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Include electric geyser in solar panel array, or install solar geyser?


Nickvdv

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Hi gents (& ladies),

 

I’m looking to install a solar panel array with the aim to reduce my dependence on grid power and Eskom’s tariff increases.

I’m in doubt between including my current 150l electric geyser in the solar panel load, keeping it separate and pay R 22k for the conversion or replace it with a solar geyser for R 30k.

 

We have a household of 4 adults and 2 kids, most of whom would like a hot shower in the morning or the evening (or both). The 150l geyser is sufficient, but it runs 4am – 10am and 2pm – 8pm to make sure there’s hot water available.
I’m assuming my current daily usage just for the geyser would be close to 20, 25kW (assuming it’s not using 3kW for the full 12 hours it’s on). Average daily usage for the entire house over the last 6 months is 37kWh, with the big spenders being the geyser, pool pump, aircon and fridge.

 

My thinking is that evacuated tube solar geysers would be far more efficient at converting solar to hot water, compared to the conversion of solar to electricity to hot water, and installing one would reduce the required capacity for the solar panel array.
Letting a solar geyser heat up the water to a higher temperature when there’s enough sun would also mean less hot water will be used (but also a risk if my kids open the tap on hot).

 

Following that line of thinking and assuming my geyser would take 20kWh a day (600kWh /month), I could possibly spend R 30k for a solar geyser and use 200kWh a month or so for “additional heating” – thinking that’s worst case scenario.

That would bring my monthly usage down from 1 100kWh to around 700kWh, and possibly reduce the battery size for the solar array.

  • 11 x 455W worth of panels would yield around 826 kWh /month, with an 8kW inverter, 7kWh of storage and installation would be around R 190k.
  • Same setup with 16 panels would yield around 1 201 kWh /month and power the electric geyser for R 217k, but for sufficient water in the mornings and evenings I’d likely need to add more batteries (which are expensive)

Approximate costs from https://solar.co.za/product/solar-power-kit, I’m in Cape Town.

 

My solar knowledge is very limited; what would your suggestions be to resolve this dilemma?

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There are several schools of thought - however spending an extra 22k over and above your solar system might not be the best use of the money. 

1. You could add the geyser to the non-essentials load and still be able to push excess solar to it. This, however, only works when there is Eskom available

2. You could add the geyser to the AUX if you are getting a Sunsynk / Deye inverter. Then when batteries are at x% (user defined) the geyser is powered by solar, below that the geyser uses Eskom

3. You could put the geyser on the essentials load and power it as normal from solar. You will then need to change some of your charging habits to make best use of the solar hours... your morning heating slot could then be configured to use some battery or run it from Eskom. 

That 22k for the geyser conversion could buy you more panels or another battery and benefit the whole house vs only being put to use for the geyser.

Edited by mzezman
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I installed a solar geyser 15 years ago. Best investment ever. I would do it again in a heart beat. 

Solar geysers still get hot enough when it's cloudy. Your solar power system might not be enough to heat a standard geyser on a cloudy day. 

Your system can be smaller with the addition of a solar geyser. 

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@NickvdvEV tubes might be more efficient to heat water looking at percentages per surface area... but once you have hot water they cannot charge your batteries or run your computer (or lets be optimistic and say charge an EV in the near future). In summer when it is hot, they also cannot run the aircon. Run the aircon in reverse cycle in winter and heat the house. Show me what those EV Tubes are good for? Pay all that money and have a system that from time-time overheats and dumps all the hot water. Rather take that money and get more panels R30K of extra panels might put your monly bill at zero.

Your best investment for hot water is an energy efficient B-rated geyser and plenty R1 insulation. If you use large amounts of water then several of those geysers heated by a heatpump. 

If you have very little space on the roof and cannot fit plenty panels then maybe the EV tubes could be your best option.

 

Edited by iiznh
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5 hours ago, mzezman said:

There are several schools of thought - however spending an extra 22k over and above your solar system might not be the best use of the money. 

