Author Topic: Solar water heaters.  (Read 1688 times)

glort

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Re: Solar water heaters.
« Reply #15 on: March 31, 2019, 10:02:49 PM »

I was reading about a guy in Canada recently who linked to a vid on PV panel angle.
Due to the odd occasion when it snows and everything gets about a 1M buildup, some Canadians have found tilting their panels 90o, Straight up and down has worked well for them. 

Snow won't block them and because everything is white anyway, the power generated is significant just by using the reflected light.
One clever guy was talking about building an angled snow bank to specifically reflect the light back to the panels he has mounted on the SIDE of his home.
I read this is becoming a thing in the cities where there is no roof on top of tall buildings but they have massive areas on the side.  Not as efficient as on the roof but in the right place with the right orientation, they can get a load more generation from the building sides than the 4 Panels they would only have room for on the roof.

For PV at least, Vertical/ wall mounting where it snows seems to be a very viable alternative  to trying to clean snow off roof mounted panels especially where there is so much snow like where the guy I was reading about lives. A parabola type Snow bank which wouldn't be all that hard to map out with a piece of cord in an arc could be VERY effective in making power where it was not otherwise available.

Perhaps this may be worth looking into for direct water heating especially if a frame for summer and winter could be constructed that tilts.
Then again, If it can be made to work in winter, it will take care of itself with the much higher radiation in summer.
I Imagine one would just have to have a direct orientation to the sun unlike the PV you can bounce the light onto off a snow bank.

I'm building an oil fired heater for the house but would oil not have to be kept somewhere warm in snow conditions to stop it going too thick?
I mainly use Veg oil which isn't much better than water when it comes to Freezing, maybe worse, but I imagine even mineral oil would start getting pretty thick at  Minus C temps and be rather difficult to pump.

Do you use the water for space heating?
I have a 100 Gallon tank ( 400L ) for domestic hot water and that's considered big/ family size. Actually the largest available her.  Why would you need 2000l of hot water?

Might get my indoor hot tank ready this week. Sun is great right now and making too much power but the nights are getting very Chilly. Seems this is about the time to start testing if nothing else.

Our power is so crap here. All night I am reading 15V+ higher than what the voltage is supposed to be.  Clearly I'm not the only one with solar ( as I can see by roofs covered down the street and when the sun comes out the voltage pushes way high even when I turn everything off to do a reading.
In summer it was good, probably because everyone was running their AC and pulling it down to where it should have been.

quinnbrian

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Re: Solar water heaters.
« Reply #16 on: April 04, 2019, 03:02:48 AM »
The large Hot Water holding tank is for "staying power" if you have a couple of day where the sun doesn't shine , you will still have heat for the house, water , etc.
The big trick is getting it up to a good temper and maintaining it, get everything just right, and your golden...

glort

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Re: Solar water heaters.
« Reply #17 on: April 04, 2019, 10:04:02 AM »

I like the idea of plenty of hot water. I can just run ours every 3 days here if I like. Even just putting a few KW a day in  extends the time before it gets too cold. I think you get to a point where the losses outweigh the use and you might have say double the amount of hot water but only 50% or less days where it remains hot. 

I don't think many heaters here are well enough insulated to go beyond about 4 days even with no use at all.
The pressure release Valve on m,y heater and all I have seen is screwed into the tank and is brass. they are non insulated and then have copper pipe screwed in for the drainage which is another heat sink.

I'm going to take the copper overflow off mine and replace it with plastic and cover the valve itself with some sort of insulation I can move to get at the Valve. I have already heavily insulated the Outlet Pipe as that was literally blowing in the breeze as well.

The solar is falling off rapidly here.  Still making more power than we are using but only just.  Not using any heating or cooling atm either so once that starts, but sucking power big time.

Been working on my tropical design outdoor bathroom which I want ready for summer. My god those white Pebbles are a fortune as are pavers and all that other outdoor decorative stuff.  I can see this being another home improvement blowing out of proportion budget wise.

 Maybe better lay off that a week or so and get the oil heater up and running instead. I have been working on the generator but it's awkward and tiring work even with a crane to lift things.  When you are playing with 170Kg gen heads you are trying to position and fab frame work up for it's tiring for me mentally and physically.


buickanddeere

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Re: Solar water heaters.
« Reply #18 on: April 08, 2019, 06:47:20 PM »
Here in the land of ice and snow . We are getting away from plate collectors and pumping water . Instead PV panels are used to power resistance heaters in an “ordinary” electric water heater .
  No risk of freezing , less to leak, no pumping and higher water temperatures.

