Good evening.

I want to find out what id the best way of saving cost on water heating. On this stage I'm using a cbi smart timer to only switch the geyser on and off, I'm also using a Sunsynk inverter to power my geyser 12:00 to 16:00 when the batteries is full to have warm water for dish washing and handwashing. Our schedule is of a kind that i need to heat the geyser between 19:00 till 22:00 in the evenings and 04:00 till 07:00 in the morning.

We are using 20 units per day.

What is the solutions that is available to do?

Carel, I have the same inverter, 20kWh LiFePO4 batteries, and just slightly more PV potential than you. I also use a CBI controller. I run my geyser from the batteries for one hour before sunrise to boost the early morning water temp, and again from 10:30 to about 14:00 after the batteries have been fully charged. Apart from a 20W trickle charge, I have used virtually no grid power for the last 10 months - but it's just my wife and I living in the house, and our power consumption is thus lower than when the kids still lived with us.

So, depending on your household load, power-hungry electronics, where you live (Bloemfontein has pretty good yearly solar radiation...) and where/how your panels are mounted (no shading...), you should be able to replicate my usage. Give us some more data, such as where you live, panel slope, if you have power-hungry air conditioners, etc. etc, and we will be able to advise more accurately.

On this stages I have 24 x 310 w panels 18 of them is at an angle of + -20 degrees the other 6 is close to flat on a carport roof. All of them is facing north. I have 4 100Ah Narada batteries that i want to try and sell to buy 4 new Greenrich 6.1kwh batteries, and maybe add an extra 2 on a later stages. We use gas kettle after 16:00 and don't have any other high power equipment after 18:00. I live in Secunda i think we have some of the sidewalk trees that have shade over the panels, I'm busy to get our municipality to cut them.

8 hours ago, Carel.Rossouw said:

I live in Secunda i think we have some of the sidewalk trees that have shade over the panels, I'm busy to get our municipality to cut them.

Do you have any data on your current power consumption, PV supply, and grid usage? I assume that you have the Sunsynk app installed on your computer and/or phone? Although not very good, it should give you all the info we need...

This is likely going to be a case of spending to save. One wat to approach this is to install a heat pump. It's more efficient than a conventional element, so takes less electrical energy to do the same heating. I do this. Helpfully the constant load is less than with an element - about 1.6kW - so I can run it on the backed up side of my PV system.

As @HennieL points out, the number of people in the home and their routines make a big difference. Insulation may help too. My heatpump runs twice a day. The second run starts at 12:00 and ends at 14:30, though the water is usually heated by that time. We still have water > 50 degrees at 22:00.

I personally went with a Geysertech unit. I just have to get and install 4x585W panels. It feeds power into the geyser as long as the MPPT controller is on. Becuase it is a standalone unit I dont need to run it off my inverter. With cabling, Panels and the unit it will cost me less than 10k. It still has the option to be connected to your inverter.

No need to be worrying about whehter your batteries are full, no worry about overloading your inverter. With my current setup I dont use anything from the grid except the geyser which is connected to the grid. Once I finish up installing the 4 panels I wont use any grid at all.

Heat pumps are just too expensive. The Geysertech requires no mods to the geyser. You just wire it in and thats it.

Edited August 5, 20251 yr by Denns

1 hour ago, Denns said:

Heat pumps are just too expensive. The Geysertech requires no mods to the geyser. You just wire it in and thats it.

One of the reasons I got a heatpump way back when is that there was no north facing roof in close proximity to the geyser. That ruled out a solar geyser (this is 14 years ago). That would be less of a consideration with a solution like this where you run cables rather than pipes. But overcast days you may not do so well. The heatpump does well early in the morning (this morning it ran at 5:00) or when there's not so much solar around - as long as you have battery capacity.

4 hours ago, HennieL said:

Do you have any data on your current power consumption, PV supply, and grid usage? I assume that you have the Sunsynk app installed on your computer and/or phone? Although not very good, it should give you all the info we need...

