New intergration in HA 2021.7 will allow for better planning and use of the thermal battery - https://www.home-assistant.io/integrations/forecast_solar/
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Thermodynamic Geyser
- Thread starter SauRoNZA
- Start date
Nerfherder
Honorary Master
So running the geyser hot during the day should be enough to leave it off at night. Just get a big enough geyser and use the solar vaccume tubes.
SauRoNZA
Honorary Master
I already have a geyser.
Don’t want to get vacuum tubes. It would be running purely off PV.
My concern originally was the danger of running 90-degree water with my kids, but didn’t realise there was a mixer valve sorting that out and only learnt about it in this thread.
Vacuum tubes are too expensive and prone to issues. I assume that's why they have short warranties. Most of my mates that put in vacuum tubes think that they are the best thing since sliced bread when they install. Then when it breaks all those savings are absorbed by the repair cost.
Vacuum tubes certainly have their place and they are efficient, I just think they are massively overpriced and well be eaten up by PV.
I have done it successfully - very cheap. Here are my steps and gradual improvements:
parts needed: 20MM class 6 water pipe (from local agri store about R4.50 per metre, I used about 85 Metres.), fish pond or any pump with lift of at least 5m and running about 2000L/h. Timer or in my case Sonoff wifi switch that works with the EweLink App on your phone,1x 6 metres of IBR roof sheeting, standard width, cut in half vertically to overlay, forming 2 channel guides, brackets self made to fit sheeting in a position to get sun from 8.30am to 3.30pm (our best sun in the highveld.), 16 plastic 22mm elbows, 32 clamps, alot of cable ties to keep pipes in place.
steps.
1. unroll the piping by circulating the roll, otherwise you will struggle and swear sorting out kinks and lay it out in the sun to get hot and roughly straight.
2. cut pipe in 6m lenghts
3. zigzag pipe in the channels, 4 should fit per channel, using elbows and small peaces of pipe to to join the elbows to each other and to the pipes for form one large flow of 72M. some of the pipes I laid on the top side of the raised channels of the sheets. cable tie as far as you got, these pipes like to mangle and to their own thing, I drilled small holes through the sheeting and ran the ties trough it.
4. one eng connects to the pump and T into the cold line feeding the geyers, the other after the geyeser into the pipes. What you want is HOT water from the outlet of the geyser to run through the pipes back to the cold feed of the geyers.
5. set a timer to the pump or use smart devices like sonoff.
optional steps:
6. incase of rainly or cloudy/cold days I used a sonoff with a temp sensor which I fit in the solar pipes facing the sun and set the unit to only start if above certain temp.
I then turned to Arduino. adding another temp sensor inside the geyser and compare the values by programming the arduino. If outside it hotter than inside the geyer turn on, if not, turn off.
I then added a display to arduino to show me both temps.
lastly I added a motion sensor to the arduino to turn on the display only when I walk by not to have the display on the whole time.
In Ermelo, MP I reached 54Deg C on sunny days and average about 43 other days.
when I showered I actually had to add cold water - so hot the geyer water was. Never used the geyser element.
To keep it simple, one could still set the geyser thermostat to 50 with a timer, so if say by 5pm the water is not 50deg the element will turn on and top up the temp for an hour or 2 which should be more than enough to get to 50Deg and maybe in the morning as well to run it for an hour but for me showering at night, it works perfect.
I used my geyser element about 2 months ago the last time.
SauRoNZA
Honorary Master
But this just sounds like those black tubes that sit in the sun all day and heats the water?
It’s not thermodynamic in nature in that it doesn’t work at night or when it’s very cold unless I missed a detail somewhere?
acidrain
Executive Member
No you read correct. If it is what you were looking for there needs to be a compressor in the mix.
Don't know what the price of the thing is now, but just assuming it's the same now, I honestly dont see how it can be so much. It's essentially a more efficient heat pump given the external, larger condensor.
SauRoNZA
Honorary Master
Well the heat pump is a part of it as the failover but the magic happens in the refrigerant based thermodynamic panel so you have the cost of that and the heat pump and the geyser itself all in one product.
And then it’s imported as well of course.
But yeah a retrofit option may have swung me, but paying this much to replace something which is working just fine didn’t make sense.
End of the day keeping it and pumping the money into upsizing my solar array was the right answer.
I don't know what they were thinking using this term.
Thermodynamics is a branch of physics dealing with energy and typically associated with a set of laws and mathematical theorems.
So it is a bit like saying it is "physics in nature".
Like what are they trying to say.
Everything in the universe plays by the laws of thermodynamics, as far as we know.
Every single water heater is thermodynamic in nature.
They use the term to try make it sound futuristic and magical.
Heat pumps are significantly less efficient than a direct solar heating solutions like solar collectors.
And they are also the least reliable way to heat water (or cool homes for example).
The most reliable way is directly turning energy into heat, resistive heaters like we use in our geysers.
After that, in terms of simplicity and reliability is using a solar panel to run the resistive heater. You only added 1 component, a solar panel.
After that you can start talking about various solar collectors which incorporate pumps and thus the reliability must come down due to component count.
But it is still simple, they are basically pumping water through glass tubes and things.