1. You could add the geyser to the non-essentials load and still be able t push excess solar to it. This, however, only works when there is Eskom available

2. You could add the geyser to the AUV if you are getting a Sunsynk / Deye inverter. Then when batteries are at x% (user defined) the geyser is powered by solar, below that the geyser uses Eskom

3. You could put the geyser on the essentials load and power it as normal from solar. You will then need to change some of your charging habits to make best use of the solar hours... your morning heating slot could then be configured to use some battery or run it from Eskom. 

That 22k for the geyser conversion could buy you more panels or another battery and benefit the whole house vs only being put to use for the geyser.

I agree with your logic, one can even replace the existing geyser element from 3kW to 2Kw, even down to 1.5kW, in order to make it load friendlier. 

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I have both EV solar and PV solar, and on full cloud cover, the EV tube solar for the geyser is useless compared to PV output. With intermittent clouds, the EV does heat up the water. On full sunny days the EV solar heats up the water to between 70-80 degrees.  I've had the EV solar long before the PV solar system. On my SunSynk 8.8 kW everything is on essential load, and I use CBI Astute's to control the  loads if needed.

If I was going for a new install, I'd go for full PV, and get a few CBI Astute's, to control different "heavy" loads.

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@Nickvdv I installed a 150L Solar Geyser seven years ago and best thing ever. I live in Somerset West and we are family of 5 along with my wife running a busy hair salon from the property.

What I learnt is to have only the collector on the roof, and the tank in the roofspace. Lekker cold winds off Helderberg mountains blow my geyser ice-cold by sunset. 

The reality though is it still needs power, especially in winter. Long term I would say go for it, but short term there is so much valuable advice on this thread on how to use your existing setup. More panels with the CBI Astute smart switch (R700, I nearly bought one yesterday) would give you better value for that R30K

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Hi all,

thank you for all the feedback, I really appreciate the time you've taken to respond.

My takeaway is that the R 22k/R 30k might be better spent on additional panels + a lower wattage heating element, and rely on batteries or grid power (if batteries are low) to prepare hot water early mornings.

The requirement would be to get an inverter which would allow to make the decision to use grid power for the geyser if batteries are below x percent. Optional additional battery if we still rely too much on grid power, but ROI calculation for that can be done afterwards depending on what the remaining grid power draw would be.

I'll try to leave space above the current geyser in case we'd ever reconsider the EV solar geyser, but we'll leave that cost out for now.

 

Thank you @mzezman, @Chris_S, @iiznh, @BritishRacingGreen, @TimCam and @cbrunsdon for your valuable inputs - much appreciated.

 

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Just a gut feeling, but I'm not convinced that solar water heating - any type - is right for your needs or your usage pattern. Just too much hot water demand at the wrong time for a solar water heater to make the impact you think it will. It follows, I think your estimates of cost savings are optimistic, and you may end up being disappointed. I really think you should consider a heat pump instead, and couple it with solar PV, but a reduced number of panels.

Why do I say this? Firstly, you can discount the solar contributing anything meaningful towards the morning hot water. The 150l geyser will be cold from the night before, and you will need to power it up using electricity, because the solar water heater won't give any useful contribution before 9-10am. It doesn't make sense using a solar PV system with storage for this either, because the cost of 7kWh of batteries should set you back around R45K-plus, and you'll need it all every morning if you keep a conventional element, leaving no room to use those batteries for anything else during the night.

In the afternoon you could heat the water from solar, and say by around 4pm you could have 150l of hot water as long as it's a sunny day, but the sun won't help you much after 4pm regardless. You'll have to keep re-heating water to 8pm as  you are doing now to ensure that everyone gets a decent shower, and a lower-wattage 1.5kW or 2kW element will just take longer to re-heat the geyser and probably frustrate everyone. Not to mention, running the geyser during peak hours is just... not nice to Eskom. But bottom line, I think you would be lucky to save 6-8kWh per day with a solar solution. Always open to debate, I stand to be corrected (best with actual measurement of power used over time), but here I stand nonetheless.

Edited by GreenFields
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56 minutes ago, GreenFields said:

Just a gut feeling, but I'm not convinced that solar water heating - any type - is right for your needs or your usage pattern. Just too much hot water demand at the wrong time for a solar water heater to make the impact you think it will. It follows, I think your estimates of cost savings are optimistic, and you may end up being disappointed. I really think you should consider a heat pump instead, and couple it with solar PV, but a reduced number of panels.