This is from my Sunsynk app, hope this will work.

I have to ask why you're heating water at 10pm... is someone bathing/showering at midnight?

You have excess solar available during the day that isn't being harvested. You will be better off if you can move some of that night time water heating to the day time. The alternative is to get a bigger battery, but that isn't nearly as cost effective.

EDIT: I see you're only using half your battery. There is no load shedding at the moment... why not allow the battery to cycle down to 10%?

Edited August 5, 20251 yr by Paulcupine

1 hour ago, Paulcupine said:

I have to ask why you're heating water at 10pm... is someone bathing/showering at midnight?

You have excess solar available during the day that isn't being harvested. You will be better off if you can move some of that night time water heating to the day time. The alternative is to get a bigger battery, but that isn't nearly as cost effective.

EDIT: I see you're only using half your battery. There is no load shedding at the moment... why not allow the battery to cycle down to 10%?

I'm heating it up sometimes we shower early other times we do later.

on the battery i dont want to drop them to low i first wat to upgrade the batteries before dropping them so low.

@Carel.Rossouw here is a screenshot of my usage, showing data for last Friday and for yesterday.

by

On Friday, the geyser was heater early morning (04:45 - 05:45), but we were not at home to bath/shower in the morning, hence the afternoon heating only required another hour before the geyser's thermostat switched it off. In contrast, yesterday (as a normal day) started off with the 04:45 geyser heating from the battery (2kWh), two people bathing between 06:00 and 07:00, followed with a normal geyser heating by PV from 10:30 to about 14:00, when the thermostat again switched off before the CBI timer did. On Friday afternoon I worked in my garage using some power tools, in addition to our usually light home load.

You will also notice that I am not discharging my batteries more than about 30% (thus not below 70% SOC). I believe that this should extend the battery life substantially when compared to discharging it down to 20% or even less, as some people might suggest - my money, my choice...

I notice that your home load during the evenings runs close to 1kW, powered by your batteries from about 16:00. Also, you have quite a high load around 19:30 - 20:00, which is presumably your oven, or a heater, but this is adequately supplied by your batteries as well. So...

Firstly, I agree with @Bobster. that a heatpump would be more efficient than a geyser, if you would rather spend more money in that direction, but personally I would first try the following:

• You have a time slot from about 13:00 to 15:30 that could provide at least 5-6kWh of additional PV power that is currently being wasted. I would move the evening geyser heating period to this time slot, as a start.

• You could also play around with your charging rate, and with your system's time and usage settings to see if you could squeeze an extra kW or two out of the PV, unless the yellow grid spikes between 12:00 and 15:00 were caused by clouds interfering with your PV generation.

• Lastly, I would suggest that you upgrade (say) one of your three MPPT strings by installing larger capacity solar panels - something like 575W, or even 600W panels (I currently have two strings of 7 panels each rated at 575W). This will allow more PV power to charge your batteries earlier in the day (notice my batteries receive 100% power before 09:00, in contrast to you's that only reached this level at around 10:00. and will also help to eliminate the grid spikes during the day. PV panels are cheap, compared to batteries 😃

4 minutes ago, HennieL said:

@Carel.Rossouw here is a screenshot of my usage, showing data for last Friday and for yesterday.

by

On Friday, the geyser was heater early morning (04:45 - 05:45), but we were not at home to bath/shower in the morning, hence the afternoon heating only required another hour before the geyser's thermostat switched it off. In contrast, yesterday (as a normal day) started off with the 04:45 geyser heating from the battery (2kWh), two people bathing between 06:00 and 07:00, followed with a normal geyser heating by PV from 10:30 to about 14:00, when the thermostat again switched off before the CBI timer did. On Friday afternoon I worked in my garage using some power tools, in addition to our usually light home load.

You will also notice that I am not discharging my batteries more than about 30% (thus not below 70% SOC). I believe that this should extend the battery life substantially when compared to discharging it down to 20% or even less, as some people might suggest - my money, my choice...