And the pump pressures are not very critical or very high.
And very far behind that are heat pumps, a system that works with pumps under various stages of pressure with a working refrigerant that has a very narrow operating band.
There is really no magic to heat pumps, and even if you move the radiator to pull heat from a solar collector, you'll still have far lower efficiency than a solar collector.
And it will be even less reliable than a standard radiator based heat pump (for example like we use on outdoor units with "AC".
A big part of heat pump design is the source and destination temperatures.
The refrigerant type and its pressure is chosen with that in mind.
Because when the refrigerant starts operating outside that window, your efficiency becomes worse than just running a resistive heater.
Most people think that a modern heat pump just compresses a gas, creating heat and then either puts that heat it created into the place where you want heat, or then cools that and releases the pressure to make it cool
But that is still very inefficient and only the very early prototypes worked like this.
They operate the refrigerant in its super critical state in order to make it very efficient, where the refrigerant is neither a gas nor liquid.
That is a very narrow band of operation and as soon as it exits that state the whole thing just doesn't work as well anymore and suddenly it takes more energy to operate than it is moving.
That is why industrial complexes use chilled water or heated water to transport energy, because transporting a refrigerant that relies on such a volatile state around is actually really not at all easy.
The whole narrow operating band is why in Canada for example they have two AC units back to back to each other.
The first AC unit is designed for the sub-zero temperatures to just bring the temperature mid way.
Then the next stage works on the mid way temperature to human level temperatures.
I mention all this to point out, you are switching something that can operate on a VERY broad temperature band (solar collectors) with far fewer components and doesn't first attempt to convert energy, to something that operates on a VERY narrow band, has a load of components that are complex, require precision parts due to the pressure differentials, and trying to claim it is more efficient or reliable somehow. It really isn't and it never will be, it is an (over)complicated solution that may have benefits in some scenarios like really cold temperatures but makes 0 sense in SA.
Sweet spot for reliability has been stated here many times, use a resistive heater and get the energy for that heater from a solar panel.
Solar panels have no moving parts and they are crazy reliable.
Last edited:
Tim_vb
Expert Member
Personally I have an evac tubes setup plumbed into my conventional electric geyser and I can turn off my geyser at the DB board for months at a time in sunny Gauteng. The only issue I had is a massive hail storm smashed the tubes (and neighbour car windscreens) a few months back but insurance covered the R6k bill to replace the tubes
On another point what are opinion on replacing the conventional electric geyser element with with a positive temp coefficient PTC element when using powering the geyser with off a solar + inverter setup. Apparently the soft start / soft stop characteristics and lower draw are more suited to inverter setups
On another point what are opinion on replacing the conventional electric geyser element with with a positive temp coefficient PTC element when using powering the geyser with off a solar + inverter setup. Apparently the soft start / soft stop characteristics and lower draw are more suited to inverter setups
PTCs are soft start? That doesn't really make sense to me. It is positive temperature coefficient, so the resistance increases as temperature increases.
Sounds more like the lower total power draw is the win?
But there is definitely not soft start on a PTC that I'm aware of.
Could be totally wrong and if that is the case, do share!
SA has had tumultuous gas supply in the past.
So 100% think gas geysers are a good idea, in SA probably a good idea to have some sort of backup or buy an extra gas canister just in case.
SauRoNZA
Honorary Master
Harmonic
Executive Member
Interesting to hear an alternate perspective. For me, gas delivery is a whatsapp away and the $$$ cost is much lower than purchasing an equivalent solar system.
Granted, in 10-15 years solar might come out ahead but that's ignoring the opportunity cost of the investment right now. I also have multiple guests so I can't expect them to work around the nuances of solar.
SauRoNZA
Honorary Master
Different strokes and all that.
To me it’s just another thing that needs to be maintained regardless of how cheap or infrequent.
And I hate it for cooking so there’s no dual purpose element either.
Guests are no people for me, I simply use the electricity when I need to.
As it stands my geyser is entirely free in summer and mostly so in winter.
You don’t need the full solar system to pump the geyser, for me it was a case of spending the extra I would have spent on alternatives and making the geyser larger.
Switching to gas also has an inherent cost, whereas I already had a perfectly functional geyser and was going to do Solar anyway.
Harmonic
Executive Member
100% different strokes. Situation is definitely different in that I charge money for guests so regardless of the weather, I need to provide hot water. Just wondered why gas was so quickly dismissed. With my 5 geysers not using power, I've been able to thrive with a much smaller backup setup.
To be fair, free is a stretch, money was spent to make it "free".
SauRoNZA
Honorary Master
Well in 3 years it will literally be free as then it’s generated what I’ve paid for it without even accounting for price increases and that will last for the next 15+ years.
But yes with guests it makes a lot of sense but I’ve also wondered in those setups if the inline electric geysers aren’t a good option as well.
Harmonic
Executive Member
That is amazing!
Looking at the accounting now, I spend around R1k average per month on gas. It would take probably 70 months to pay off the extra batteries, given that I can't limit/manage the supply of hot water. Adding opportunity cost and that probably goes up to a decade.
Then I ask myself, will I and/or this business even be around/in the same space in a decade. Most likely not.