading and much to my amazement, The mrs said yes. Exactly except most people won't do any homework on things and just want to follow the parroted mantra's or worse still, what a salesman tells them. Edited 2019-10-12 21:13 by Davo99 |
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| mackoffgrid Guru Joined: 13/03/2017 Location: AustraliaPosts: 460 |
Davo99 I thought this might interest you. I've not read it thoroughly - basically heats hot water by a variable amount according to what energy is spare. myenergi - eddi - Energy Redirector cheers Andrew |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Thanks for the link. I have seen similar products but this one seem to have a high power rating and two controllers for different loads which could make it much more practical than others which only seem to be for water heating. They seem to be expensive for what they are and one would want to have plenty of solar to get the best return on it I'd say. The philosophy is good though, always cheaper to use your own power than that from the grid. There are more inverters being made now that have the hot water diversion feature built in. I always thought this was a glaring omission. Get 6 cents for the power you send to the grid in the day and buy it back at 11C during the night. It is that difference you have to play off against the cost of the diverter though. Things sure change quick with solar. Month ago I was still not quite breaking even. Now, Making more power than I know what to do with. Still looking for that power hungry summer business where I can put it all to use. One thing I do is boil water. I use that on the garden for a non chemical weed killer. Does a great job and I can plant in the garden an hour later If I want. The Mrs is wanting to get a Spa. That would be something the excess power could be put into but I think I'd probably go for an oil burning heater to get the temp up a lot faster and not have the power drain in winter... If I wanted to use it then. |
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| Boxelder Newbie  Joined: 25/07/2019 Location: United StatesPosts: 4 |
Hi Tony, First post here. I'd like to put together a system like this but I'm running into trouble finding the postage stamp size SM12 12v power supply. Could you please pass on a link to an example of which one you'd recommend? I'm assuming it's a DC-DC step down able to handle the 288vdc on the input from your example, but I just want to make sure. My system will be very close to these specs, as the panels have a max power voltage of 30.2v. Really appreciate you sharing this with the rest of the class, thanks very much! |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Welcome to the Forum Boxelder. These little two dollar power supply boards are the "guts" out of standard dc wall packs, or dc plug packs. Made by the million in China, and available from many sources such as e-bay and Ali. https://www.ebay.com.au/itm/AC-DC-Power-Supply-Buck-Converter-Step-Down-Module-5V-12V-3-3V-9V-24V-500mA/262807265342?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D94f27eb622014f518356976f95a1a734%26pid%3D100675%26rk%3D5%26rkt%3D15%26sd%3D192619265858%26itm%3D262807265342%26pmt%3D1%26noa%3D1%26pg%3D2380057&_trksid=p2380057.c100675.m4236&_trkparms=pageci%3Ae317b2a2-ff6d-11e9-82f5-74dbd180777b%7Cparentrq%3A393c9c0516e0a4b7fcafaa6cfff27579%7Ciid%3A1 They are designed to run of ac mains voltage anywhere in the world from 85v to 265v, but also work perfectly well (at reduced load at minimum voltage) when powered directly from dc, between about 45 volts to 400 volts. The very well regulated dc output voltage is completely isolated from the input, and the output is current limited and short circuit protected. Edited 2019-11-05 13:07 by Warpspeed Cheers, Tony. |
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| Boxelder Newbie Joined: 25/07/2019 Location: United StatesPosts: 4 |
Thank you so much! I really appreciate the insight. Looking forward to trying out your design. This forum is an excellent resource. It's also greatly appreciated, and thanks to its operators as well. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
I bought a bunch of those a while back after seeing Tonys Recommendation and they have come in Very handy and work very well. Bought a lot of stuff off Sheildsfans and deepinmind on ebay and always been reliable. I suspect they are the same company ( along with a few more) under different names. I have a very simple solar hot water setup atm. Put about 6Kw of panels on a 3600W element. It's not efficient but it is simple! Boiled water yesterday about every 2.5 Hours for a 100L. I reckon the first batch will be ready by about 11 am if not sooner. The weeds are getting a hammering round here. :0) |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I used to buy a lot of small transformers to make 12v and 15v dc power supplies for various small projects. The transformer was often the largest and most expensive individual part. These little Chinese power boards are perfect for all kinds of things, and so cheap  Cheers, Tony. |
