Solar water heater

[Daddy Tanuki]

What I realized, if you put up solar panels to heat a geyser, that geyser will be heated in a couple of hours.

So what then happens with the panels?

So a penny dropped ... get a Solis grid-tied inverter, slap the panels on it, connect it to the main DB, put in a timer for when to switch the geyser on, like a Shelly relay that gets one very far ito what time/s to come on and with a temp sensor, for when to switch on/off if the geyser temp is too low/high, and one can automate it all.

Can even use Home Assistant/NodeRED if that is ones flavor.

Then when the geyser is heated, when the solar panels are sitting idly on the roof, use that free power for other loads in the house.

My 2 cents.

The TT, I looked at link real quick but how do you program it? via bluetooth or what? how does it work? sorry not up to speed on IOT and home controls.

 

[The Terrible Triplett]

The TT, I looked at link real quick but how do you program it? via bluetooth or what? how does it work? sorry not up to speed on IOT and home controls.

It comes with a nice easy-to-use interface, type in the IP address at home using any browser, or on your phone at home, and you can get to it.



I connect it like so, to a bigger relay, being 3kw element, just because it made sense to me, less stress on the Shelly.

 

[The Terrible Triplett]

FWIW, that Shelly, it is controlled, in my case, by NodeRED running on the Venus/Cerbo Large OS.

When the solar panels are >3.6kw, utilities draw is near zero, the "Victron system" switches on the Shelly to heat the geyser up to 50 deg Celcius. Can adjust higher if I want.

Then, as long as the utilities draw stays below 600w, to cater for house loads coming on in that time, the geyser will stay on.
EDIT: For bad weather days, late afternoon the geyser will switch on if the temp is not reached.
Evenings, IF the temp goes below 30 deg C, the geyser will go on ... I call it the "marriage saver" setting

The NodeRED part to switch the geyser on/off based on solar production, utilities draw:

 

[Daddy Tanuki]

It comes with a nice easy-to-use interface, type in the IP address at home using any browser, or on your phone at home, and you can get to it.

View attachment 211466

I connect it like so, to a bigger relay, being 3kw element, just because it made sense to me, less stress on the Shelly.
View attachment 211467

so could you hook this up to measure the temp of a tank, and the voltage of your battery bank and have it turn on a load as long as voltage is greater than or equal too xx.xx volts, and water temp was below say 80°c?

Scenario is a 1600 liter tank that is a hot water boiler using two 4500 watt heating elements in series. when battery is over lets say 53.9 volts the "shelley" could turn on a relay to the elements that allows voltage to flow.

why? I am over paneled for winter months, winter the battery bank is generally full by 1030-1100 and floating. On bad days it might not hit float but generally it does. (free hot water all winter?)

In the summer I run a a/c split pack 24/7 for humidity control and yet my bank is generally full by the same time.

So if the "shelley" can control taht it would automate something I have been trying to piece together.

 

[The Terrible Triplett]

So if the "shelley" can control taht it would automate something I have been trying to piece together.

Shelly is just the on/off switch, it needs to be told when to do that, its built-in software the catchall if you want.

Hence I use NodeRED on the Victron Cerbo as the "instructor" of the shelly, using the volts if I wanted. I chose to rather use the panel's incoming watts.

 

[willem wikkel spies]

just a update.
We had two days of really bad weather.
a cut off low which caused complete cloudy days.
highest was 38 degrees the one day and the other day it was 42 degrees, which was still not too bad.
so the solar panels could not heat the system to 75 degrees celcius as we had no sun.
it was not such a concern as we could see the water temp was down and we quickly boiled some water.
our day temps was around 26 degrees and night temps 20 degrees.

since then we just had plenty of sun, and water has been up to 75 degrees at 10:30 in the morning.
so we need to plan for things like this, and it is easy.

now, to use excess power, when you have it.....

so, if you need solar and you do not have solar, then what?
so using extra solar for something else can work, but if you cannot give power as you planned, then there is no use to budget/ think about it.
a full day of solar is not guaranteed!
just plan your system, see that it works and live with the fact, that at times you will have excess power, but it will still be waisted.
you cannot drink the last drop of every bottle water.

you can thank and pay me later for the above information.

ohms law is wrong, do some research lol

 

[The Terrible Triplett]

you can thank and pay me later for the above information.

