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Old 05-13-2016, 09:54 PM   #16
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Re: Solar hot water - hard to find kits


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How about install PV panels to run an electric on demand hot water system? I didn't read everything on this thread so if already mentioned ignore
and at night this works how?
maybe the on demand can run from AM to mid afternoon, and then circ to storage tanks before sunset, this way you have some hot water when there is no sun, and then no need for batteries.
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Old 05-14-2016, 02:14 AM   #17
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Re: Solar hot water - hard to find kits


Your whole house on demand electric water heater will need somewhere between 80-120 amps at 240v to run it, depending on the flow you require and the incoming water temperature.

Many homes need a major electrical upgrade just to handle the electric load.
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Old 05-14-2016, 07:34 AM   #18
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Re: Solar hot water - hard to find kits


All solar PV have to be tied into electrical system & switches between the two depending on sun. At night will the system will need house electric but should offset by the electric that us sold back to power during the day when hit being used.
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Old 05-14-2016, 12:27 PM   #19
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Re: Solar hot water - hard to find kits


If you want to put $20,000 or more into a hot water system, you've picked a good way to do it.
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Old 06-25-2016, 02:36 PM   #20
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Re: Solar hot water - hard to find kits


an interesting thread. I too have experienced similar things. and have not found the answer
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Old 08-13-2016, 02:22 PM   #21
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Re: Solar hot water - hard to find kits


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Update : more google revealed that SRCC is the main rating agency. And they rate a lot more panels. Evacuated tube collectors give the best and most consistent double beds performance because they prevent conduction of the hot water back to the environment. So, like this one.

The easiest setup to install would be to stick one array facing East and the other West. A third component of my roof faces South, which is optimal, but it means much longer plumbing runs.

I would also need an accumulator tank. Thinking about it, there has to be a few temperature sensors and a pump. And a relay and a controller, though the logic the controller has to be able to do is pathetically simple.
I've never seen this used to generate hot water.
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Old 08-13-2016, 05:27 PM   #22
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Re: Solar hot water - hard to find kits


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I've never seen this used to generate hot water.
What are you implying?
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Old 08-15-2016, 06:46 PM   #23
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Re: Solar hot water - hard to find kits


They injected an ad for beds, already notified Adm.

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Old 09-07-2016, 05:25 PM   #24
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Re: Solar hot water - hard to find kits


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Update : more google revealed that SRCC is the main rating agency. And they rate a lot more panels. Evacuated tube collectors give the best and most consistent performance because they prevent conduction of the hot water back to the environment. So, like this one.
This is old, but others may come across this. Yes and no. Yes the SRCC rates panels and can be trusted. However, evacuated tubes DO NOT give the best and most consistent performance. Here's the issues with evacuated tubes.

1.) They advertise they collect more morning & evening sunlight because of their round shape. That's true, however morning/evening sun is only 1/3rd -1/4th as strong as noon sun so the name of the game is noon-time sun, it's the full cake whereas morning & evening are the crumbs. Do you want more full pieces of cake, or more crumbs? Because of the space between each evacuated tube at noon they can let 50% of the noon sunlight fall wasted between each tube when sunlight is at its strongest.

2.) Evacuated tubes are often rated in aperture efficiency/size instead of the physical size of the unit. That's to say, it will say it's 85% efficient per square foot of sunlight it can collect vs. a flat panels 75%. The problem with this is, to collect 32 sq ft of sunlight an evacuated tube system can take up 64 sq ft of your roof (again spaces between each tube) whereas a flat panel to collect 32 sq ft of sunlight will only take up 32 sq ft of roof. So they're comparing a 64 sq ft evac system to a 32 sq ft Flatpanel system and finding it's 10% more efficient. Compare a 64 sq ft Evac system that collects 32 sq ft of sunlight to a 64 sq ft FP system that collects 64 sq ft of sunlight and the FP system kills the evac.

3.) Longevity. FP's typically have a 25-30 year warranty on the fins which is the component most likely to fail (My AE-32 panels are this way). The glass face won't fail, the copper pipes in them won't fail before 25 years, the aluminum frame won't fail, the fins are about it. Evacs depend on a gasket that must maintain an air tight seal with temps swinging from 20F - 300F+ each day. Think it will last 25+ years? I don't. The evacs are designed to be easily replaceable, which tells me they fail. They also come with a 5 year warranty not the 25 like many flat panels. Lastly, if you have an evac fail in 7 years think you'll be able to find the exact model/replacement? How do you tell if they fail, do you go on the roof and inspect them regularly? There's nothing on FP's to really fail.

4.) Some will say a failed evac whose seal has broken will behave just like a flat panel. Their heating process is similar to dumping a bucket full of boiling water into a cold tub to warm it up. With a broken seal, it becomes dumping a bucket full of warm water into a cold tub... Good luck having it be much use. An FP system warms the whole tub.

5.) Evacs can't melt snow because they're evacuated. This is killer if you have snow they can be buried for weeks or months under snow.

6.) They say because they're evacuated they produce more energy in the winter/rain/storm. If it snows, they don't melt snow you can go weeks/months without collecting. Because their aperture (sunlight area they collect) is smaller than FP's, your temps need to be 10F or less at noon to be more efficient. How many times are temps 10F or less at noon in winter where you live? They don't collect any energy when it's stormy, and the little bit more they collect when cloudy is enough to get you a few more degrees, but not enough to warrant their purchase since clouds block 50%+ of the sunlight reaching them. Stick to the motto "the cake is noon sun", not the crumbs of morning/evening/cloudy/stormy sunlight.

