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Titanium AC / DC element


viceroy
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I'm looking to start converting my home to run mostly off Solar, and I've seen adverts for converting a std. geyser to use a titanium element which can run on AC or DC and uses much less power than a normal element.

Apparently running one of these off 3 panels and a few batteries is a cost effective way to go.

 

Any insight on this would be greatly appreciated.

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There is loads of options now available for heating water.

 

Directly heating the water via heat exchange, like with vacuum tubes.

Retro fitting existing geysers with vacuum tubes.

Retro fitting existing geysers with solar PV power.

Changing the element??? No way can that save power. Heating 100L or water by 10 degrees will always take the same amount of energy. A larger element will just do it in less time.

 

The PV option is good for problem locations where the roof is not suited for external geysers etc.

My grip is just once all the water is heated, the extra energy is wasted :(

Retro fitting is a good option, as long as you realise the system constraints, like small water storage volume.

With solar you want to heat as much water as possable!!!

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Did some more research into this, and if we didn't have a maid using water thoughout the day, a DC titanium element would have been fine, since it would slowly heat up the water during the day, and maybe only needing a bit of a jolt from eishkom in the morning.

 

Having a maid using water throughout the day ruins this as the tank would never be able to get up to temp.

Have now decided to go with vacuum tubes retrofitted

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  • 2 months later...
  • 2 months later...

  • Studies have shown that within the domestic market, 40-60% of your power bill is in heating from geysers. As an Energy Efficiency Advisor, I can confirm that the titanium element is far superior to the conventional element in your geyser. The 150 litre geyser is probably the most common on the market...about 80% and the 200 litre accounts for about 20%. The 150 litre geyser, when on, generates 3000 watts per hour. The 200 litre generates 4000 watts. The main difference between a conventional element and a titanium element is the technology with which it is made. Heating elements made with PTC (Positive Temperature Co-efficient) chips do not use resistance wire as a source of heat. Instead, it uses a number of ceramic chips that have self-limiting temperature characteristics. What this means is that the water in the geyser is heated up at the same rate as your regular element (3 kwh) would but at 50% less power (1.5 kwh), hence a 50% saving in costs. 

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I'm with Wetkit on this. It takes 1.16Wh to heat one liter of water by one degree celsius (of course this linear formula breaks down as you approach boiling point, but it's close enough at normal geyser temperatures). Geyser elements are just about 100% efficient. So I don't buy the idea that some or other element can somehow save you electricity.

 

A while ago there was this turbo-element. I think the tech was taken over by another company here in Somerset West. They also claimed to save you electricity. When I enquired I realised how they do it. The heating element layers your hot water at the top of the tank, thereby reducing the volume of water it heats. This means your standing loss comes down, and unless you use large amounts of water it does reduce your consumption somewhat.

 

The only exception is heat pumps, which don't convert electricity into heat, but instead use electricity to move heat from the environment into the water.

 

But on a similar note: I've been messing around with SMPS (switch mode power supplies) lately. Well, more reading than anything, and writing some code to do PWM at 100khz on an arduino. So first little factiod: They geyser element doesn't care whether you feed it AC or DC. The AC you feed it with is 230VRMS (325V peak), which means that the equivalent DC voltage it would do the same work at is 230VDC. Second little factoid, because it is completely resistive, it's not going to care if you drive it at 110VDC, 50VDC, etc, it will just take longer. Third little factoid, with a boost converter you can relatively easily convert a low DC voltage to a higher one, a bit like an MPPT controller in reverse.

So this leads me to believe that it should be relatively simply to drive an ordinary geyser element with a boost converter from DC panels at any power level you choose.

Small issue at present, since I'm an amateur electronics guy: Usually you use schottky diodes in the boost converter, but schottkys have rather low reverse breakdown voltages... anyway... still thinking about it.

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I agree with wetkit and plonkster... it takes a fixed amount of energy to raise the temp 1 L of water by 1 degC... where you can save is:

heating less water, heating a smaller temperature differential and saving/preventing unwanted losses (that indirectly create a larger temperature differential)

 

@ plonkster: I've been playing with the same idea you have... AC in one side, Solar panel other side and small controller that aims to get my geyser to a set temp at a set time... and if solar is not enough or not available it switches back to AC...

