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Solar Water Heating Recommendations


Kloon
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Hey everyone

First post, but have been lurking the forums for a while and reading up, learned a lot so far regarding solar.

I have purchased a new home and with that I am wanting to move most of my electricity needs towards solar, my first step would be to convert to solar water heating, after that I would like to move to a grid tied PV setup with no battery backup at first and then later maybe add some batteries.

Anybody got some recommendations on systems and installers for a solar water heating setup in the northern suburbs of Cape Town? I know I want a vacuum setup and it should provide adequate warm water for a family of 5.

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Welcome Kloon.

My 2 cents, with EV tubes, go for a BIG geyser. I did 200l and I regret it a few years later. 

Heat the water for free, have as much spare as you ever could need.

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My 2 cents on solar and water heating. If you are going to go Solar I would not buy a rooftop water heating system. What I have found is that I wasted R30K. If I was you I would install a heat pump or the new device my friend Johan Booysen will make available soon. It then uses your solar power panels to heat your water using any extra power you have. And you always have extra as your system is not 100% busy all the time. And then you will have hot water in the winter as well as you only need light for the panels to work not UV, The UV drops a lot in winter and then you are going to use electricity anyway. The Tube also have a lot of problems in summer if you go away on holiday. They tend to overheat as nobody uses any hot water. I am busy working on a solution to stop that from happening.

Just my 2 cents after going solar.

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Hi Kloon,

Some years back I installed a 300L EV tube pumped system and could not be happier. We are only 3 people in the house and during the coldest, cloudy winters day do we use electricity to boost the temperature. During autumn, spring and summer months we have plenty of hot water. We have a geyserwise controller that manages everything for us. It just runs on its own.  I agree with TTT the bigger the geyser the more energy it stores. In effect its like a battery. The bigger the better  especially with a large family.

Before I bought the system I did a lot of research into the various options. I decided on a Kingspan system (not a local product but they are sold here). The thing I liked about it (that nobody else did at the time) was that it has a thermal cutoff device in the tubes. It stops (as much as possible) the transfer of heat from the tube to the water in the manifold when the temperature in the manifold gets to very close to boiling point. In theory this reduces the chances of the geyser boiling over. I must say, I've never seen my geyser boil over, not even in the summer. It might have, but I was not there to see it.

 

 

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Also never had overheating problems since I installed system many many many years ago.

When we do go away in summer we simply switch the system over to cool itself off at night, thanks to the Geyserwise controller having that feature.

And in winter, EV tunes and panels, both are affected by clouds, seeing as I have both. In MY opinion, EV tubes gets more out of a cloudy day ito heating water, than what PV panels would get, for all the spare power on cloudy days are used up by devices. :P

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56 minutes ago, jdp said:

And then you will have hot water in the winter as well as you only need light for the panels to work not UV, The UV drops a lot in winter

I heard the exact reverse of that argument. In winter the visible light drops a lot. That much is true, on the cloudiest days my array makes 10% of its normal capacity. But -- so I was told -- a lot of unseen UV gets through and the EV-tubes can use it, while flat panels cannot. So I was told at least. I can hardly imagine that a PV panel at <20% effiency is going to beat an EV tube, but if someone has hard numbers I will gladly take that back.

Given some of the pretty bad sunburn incidents I've had on cloudy days, this sort of feels right at least :-)

I have a flat-panel on my roof. I can confirm that it is next to useless on a cloudy day.

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My system also has the holiday function and it works but I don't trust it. Plonky I have both systems and can tell you that the Tube make less hot water now than in Desember. The heat pump now runs every day.

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I sincerely hope they generate less now than Dec! Less irradiation, as do our PV panels.

Point I was subtly trying to get across was that you cannot diss EV tubes due to one bad experience you had and now advocate that PV panels are better.

They are not.

BUT, if you have spare power generated from panels, and no EV tubes, by all means, USE that, it is cheaper than hauling out more tom for EV tubes.

The fact remains EV tubes are more efficient in heating water over 12 month period than PV panels over same period.

Einde vd storie ... unless someone can produce real facts and figures proving the contrary, as Plonkster said.

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I quote from a supplier that made it in solar geysers and then moved over to PV installations.

Question was: 
Geysers, which are better:
PV heated geysers?
EV tubes heated geysers?

Answer, and I Quote: "EV tubes are far superior. A m2 of PV produces 5KWh per month, a EVT does that in equivalent water heating by 12.30pm."

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I've read somewhere that the EVT uses a lot more of the infrared spectrum (heat) whereas the silicon in the PV can not convert this part of the light spectrum into electricity. That is why our PV panels heat up in the sun. It's got to do with the wave length of the light that falls on the silicon. Shorter wave lengths carry more energy and can be converted by the PV. If the wave length is too long (deep infrared) then the PV can not convert it into electricity. That is why the EVT is more efficient at heating, it does make use of it.  If anybody has more info on this please share.  

