very simple solar water heating

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very simple solar water heating

Postby el pocito » Tue Apr 12, 2011 6:41 pm

Hi, I want to heat water simply by running a 70m water pipe above ground, from my water tank, down to the house. However there is a problem. How to prevent the heat rising past this pipe into the water tank. In a household system I could use a one-way valve. However with this one I am drawing the water from a tank and where the "hot water" pipe connects, the pressure is only one metre of "head". What other method can I use to stop heat passing back into the tank?
Phil
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Re: very simple solar water heating

Postby karlajensen » Sat Apr 16, 2011 3:04 pm

add another few metres (10m??) of pipe buried in the ground at the base of the tank.

this would cool it off again ans stop the conduction back up into the tank.

A simple flap type one way valve should do the job -Conergy use them in their SHW split systems to stop them working in reverse at night.
You would need a u shaped bend for this to operate the valve properly as they are intended as gravity close
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Re: very simple solar water heating

Postby el pocito » Tue Apr 19, 2011 6:06 pm

thanks, sounds just the job.
One other question while I have someone who knows about these things. I use solar power. Yet I have been unable to discover how to work out what the state of charge in the battery is, using volts. I assume fully charged is 13.2 volts (this is a 12 volt system), as this is what it always settles out on after charging (at 14.8 volts). But how do I work out 90%, 80% and any other figure, from the voltage reading. Currently I stop using the battery when it reads 12.6 volts, and this seems to work okay, but it would be really great to know precisely what is going on. PS. I have tried using one of those meters that calculate amp hours but draw both 12 volt DC and 220 volt AC at the same time, so it doesn´t work.
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Re: very simple solar water heating

Postby Gordon-Loomberah » Tue Apr 19, 2011 6:44 pm

The best way is to measure the Specific Gravity of the electrolyte if you have flooded cells, but you have to rely on voltage if they are gell cells... so more information required! What sort of batteries are they? The batteries should rest with no charging or load for ~6 hours to get a correct voltage reading for the purpose of determining SOC.
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Re: very simple solar water heating

Postby el pocito » Tue Apr 19, 2011 7:22 pm

hang on, getting a bit too technical already. I want a method soley using the charge controller´s voltmeter. So that I can see at a glance what percentage of charge the battery has remaining.
PS am using an internet cafe to write so won´t be able to reply now until next week.
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Re: very simple solar water heating

Postby Gordon-Loomberah » Wed Apr 20, 2011 6:38 am

el pocito wrote:I want a method soley using the charge controller´s voltmeter. So that I can see at a glance what percentage of charge the battery has remaining.


Unfortunately, that's not going to give you any more than a very rough estimate of State of Charge, even taking into account the load and charging currents at the time. Of course you could watch the charge controller voltage display and make a note of how fast it changes with time under various load and charging currents, and that could give you a good indication of SOC, but it means sitting there with pen and paper and calculator for a while, which I doubt is what you were thinking of! ;)

Without knowing what brand or type your batteries are it's not possible to say what SOC your 12.6V represents, but if they were Trojan flooded cell batteries and had not been charged or discharged for at least 6 (or up to 24 is better) hours, then they would be at about 89% SOC.
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Re: very simple solar water heating

Postby el pocito » Fri Apr 22, 2011 6:06 pm

thanks for the reply. Amazing isn't it. We have all this technology, and folk pay out a vast fortune for it, yet NO-ONE has come up with a way of telling exactly how much power is in the system at any specific time. And I thought I was the crazy one, asking such an obvious question. I guess as the battery is just an auto one, and has lasted seven years of continuous service, I must be doing something right.
I'll let you get back to your life.
All the best for confirming my suspicions.
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Re: very simple solar water heating

Postby Gordon-Loomberah » Fri Apr 22, 2011 6:37 pm

el pocito wrote: yet NO-ONE has come up with a way of telling exactly how much power is in the system at any specific time.


There is equipment to tell you that, but its a lot more involved than just reading a voltmeter, and it does cost a bit. Even then though, it's only ever an estimate, and often needs re-setting to bring it back into line with reality.
I think that if you know your system fairly well, as in you keep a fairly close eye on it, you can easily keep track of how the batteries are going. For batteries in good condition, they should be pretty well at 100% when the absorb stage charging gets down to about (net) 1% rate. For older batteries that will be closer to 2%. IE, for a 500AH battery, 5A charge rate to maintain the absorb voltage means you are pretty well at 100% SOC for batteries in good condition.
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