BruceM

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Re: Solar water heaters.
« Reply #19 on: April 08, 2019, 09:58:13 PM »
Big 4'x32' plate collector and 800 gallon insulated storage tank work great here for home and domestic water heating...but since I changed to 1/16 single glaze polycarbonate on the panel my winter peak temps are a lower, about 110F.  In Canada that might let the high temps too low from glazing losses. 

DO NOT use greenhouse double wall polycarbonate for flat plate collectors.  It will fail from heat stress/distortion; too much temperature difference between inside and outside, and the poly is too thin to take that much stress.  I've been very happy with the 1/16 single layer polyc.  I replaced it with.

Direct water heating gives you about 85% efficient energy collection, so for space heating, it's worth it.


mikenash

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Re: Solar water heaters.
« Reply #20 on: April 09, 2019, 09:18:10 AM »
A question from my electrically-challenged self, so excuse me . . .

Am I right in thinking that the element in my hot water cylinder is simply a resistance-becomes-heat device and that it won't give a hit whether electricity fed to it is AC or DC or what voltage it is?

(I was just reading the components of this and related threads about finding ways to "store" excess solar . . .)

Cheers

glort

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Re: Solar water heaters.
« Reply #21 on: April 09, 2019, 09:43:40 AM »
Here in the land of ice and snow . We are getting away from plate collectors and pumping water . Instead PV panels are used to power resistance heaters in an “ordinary” electric water heater .
  No risk of freezing , less to leak, no pumping and higher water temperatures.

I think the ease of PV and the fact the power can be dedicated to other uses when the water is hot has turned the preference for water heating around in a lot of places.

PV used to be considered a waste for water heating but that has now turned around. A lot easier to run wires, If you even have to, than do the plumbing for Direct.

That said, .....

Quote
Direct water heating gives you about 85% efficient energy collection, so for space heating, it's worth it.

What do you think of the evacuated Tube Heaters Bruce?
I have read and spoken to people first hand with very differing opinions of their effectiveness.

glort

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Re: Solar water heaters.
« Reply #22 on: April 09, 2019, 09:49:51 AM »
A question from my electrically-challenged self, so excuse me . . .

Am I right in thinking that the element in my hot water cylinder is simply a resistance-becomes-heat device and that it won't give a hit whether electricity fed to it is AC or DC or what voltage it is?


Sorry Mike, Much as I'd love to answer your question, I'm not going to waste 2 Minutes of my life I'll never get back writing a reply your lack of comprehension and reading concentration would be unable to cope with. 

old seagull man

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Re: Solar water heaters.
« Reply #23 on: April 09, 2019, 01:24:49 PM »
A link some my find interesting, much has been covered, by Glort.
But interesting reading, and we all love more information, don't we.


http://waterheatertimer.org/index.html

veggie

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Re: Solar water heaters.
« Reply #24 on: April 09, 2019, 02:27:26 PM »

I was reading about a guy in Canada recently who linked to a vid on PV panel angle.
Due to the odd occasion when it snows and everything gets about a 1M buildup, some Canadians have found tilting their panels 90o, Straight up and down has worked well for them. 


The tilting of of the panels to a vertical position (90 degree from horizontal) is to capture the low winter sun.
Here in Canada (Especially northern Canada) the sun does not rise much above the horizon through the day.
Some orient part of their array vertically and part of it angled upwards. Others build a winter/summer angle adjustment into the array framework.
The rule of thumb here is to angle the panels at the same value as your location latitude +5 degrees.
So if you live at 55 degrees north, then angle the panels at 60 degrees for the best year round performance.
There are many application of evacuated tube solar water heating systems here.
They work very well in winter.