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For me it is a no brainer that over a 12 month period both flat panel and EV will make more than PV. No contest really, the efficiency is just better. The business case for PV is 1) it looks better, 2) more flexible, use electricity, dump the rest in water, 3) easier to install in some ways, as cable is easier to work with/route than copper pipe.

The real question I'm interested in is EV vs flat panel. I heard that EV does better because it uses more of the UV range, but because the tubes are round and sunlight only hits a small portion of it, you need slightly more surface area with the tubes.

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34 minutes ago, plonkster said:

you need slightly more surface area with the tubes.

EDITED: My EV tubes have a absorber plate inside, like this: 

Absorber plate.jpg

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TTT and Plonky  I will not buy tubes again, my opinion. I have the right to it so please stop trying to downplay it.You can buy it if you like, your choice. I wont do it again. I learnt my lesson.  It almost burnt my house down when the council switched the water off to fix some pipes. There was no water to run between the tanks and the tubes. The tubes went to 140 degrees and everything melted. Yes the installation was done the wrong way but so can the next persons be. But if I stayed with my heat pump I would still have hot water and that made by the panels like it is doing now.  The tubes are like a nuclear reactor. Yes it is very efficient but very dangerous if it runts away with you. That is why I am working on a why to shut them off by blocking the sun. I have the tubes now but if I had to decide again to go that way I would rather add more solar panels. The Tubes make like no hot water on Cloudy days. the PV panels still make power. I am talking about my systems, Maybe they are faulty then but the make a lot less in cloudy days where my solar panels make more power with the cloud edge effect.

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I'd think that the dangers of those hot tubes are rather greater with a pumped retrofit system than thermo siphon. If I do install tubes it would be thermo siphon.

Sent from my GT-I9195 using Tapatalk

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I say again: A m2 of PV produces 5KWh per month, a EVT does that in equivalent water heating by 12.30pm.

JDP, I accept your opinion and experiences but could you consider that when people ask the question, to rather state they need to be careful of the product they purchase than to tell them PV is better than EV tubes for as Janma also said, EV tubes use infrared predominately, so on cloudy days they will outgun your PV panels by a long shot ... IF you have the proper ones installed. As I said before, I, as you, have both PV and EV and I am sorry JDP, geyser is warmer at the end of each day, PV sukkel sy gat af. Yes, I do also use Eskom, but only every 2nd day or so.

Now JDP, I am going to say this with respect and a smile: 
Lets agree that you may have dud tubes, and they where installed wrong.

If you can do that, I will not jump in every time to avert an opinion / experience from becoming a fact, probably due to you being sold, unbeknownst to you, dud tubes that was installed incorrectly to boot.

Deal? :D

 

EDIT: There are thousands and thousands of EV tubes installed in SA, all working as designed, not danger no houses burning down.

The only one I know of is yours JDP, that had a problem, and that was due to, as you said, bad installation.

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TTT no deal, I dont agree. My installation was fixed so it is not that. In summer it does make the water hotter but not when its cloudy, I totally disagree with you there. You can ask my wife, she is the one that wants all the hot water. My brother has tubes and he has the tank on the roof. It also overheats in summer blowing steam all over the place. There are 2 people who work with me that also have tubes with the tanks on the roof. They overheat blowing steam. So much that they cover it with shade cloth to stop it . I do the same now when we go away as I dont want to come back to a home whr a tank burst because the water started to boil. They both asked me for the same solution I am working on now  

If I am the only one with issues the why is the Internet full of articles like this one. 

http://www.homepower.com/articles/solar-water-heating/domestic-hot-water/overcoming-overheating

And this one, I can go on and on.

http://www.radiantcompany.com/system/solar/heatdump/

You also sit with the problem that you only have hot water production in the day when most people dont need it. We use most hot water at night, now we have 2 tanks and the water is still hot enough for me the next morning but not for my wife. It is around 40 degrees. So we end up running the heat pump anyway to get it back to 54 degrees.

I am not saying that the solar panels makes the water hotter than the tubes. I am saying out of experiance I wasted R30k on a system that my heat pump was doing for the last 3 years, it heats up the tanks using 1kw for 1 hour to 54 degrees. The tubes takes all day to get it to about 60 if we use water. Now with my grid tied inverter I can run the heat pump any time, night and day.

Use it dont use it.

 

 

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Cool and noted that we have no agreement ... and I am not going to post articles of EV tubes successes from the web. ;)

I am rather confused. I thought one uses the hot water evenings, early mornings and then the water is heated during the day, for the next evenings use? Have I missed that memo again! :P

Since Sept 2010, when the system was installed, I have never seen steam exit it nor has the water in the geyser ever exceeded 85deg in middle of summer, even after a week away with no use during a Dec. In winter I get up to about between 50-55deg late afternoon after hot water was used previous evening / early morning, provided there is no rain. Even then I get to about 40-45deg before I switch Eskom on.

System costed, installed, quite a bit less than 30k. :P
With a regime I put in place in 2010 it took less than 22 months to pay for itself. I have since relaxed marginally. ;)

So I can say with confidence that my EV tubes and accompanying system is a huge success and have worked perfectly since Sept 2010.