 

two things to remember:

1. switchmode supplies for large power don't have the same charachteristics as ones for small power (and are a lot more lossy)

2. once your voltage goes too low, there just simply is not enough energy to heat the element

 

I have 4x 300W panels that I'm planning to use.. and then seeing what I can do with 3... (minimizing the capital outlay)... however another way of thinking about it, is what do people have that already have solar strings... If one repurposes the string, one could use it as is... (then probably a buck converter, as many of the strings are above 250V) - but quite doable....

 

maybe a short survey:

 - what is your installed PV rating (voltage and Power)

 - are you already making max use of it (or does it have idle time)

 

now granted if most don't have idle time, then you would need additional panels and then one would like to optimize for minimum panels for maximum effect...

 

best

Stephan

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two things to remember:

1. switchmode supplies for large power don't have the same charachteristics as ones for small power (and are a lot more lossy)

2. once your voltage goes too low, there just simply is not enough energy to heat the element

 

 

 

True. From what I've seen, unless you put a lot of time, effort and money into it, these converters usually do around 80% efficiency. There's also the standing loss on a geyser, around 2.5kwh a day, so that if you put less than that into it you're not really heating it (just counteracting some of the losses).

 

I don't have  a large array at present, a mere 900Wp. My system isn't very big, it's only job is to run fridge, freezer, computers and television, I installed it mostly for load shedding. But I do intend to add more to it, and would make a heck of a lot of sense if I could dump around 2kwh into a geyser instead of charging a battery with it. Of course there are many ways to get this done... the easiest might be to simply add grid-tied capacity and put the geyser on a timer... then run after lunch :-)

But I do enjoy playing with these things. I have dreams of eventually building my own charge controller. I want to mess with Victron's Hub-4 and for that plan to work you really need control of the charge controller. On the upside, since my Microcare controller broke down and I started reverse-engineering the insides, that might just be the base for version 1.

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  • 1 year later...
On 8/16/2015 at 4:46 AM, EcoElement said:

Heating elements made with PTC (Positive Temperature Co-efficient) chips do not use resistance wire as a source of heat. Instead, it uses a number of ceramic chips that have self-limiting temperature characteristics. What this means is that the water in the geyser is heated up at the same rate as your regular element (3 kwh) would but at 50% less power (1.5 kwh), hence a 50% saving in costs. 

Interesting. Using a PTC element means it's somewhat able to overcome the problem that as the voltage across a fixed resistor decreases by a factor f, the power dissipated decreases by f². (Since power = V²/R and R is fixed.) So using a few panels is pointless - you get next to no heat.

But using a PTC (positive temperature coefficient) element, it can run at say 30% power at 40% of the voltage. (30% of a common 2.4 kW element is 720 W, about what you could get out of three 250 W panels in full sun.) And if you need to boost, you can connect 240 VAC to it, and it will not overheat or draw insane amounts of power. That's because the R (element resistance) is no longer fixed - it depends on the temperature of the element. It's non-linear, like a light bulb. A light bulb will draw lots of power when it's cold, but will quickly draw less power as the filament increases in temperature. A PTC element has this effect, but more so.

However, the claim that you can use 1.5 kW to get the same effect as 3.0 kW is simply nonsense. I *might* believe that you can get 6% more power from the element through titanium as through stainless steel, but 6% is a lot less than 100%.

Presumably, these elements are designed to be a crude MPPT (maximum power point tracker), designed to work with a particular set of panels. In this case, it seems to be 3 250 W panels in series. It's not clear to me what happens if you add more panels; I think it might work but only give say 70-90% of the maximum power available from the panels (depending on how bad the mismatch is, between the design number of panels and the supplied number of panels). So you can feed it say three panels all day, or boost it with an hour of 240 VAC if necessary. With the three panels, the voltage is low so the element temperature is low, so its resistance is low, so it draws more current from the three panels than a fixed resistor (that could also take 240 VAC) would. If there is shade, then the panel voltage under load goes down even further, but the resistance goes down even further to keep the E² factor from losing most of the available power. In a way, the element  adjusts its resistance to get close to the maximum power available from the panels.