I notice that your home load during the evenings runs close to 1kW, powered by your batteries from about 16:00. Also, you have quite a high load around 19:30 - 20:00, which is presumably your oven, or a heater, but this is adequately supplied by your batteries as well. So...

Firstly, I agree with @Bobster. that a heatpump would be more efficient than a geyser, if you would rather spend more money in that direction, but personally I would first try the following:

• You have a time slot from about 13:00 to 15:30 that could provide at least 5-6kWh of additional PV power that is currently being wasted. I would move the evening geyser heating period to this time slot, as a start.

• You could also play around with your charging rate, and with your system's time and usage settings to see if you could squeeze an extra kW or two out of the PV, unless the yellow grid spikes between 12:00 and 15:00 were caused by clouds interfering with your PV generation.

• Lastly, I would suggest that you upgrade (say) one of your three MPPT strings by installing larger capacity solar panels - something like 575W, or even 600W panels (I currently have two strings of 7 panels each rated at 575W). This will allow more PV power to charge your batteries earlier in the day (notice my batteries receive 100% power before 09:00, in contrast to you's that only reached this level at around 10:00. and will also help to eliminate the grid spikes during the day. PV panels are cheap, compared to batteries 😃

Try not to confuse lithium with LA. LA lifespans is greatly increased if you do low discharges and kept at 100%. Lithium no so much. Avoid charging to over 90% if longevity is what you want.

If you take note, 100 to 50 discharge CS 100 to 25 discharge has no little difference. You better off using more capacity from your battery.

34 minutes ago, HennieL said:

@Carel.Rossouw here is a screenshot of my usage, showing data for last Friday and for yesterday.

by

On Friday, the geyser was heater early morning (04:45 - 05:45), but we were not at home to bath/shower in the morning, hence the afternoon heating only required another hour before the geyser's thermostat switched it off. In contrast, yesterday (as a normal day) started off with the 04:45 geyser heating from the battery (2kWh), two people bathing between 06:00 and 07:00, followed with a normal geyser heating by PV from 10:30 to about 14:00, when the thermostat again switched off before the CBI timer did. On Friday afternoon I worked in my garage using some power tools, in addition to our usually light home load.

You will also notice that I am not discharging my batteries more than about 30% (thus not below 70% SOC). I believe that this should extend the battery life substantially when compared to discharging it down to 20% or even less, as some people might suggest - my money, my choice...

I notice that your home load during the evenings runs close to 1kW, powered by your batteries from about 16:00. Also, you have quite a high load around 19:30 - 20:00, which is presumably your oven, or a heater, but this is adequately supplied by your batteries as well. So...

Firstly, I agree with @Bobster. that a heatpump would be more efficient than a geyser, if you would rather spend more money in that direction, but personally I would first try the following:

• You have a time slot from about 13:00 to 15:30 that could provide at least 5-6kWh of additional PV power that is currently being wasted. I would move the evening geyser heating period to this time slot, as a start.

• You could also play around with your charging rate, and with your system's time and usage settings to see if you could squeeze an extra kW or two out of the PV, unless the yellow grid spikes between 12:00 and 15:00 were caused by clouds interfering with your PV generation.

• Lastly, I would suggest that you upgrade (say) one of your three MPPT strings by installing larger capacity solar panels - something like 575W, or even 600W panels (I currently have two strings of 7 panels each rated at 575W). This will allow more PV power to charge your batteries earlier in the day (notice my batteries receive 100% power before 09:00, in contrast to you's that only reached this level at around 10:00. and will also help to eliminate the grid spikes during the day. PV panels are cheap, compared to batteries 😃

This is my time that my geyser is on. It is a 200l 4kw geyser that is mounted outside under the roof overhang in a closed corner. Between 12:00 and 16:00 i’m using the pv to charges.

my batteries is starting to drop in ah i have 4 Narada 48npfc100 the oldest one is on 111 then two is 91ah and one of the latest batteries is on 30 ah. I want to first upgrade my battery bank before i wil go lower in the discharge. I have switched off that one with 30ah it feels that that batterie is pulling down the rest of the bank.

