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Input on proposed new setup


Charl_CCU

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Hi everyone,

I've had a grid-tie solar PV system for almost 30 months now. Recently, I've revisited the idea of going "off-grid" and only using Eskom when absolutely necessary and then disconnecting once Eskom/Tshwane starts implementing kWp limits or capacity charges.

To accompany this, I feel a solar geyser is a no-brainer. Any input would be greatly appreciated. From what I've read on the forum, it seems like there isn't a "best" solution and that there are a lot of "it depends..." My experience is that I feel that there are just so many different approaches and everyone has a different opinion on what is best.

1. Evacuated tubes or flat-plate collectors?
From what I've seen in person in my area, it seems like flat-plate collectors are a lot more popular. Is durability/quality an issue with EV tubes? If not, it seems like there is no disadvantage to using them besides upfront cost. Will there be a performance difference in my scenario? Is there a big difference between high-pressure and direct flow EV tubes? I believe that is the correct terminology?

2. Indirect or direct?
KwikSol/Sustainable claims that their indirect systems should be used "where the ambient temperature falls below 5°C and where the water quality is poor (more than 600ppm Total Dissolved Solids / Minerals)". Tshwane claims their water is soft at 80-100ppm.  Suntank states that in Pretoria Indirect systems should definitely be used.
What sort of maintenance and reliability can I realistically expect with either setup? For indirect systems, I've seen the mention of having to replace the glycol every 3-5 years. If it means the solar system isn't getting fouled up, indirect seems like a big benefit and especially with direct flow collectors.

3. How many geysers, which size and in which arrangement?
At the moment I have 3 x 150L geysers which have been kept in the same setup since I moved in. They've been replaced as they burst. Geyser 1 (G1) is located centrally to the house mounted outdoor in a ground-level enclosure against the exterior wall of the kitchen. All hot-water consumption points are within 15m at the most. G2 is located at the edge of the house and provides water for one bathroom. G3 is used for the domestic worker's shower which I plan on replacing with a gas geyser.
Is there any reason (barring piping issues) a single 300L geyser shouldn't be used to replace G1 and G2 and installed at the location of G1? I understand that it means a lot more energy is necessary to heat the water up when using an electrical element but it also means I shouldn't have any capacity issues? With the current setup of running the geysers on a timer with the PV system, supply is no regularly an issue except for when guests stay over. In that case G2 has plenty of hot water but G1 must be run on non-solar time to keep up with the demand.
It seems like putting 2 geysers in series is a popular option? I don't quite understand (and I would appreciate it if someone could help with that) it unless rarely need more than 1 geyser full of hot water. Why not just one big geyser with twice the collectors?
It seems like having one big geyser would be a benefit from a heat loss point of view as per @plonkster's post but it also seems like all the manufacturers I've looked at keep their diameter the same across all models and just extend the length.

4. Thermosyphon or pumped?
I think it is unlikely that my corrugated-iron roof will be able to support a large solar geyser with its collectors but in the scenario where a professional is able to determine that it is a safe option, is it specifically advised that I should or shouldn't make use of a thermosyphon setup? How reliable are the 12v Geyserwise pumps when used in a pumped system? I've seen a lot of complaints about it online, especially with direct systems.
What sort of maintenance and reliability can I realistically expect with either setup?

5. For EV tubes and direct/indirect geysers, which brands are known for their quality and performance?
Solar Ray seems like a good option for an EV tube setup. They only manufacture geysers up to 200lt for both integrated and non-integrated EV tubes so (unless you guys suggest a series setup) I would only be able to make use of their manifold collector. They provide a 10 year warranty. I'm not sure if that's only on the collectors or if it also includes their geysers. Solar Ray sells their 200lt 25-tube unit for R12.3k excl.
Suntank seems like a good option for the geyser and flat-plate collector as they also provide a 10-year warranty. Again, I'm not sure of the specifics.

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Unless you guys suggest there is a better approach (such as purchasing the parts myself and getting a plumber to install it), I plan on getting a professional to quote and install the system. The reason I'm asking for everyone's input is that, from my research, I've gotten the impression that a lot of installers have their preferred setup/brand which isn't necessarily what I would have wanted to go with if I didn't know any better. I made that mistake with my PV system.

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My feeling is that if you go offgrid, then you must stay with regular electric geysers. The more the merrier. Rather invest in more capacity pv and inv. 

