diy solar

diy solar

Direct to water heating.

Keith C

Ahhh, the sharks have him.
Joined
Dec 2, 2019
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189
Location
Coastal Silicon Valley
Is there any off-the-shelf stuff you guys know about that one could set up a mess of solar panels and magic box 1 and maybe a magic box 2 and directly drive a 240V 4,800W standard water heater element?

Any ideas welcome.
 
magic box 1 would be a solar charge controller.
magic box 2 would be a battery.
additional magic component would be a dc heating element.
There may be better ways but on 200ml of rocket fuel thats the best I can do.
 
Don't forgot the over current protection and a shunt.
Get an empty box and put the magic components inside.
This might be an opportunity as I think others have expressed similar interest before.
 
Magick box 1 would be to series connect panels to make 240v to heat the element direct from panels. I would use a breaker and a fuse or 2 somewhere along the line.

I do not know if a heating element with a thermostat would work as I am not sure what the thermostat control will do with DC
 
I will let you know how direct to a 600w/12v element from 4/180w12v panels go when the element arrives from China.
30 similar panels needed for a 4800w system would be something else and require a solution to that thermostat problem.
 
Here is the way I've been looking at:

The magic box is a small circuit that modifies the DC solar into rough AC suitable to be directly plugged into an existing electric water heater without needing to modify the water heater safety systems or temperature control.

I watched the video but I didn't get the particulars of the solar direct output nor the heater element nor the thermostat.
 
Rheem makes plastic hot water tanks, wire direct from panel to tank.. I just installed a rheem heat pump unit...
 
This is interesting.
Craig; I don't see how 240V of panels can work since they can wander all over the place in voltage and a string of them will probably wander 50V or more.

The more I think about this the more sense it makes to go for more than just water heating. I mean if you're not using the hot water during the day the water will heat up and then you need to stop heating and now the panels are essentially doing nothing. While it also doesn't make sense to pay for tight 'house power' quality for water heating when any frequency and +10%-40% voltage regulation would heat water just fine, it would still be wasting the solar the rest of the day. Maybe smoothJoe's Majic Box and a battery does make more sense. You could then heat water after dark or run a house after PG&E makes it dark.
 
Coincidentally, last week I ordered
I got lucky and found a new 50-gal water heater on Craiglist for $200. This will be a preheat tank feeding my existing water heater, which I will leave intact. I've been doing research and thinking on the pros and cons of different methods for a couple of months, and settled on this approach.

Selling points of this controller are the mppt, and that it rapidly switches the dc to simulate ac, to prevent arcing on the heater's thermostat contacts. It also has a settable temperature sensor which I don't think I'll need. I don't know when I'll start on the installation, but I will post the progress.
 
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This is interesting.
Craig; I don't see how 240V of panels can work since they can wander all over the place in voltage and a string of them will probably wander 50V or more.

The more I think about this the more sense it makes to go for more than just water heating. I mean if you're not using the hot water during the day the water will heat up and then you need to stop heating and now the panels are essentially doing nothing. While it also doesn't make sense to pay for tight 'house power' quality for water heating when any frequency and +10%-40% voltage regulation would heat water just fine, it would still be wasting the solar the rest of the day. Maybe smoothJoe's Majic Box and a battery does make more sense. You could then heat water after dark or run a house after PG&E makes it dark.
It doesn't matter if they wander you can use 12v with a 240 volt heating element. It won't get you that far but it will get warmer than nothing. I was just answering the question as it was posted. I actually would do it the other way around. Use my solar to fill my batteries then use excess to hear water. But that is not what you asked so I gave simplest answer. Sorry if that is not what you were looking for.
 
I spent a lot of time this past winter trying the same thing. The problem I ran into is that the low resistance of the heating element pulls the voltage down so low, there is not much power coming from the panels until midday. I found reasonable success with a dc-to-dc boost converter. 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. I started to build one, but then I found one on EBay for 25 bucks delivered. I used 2- 250 watt 72 cell modules in parallel. Was putting 4A @ 120 VDC into a 1000 watt / 120 VAC element. Works fine. Those modules are still available. Just search 900w DC-DC boost converter.
 
Cool idea! The panel voltage can't ever overload the boost's 60v limit, and the boost always gives you 120v. And 500w is great, I bet that's close enough to the mppt approach. If I had known, I'd have probably just used this. I'll go ahead and proceed with the mppt since it's in the mail from europe, and we'll see what power I get at the elements.
 
Coincidentally, last week I ordered
I got lucky and found a new 50-gal water heater on Craiglist for $200. This will be a preheat tank feeding my existing water heater, which I will leave intact. I've been doing research and thinking on the pros and cons of different methods for a couple of months, and settled on this approach.

Selling points of this controller are the mppt, and that it rapidly switches the dc to simulate ac, to prevent arcing on the heater's thermostat contacts. It also has a settable temperature sensor which I don't think I'll need. I don't know when I'll start on the installation, but I will post the progress.

Interesting product! They seem to have thought of a lot of angles.. We await your review. :LOL:
 
Sorry if that is not what you were looking for.

No Craig tiz I who have sort of changed the plan. I get what you're saying in that anything is heating water as the resistive element will dissipate with 100% efficiency whatever it gets. That actually could make a heater-only system make more sense. If someone doesn't use hot water during the day because they work elsewhere, then maybe two 250W panels is plenty even if they might take all day to heat the water.
 
search 900w DC-DC boost converter

Interesting yes! Need an MPPT that spits out into a capacitor bank whatever the best solar array draw is at the moment then a DC-DC to put out steady AC at whatever voltage results in an equivalent draw from the caps to keep the MPPT in to the caps in balance. Sounds like a fun project. Just what I need - another project. LOL
 
I watched the video but I didn't get the particulars of the solar direct output nor the heater element nor the thermostat.

Directly to the time when he discusses the thermostat and connection.

This is directly from

MPPT – Microprocessor controlled constant Maximum Power Point Tracking
Light Cloudy Days – MPPT technology keeps the heat coming!

Uses Installed Heater – Uses the existing electric water heater in most cases
No Element Change – No heating element change is needed in most cases
No Thermostat Change – No thermostat change is needed in most cases

Made in the USA – Designed and manufactured in the USA
 
.... If someone doesn't use hot water during the day because they work elsewhere, then maybe two 250W panels is plenty even if they might take all day to heat the water.

That's exactly my situation. No one is home during the day. Most of our hot water use takes place in the evening. The solar is tied to the bottom element, the top element is still on grid but set 15 degrees cooler. I have generator hour meters to see how many hours the solar is working, and how many hours the top element is on. It's only been installed for a few months. But the numbers look encouraging...
 

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