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Old 10-04-2012, 06:14 PM   #1
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PV Solar electricity tied directly to a DC Water Heater


There are DC heater elements available for use in electric water heaters. Therefore, can PV Solar panel output (DC) be directly wired to a DC Water Heater of the matching voltage (assuming a thermal controller is installed to prevent over heating). Any ideas or brain storming?

Thanks,
Joe

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Old 10-04-2012, 08:41 PM   #2
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PV Solar electricity tied directly to a DC Water Heater


Why not? What heats the water when it's cloudy?

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Old 10-05-2012, 09:15 AM   #3
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PV Solar electricity tied directly to a DC Water Heater


On cloudy days, the existing gas hot water heater will supply hot water. It will be plumbed so the DC electric is a feed tank to the existing gas water heater.
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Old 10-05-2012, 09:24 AM   #4
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PV Solar electricity tied directly to a DC Water Heater


Got it!
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Old 11-09-2012, 09:50 PM   #5
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PV Solar electricity tied directly to a DC Water Heater


You can do this, but energy-wise it is a waste of panel area. You would get more heat into the water using indirect solar thermal instead of PV.

You generally only get about 10% of your incident solar into the form of electricity in PV. Solar thermal is far more efficient if your goal is to make hot water.
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Old 08-23-2013, 05:16 PM   #6
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PV Solar electricity tied directly to a DC Water Heater


There are some situations where a PV to thermal might be considered...the collectors are lighter and easier to anchor. Wire is easier to run than pipe, especially if you have a long and complicated pipe run. PV system doesn't need freeze protection. There should be some efficiency gain without an inverter, and no batteries or grid tie is needed.
But you are right, Thunder Chicken...last I checked, it took 5X's the money and 7X's the collector area for PV's to match thermal solar.
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Old 08-24-2013, 11:35 AM   #7
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PV Solar electricity tied directly to a DC Water Heater


Quote:
There should be some efficiency gain without an inverter, and no batteries or grid tie is needed.
Wiring PV directly to a heating element is not efficient. In fact, it may not work at all. The resistance of the heater will drive up the panel voltage. When you hit open circuit voltage, there will be no current flow.

You will need at minimum some type of heater controller, or a solar charge controller and a battery.
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Old 08-24-2013, 03:32 PM   #8
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PV Solar electricity tied directly to a DC Water Heater


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Originally Posted by Oso954 View Post
Wiring PV directly to a heating element is not efficient. In fact, it may not work at all. The resistance of the heater will drive up the panel voltage. When you hit open circuit voltage, there will be no current flow.

You will need at minimum some type of heater controller, or a solar charge controller and a battery.
So 1 ohm of resistance is too much?
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Old 08-24-2013, 08:37 PM   #9
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PV Solar electricity tied directly to a DC Water Heater


While PV is not my field (thermal solar is my thing) my gut instinct says that PV panels producing DC, into DC heating elements...without an inverter should be more efficient overall. I don't know "what it would take", but the fewer conversions the better, as a general rule. A charge controller and battery? Ok....so the PV's charge the battery and the battery runs the heater?
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Old 08-27-2013, 10:59 PM   #10
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PV Solar electricity tied directly to a DC Water Heater


any links?
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Old 02-16-2015, 03:50 PM   #11
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PV Solar electricity tied directly to a DC Water Heater


Testing shows that ordinary water heater AC elements work fine with DC,
... but ordinary water heater thermostats melt
Resistance can be varied by toggling between 1 or 2 elements... depending on intensity of solar.

Consider several diagrams posted on following link for making a DC water heater that is connected directly to solar panels.
http://waterheatertimer.org/Convert-...ml#best-design
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Old 02-16-2015, 04:09 PM   #12
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PV Solar electricity tied directly to a DC Water Heater


Warnings from your posted link.

"This wiring violates water heater safety code and voids water heater warranty.
This wiring by-passes normal use of ECO thermal reset button located on upper thermostat.
This wiring is not guaranteed to work... it should work... but solid state relays are never completely OFF."
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Old 02-16-2015, 04:41 PM   #13
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PV Solar electricity tied directly to a DC Water Heater


Thanks for rely...
Here's my take on it... please check errors in logic...

The water heater is ECO-protected in the usual manner... if water at top of tank exceeds ECO set point, the ECO trips and all power is cut to water heater.
This is particularly true since the specified DC-DC relay is Normally Open.

The TP valve would also function normally, and the power source coming from solar panels would have to be breaker-protected, and solar panels and water heater grounded per usual

Violate code??
Commercial electric 3-phase water heaters have a box attached to water heater that contains 3-pole contactors?
http://waterheatertimer.org/images/3...-phase-400.jpg

There is not much difference between relay and contactor.
The DC solar water heater design seems electrically safe as long as functioning electrical parts are properly contained inside a box and all component parts are properly fused and grounded, with proper safety cut off.

Yes the water heater warranty is voided .,... the entire topic of connecting DC directly to a water heater voids product warranty

I think the DC water heater is a solid idea?
http://waterheatertimer.org/Convert-...html#best-idea

Last edited by geno03245w; 02-16-2015 at 04:43 PM.
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Old 02-16-2015, 05:24 PM   #14
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PV Solar electricity tied directly to a DC Water Heater


The warnings were written by the owner of the webpage you linked to. If you want to argue them, argue with him.

It is one thing to experiment with something, another to suggest that you can safely install such experimental gear in a residence where people other than the experimenter reside. Or in many subdivisions, where people reside next door.

Quote:
There is not much difference between relay and contactor.
I will agree with that, IF they are both electrical mechanical. But, there is a big difference between an electrical mechanical relay and a solid state relay. The difference in their failure modes could have dire consequences in this application.

The last warning "This wiring is not guaranteed to work... it should work.." indicates to me that he probably never built the thing. That is a good enough reason not to offer the link as a possible solution.
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Old 02-19-2015, 02:16 AM   #15
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PV Solar electricity tied directly to a DC Water Heater


What warning are you giving that is not already shown on the webpage?
The webpage does not tell folks to wire their homes with DC power.

Objections might include what the code says about DC wiring.
Certainly there are facilities that are wired with DC power.
Certainly the discussion would benefit from knowing the code.

Singh writes in his power-generation book that long distance electric transmission is more efficient using DC... somebody invented that... somebody stepped forward with an idea.... sure folks need to be careful with any electric appliance, but I worked with electric water heaters for years and the DC water heater illustrations look good to me.

Illustrations at top of webpage look like valid DC water heaters.

You sorta cherry-picked objection from bottom of page...
... where the webpage clearly says that the illustrations showing solid state relays appearing at bottom of page are experimental....
I assume the solid state relays are included because they are cheap to buy if somebody wants to 'experiment' with DC.
Your warning is the same one that shows on the webpage.

The illustrations at top of page look look good to me.
The top-page illustrations use expensive Omron DC-DC relay. The Omron spec sheet shows these relays are made for switching high-voltage high-amperage DC loads. They sell on the internet... Amazon sells them too.

The DC water heater webpage looks like a good invention... I'm sure if Rheem rolled it off the assembly line, they'd tell people to have qualified DC electrician install it.
The real problem is there are no qualified DC electricians...
Which is why I would appreciate input on the code that covers DC installation.

I worked with electric water heaters for years. The illustrations look good to me.
Look at it again carefully. What do you see that causes alarm?
http://waterheatertimer.org/Convert-...html#best-idea

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