Living in Cape Town, trust me when I say, you are pretty aware of the weeks of the year when you will have to fall back on utilities.

Living in Canada, Alaska, some USA states, Europe, and you have a whole new world of challenges to sort for months at a time.

You gain this experience from being on solar for more than a year.

Living where you live in South Africa, after a year you may look at it all again and think: I have these panels, they just sit there idling, the geyser being heated. How can I use that wasted energy just sitting there, already paid for?

You have to walk the talk first in your own shoes.

You can thank and pay ME when you are ready.

 

[willem wikkel spies]

Living in Cape Town, trust me when I say, you are pretty aware of the weeks of the year when you will have to fall back on utilities.

Living in Canada, Alaska, some USA states, Europe, and you have a whole new world of challenges to sort for months at a time.

You gain this experience from being on solar for more than a year.

Living where you live in South Africa, after a year you may look at it all again and think: I have these panels, they just sit there idling, the geyser being heated. How can I use that wasted energy just sitting there, already paid for?

You have to walk the talk first in your own shoes.

You can thank and pay ME when you are ready.

So you are the bastard that licks the last of the milkshake out the bowl, because you paid for it?
or just because you can.
area where you reside is important, over the escarpment i think you would have to over spec your system.
east, west and north side to get all the sun possible. that would make the system not cost effective,

but loadshedding is at a minimum now, because of the elections.
just wait after 29 may
panels are getting dirt cheap already.
but dont skimp, get ja or canadian.

i think the best option would be to get a geyser of 200 liters.
150 works well, that 50 extra liters would work well when you have children.

still waiting to see high voltage, no load we should be getting to 300 volts dc.
but still only 210 dc over element.

 

[willem wikkel spies]

Just a update.
system has been working flawlessly since inception.
No real hick ups, apart from the geyser popping due to old age.
had the geyser moved to the outside in a vertical position.
the new geyser is working better, obviously element is not clogged up.
with winter here, it is on the hole day, to get to 70 degrees.
i have a option to build a frame to get more aligned with the sun during winter time.
but for now, thats on the back burner as we have enough hot water to sustain us.

 

[robby]

so, if you need solar and you do not have solar, then what?
so using extra solar for something else can work, but if you cannot give power as you planned, then there is no use to budget/ think about it.
a full day of solar is not guaranteed!
just plan your system, see that it works and live with the fact, that at times you will have excess power, but it will still be waisted.
you cannot drink the last drop of every bottle water.

Actually there are a lot of people on here that are drinking the Last Drop of water everyday.
You just need to have a huge bank of batteries that can take you through multiple days.

 

[Daddy Tanuki]

Actually there are a lot of people on here that are drinking the Last Drop of water everyday.
You just need to have a huge bank of batteries that can take you through multiple days.

That’s my plan…. Just need to finish up my boiler unit…

 

[Warpspeed]

Yes, @efficientPV has it all figured out, that is definitely the best way to do it.

I have built something very similar myself and it works very well indeed.
DC is fine, as long as its interrupted dc pulse width modulated.
You also obviously need to have a reasonably high voltage solar system if using the original heating element(s) to work at a useful power level.

For safety there need to be multiple redundant safety systems to shut off power if over temperature is detected.

Main modulated load control should be by a completely electronic separate temperature sensor that cycles the pwm on and off electronically.
If you can ditch the original mechanical contacts, and have a digital readout of temperature, and electronic modulation of the pwm, that will be a huge step forward.

The original mechanical temperature control contact can still be used to completely shut off the pwm electronically as a backup to the new temperature sensor and digital readout and control system, but not for normal temperature control.

