diy solar

diy solar

Direct to water heating.

Mtour said:
Solar panel direct to tank.. My understanding is the big issue is, dc current will destroy the tank with electrolisys in no time.
Click to expand...

I have also heard this stated often. However my understanding is the dc heater part is inside the stainless steel enclosure so the tank sees no polarity. Maybe if a copper element was used in an old galvanised zinc tank then there would be problems particularly if earthed to the wrong polarity.
 
Too bad there aren't builders in the solar community. I built my water heater controllers and have been using them for years. Works in parallel with existing MPPT controller directly off panels sending any excess energy 5-500W to heating element. Much like that two module solution does. Any camp can have hot water cheap.
 

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Very cool. Can you share a schematic? Crayon on a sheet of paper is as fancy as it needs to be. Would help a lot of folks save some money. :)
 
SmartElectric said:
Directly to the time when he discusses the thermostat and connection.

This is directly from
practicalpreppers.com

Hot Water - Practical Preppers

We all enjoy a nice hot shower, but hot water is also necessary for sanitation purposes in an emergency situation. Our solar direct hot water systems are our favorite sustainable solution for hot water. No batteries, inverters, or charge controllers necessary!
practicalpreppers.com practicalpreppers.com
Click to expand...

I made some enquiries.
"This output is a pulsed DC acting like AC."
"The voltage? Variable- depends on how many panels you put on. Do not use more than 1400W of panels on this board."
Very neat.
Pulsed DC makes my mind perk.
I would guess that pulsed DC would address the arcing problem.
I wonder the conversion efficiency is?
Is this just PWM?
 
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I have thought about this in the past when I found a good deal on some used panels. The two biggest issue were:
The inefficiency of heating water with resistive heat.
The idle infrastructure of panels when the hot water was not being used.

I already had an existing GT system and just added enough of the panels to stay within my 1000 Watts of my PTO and replaced my natural gas water heater with a heat pump model. In terms of overall efficiency of electric energy to heat you can't beat a heat pump. When I am not using or needing the hot water the extra energy gets credited to my NEM agreement.
 
Mtour said:
Solar panel direct to tank.. My understanding is the big issue is, dc current will destroy the tank with electrolisys in no time.
Click to expand...
The heating element (and other wiring) should be electrically isolated from the tank and water, so no electrolysis should occur. Standard 240 volt is line to line voltage (no 'zero' volt neutral), any electrical connection to the tank or water would be a serious shock hazard.
 
1. Heat pump water heater is the best option, if upfront cost is not a consideration, combined with PV panels or not.

2. Using the pulsed DC conversion of PV panels into the bottom input on a standard electric resistance water heater costs money, time, effort and panels that serve only this purpose, the advantage is primarily those who (a) have an existing water heater than can be modified and (b) have no existing PV panels and want to start a project without needing permits, changes to electric meter or other limitations generally seen when adding PV panels to power the house, this option is purely connected to water heater and therefore out of the requirements to inform city/county/etc governments or regulatory orgs and/or (c) have access to truly cheap PV panels and are a DIY'r


I would note that I researched and decided on #1. Heat pump is vastly more efficient in terms of long term cost efficiency.
 
Bill Taylor said:
It takes 20-60 VDC, and converts it to 120 VDC. Of course, it is pulsed DC, but the element doesn't care about that. The best part is you can use the existing thermostat without burning out the contacts
Click to expand...

Great find!
The eBay link details says "Frequency :150KHz "

Does this mean the pulsed DC is effectively a square wave 150 kHz output at the desired output voltage, and therefore the thermostat which expects AC voltage continues to work? If this was pure DC only, the thermostat would arc weld itself with that high of DC voltage as per the video I posted upthread on the alternative device I found that performed what looks like a similar function.

$25 USD is a real find compared to what I posted!

As for this quote "Conversion efficiency: 85%", with 500 W of panels, this would be 75 W of heat to dissipate, presume this runs hot eh?
 
SmartElectric said:
Great find!
The eBay link details says "Frequency :150KHz "

Does this mean the pulsed DC is effectively a square wave 150 kHz output at the desired output voltage, and therefore the thermostat which expects AC voltage continues to work? If this was pure DC only, the thermostat would arc weld itself with that high of DC voltage as per the video I posted upthread on the alternative device I found that performed what looks like a similar function.

$25 USD is a real find compared to what I posted!

As for this quote "Conversion efficiency: 85%", with 500 W of panels, this would be 75 W of heat to dissipate, presume this runs hot eh?
Click to expand...
 
