PV water heating

[Naptown]

I had a potential customer call me yesterday about installing a couple of panels and running the line to one of these things to heat his water.
I told him that I was not interested as the unit has no UL listing and I would not assume the risk of a fire or failure with my name on it in any way.

So any of you EE's have any idea of how this thing works? (or doesn't as the case probably is.)

Broken link but you can see what it is here
techluck.com

[SunEagle]

I had a potential customer call me yesterday about installing a couple of panels and running the line to one of these things to heat his water.
I told him that I was not interested as the unit has no UL listing and I would not assume the risk of a fire or failure with my name on it in any way.

So any of you EE's have any idea of how this thing works? (or doesn't as the case probably is.)

Broken link but you can see what it is here
techluck.com

The control board looks like it is just an inverter of some kind taking the DC voltage from the PV panel and changing it to AC voltage. I am not sure what that AC voltage is but without a transformer I would say it is still low. It maybe enough to energize that water tank element to get some heat into it but I doubt it will be much.

Now a good reason to stay away from that thing is that the web site kept showing the "UL Listed electrical box" that you must purchase elsewhere like HD. There was no mention of the "control board" having a UL listing so I think the seller is trying to convince you everything is ok by having the UL listed box.

There was also mention about using this board for a "grid tie" system up to 600 watts using a "higher" voltage. Way too fuzzy for me.

I would say stay away from this stuff. It is probably junk at best and dangerous like them cheap plug in grid tie inverters at worst.

Anyway that is my 2 cents on the TechLuck

[Naptown]

That and the fact that there is no high limit I could see built into it what happens if yu go on vacation for 2 weeks?

[SunEagle]

That and the fact that there is no high limit I could see built into it what happens if yu go on vacation for 2 weeks?

It will either light off the water heater and burn the house down or barely make it luke warm. I don't see how it can boost the DC panel voltage high enough to get that heater element warm enough to increase the water temp.

Most water heaters require 230 volt to work. Some can work at 120 volt but how does that little control board get a 12 volt DC solar panel voltage up to 120 volt AC. Looking at the board I just see a few capacitors, a process chip, resistors and a couple of other circuit components. I did not see any transformer of any kind to increase the voltage.

I didn't watch all of the videos but did he show what the voltage was coming out of that control board?

Oh wait. The website states you need to use 4 x 12 volt panels mininum so at least we are talking about over 40 volts DC.

[Naptown]

I topped when I could not find a UL listing and they said to buy a UL listed enclosure. Which mounting that into it would probably void the ul listing.

[SunEagle]

I topped when I could not find a UL listing and they said to buy a UL listed enclosure. Which mounting that into it would probably void the ul listing.

I wouldn't touch it with a ten foot pole.

[LucMan]

It makes no sense to me why the controller is required, just wire the panels direct to the lower element and use the DC directly from the panels .
It looks like someone is trying to sell a fancy voltage indicator to the uninformed.

[SolarEU]

PV water heating - direct DC water heaters

Do you know about water heaters that support direct DC voltage from solar panels? I was trying to search some, but did not find any. Keep searching....

[LucMan]

Do you know about water heaters that support direct DC voltage from solar panels? I was trying to search some, but did not find any. Keep searching....

Resistance elements don't care if they are supplied by ac or dc. For dc you will need a dc rated switch or relay for control. Be careful of your total wattage.

[inetdog]

Resistance elements don't care if they are supplied by ac or dc. For dc you will need a dc rated switch or relay for control. Be careful of your total wattage.

But the problem with driving resistance elements directly from panels is that the resistance has to be varied with time to get the panels to operate at their maximum power point.
If the device includes MPPT circuitry, it could at least get the maximum panel power into a fixed resistance heater.
There are some similar devices which are UL listed and are being installed in apartments and condos where running water/fluid lines from roof to heater is prohibitively difficult. But the concept has not been proven.

Economically, using a grid tie inverter will give you much more money saving than the most efficient use of PV to heat water.
The concept has also been used in the EU where backfeeding the utility grid is not allowed, and a local load has to be provided to use up all of the panel power above local electrical loads.

The size unit mentioned, especially if not UL listed, does not fall into any of the above categories.

[FunGas]

how this thing works?

very slowly?

That and the fact that there is no high limit

That was my first thought.


Water heaters need a lot of power, more than 500W...
There's no way those little panel meters are 500W either

On the other hand, the system should heat water, albeit very slowly.

[bcroe]

But the problem with driving resistance elements directly from panels is that the resistance has to be varied with time to get the panels to operate at their maximum power point.
If the device includes MPPT circuitry, it could at least get the maximum panel power into a fixed resistance heater.
There are some similar devices which are UL listed and are being installed in apartments and condos where running water/fluid lines from roof to heater is prohibitively difficult. But the concept has not been proven.
Economically, using a grid tie inverter will give you much more money saving than the most efficient use of PV to heat water. The concept has also been used in the EU where backfeeding the utility grid is not allowed, and a local load has to be provided to use up all of the panel power above local electrical loads.
The size unit mentioned, especially if not UL listed, does not fall into any of the above categories.

I studied that for a while, then went to grid tie. Now that I am over powering my grid tie, am
looking at it again. To be useful, the system needs A LOT of power. If it has big power coming
into your house, there are SERIOUS safety issues. Getting a higher voltage array into MPPT isn't
too hard with a buck regulator; without that its pretty useless. Since its DC, but your grid tie is
AC, it probably means ANOTHER DC safety disconnect box with the others. Heck, I even thought
of putting an electric water preheater OUTSIDE the house. The normal heater thermal cutoff
switches won't handle DC; just make a heck of an arc.

Best to see what the EU worked out; no doubt involves a many KW array. Bruce Roe

[inetdog]

Best to see what the EU worked out; no doubt involves a many KW array. Bruce Roe

What I have seen advertised is mostly a feature of an overall grid-tie system and it uses the output of the same inverter with a proportionally controlled diversion to the water heating load switched in to just balance the production to avoid sell back.

Not sure if it is still true but at one time in the UK the incentives using production metering actually paid you more for power you generate and use yourself (however wastefully) than for power you feed back into the grid.
Go figure.....

[bcroe]

What I have seen advertised is mostly a feature of an overall grid-tie system and it uses the output of the same inverter with a proportionally controlled diversion to the water heating load switched in to just balance the production to avoid sell back.

Sounds like EU solutions won't help me. With inverters pegged, I would have to tap off
excess panel DC somehow. Bruce Roe

[SolarEU]

DC Solar from USA

Sounds like EU solutions won't help me...

I found this US Patent: US8536495B2

US-Patent-8536495B2.jpg