7.) Their temps are incredibly variable. What they do is all the sunlight's energy they collect in the tubes rises to the tip (called the header) where it dumps all the energy into the small tip. That tip can reach over 300F with evacs and there's glycol running through it. Those temps will fry most glycols (even car engine), you need special high temp glycol. Even so, if there's a power failure in summer evacs will fry high temp glycol... just ask my friend who has them. The most I've seen in my panels is 225F when I shut the pump off, not enough to damage the glycol. My friend has had all the glycol dump out of his evac system twice from turning the glycol to steam. Now he has special high temp glycol, but if he has a power failure in summer we're waiting to see if it dumps. Since there is no limit to the temps evacs can reach I'm pretty sure he'll be able to exceed even the high-temp glycol. Just remember, he's depending on the gaskets to keep the evac seal and he's reached over 300F on his system that's got to be hard on a gasket.

Last edited by Piedmont; 09-07-2016 at 05:34 PM.
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Old 10-24-2016, 06:51 PM   #25
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Re: Solar hot water - hard to find kits


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So I'm proposing sending pre-heated water through an electric tankless heater. Only if the water isn't hot enough - because there wasn't enough solar power - would the electric tankless heater come on.
You are correct…to a point. I want to do much the same with a solar batch heater to hold preheated water, which would be used to supply my electric HWOD unit. Theoretically, that should make the demand on the electrical tanks much less, because the HWOD unit has a preset "maximum" temperature and the amount of electricity being used would only be enough to heat the incoming water to the maximum output the HWOD is designed to create.

Things get a little more mixed up in the winter, because regardless of the input temperature each HWOD is capable of only a certain "gain" in degrees. If the water is cold, of course, as it is coming into the basement during the winter, the unit will use all of its heating capacity and perhaps if you are in a VERY cold climate not heat the water to a temperature you would prefer. If the water going into the HWOD, however, is of a temperature that it does not require full power to heat it to the pre-programmed maximum temperature (such as that having been pre-heated in a tank with a solar panel), then you'll get the full temperature the HWOD can provide with less energy use.

I've been toying with the idea of using radiant floor heat in my almost 100 year old home…that would be a closed-loop system with the heat provided by an HWOD and a pump to circulate the water. IF, however…IF I were to build or buy a solar system that will allow a large tank of water to be heated and just put a long piece of the PEX tubing that ultimately transmits the heath to the underneath of the flooring (perhaps a full roll of PEX, stretched and uncoiled like a "Slinky" in the heated water) into that tank, the process of pre-heating the water that will be recirculated to heat my house would mean that the HWOD would require much less energy to heat to temperature because of the pre-heated nature of the water.

My house's main structure is 30' X 30', and is a flat-roof structure, so I have plenty of opportunity to put solar panels on the roof (if it weren't for that ONE huge elm tree that provides valuable shade during hot summer weather). My only issue is do I want a drain-back system or not…it would be better if I did not need a drain-back system, but there will be a lot of time during the winter when overnight temps fall low enough to freeze the water in the tubing, so I expect I do need a drain-back system. it just complicates the issue, that's all.

We all hear that there ought to be a great price break coming on solar…but when? I've been waiting for 15 years….hasn't happened yet. I hate to rely on rebates or tax breaks, but every penny helps, that's for sure.

Carry on….ONWARD, thru the fog!!

Cheers!

Dugly
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Old 10-24-2016, 06:57 PM   #26
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Re: Solar hot water - hard to find kits


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We all hear that there ought to be a great price break coming on solar…but when? I've been waiting for 15 years….hasn't happened yet. I hate to rely on rebates or tax breaks, but every penny helps, that's for sure.
I concluded a couple weeks after I made the OP that solar hot water is a dead and obsolete technology. It's simple arithmetic and the alternative gets better with every week that passes.

The alternative is simple : PV panels (they are under 50 cents a watt now) and SMA inverters (the 6.0 model supports 3 strings, 2000 watt batteryless backup power, and is 27 cents a watt).

You use the PV power to drive a heat pump hot water heater. The GE model is $1000 at the hardware store and this year has a $300 rebate on it. 10 year warranty. Also it's a lot easier and safer to just replace 1 hot water heater and run a simple conduit to your roof carrying the solar wires than it is to try to plumb a heavy heat collector on your roof. In hot climates you get an extra bonus that the heat pump hot water heater should be inside your house so the cold air it produces as exhaust helps cool the house. (or it can make it less sweltering in a garage, I suppose)

No risk of freezing, no risk of plumbing leaks, and it's cheaper. A no brainer, and this also is why it was so hard for me to even find available kits for solar hot water and why they were so expensive.

One custom thing I did think of doing was setting up a data link between the hot water heater (which has USB and bluetooth) and the solar inverter (which has wifi). Basically, if the sun's out, fire up the heat pump. In series right after the hot water heater would be an electric tankless heater. So it would "top up" the possibly cold water coming out of the heat pump heater, since the heat pump would only run when the power is "free". (and the tankless would only run when hot water is needed but the free power didn't make the water hot enough)

Last edited by Habeed; 10-24-2016 at 07:04 PM.
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