It does get warm. I noticed that right away. Within about 5 minutes it was pretty hot. So I did a naughty thing and mounted it on the wall using 2-inch standoffs. No enclosure. It's up high in the utility closet and I'm the only one that has access to it, so I didn't worry too much about it. The fan seems to keep it within manageable temperature range, though. It is in a house that I rent to a friend. I was down there last weekend and checked on it, still working fine.
 
SmartElectric said:
Great find!
The eBay link details says "Frequency :150KHz "

Does this mean the pulsed DC is effectively a square wave 150 kHz output at the desired output voltage, and therefore the thermostat which expects AC voltage continues to work? If this was pure DC only, the thermostat would arc weld itself with that high of DC voltage as per the video I posted upthread on the alternative device I found that performed what looks like a similar function.

$25 USD is a real find compared to what I posted!

As for this quote "Conversion efficiency: 85%", with 500 W of panels, this would be 75 W of heat to dissipate, presume this runs hot eh?
Click to expand...
No the output is not a 150 kHz square wave but a DC level up to 120 volts.

The 150 kHz is the frequency used to drive the switch in the boost circuit shown here
 
I like this solution. I am going to try it another way but if all fails i will come back to this. My 600 watt heating element came in today and frankly heats water in a pitcher @300 watt way faster than expected. This is going to be fun!
 
We are using a 300w 24v element in the bottom of a standard water heater driven by two 24v panels in 1s2p configuration. We were given the advice to setup this way by someone local, he said if you match the wattage to your panel it doesn’t perform as well as roughly doubling the wattage input to the element. It takes a couple days to get a full tank of hot water but if you plan your showers/usage accordingly it’s not a big deal. If you have a higher usage of hot water you may want to go the AC route, if you can get by waiting for hot water the direct panel to element is the cheapest way to go.
 
Interesting thread. I have been wondering how to divert solar Vdc * whatever amps when available directly to water heating.
I originally considered over-sizing my upcoming solar panel array build by upping from 2000 watt input to 3000 watt (thinking we all rarely get the full watt rating, ... and then switch off three (1000 watts worth of ) panels to water heating when more than 2000 watts shows up at MPPT (still not sure best economical way to do that total picture on automatic ??? but getting closer. I will stick with 2000 watts worth of solar panels for awhile, and maybe experiment with oversizing solar panel later.

Re: Inexpensive Control Ideas: This made sense for one or more steps, so I copied this from some other thread water heating related thread in the forum: *** as model to remember: for when I get around to configuring a dump into water heating:

... from a different, but related thread ***

*** I'm using a cheap $40 80amp pwm charge controller for a dump switch. I can program it to turn on and off the load at whatever voltage I want. I charge my Lifepo4's @ 14.2v and set my load to turn on @14.1v and turn off @ 14.0v. When the water heater reaches 140 degrees it's thermostat turns it off. (Note: I do not think the poster used a relay for this, and likely the PWM charge controller is wired to Solar Vdc In to main MPPT charger, and it acts like a relay.

But if a relay was needed to divert Vdc for solar; in considering what dc relay to kick on to send Vdc directly to a water heater element, this might seem like overkill, but is inexpensive, plus would take the amps:
www.ebay.com

TE Connectivity Kilovac EV200AAANA Contactor 500A 12~24VDC Coil USA Shipper. | eBay

<p dir="ltr">TE Connectivity Kilovac EV200AAANA Contactor 500A, 12~24VDC Coil. USA Shipper.. Shipped with USPS Priority Mail. Used. TESTED!. Sold as is.<br> Listing is for one unit willing to make a deal for bulk orders! Units may have scuffing and may be a bit dirty from being moved about!</p>
www.ebay.com

If you were looking for a BMS control relay that is on 24/7 until released, I would looking a little further for the later fuller version of same 500 amp Relay with "coil energizer" feature; to get down to 0.13 amp @ 12v = for only 1.7 Watts / spec on coil hold.
 
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SmartElectric said:
120V continuous DC will arc weld the AC 120V designed thermostat of a conventional water heater.
Clearly this then requires an alternative thermostat, or perhaps just relying on a pop off valve if the water overheats...
Click to expand...
You can use a DC rated solid state relay to switch the high current DC to the water heater, then just wire the water heater thermostat in series with the control circuit for the relay, so all it switches is a low voltage control signal when the water gets up to temp.
One example, it uses a 3-32 volt dc control signal, and can handle up to 220 volts DC and 80 amps of current on the output: https://www.amazon.com/Hoymk-AMR-10-Actually-5-220v-AMR-40A/dp/B07TVH6GZ9
 
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