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rwilkinson

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Posts: 10
Reply with quote  #1 
I retired at 58, sold my house I built 15 years ago, bought a lake lot, and started building my retirement home with solar energy in mind.
I had a 10.3kw solar PV system installed on the standing seam metal roof. After all rebates and IRS 30% it cost me about 16,000, so far I have had 0 problems and it is looking like payback will be around 8 years. We use Green Mountain Energy as our electric company which pays back full price for what I put back on the grid. The panels have been operational for 20 months and Green Mountain owes me almost 1,000, our electric bill has been 0 for the last 20 months.
Now my Solar Water heater. DIY
I built the house with a solar water heater in mind. I plumbed in 2 on demand electric water heaters, one in the kitchen 24kw and one in the master bath 27kw. I had to up the electric service to 400 amp and install 2 200 amp panels. I installed a 40 gal. stainless steel water heater in the garage as a backup to the one demand and solar storage tank. There is a 20 gal. heat exchanger in the garage that will eventually circulate to the tank water heater and both on demand heaters, then back to the heat exchanger. The circulation pumps will be controlled with a small PLC.
I first built the water collector in a serpentine configuration (before I know better) and I had the collector on the roof with the supply and return lines above the collector. No way to change it to a drainback without changing the supply and return to below the collector. I decided to move the collector to a stand beside the garage (have not built it yet) this will be a drainback design. I have modified the piping in the collector for drainback. If anyone sees a problem with my mods please let me know.
My plan is to glaze the collector with 3.0mm glass, I used to work at a glass manufacturing plant and I still have friends there that can get me free glass, hopefully it will be tempered. I am still a little leary  about using twin wall poly for glazing. In the summer I plan to use a small instrument fan to reduce the stagnation temp. (has anyone used glass (non tempered) for glazing.

That is pretty much all I have for my solar plan, I will add a link to some pictures on google photos, you may have to copy and paste the link.

Thanks for the forum... Rick Wilkinson N. Central TX
https://photos.app.goo.gl/ty1CBpR8sqYsDQ1j8

SolarInterested

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Reply with quote  #2 
Quote:
Originally Posted by rwilkinson
...I have modified the piping in the collector for drainback. If anyone sees a problem with my mods please let me know.
https://photos.app.goo.gl/ty1CBpR8sqYsDQ1j8


Welcome to our forum. That's an interesting conversion from serpentine to parallel flow. Looks like it should work.

To include photos in your posts see the following:

How to Add Photos (link)

Please Resize Your Pictures to 1000 Pixels
http://simplysolar.supporttopics.com/post?id=6686613

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Both temperature rise and airflow are integral to comparing hot air collectors
Rick H Parker

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Can you turn the $1000 Green Mountain Energy credit into cash? .....


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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
rwilkinson

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Posts: 10
Reply with quote  #4 
If I terminate Green Mountain as my electric provider then they are supposed to pay me for my generation. At least that is how the term of service is written.
Bruce

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Posts: 136
Reply with quote  #5 
Welcome to the forum, although I suspect you may have researched a lot before you joined and posted here. It must be nice to work with new construction ;-)  I like your ideas...I have a drain back water collector that has already paid for itself in the 4 years I have had it running.  I am not sure what you have as storage for the drain back, but go big as you can.  Also , I would definitely go for tempered glass if you can.  3.0 mm glass will take a beating in the sun and there are lots of other threats to the collector to make tempered a wise choice.  Please keep us updated as you go with your project!
rwilkinson

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Posts: 10
Reply with quote  #6 
Thanks for the welcome post, I did do research on heating water via sun power. Where I dropped the ball was in not realizing just how hot the collector can get. If I had known this from the beginning I would of gone with a drainback design. We all have to learn, even if it is learning the hard way.
You talk about using an extra large storage tank, why would you go with more storage than what is required for drainback. Also, I am assuming the return line from the collector will dump into the storage tank (with an air gap). It looks like I will need .7 gallon of storage space, I will go bigger than that but I don't know how much bigger. Has anyone used 4 or 6" PVC pipe as a storage tank.
Rick H Parker

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Reply with quote  #7 

"Has anyone used 4 or 6" PVC pipe as a storage tank."

Surface area to volume ratio would be high and the heat losses would also be high, this is why a radiator has a high surface area to volume ratio.
I
deally, you want the least amount of surface to a given volume, for storage.

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Rick H Parker
Kansas, USA
Electronics Engineering Technologist
rwilkinson

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Reply with quote  #8 
I was referring to PVC pipe used as a drainback storage tank, something around 2 gal. in size
Bruce

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Reply with quote  #9 
Maybe I am missing something here...what will you use the heated water for and when?  The exchanger will work on demand and any stored water will be heated during sunny weather, whether it is being used or not.  It will build up heat fast if not used or stored in quantity.   Think of the water in the storage tank being used to cool the collector. Without adequate volume, the stored water will over heat and cause your collector to overheat.  Also, with less volume the exchanger will quickly drain the heat out of the storage when it does come on. 
rwilkinson

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Posts: 10
Reply with quote  #10 
The plc will monitor the temperature inside the collector, when it sees heat it will turn on the collector pump that will heat the exchanger 20 gal. and when the plc sees at least 80 f. inside the exchanger it will turn on the DHW circulate pump. This will circulate to the tank water heater 40 gal. (that is turned off at the breaker) and to both on demand water heaters that are located in the house close to point of use. The storage tank I am referring to will be on the collector water for drainback only. I may need to monitor the tank water heater temp. and not turn the DHW pump on until the exchanger is at least as hot as the tank water heater. My main goal is for the on demand water heaters to be fed hot water so they don't have to turn on. If all of this works well then maybe I will install a water coil in the attic to add some heat to the house in the winter.
When the plc sees 140 f. in the DHW it will turn off the collector pump and allow it to drain back to the storage tank, if I see to much heat inside the collector I will turn on fans in the collector to help cool the stagnation.
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