Why do I say this? Firstly, you can discount the solar contributing anything meaningful towards the morning hot water. The 150l geyser will be cold from the night before, and you will need to power it up using electricity, because the solar water heater won't give any useful contribution before 9-10am. It doesn't make sense using a solar PV system with storage for this either, because the cost of 7kWh of batteries should set you back around R45K-plus, and you'll need it all every morning if you keep a conventional element, leaving no room to use those batteries for anything else during the night.

In the afternoon you could heat the water from solar, and say by around 4pm you could have 150l of hot water as long as it's a sunny day, but the sun won't help you much after 4pm regardless. You'll have to keep re-heating water to 8pm as  you are doing now to ensure that everyone gets a decent shower, and a lower-wattage 1.5kW or 2kW element will just take longer to re-heat the geyser and probably frustrate everyone. Not to mention, running the geyser during peak hours is just... not nice to Eskom. But bottom line, I think you would be lucky to save 6-8kWh per day with a solar solution. Always open to debate, I stand to be corrected (best with actual measurement of power used over time), but here I stand nonetheless.

I have to say I sometimes think I'm a stuck record-he'll do the younger generation even know what that is🙄. Well my call would also be the heat pump system. 

What you saying makes sense and for the right reasons. Yes a heat pump will save a lot of power over times and also much kinder on whatever batteries are employed. Due to the up front extra cost I have not mentioned it myself. 

Yes I am a user of one now for 9 years and still going strong. Forget the negative of the cost to maintain it. That is but a small part of your savings. 

To be efficient and heat water 24/7 and not only when the sun is shining I don't think one can beat a heat pump. 

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1 hour ago, GreenFields said:

I really think you should consider a heat pump instead, and couple it with solar PV

As @GreenFields and @Scorp007 suggest, a heat pump is expensive, but gentile on inverters and batteries. If you are starting from scratch, you can choose different options, by learning from other peoples mistakes. 😄

Oh, and as for lithium batteries running a geyser element or heat pump, a friend of mine just bought a new Hubble AM-2 today with updated spec's of 6kW, i.e 125Ah for a little over R28 000.

This is his fourth AM-2, and his geyser runs happily on battery and/or solar.

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Thank you @GreenFields, @Scorp007 & @TimCam - I was previously looking at heat pump but didn't follow through.

Got quotes towards the end of last year for a 3.6kW ITS heatpump for R 23k, 5.4kW pump for R 32k - including installation.

Going with my initial estimates above of geyser usage being around 600kWh /month and a heat pump possibly saving 50% of that cost, it could approximately save 300kWh a month. That's an estimated saving of R 800 /month on grid power, not sure how to calculate it on solar panel yields seeing as the hot water needs are barely overlapping with the optimal period for solar energy generation. I suppose it'll partly save on grid power expenses, and partly on reduced battery usage.

With an ROI of around 2 to 3 years for the R 23k installation when calculated on grid power costs it's perhaps worth considering.
But how would it reduce the requirements for the solar array, seeing as those batteries would still have to be full to power it at night (and thus you'll need excess panels)?

--

Off topic; @TimCam where did your friend buy the Hubble AM2 for that price? I was quoted R 31k for the 5kWh model.
Cheapest I can find is R 30k at https://www.inverter-warehouse.co.za/products/hubble-am-2-5-5kwh-lithium-battery-1?variant=43525702189305&currency=ZAR&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&gclid=EAIaIQobChMI7ezbpqS0_gIV0u3tCh1RmgjOEAQYASABEgKrgfD_BwE

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43 minutes ago, Nickvdv said:

Thank you @GreenFields, @Scorp007 & @TimCam - I was previously looking at heat pump but didn't follow through.

Got quotes towards the end of last year for a 3.6kW ITS heatpump for R 23k, 5.4kW pump for R 32k - including installation.

Going with my initial estimates above of geyser usage being around 600kWh /month and a heat pump possibly saving 50% of that cost, it could approximately save 300kWh a month. That's an estimated saving of R 800 /month on grid power, not sure how to calculate it on solar panel yields seeing as the hot water needs are barely overlapping with the optimal period for solar energy generation. I suppose it'll partly save on grid power expenses, and partly on reduced battery usage.