Lastly, the internal over temperature protection contact can be left in series with the heating element in the original way.
Although not designed to break dc, that will only ever open as an absolute last resort protection.
This will latch the protection contact open (rather like a circuit breaker) and you then need to push a mechanical reset button to reset the system.
Multiple other things will have to fail first before it ever gets that bad enough to operate the last resort level of protection that must be manually reset.

Its not difficult, but it all needs to be very carefully thought through, and all possible failure modes taken into account.

 

[Offgrid Jungle]

It comes with a nice easy-to-use interface, type in the IP address at home using any browser, or on your phone at home, and you can get to it.

View attachment 211466

I connect it like so, to a bigger relay, being 3kw element, just because it made sense to me, less stress on the Shelly.
View attachment 211467

There's an even better Shelly that will read the thermistor probe in the hot water heater and shut down the feed for you automatically.
These two items snap together to make a slick device that reads the thermistor and automates on and off up to 15 amps. The Shelly app is good but I integrate them into my Home Assistant system. Awesome products.

 

[willem wikkel spies]

some more feedback.
we have had some real cloudy days and water temp got up to 43 degrees Celsius.
we had a day or two in colder spell where we had to boil some water.
so not ideal.
but our winters are so short.
back to spring and voltage is 250 vdc on 6x panels over a 3000 watt element.
some days you will need all the power you can get "winter", and in summer, by 10:30 its 75 degrees.
my system is controlled by 2x temp sensors in series which activates a 12 vdc contactor.
units of electricity consumed since march 2024 is 694 units in 7 months = 99units a month.
down from January 235 and feb 328.

wil monitor and give more feedback
stay safe all

 

[efficientPV]

You have to record the voltage on the element to have any real data on the project. It will soon be evident of just how big a mismatch the heating element. Below is an example of a fixed element system vs electronic matching. It is the worst days you need the best performance. Electronic matching can outperform your system by 3 or 4 times.

% Rated Increase over Voltage Power
Panel Amp Direct Connect 10 ohm 10A panel Direct Connect

100% 0% 100V 1,000W
90% 10% 90V 810W
80% 25% 80V 640W
70% 50% 70V 490W
60% 67% 60V 360W
50% 100% 50V 250W
40% 250% 40V 160W
30% 333% 30V 90W
20% 500% 20V 40W
10% 1000% 10V 10W

 

[willem wikkel spies]

You have to record the voltage on the element to have any real data on the project. It will soon be evident of just how big a mismatch the heating element. Below is an example of a fixed element system vs electronic matching. It is the worst days you need the best performance. Electronic matching can outperform your system by 3 or 4 times.

% Rated Increase over Voltage Power
Panel Amp Direct Connect 10 ohm 10A panel Direct Connect

100% 0% 100V 1,000W
90% 10% 90V 810W
80% 25% 80V 640W
70% 50% 70V 490W
60% 67% 60V 360W
50% 100% 50V 250W
40% 250% 40V 160W
30% 333% 30V 90W
20% 500% 20V 40W
10% 1000% 10V 10W

i agree with you.
just note im in south africa.
and we do not have any stuff that we can just buy and connect.
i could always fit the 2000watt element in it, that will be much closer to the average of the system.
but its working 98% of the time, like i have to worry about it, 6x days out of 365 (which could be cloudy / rainy days)
so why spend more money? and effort to try and gain 10%

my roof could have been build better to catch the winter sun more, but to go and build steel frames and angle the system is more work.
i could always split the system, 3x solar panels facing east and 3x solar panels facing west, still a series connection. but that again will open a whole can of worms again..... i think.

Time will tell where we end up.

 

[efficientPV]

"its working 98% of the time, like i have to worry about it, 6x days out of 365 (which could be cloudy / rainy days)
so why spend more money? and effort to try and gain 10%"

That is the truth, like most people here you don't care. From you statement you don't really know how your system is working. Performance varies widely thru the day. Improvements do not need to cost money. No need to report back if you don't have any data.

 

[parksnorris]

just a update.
We had two days of really bad weather.
a cut off low which caused complete cloudy days.
highest was 38 degrees the one day and the other day it was 42 degrees, which was still not too bad.
so the solar panels could not heat the system to 75 degrees celcius as we had no sun.
it was not such a concern as we could see the water temp was down and we quickly boiled some water.
our day temps was around 26 degrees and night temps 20 degrees.