I will recommend EV tubes to newbies any day and if their system has similar problems to yours, they have been conned with inferior product at a huge profit to said supplier (ROFL) and must demand a refund immediately and get a better product.

Ta.

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Eish guys, wat is dit met die happery? *NJAF!*

I know about the heat problems. Some say it is when you use European-designed tubes in the African sun. All I know is that when I drive past a township all those little houses have a low-pressure tank with evac-tubes on the roof... facing the wrong way. Seems to work for them... :-)

In any case, I think I'll stick with the flat panel then. That thing does the job from around September to May. I only really see the electric element come on from May to August. Installed it as an insurance job after a burst geyser. Shortfall after the rebate (we still had rebates) and the Insurance pay-out was 2k... pretty hard to beat with PV, even if it only works 9 months in the year :-)

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Re heat pump. Wish I could afford one. With a bit of effort I might be able to, it's just that when you already have the thermo siphon tank on the roof and it works well enough most of the year, you're really putting in the heat pump for that last 3 months in the year. So your repayment just became 4 times longer. Arguing that you should leave the solar geyser to shorten the repayment on the heat pump is a bit like taking a big heavy rock with you when you need to run fast, because you can drop the rock to gain speed! With that said... how come I can install a 9000btu inverter AC for around 7k, but a heat pump is 3 times as much? What am I missing?

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Can only comment on my own setup:

Originally 150l Solar Geyser with Geyserwise - With 2.2m x 1.5m Flat Plate Thermosiphon. Temps never exceeded 55, temp drops quickly at night (maybe the thermosiphon working backwards?)

Currently (now that new geyserwise installed again). Same geyser as above - With 12 tube EV and 12v Solar pump. Without pump the thermosiphon didn't seem to work properly, temps at collector in excess of 90 (tested with WENCH's baking temp thermometer), but geyser temps never properly up, staying at about 40. The pump changed that picture drastically. Just with a temporary connection to the same pv panel that cools the roof, we have hit over 75 (Wed/Fri) and overnight temps still was 61 when I showered on Thursday morning. Wed & Fri (today) were belters heat/sun wise so I doubt we could get to the steam/boiling point. Obviously a pressure valve should be installed anyway (even on a standard geyser) and we have a safety mixer (only allows a max of 65, which by the time it gets to shower and taps (due to our long run) is probably (guessing) 58.

Anyway, not conclusive one way or another, other than to say that the flat panel setup was not effective for us, we still used the geyserwise timer to heat water twice a day. The new geyserwise was only installed this week, but haven't had to use the timer yet (not saying never).

Edited by KLEVA
Clarification of terms
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I have a thermo siphon system on my house and only lose on average about 3 - 4 C overnight and the geyser is installed outside. 

It may be ugly (to some people) but it has given me 8 years of fantastic service so far.

If you are losing temperature overnight (beyond the expected couple of degrees) would suggest checking the following:

1) The tank must be installed at least 200 mm above the upper edge of the collector.

2) The interconnecting pipes between collector and tank should be as short, straight and thick as possible (22 mm instead of 15 mm).

(Note: The thermo siphon force is based on the gravity differences between hot and cold water and as it is a relatively small force you need to reduce the resistance to flow.)

3) Insulate all piping to and from the geyser. (Imagine sleeping out in the cold with a warm duvet but your little toe or in my case my big nose sticking out?)

4) Install a heat trap on the hot water outlet piping. (similar to a basin trap to prevent odors) 

Pumped Versus Thermo Siphon:

On my guest house i was forced into installing a pumped system as it was not practical to get the tank above the collector.

The system also works really well and only loses a couple of degrees overnight.

But the system was a lot more expensive to install (pump, differential controller, non return valve & 1 extra isolation valve) and i have an ongoing maintenance program.

So far in 3 years i have had to replace the pump, collector probe and the non return valve.

To be fair these problems can be attributed to my pumped system going into stagnation during the load shedding days. 

Conclusion:

I am a huge Thermo Siphon fan due to the simplicity, cost and maintenance factors.

Why not harness the forces of nature (to quote Green Bum) to do your pumping for you?

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1 hour ago, Carl said:

It may be ugly

That's a very subjective status though. People said the same of PV panels... at least some people... they were all wrong as far as I'm concerned. My tank sits on the side of the house where you almost don't notice it from street level, and definitely don't see it from the area of the house where we actually live/entertain, so even if it is ugly... pfffft.

1 hour ago, Carl said:

I am a huge Thermo Siphon fan due to the simplicity, cost and maintenance factors.

Me too. If it does not properly cycle on its own, you did something wrong. I remember my father had the same problem on his first system in the 80s (a low pressure system that used pool-style panels... works just fine in the hot Namibian sun), he had to take out a few bends in the pipe, move things around a bit, and it worked fine for many many years. After that... it just works. I can also recommend a prefeed system, so that you don't have an electrical element heating the outside tank (which necessarily sees a slightly faster cool down rate due to Newton's law of cooling).

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