With an ROI of around 2 to 3 years for the R 23k installation when calculated on grid power costs it's perhaps worth considering.
But how would it reduce the requirements for the solar array, seeing as those batteries would still have to be full to power it at night (and thus you'll need excess panels)?

--

Off topic; @TimCam where did your friend buy the Hubble AM2 for that price? I was quoted R 31k for the 5kWh model.
Cheapest I can find is R 30k at https://www.inverter-warehouse.co.za/products/hubble-am-2-5-5kwh-lithium-battery-1?variant=43525702189305&currency=ZAR&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&gclid=EAIaIQobChMI7ezbpqS0_gIV0u3tCh1RmgjOEAQYASABEgKrgfD_BwE

A heatpump is actually a pretty good idea, it uses less power to heat the water compared to a traditional element. So you wouldn't need full batteries, just enough juice to draw between 1 and 2kWh from them, especially for the morning run. 

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My 2c worth

>I’m looking to install a solar panel array with the aim to reduce my dependence on grid power and Eskom’s tariff increases.
>
>I’m in doubt between:
>(a) including my current 150l electric geyser in the solar panel load,
>(b) keeping it separate and pay R 22k for the conversion or
>(c) replace it with a solar geyser for R 30k.

>We have a household of 4 adults and 2 kids, most of whom would like a hot shower in the morning or the evening (or both).
>The 150l geyser is sufficient, but it runs 4am – 10am and 2pm – 8pm to make sure there’s hot water available.


Option (a) + a timer - which you seem to have.

With Solar-PV, you have free electricity during the day, so using a timer you can heat the water.
I use a timer with 4am-6am and 10:30am to 17:00pm
The 4am-6am slot is to heat water for people washing in the morning - uses Eskom.
The 10:30am-17:00pm slot uses excess sun to heat water for evening use.

Same if you have a swimming pool, under floor heating, etc run them 10:30 to 15:00

Using home automation (eg Home Assistant) and sensors you can be quite creative to prevent discharging the inverter battery.

 

Edited by system32
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20 hours ago, Nickvdv said:

We have a household of 4 adults and 2 kids, most of whom would like a hot shower in the morning or the evening (or both). The 150l geyser is sufficient, but it runs 4am – 10am and 2pm – 8pm to make sure there’s hot water available.

Those times suggest you may not get a lot of help from a solar geyser. You'll get some hot water in the PM, but solar won't reheat if there are multiple showers, so you'll have to fall back on grid or battery. 

But how are you managing now with 8 to 10 hours a day with no power? 

I've had a solar geyser. I now have PV and a heat pump. The truth of any system using solar is that to get the most benefit, you have to make sun while the sun shines. IE you need to align your routines with the solar as far as possible. 

This may extend to charging as much battery as you can during the day and then reducing consumption after sundown. 

My situation: two of us; heat pump; one shower each per day; lots of insulation on the main geyser (guest geyser is usually kept off); 10kWh of battery; full gas cooking. 

So at night our consumption is low. 

Usually I have 65 to 70% of the battery at 6:00 and so I can run the heat pump then, using energy stored the day before. 

Even then the evening heating is problematic because you will draw from the battery. 

The guest geyser... I had this downgraded to a 1.5kW element. It's a 150l geyser. I can usually heat this once in the early afternoon. By then the battery is usually charged and I have excess PV. The 3kW element plus the other loads at that time of day would likely exceed PV and so I'd start depleting the battery, but with the 1.5 I get away with it. 

My real recommendation though is to not back up the geyser at first, and observe how the system behaves and what loads you can move into the sunny hours. Then decide what to do with the geyser. Moving it from non-essential to essential would not be a big job. 

Edited by Bobster.
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I spent the 20k on extra panels when I did my install, summer works fine, 200l geyser and I replaced the element with a 3kw one and installed a geyserwise timer to take the geyser to 65 degrees. Geyser comes on at 10:00 and runs until 13:00. We are 4 people in the house, winter is another story I have to let the geyser run in the morning to have a hot shower.

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