Since then, we just had plenty of sun, and the water has been up to 75 degrees at 10:30 in the morning, thanks to the advice I found on etrailer.
so we need to plan for things like this, and it is easy.

now, to use excess power, when you have it.....

so, if you need solar and you do not have solar, then what?
so using extra solar for something else can work, but if you cannot give power as you planned, then there is no use to budget/ think about it.
a full day of solar is not guaranteed!
just plan your system, see that it works and live with the fact, that at times you will have excess power, but it will still be waisted.
you cannot drink the last drop of every bottle water.

you can thank and pay me later for the above information.

ohms law is wrong, do some research lol

Which companies did you buy your water heaters from on eBay? They don’t have any priced at £90, only the £200 ones. Thanks in advance!

 

[Daddy Tanuki]

"its working 98% of the time, like i have to worry about it, 6x days out of 365 (which could be cloudy / rainy days)
so why spend more money? and effort to try and gain 10%"

That is the truth, like most people here you don't care. From you statement you don't really know how your system is working. Performance varies widely thru the day. Improvements do not need to cost money. No need to report back if you don't have any data.

Wow... how would you know if he cares or not? maybe he has more important things to do, like earn a living...or take care of a bed ridden family member... or anything that is of more importance than a mere...hobby.

 

[efficientPV]

Everything here is made personal. This sounds like a system just thrown together and hoping for the best. How much time does it take to make a simple voltage reading. He has time to waste posting. Your comment is ridiculous.

 

[Daddy Tanuki]

Everything here is made personal. This sounds like a system just thrown together and hoping for the best. How much time does it take to make a simple voltage reading. He has time to waste posting. Your comment is ridiculous.

No the way you respond to people is off the rails. If some one does not want to do it your way, get over it, You want to teach people, but you drive them away with how you interact with them... what do you expect? honestly... nobody wants to listen to a person who is criticizing them all the time. (just as you will not want to listen to me criticizing you.)

 

[HighDesertDrifter]

Are you saying that ONE DC rated element will prevent an explosion? Because it will not.
You need some kind of Thermostat if the Heater is completely sealed. Heating water in a sealed container is a Bomb, you have to have the means to prevent it from going critical. Pressure relief valves do that but they are a last resort and they can possibly fail. The thermostat is the main control mechanism and HVDC will weld the contacts shuts on an AC thermostat.

Why not plumb in a 2nd pressure relief valve for redundancy? If it's good enough for aircraft, why not use redundant safety techniques on everything else where there is danger of catastrophic failure?

 

[Daddy Tanuki]

Why not plumb in a 2nd pressure relief valve for redundancy? If it's good enough for aircraft, why not use redundant safety techniques on everything else where there is danger of catastrophic failure?

that or a pressure relief valve and a burst disc. get your pressure valve at whatever is normal and then a burst disc that is say 10 or 15 PSI above the pressure valve as a last chance oh shit release. most water heaters I would think could handle that much without exploding, but I am not a pro, so YMMV.

 

[HighDesertDrifter]

So i think i have some idea what you are getting at, but the math you posted is not helping me get closer to it..
Is that a correct way of thinking of it?

the math you posted is not helping me get closer to it..

Man, can I ever relate to that statement. Why do so many "highly articulated mathematicians" seem to just assume if they get the equation than everyone else does also?

Thanks for your review of the discussion at hand, I actually understood your reply thesis. However my mathematic skills are severally limited... Lol
I never made it into "The equations are us club."
I was happy to ride on the little bus hahaha
I really thought it was something to figure out the little hand points to the minutes and the big hand points to the hours!

KISS has always worked for me, when I have a question about a certain build, I just make one and then improve where needed as we go.
All the over thinking makes my tiny lil brain hurt! Ouch! Besides I must be an inventor at heart, with just enough basic understanding of things to stay alive along the way and not burn the house down.