I hope the above isn't too confusing.

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isn't it many times the marketing w#nk that fails the product. like i had to sit and listen to a guy ramble on how his 600W motor was stronger and used less energy than a 2000W motor, i had to concentrate so hard to not roll my eyes. same guy will refer to fibre glass as carbon fibre (oh no you didn't) and out of politeness i can only say oooh & aah, that's nice. 

But yea If you think about it the crude mppt as @Coulomb put it its cleverly cost effective and putting wasted pv to water heating is fine, its just that the application is only useful to some. Putting up panels dedicated to this doesn't make sense to me.

 

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34 minutes ago, Weasel said:

Putting up panels dedicated to this doesn't make sense to me.

Plus one on that statement. Using spare PV to heat a geyser is perfect, but not panels just for heating water.

But then, if you have spare, why? Okaaayyy, not opening that door. There, I closed it.

 

I quoted a answer before on the forum, from a large supplier in Cape Town, when I asked him the question on these new elements and PV panels and why they don't install them.

 

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55 minutes ago, DeepBass9 said:

150litres x 40 degrees x 1.18 =  7.08kWh

You will need at least 1500W of PV to generate that every day. Rather use an EV tube geyser with Eskom backup, much cheaper.

Doing the heating alone, those extra panels will be paid off in less than 3 years (when added to an existing SCC/Inverter) and you get the added luxury of running other high loads daytime for free and bonus in crappy weather too.
A win for me over EV tubes 

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1 hour ago, DeepBass9 said:

150litres x 40 degrees x 1.18 =  7.08kWh

You will need at least 1500W of PV to generate that every day. Rather use an EV tube geyser with Eskom backup, much cheaper.

That maths is correct but do you empty 150L of hot water from a single geyser daily?

We have a 200L geyser and mostly shower. We have a water saving showerhead (6L/min) so if we each shower for 10 minutes then we use 120L to shower. Divide that by 2 because you don't use 100% hot water and you get 60L of hot water for 2 showers. So 60x40x1.16 = 2.83Kwh

In reality we don't shower for 10 minutes so we need even less power.

In our case we have 1020w of panels on the roof, currently producing roughly 6kw per day in these winter months. Our geyser reaches 75C by midday on most days.

I have noticed the system is heating 200L by 20C daily which means the energy going into the water is 6.7KW (200Lx20x1.18 - 2KW for thermal loss). This is perfect since our geyser never goes below 50C even with 3-4 people showering.

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There is no way that PV is better than EV tubes, unless you have lots of money to burn, in that case go for it. A R3000 EV geyser will do the exact same job as your R10 000 of panels, plus fittings, plus geyser etc etc.

In our case we have a 300l solar geyser, which provides 2 deep baths (we have massive cast iron baths) for my wife and daughters, and I have a shower for as long as I want under a gush of water. So the sun directly heats up 300l, by at least 30 degrees so that is a minimum of 10kWh if not more. Not worth it to trying and do that with PV, it would cost too much.

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2 hours ago, DeepBass9 said:

150litres x 40 degrees x 1.18 =  7.08kWh

Shouldn't that be 1.16? Of course the amount of energy required does vary according to temperature and atmospheric pressure, so it could be as much as 1.17 under some conditions. Your answer is still correct within 2% though :-)

Other than that, I think we had the debate already. For the paltry investment of 30k or less I can harvest the equivalent of 10kwh a day and practically eliminate the biggest load in my house. Unless you're a rich man, I have no idea how you can say PV is better, and the debate between flat panel and EV-tube is much more relevant.

If you're looking at the bigger picture though, involving a PV setup you're putting in anyway, heat pumps you need anyway (because you don't have enough sun in winter for example), then the picture changes and you might say that if you're going to do PV anyway, you might as well heat your water with that too.

I make that same argument about gas stoves. Gas is not cheaper than electricity. If you have natural gas piped into your home it is about on par and maybe slightly cheaper, but not much. This is simply due to the cost per unit of energy being very similar AND the efficiency of gas being significantly less... BUT, once again, as part of the bigger picture, where you're putting in PV anyway and moving the stove to gas means buying a smaller inverter/battery bank... yes, absolutely, go for gas instead!