- 6/1 GM90 Listeroid - Delco 33si Alternator
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- Kubota Z482 - 4kw
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veggie

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Re: Solar water heaters.
« Reply #25 on: April 09, 2019, 02:38:24 PM »

Here's an example of an application in Calgary, Canada which provides winter home heating.
Notice the steep angle of the panels to capture winter heat as efficiently as possible.

https://www.youtube.com/watch?v=CTpEj5XPpc0
- 6/1 GM90 Listeroid - Delco 33si Alternator
- Changfa R175 - Lease/Neville Alternator
- Kubota Z482 - 4kw
- JiangDong R165 Air cooled - 2 kw

BruceM

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Re: Solar water heaters.
« Reply #26 on: April 09, 2019, 04:39:43 PM »
Mikenash, yes, resistive heating elements will work just as expected with the rated RMS voltage of DC or AC.  The DC voltage must be regulated in some manner, and this kit is not commonly available, so AC operation is common.  If there is a dedicated PV array for a water heater element, matching panel array voltage to element voltage should be sufficient as long as you keep at or below the heating element voltage.  PWM regulation is also possible but I haven't seen a commercial DC to DC converter of that sort of capacity and voltages. DC switching on the low voltage leg is simple via HV mosfet(s).

Thanks for the great links on VE hot water Veggie. Vacuum Evacuated hot water collectors can be a DIY project, as Carl showed us years ago. A great solution for cold climates; flat panel collectors are by far the most economical where winters are mild to moderate. 


mikenash

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Re: Solar water heaters.
« Reply #27 on: April 09, 2019, 05:08:03 PM »
Thanks Bruce& others.   Good thoughts

dieselspanner

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Re: Solar water heaters.
« Reply #28 on: April 09, 2019, 08:54:15 PM »
Hi Bruce

Thanks for taking 2 minuets of you life to explain to Mike that you can run an immersion heater on DC.

I've just used up 4 minuets of mine reading about RMS, the Wikipedia page had some great Greek symbols, gotta love that sigma....

If it was down to me I'd run my solar power into a small 12v battery bank through a solar charge controller, with a low voltage cut out feeding the  inverter supplying the immersion heater, this I think I understand!

A. Would it work?

B. Is the gain, from a 100w panel for example, enough to make the system worth while? 

C. Am I just being lazy and trying to avoid complicated formulas and a bit of soldering?

Cheers Stef
Tighten 'til it strips, weld nut to chassis, peen stud, adjust with angle grinder.

glort

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Re: Solar water heaters.
« Reply #29 on: April 09, 2019, 11:45:53 PM »

12v will work but be low powered. We have 240 ac here so you would need to use 20x more amps wphic is a lot of amps to get the same input..

Im testing a 24v setup atm which shows promise. 24v has much more going for it..
Amps are lower, domestic solar panels are better matched as are cheaper controllers, there are more 24v elements availabe and you just need 2 batteries instead of 1 which if you are using the setup for something else give you more capacity.

You would want a LOT more than 100w to heat any useful amount of water. Off the top of my head ,if you had 6 hours of iseful sunlight, aat 100w ( which will rarely if ever produce the full 100w) id guess you be lucky to heat a bucet of watery above about 70c. Maybe youd get 2 buckets in summer with a good start temp but in winter, i think that wpuld be about the limit..

24v isnt complicated nor need  much more than simple maths even i can handle.

Where it gets more complicated is where you start chasing real efficency using mains rated elements with solar panels.

Because of the resistance built into both, its not a matter of just volt and Amp input, its matching the resistance in ohms.  You cant just have say 1000w of panels on 2000w element and expect to get 1000w of heating. One has to know or calculate the ohms of the panels to be used and the resistance in ohms of the element.

I am currently heating 120l barrel VERY warm using 3 190w panels on a 240v, 2000w element.
Although the volts and amps are way out, the resistance is well matched and i get the full heat value of the power the panels. Thing is if i said great, it add another panel, id actually get LESS power because the resistance would be out of the matched window. To up the input, id have to recalculate the resistance and probably  go from 3 panels in one string to 2 strings of 4 panels or whatever  the window allowed . You dont have to be exact but one does have to take volts,amps,and the resistance in ohms into account and match them all up within the limits.

One can always put whatever panels with whatever  element within limits but the actual heating power one may get without properly taking into account the resistances involved  stands a good chance of putting say 125w of heat into the element from say 1000w of panels. Match them up and you could be getting say 900w or 450w from 2 panels.

Now that WAS
a good 20 min of my life sitting here hen pecking on my tablet while looking after the paitent.
Dad had a cataract op yesterday not even 2 hours from calling him in to the call to come fetch him . Scared the shit out of me when they rang so quick. Said last night the tv looks brighter so seems good already.
2 min just for that add on.

Wheres my laptop?
 :laugh: