diy solar

diy solar

Direct to water heating.

It doesn't care what type of voltage is applied to it, AC is simply instantaneous DC.
The ratings for switches of the same amperage always have DC V much lower than AC V

example-

 
The heating element is a passive resistor.

It doesn't care what type of voltage is applied to it, AC is simply instantaneous DC.

The problem isn't the the heating element but the thermostat. As DC never cross zero, it can sustain an arc indefinitely, which is why it's much harder to quench it than with AC.
 
Please prove that the components will fail ?


Can't see how sensationalist photos of burst water jackets has anything to do with the price of fish.

Here's a posting showing what happens when a device (circuit breaker in this case) rated for AC was used to interrupt DC:


You've seen the still photo.
Now watch the movie from Myth Busters.


They say this has happened a couple of times with real houses.

All I'm saying, is don't use the thermostat and overtemp device in a water heater for high voltage DC.
Run either AC or low voltage DC through them to control DC switches. Two separate devices, not combining to one relay, so as to not reduce the amount of redundant safety.

Or, easiest these days, just run the water heater off your inverter when you have surplus PV.
 
Go direct heat.


Photovoltaic is 10-20% efficient (maybe a little more now I haven't kept up). Direct to heat is 80-95% efficient.
$700 gets you two, 24" x 24" thermal solar panels. 8 square feet.

PV panels are now 20% efficient. If solar thermal is 100% efficient, 1/5th as much area is required (I'm guessing its only 50% efficient). So 40 square feet of PV delivers same power.
Assuming your system isn't perpetually leaving batteries drained, you have surplus PV generation sometimes, and charge controller leaves the electrons in the panels.

A typical PV panel is 5' x 3' for 15 square feet, delivers 250W. Costs $70.
For $210 I get 45 square feet of PV panel, able to deliver same power as that $700 solar thermal water heater.

A modest size PV system might be 2500W, ten 250W panels for $700. By simply switching on an electric water heater powered by the AC inverter whenever batteries reach full, surplus power gives you the same hot water as the solar thermal. You get hot water for free, having spend the money on PV panels needed for electrical power assuming they produce 30% surplus above average usage.

I think solar thermal might make sense on a larger scale system, where you're not paying $11 to $12 per square foot of collector.

US parks department did a study on cost-effectiveness of solar thermal hot water. Not a paper study, actually installed and operated at rest stops. This was decades ago, but back then solar thermal was cheaper than electric heat (including equipment and maintenance), but more expensive than gas (only some sites had gas available). PV cost 15 times as much back then.
 
$700 gets you two, 24" x 24" thermal solar panels. 8 square feet.

PV panels are now 20% efficient. If solar thermal is 100% efficient, 1/5th as much area is required (I'm guessing its only 50% efficient). So 40 square feet of PV delivers same power.
Assuming your system isn't perpetually leaving batteries drained, you have surplus PV generation sometimes, and charge controller leaves the electrons in the panels.

A typical PV panel is 5' x 3' for 15 square feet, delivers 250W. Costs $70.
For $210 I get 45 square feet of PV panel, able to deliver same power as that $700 solar thermal water heater.

A modest size PV system might be 2500W, ten 250W panels for $700. By simply switching on an electric water heater powered by the AC inverter whenever batteries reach full, surplus power gives you the same hot water as the solar thermal. You get hot water for free, having spend the money on PV panels needed for electrical power assuming they produce 30% surplus above average usage.

I think solar thermal might make sense on a larger scale system, where you're not paying $11 to $12 per square foot of collector.

US parks department did a study on cost-effectiveness of solar thermal hot water. Not a paper study, actually installed and operated at rest stops. This was decades ago, but back then solar thermal was cheaper than electric heat (including equipment and maintenance), but more expensive than gas (only some sites had gas available). PV cost 15 times as much back then.
I think the one I linked is a little expensive for the performance. The pool ones seem more cost effective. Heat could also possibly be done cheaper with scrap hose or something, low tech easy to build your own. PV cells are kind of just have to buy.

I might do some setup with my sestem where an extra inverter goes to my rv water heater, and electric heater, only run them once the batteries are topped, and PV solar has nowhere to go.. might put something similar in as the system I linked.

Mobile in the middle of nowhere right now, I'll be back home on desktop in a few hrs.
 
All depending on weather conditions, how much heat you need, high or low grade heat.

And then the fun of designing in freeze protection.
Could be polyethylene glycol loop. Could pump hot water into the panels during freezing weather.
Each system, PV or thermal, is somewhat site specific, needs to be engineered and debugged.

Home made PV panels simply aren't practical. The encapsulation, weather protection, safety are engineered in. They are a dirt-cheap commodity today, can't beat commercial units with home build.

Electronics like PCs and stereos used to cost 10x the component costs. Today they're 1/10th the component costs.
Once upon a time we built our own to save money. Today cheaper to throw away and replace than to repair.
 
The problem isn't the the heating element but the thermostat. As DC never cross zero, it can sustain an arc indefinitely, which is why it's much harder to quench it than with AC.
Oooh….really? an arc can be sustained by any voltage indefinitely as long as it is applied indefinitely.

Absolute nonsense buddy.
 
Here's a posting showing what happens when a device (circuit breaker in this case) rated for AC was used to interrupt DC:


You've seen the still photo.
Now watch the movie from Myth Busters.


They say this has happened a couple of times with real houses.

All I'm saying, is don't use the thermostat and overtemp device in a water heater for high voltage DC.
Run either AC or low voltage DC through them to control DC switches. Two separate devices, not combining to one relay, so as to not reduce the amount of redundant safety.

Or, easiest these days, just run the water heater off your inverter when you have surplus PV.



Mate....noone is saying use 600v from the panels...the formula is to use the same voltage as the element and hence the whole hot water unit is rated at.

You are scaremongering either through self promotion or ignorance.
 
Mate....noone is saying use 600v from the panels...the formula is to use the same voltage as the element and hence the whole hot water unit is rated at.

You are scaremongering either through self promotion or ignorance.
That was 200V, 10A, through a breaker designed to interrupt fault currents (like 5000A).

Water heater is typically 230Vrms. So perhaps you would apply 230Vdc.

The thermostat will fail. It just has a narrow gap between contacts, since designed to interrupt AC with a low maximum current.

The more interesting questions is, "How will it fail?"
Will the contact arm burn back and become open?
Or will it melt and fuse onto the other contact?
 
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Do you know why?

Hint: RMS versus Peak to Peak.
No, not at all.

First of all, not "peak to peak", because that is positive polarity (at one instant in time) minus negative polarity (at a different time.)
Let's talk about RMS vs. Zero to Peak. 230 Vrms x 2^0.5 = 325 Vpeak.

The DC ratings of the switches are typically 10x lower voltage than the AC ratings. Or, if rated for same voltage, current ratings are typically 100x lower.

Extinguishing an arc is difficult. AC makes it trivial. Otherwise, there is some serious engineering put into it.
 
Oooh….really? an arc can be sustained by any voltage indefinitely as long as it is applied indefinitely.

Nope, with AC the arc is extinguished at each zero crossing and a new arc forms with the next half cycle. You can clearly see that on high speed footage of AC arcs.

And you can see the difference very clearly on this video for example:



Absolute nonsense buddy.

Wow, I don't know why you're so rude but don't expect much answers from others if you continue like that...
 
I'm for the first time delving into the world of solar power. Although I have wanted to get into it for at least 20 years it has always been expensive and my location unsuitable.
The place I own now is darn near perfect for solar. I have a large south facing roof & no trees that would block the sun.
Will along with this site have been very educational, and if not for that I would have not have considered heating my water with my excess solar power. I originally was going to feed my two 3K growatt split phase inverters with twelve 305watt panels which would be less then what they could handle, but learned you can over panel as long as the volts don't exceed the inverters rating.
But looking at the way some are using there excess solar, and my aging minds ability to comprehend some of the circuitry being used I had to come up with something I could do that works within my limitations.
My house is a little unique as it used to be a Church run children's home and has a large laundry room with two 80 gallon electric water heaters. I have only been using one and for my household needs it's more than enough.
My plan is to replace the 4500 watt elements with 2000 watt one's and use a timer to turn water heaters on & off. The times to be determined once my system is up & running. I will also be replacing the first water heaters lower thermostat with another upper thermostat and wiring it so that when the first one's water is hot enough it will send power to the second water heater to preheat it.
Although I don't have everything yet. I will have two growatt 3k inverters, 5500 watts of solar & 13 kilowatts of lithium battery backup.
My house has two 200 amp breaker panels and I plan on feeding one panel to power most of my 120v circuits with solar and the other panel I plan on using the grid to power the rest of my 120v and all my 240v circuits, (with the exception of my water heaters.) In pinch I can also easily back feed the other panel.
 
If you connect two 4500W elements in series for half the voltage, each will consume about 1125W.

Instead of timer based, can you generate a signal based on state of charge or excess production?

Are the two water heaters in parallel? If your water needs are lower, maybe plumb them in series. One can pre-heat gradually and the second brings to full desired temperature.

A tempering valve on the output would let you hold water hotter than desired for use (more storage) and have constant water temperature at the tap. Maybe surplus heat could provide space heating.
 
If you connect two 4500W elements in series for half the voltage, each will consume about 1125W.

Instead of timer based, can you generate a signal based on state of charge or excess production?

Are the two water heaters in parallel? If your water needs are lower, maybe plumb them in series. One can pre-heat gradually and the second brings to full desired temperature.

A tempering valve on the output would let you hold water hotter than desired for use (more storage) and have constant water temperature at the tap. Maybe surplus heat could provide space heating.
The tanks are plumed in series but I'm not sure if I wire my current elements in series I would still be able to use the thermostats to feed the the second tank. I don't know if I would go the tempering valve route because in order to use that for heating it would also involve coming up with some sort of plumbing and or fan arrangement to harvest that heat and I will be working hard enough just to get everything on my plate done as it is. Perhaps at a later date I could revisit the idea. I could however also wire the second tank so that if it also heated up completely it could send excess power to an electric heater of some type, but in the winter when I would most likely need the excess power for heating I might not generate enough to do much of that.
One of my goals is to keep things as simple as I can while extracting as much usable energy without giving my tired old brain a headache.
I do like the idea of sending excess power to the water heaters based on state of charge but from looking at the different ways others are doing it I feel that it may be one of those brain racking headache generating things I should avoid.
One of the methods I think might work for me is to use the dry contact feature on my Growatt inverter. But I'm having trouble understanding their explanation on how it works.
I know it may sound like I'm an ignorant dolt, but I have a lot of basic electrical & mechanical experience but can't seem to grasp some things that should be easy to understand which is why I'm trying to keep it simple.
 
Relay contacts, and therefore thermostat contacts, rated 120VAC might only handle 30VDC. Check the manufacturers DC spec.
Arcing while contacts opening is the issue. VAC goes through zero volts breaking the arc. Arcing can weld the contacts together. That's why there is a RED button high temp cutoff thermostat. Usually 1 per tank for both controllers. Splitting them to 2 circuits leaves 1 without the protection.
 
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"Dry contact" may be the simple way to do it.
I think Outback and/or Midnight has that, programmable for something like voltage or SoC.

Considering the curves of lithium, if Growatt can switch a relay on and off part way up the voltage curve, it could cycle up and down a few percent near fully charged, diverting power to the heater without curtailing PV production.

Analog control could be most ideal. If the waveform didn't cause issues, a dimmer (uses SCR to cut in part way through sine wave) with servo circuit could hover at some battery voltage without charge/discharge cycling.

(AC not DC circuits feeding water heater, of course. Unless you buy the heating elements with DC thermostat built in. Would still need DC relays for timing or dump load functions in that case.)
 
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