Off grid means you can do absolutely nothing with the eccess power you generate, except use it. Now it is actually quite difficult thing to do that. A few 200 litre geysers will help. Just 'rev' then up to max temp (that's about 64 °C), then family of 4 can have a shower in the evening and another the next morning. I put mine in series, not parallel. 

Oh, and downgrade the element to 2kW, so if needed, you can run a few more things whilst one of the geysers is on. Like hairdriers, microwaves etc. 1 or 1.5 kW elements are not easy to come by. 

Edited by Sidewinder
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Hi Charl

To answer some of your original question/s:

  • Solar water heating is definately far more affordable than electricity - Recovery cost drops to months, not years
  • Evacuated Tubes are far more efficient than flat panel systems (most solar guys won't even offer flat panel anymore)
  • A 150l geyser in your part of the world only needs 12-18 tubes to get "bliksem" hot (over 60 degrees)
  • A pump is always a good idea rather than thermosyphon. Despite assurances, thermosyphon is actually quite difficult to achieve in most scenarios as your geyser is usually at almost the same/similar height as the input.
  • GeyserWise Max, GeyserWise Max, GeyserWise Max - They are damned expensive for what they actually are, and also damned ugly, but they work, and can properly control a pump without running it constantly. The GeyserWise also allows a bypass to municipal supply if or when you need. The pump and Geyserwise will also work off a small battery and solar setup, even further reducing municipal electricity input.
  • My geyser is a bog standard Kwikhot. Not ness the best brand, but covered by insurance and has already once (in 20 years) been completely replaced by insurance.
  • From your explanation (about your roof), I expect that only the collector should be mounted there due to weight. Your geysers should be under roof or wall mounted. Note: Wall mounting a solar geyser needs a proper company to sort, not something I can comment on about how/where, especially since you might require a larger pump.

Without looking at your exact scenario, I would go with the 300l geyser and 24 evacuated tubes, with a Geyserwise Max and a small 12VDC pump. And if have a few bucks to spare after, add a 30-50W solar panel, a 14-30Ah battery supply, and a cheap PWM charge controller and it will be totally self sufficient.

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20 hours ago, Sidewinder said:

My feeling is that if you go offgrid, then you must stay with regular electric geysers. The more the merrier. Rather invest in more capacity pv and inv. 

Off grid means you can do absolutely nothing with the eccess power you generate, except use it. Now it is actually quite difficult thing to do that. A few 200 litre geysers will help. Just 'rev' then up to max temp (that's about 64 °C), then family of 4 can have a shower in the evening and another the next morning. I put mine in series, not parallel. 

Oh, and downgrade the element to 2kW, so if needed, you can run a few more things whilst one of the geysers is on. Like hairdriers, microwaves etc. 1 or 1.5 kW elements are not easy to come by. 

With the current prices of batteries, I'm hoping to get enough batteries to be self-sufficient which I believe is possible if I take the geysers out of the equation. At the moment I'm running purely grid tied with no batteries. I'm running the geysers as a "battery" but there is still a lot of wasted potential output as this solution isn't perfect and relies on timers.

Without the 3 geysers, the only high-current appliances will be heating of the dishwasher and stove/oven which I plan on eventually replacing either with gas/induction.

 

19 hours ago, DeepBass9 said:

Solar geyser definitely. And a generator. You can get a week of cloudy weather sometimes. But grid tie is much cheaper and easier. 

Yeah, I definitely agree with the fact that I'd need a generator and that grid-tie is cheaper. I plan on having an automatic controller retrofitted to my 9kVA generator. I feel that adding a battery and solar geyser system would actually improve my overall ROI.

Because of technical limitations, I plan on being disconnected from the grid unless the battery starts to get low or there is an extremely high demand for power for whatever reason. This will also allow me to do a dry-run of going off-grid to see what needs to be adjusted/added/removed.

 

15 hours ago, DaveSA said:

Ring feed and properly insulate the other 2 units.

Thanks a lot for the info! What are you referring to with the above statement? I'm assuming you might be referring to creating a hot water "circuit" (kinda like a bus-bar or perhaps an actual loop with continuity) and having both of the geysers feed into it? How would this work with regards to how much hot water each geyser will output?

15 hours ago, DaveSA said:

it is user specific so pointless speculating without all the (usage pattern) info.

The information is greatly appreciated nonetheless. I never took a second to consider if heat loss to temperature isn't linear. In an ideal world, I shouldn't have to rely on the electrical element too often but as per your suggestions, I'll get a smaller element and also set the minimum temperature 55c..