:-)

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41 minutes ago, plonkster said:

Other than that, I think we had the debate already. For the paltry investment of 30k or less I can harvest the equivalent of 10kwh a day and practically eliminate the biggest load in my house. Unless you're a rich man, I have no idea how you can say PV is better, and the debate between flat panel and EV-tube is much more relevant.

This is true if you don't have PV for power, but now the moment you run PV power(with backup) you already invested in some of the panels to run base load and charge the bank at the 10% rate minimum it needs.
Now for me running my cheap inverter capable of doing more than what it's currently doing, the 30k (just need 10k for another 900w) you mentioned is much better spent on expanding the array and dumping the excess power when the batts are fully charged/absorbing into my geyser for heating. Running a 1.5kw element using the maths above I need only 4.7hours good sun shine to heat my water in the mid of the absorb stage(mine hits this at around 11:00AM) of charging (doable in winter even). Cloudy days I just use Eskom as backup.
Also say you don't cycle the batts at all at night just use them for backup, then you can start heating way earlier too.

Then the PV panels in summer can be used for so much more as you tend to need less heating time for the geyser with the water entering being warmer than winter. So now my PV panels are not only limited to heating water (like EV tubes) but they also cool my place with aircons/fans when the bank is full. You just need to control this.
This to me adds way more value to the system.

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15 minutes ago, viper_za said:

you already invested in some of the panels

Yup, I think we agree here. I'm sort-of taking aim at people selling retrofit kits that literally just wire solar modules to an existing geyser, and then claim it is better. No friggin way. It's better in only one, maybe two respects: No pipes in the roof that can go boom. More aesthetically pleasing. In terms of efficiency (energy wise), and bang for buck (which is also a kind of efficiency) there is simply no comparison.

What I'm actually doing right now is spending a little extra to put the hybrid capabilities of my inverter to good use. It's pretty similar really: I already invested in some panels. Already have the equipment. For 30k I can buy the equipment needed to safely grid-tie AND another 1kwp of solar modules, so even with the high cost of the equipment I like to use, I will trivially concede that PV is better here.

Except... I put the Solar Geyser in in 2011 already... so it's a little pointless to do it for hot water only. Do have many other daytime loads though, dish washer, tumble drier, washing machine...

Man, I bought a second washing machine this year. Got a special, some guy bought a machine for 4k and it didn't fit in his bathroom, so I bought it from him for 3k, literally so new that the drum-supports was still in place when I got it. The idea was that this machine would 1) save us from having to walk into the garage at all times of the day and night to access the top-loader there and 2) save time on drying because it spins faster. It does help a little with that, but the wife still prefers the top-loader for certain tasks so that in many respects I now have TWO washing machines operating at various times of the week. I swear I'm running a laundromat or something :-) To make things more interesting, the old top-loader (13 years old now) had a bit of a mishap this weekend. It went out of balance at spin speed (700rpm), because the drum dampers are completely shot after all this time, and it bashed the drum around so hard that the machine literally has two massive dents on the sides! So now I'm actually shopping for a replacement top-loader too! Off-topic I know, just saying, I'll find a use for all that extra power I plan on backfeeding :-)

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Found it, and this comes from a solar expert that started with solar geysers, made a ton of money, then sold the business when it peaked for he saw the slump coming. They then re-skilled themselves and are now not only geyser install experts, but also solar PV installations, grid tied with all the T and I's in place, crossed and dotted.

I quote him: "EV tubes are far superior. A m2 of PV produces 5KWh per month, a EV tube system does that in equivalent water heating by 12.30pm."

So if you have too much panel, yes use it, but buying more panels for geyser heating, you need to keep in mind that PV panels produce near nothing under clouds in winter and in summer so on cloudy days you tend to use all the solar the PV array can generate for all but a geyser versus EV tubes continue under those conditions much better than PV panels, by far.

So the sums should be over 1 year, and not be for just summer. Winter is as long. 

And FWIW, with alterations of when and how long one showers, we paid the system off in savings in under 22 months. For the last 7 years near as damn free hot water.  Now and then we use Eskom in winter, never in summer.

My 2 sents.