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| nickskethisniks Guru Joined: 17/10/2017 Location: BelgiumPosts: 409 |
oops Edited 2019-11-07 19:11 by nickskethisniks |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Last couple of days have been bright, warm and sunny here, and windy. The tank I am heating is a 120L plastic drum that is uninsulated. I have covered the top with styrofoam but it is very evident how much longer it has taken to boil thanks to the wind. Yesterday I looked at it and there was 250V at the element indicating there was more than enough solar going to it. Barely got to the boil all day thanks to the rotten wind and when it did it got cloudy and went off the boil anyway. I discovered this is a lot more useful than just killing weeds. I threw some of the Mrs baking dishes in the boiling water and left them there a few hours. Didn't exactly come out like new but they were certainly at least 80% cleaner. A day in there with some soap would probably have them perfect. Might try some of my old work pants next with some washing liquid. My neighbours years ago never had a washing machine but used to boil all their clothes in an old copper. Might be a modern way of using an old technique. Then again, with todays synthetic fabrics, you might just pull out a lump of molten plastic from the bottom of the drum. |
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| Boxelder Newbie Joined: 25/07/2019 Location: United StatesPosts: 4 |
Hi Tony, Sorry for the amateur hour question, but I have to ask - on the transition between the first slide with the solar, capacitor, indicator, and heating element it's numbered 123 top to bottom but on the second Circuit Board slide it's reversed 321. I built this circuit both on breadboard and then on perf - which was my first attempt at this type of build. I probably screwed it up somewhere. Nevertheless, I find myself getting all confused when I try to make the connections between the "Circuit Board" on slide 1 and "Power" on slide 2. By following the numbering it ties the negative side of the heating element directly to ground, which has the effect of bypassing all the other circuitry. To verify this I disconnected the circuit board and capacitor, and it runs at the exact same voltage and amperage, about 150v and 8a. The amperage is dead nuts on rating, but the VMP voltage on the panels should be about 240v with 8 in series. The neon indicator is lit steady on, but I'm assuming it should be pulsating varied speeds based on how often the capacitor is discharged? Any thoughts or hints would be greatly appreciated. I'm very sorry if I'm misunderstanding something, which is entirely likely. Thanks very much in advance. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Yes you are quite right about the 123 and 321 numbering mistake. I did not spot that error until long after it was too late to correct. A Forum post can only be edited while its still the most recent. If anything is posted after that, editing it later on cannot be done. Anyhow, the connections on both diagrams are in the right physical order and labeled correctly, just ignore the numbers. Top is the heating element connection, middle is the full positive solar voltage, and bottom is common negative. The heating element will remain off until the capacitor and solar voltage reaches the upper voltage threshold. The mosfet should then turn on and connect the heating load to the electrolytic and solar panels. Now if there is a clear blue sky, plenty of sun, and there is enough power from solar, there is the possibility that the voltage may not be pulled down far enough by the heating element to ever disconnect the heating element, and the neon indicator stays on all the time. That is actually very good, the heating element will be using all of the available power continuously. However at dawn, dusk, or in cloud where solar is marginal, it should then cycle on and off at a rate that varies with the amount of available solar. Cheers, Tony. |
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| Boxelder Newbie Joined: 25/07/2019 Location: United StatesPosts: 4 |
Excellent, thank you so much Tony! Will give it a shot. |
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| iispip Newbie Joined: 03/12/2019 Location: IrelandPosts: 4 |
good day Guys - thanks Tony for this info. has anyone made this device and what is the max watts - volts ye guys are operating the device at ? i would like to run with this option so any info would be great... |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Welcome to the Forum iispip. Its still very early days yet, just be patient its winter up your way anyway. Much more likely for one of us Aussies to cobble together something first. Cheers, Tony. |
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