 

14 hours ago, KLEVA said:

Without looking at your exact scenario, I would go with the 300l geyser and 24 evacuated tubes, with a Geyserwise Max and a small 12VDC pump. And if have a few bucks to spare after, add a 30-50W solar panel, a 14-30Ah battery supply, and a cheap PWM charge controller and it will be totally self sufficient.

Hi, thanks a lot for all the information. That addresses a lot of my uncertainty.

14 hours ago, KLEVA said:

Wall mounting a solar geyser needs a proper company to sort

Thanks a lot. I will definitely get a professional to sort this out. Is this purely from a pressure POV for pump requirements or are you also referring to structural concerns?

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Is it possible to oversize the panels or does pressure really become an issue? I also wouldn't want it to constantly be pushing out hot water when the pressure becomes an issue. What is the max "happy" temperature for a geyser so that it doesn't wear and tear too quickly?

If I had extra heating capacity, I love the idea of setting up a closed loop hot water return system which will circulate during the day and only when the temperature is above X to try save water at the taps. Would this have a significant impact on standing losses (even with insulation) when the circulation pump isn't running?

How will the geyser manage during the summer when I'm away and there is no hot water usage? Is it not going to dump a lot of water?

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11 hours ago, Charl_CCU said:

bad idea?

Energy losses over the loop is untenable IMHO. There is a type with a button that allows you to "summon" hot water. That means you don't have to run the tap and wait for hot water. But if you run it permanently, the losses are just too high. 

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If the pipes are either lagged or plastered into a wall they shouldn't lose heat too quickly? You could also put the system on a timer so it runs early morning and evening perhaps?  How much of a problem is a bit of wasted waster? Catch it in a bucket and water something with it.

Edited by DeepBass9
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3 hours ago, DeepBass9 said:

How much of a problem is a bit of wasted waster? Catch it in a bucket and water something with it.

Luxury houses sometimes have this sort of system installed... because waiting for hot water to arrive is the worst. I mean, it's almost as bad having to take a bath in a bucket somewhere in an African village! We're not savages you know!

(No, I'm not being serious... I'm having fun).

I think the system makes a lot of sense in places where water is scarce, and I mean really scarce. In my case, a little bit of wastage is acceptable, since it gets piped into the grey-water system anyway and is used to keep the garden alive. It's not just dumped into the drain.

The other option is to install a water heater closer to the point of use.

Or you could use a timer-setup, or a button that "summons" the hot water. The button system takes the same amount of time to get the hot water to you, but you're not wasting any of it. I've only read about the summon-system. I've never seen one nor do I know of a local outfit that does it. You could even integrate that with your smart home... Alexa... ready the shower!

😛

 

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On 2019/10/18 at 9:06 AM, plonkster said:

Energy losses over the loop is untenable IMHO.

Yea, now that I think about how quickly the hot water in the taps cools down, you're right. The more it runs, the closer it is to just being an inefficient house heating solution.

On 2019/10/18 at 12:56 PM, plonkster said:

timer-setup, or a button that "summons" the hot water.

Even if I had to wait a similar amount of time after pushing an activation button, that would still be a really attractive option for me. It just feels so wasteful if I need to run the hot water taps for so long just to get hot water. And this would apply to another hot water point if I consolidated the geysers. I've been meaning to sit down with a plumber and have a look at the hot-water line because at one or two of the points it doesn't make any sense how long it takes the hot water to get there especially considering how close they are. I can't expect this is the norm. It always feels like such a waste of water to run the kitchen tap for so long just to wash a few things.

But in any case, it seems like these systems don't exist much in SA. Or at least in the home-plumbing market. I wouldn't want to get a system installed where I need to worry about whether or not a given plumber will immediately understand what it is and how it works in the future.

On 2019/10/18 at 12:56 PM, plonkster said:

Alexa... ready the shower!

Haha yeah, that would be amusing to see  😆. I'd feel like Iron Man.

 

On 2019/10/18 at 9:23 AM, DeepBass9 said:

If the pipes are either lagged or plastered into a wall they shouldn't lose heat too quickly?

I would think they'd be a good insulator but I'm speculating that bricks probably act as a giant thermal mass which absorbs all heat from the water as soon as the water isn't flowing.

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I think that I'll revisit the idea after the installation if the geyser temps are ever unnecessarily high. I'll also see what the solar-geyser installer says about the idea when he comes to quote.

 

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