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23 minutes ago, The Terrible Triplett said:

So if you have too much panel, yes use it, but buying more panels for geyser heating, you need to keep in mind that PV panels produce near nothing under clouds in winter and in summer so on cloudy days you tend to use all the solar the PV array can generate for all but a geyser versus EV tubes continue under those conditions much better than PV panels, by far.

Sigh.
The thing is it is not only for water heating, so much more you can do with it then only heating water. So what if it's not as efficient as EV tubes, the value you get out of them doing other things is so much more. So now you would come and recommend I rather spend money on something that can only add value to one task alone.
We starting month number 9 now for me and so far I have had 8-10 days where I had to swap to Eskom during the day to not drain the bank every now and then, all other days have been able to run the base load and charge the bank.
Now with an expanded array on those very bad cloudy days I might not be able to heat my water with PV but I will be able to charge the bank or run a few more smaller loads and heat the water with Eskom at night.
Then for the good days I run my heaters/aircons/fans/dishwashers/pressure cooker/etc,etc after the water is heated and the bank is in absorb/float and get even more value out of the panels thus making even more savings then the limited water heating EV tubes have.
Not every one want's to only run the bare essentials on solar

39 minutes ago, The Terrible Triplett said:

Now and then we use Eskom in winter, never in summer.

Yes in summer you tend not to want water that hot, I know of a couple of people that even turn of the regular non solar(PV or EV/flat panel) geyser for 2-3 days as it's hot enough on it's own

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11 minutes ago, TinkerBoy said:

so if you don't have PV then yes Tubes will work. But if you do have PV then my advice out of first hand practical experience will be install a heat pump.

Thank you.

As a matter of fact, if you have more than 200l or 4 people in the household, heat pumps are far cheaper and better than EV /FP. That advice was researched by more clever people than I, with the numbers to prove it, and you have same factual experience.

 

33 minutes ago, viper_za said:

Not every one want's to only run the bare essentials on solar

Sug ... 5kva inverter, BIG array and 48v BIG ah battery = one size fits all. We have had this conversation also.

For the rest of what you said, well done, I like it, but not for me and I would hazard and say a few others.

Personally I will rather go grid tie when Eskom and co has sorted their drama and fees, if I could have done it back then, I would not have installed EV tubes even.

 

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1 hour ago, viper_za said:

The thing is it is not only for water heating, so much more you can do with it then only heating water.

So you pay more for the extra flexibility. That's my argument for the blue stuff... :-) How much more would you be willing to pay... that is the eternal question, is it not?

I'm not a financial planner or anything, but I think there's more or less two ways to handle your finances. One is to optimise for the least cost. The other is to optimise for the best cash flow. If you optimise for the least cost, you buy your cars cash, you install the whole 250k of PV system in one go, pay debt off as soon as possible, and so forth. If you optimise for best cash flow, you might pay the minimum amount on debts, buy a car with no cash down (and a residual, with insurance for the shortfall), and your solar system is likely made up of Micro-Inverters :-)

I think there is a time and place for every approach. For example, it might make sense to pay off the house that you live in fast, but the rental property must pay for itself and you will spend the minimum to service that loan so that future rental income takes care of things. That might be one approach. When you have a regular income (such as a salary) you might pay things off more aggressively, when you're freelancing and you don't know when the money is coming, you might prefer to optimise cash flow.

In my experience (having been retrenched once), you're going to need both approaches at some point in your life.

Now, the solar geyser strikes me as the least-cost approach. I need hot water. It will cost this much. Bang. Hot water sorted. The PV option strikes me as the flexible cash-flow approach: I don't want to tie it all down into "hot water", and for that I am prepared to pay extra.

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1 hour ago, The Terrible Triplett said:

BIG array and 48v BIG ah battery

You still don't get this, what the hell, sometimes you agree with this and sometimes not, mostly when it suits you if not you just pull the disappearing act.
How many times have we said that no matter what voltage your bank for the same amount of storage\backup for the load you need it works out more or less the same cost wise on the bank.
Just the equipment works out more.

1 hour ago, The Terrible Triplett said:

We have had this conversation also.

Yeah it came up every time you tried to tell someone to sell the 48v system he already bought

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