I also want to upgrade my panels up to 600w-650w per panels i think that i will be able to use the old structure but that wil only be after the batteries.

I don't think you need more panels. The 24x310W panels (7440W) is plenty considering that you've got spare unused capacity during the afternoons, and we're still in Winter, and you're only using 20kWh per day. Even if you replace your batteries, you'll probably not need to add or replace panels. Neither do I think you need an alternative timer or DC element or whatnot. Just be sure to resolve the shading issues.

One of the no-cost options could be to increase the thermostat's temperature so that you have more heat stored to be usable later during the evening. Just be careful of scalding.

You could consider also dropping from a 4kW to 3kW element. That will of course increase the heating time, but you could run off solar for maybe an extra half-hour in the afternoon to around 16:30 or later in summer, without switching yet to grid. I wouldn't go as low as a 2kW element for that.

For the morning slots, try turning the timer off before the last person starts to use hot water. Perhaps 6am? That is to say, try to avoid re-heating spikes when there's nobody else that will need water next.

Other thought with that, you don't need 200litres of hot water for dishwashing and handwashing. Maybe a small 10-20 litre water heater could be useful for those times. Or a dishwasher.

In the end, the only way to save electricity during the early-morning time slot is to switch to a heat pump, but it's not clear if the savings will be worth the outlay.

Edited August 6, 20251 yr by GreenFields

1 hour ago, Carel.Rossouw said:

This is my time that my geyser is on. It is a 200l 4kw geyser that is mounted outside under the roof overhang in a closed corner. Between 12:00 and 16:00 i’m using the pv to charges.

my batteries is starting to drop in ah i have 4 Narada 48npfc100 the oldest one is on 111 then two is 91ah and one of the latest batteries is on 30 ah. I want to first upgrade my battery bank before i wil go lower in the discharge. I have switched off that one with 30ah it feels that that batterie is pulling down the rest of the bank.

I also want to upgrade my panels up to 600w-650w per panels i think that i will be able to use the old structure but that wil only be after the batteries.

How old are the batteries? What was your typical usage on them. Just curious if you managed to get the claimed 10 years plus out of them.

27 minutes ago, Denns said:

How old are the batteries? What was your typical usage on them. Just curious if you managed to get the claimed 10 years plus out of them.

This was pulled of from SMH. Some of the first batteries was 2021

2 hours ago, Denns said:

Try not to confuse lithium with LA. LA lifespans is greatly increased if you do low discharges and kept at 100%. Lithium no so much. Avoid charging to over 90% if longevity is what you want.

I am certainly not confused - but I do tend to do my homework before I invest a larger some of money on anything...

Here is an in-depth extracts from peer reviewed scientific studies:

Energies article: Analysis of On-Board Photovoltaics for a Battery Electric Bus and Their Impact on Battery Lifespan - Kevin R. Mallon *, Francis Assadian and Bo Fu, Department of Mechanical and Aerospace Engineering, University of California, Davis

Here are some extracts from various manufacturers:

The Powerech Systems Company: PowerTech Systems is a French company founded in 2013: Internal publication.

Brava Batteries LiFePO4 Battery Discharge and charge Curve

4. Cycle Life Curve at Different DOD

Different DOD Discharge Cycle Life Curve @ 1C 25 0C

And here's an extract from the Battery University: https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries

Table 2 estimates the number of discharge/charge cycles Li-ion can deliver at various DoD levels before the battery capacity drops to 70 percent. DoD constitutes a full charge followed by a discharge to the indicated state-of-charge (SoC) level in the table.

Depth of Discharge	Discharge cycles
	NMC	LiPO4
100% DoD	~300	~600
80% DoD	~400	~900
60% DoD	~600	~1,500and located in Saint Cyr L’Ecole, France.
40% DoD	~1,000	~3,000
20% DoD	~2,000	~9,000
10% DoD	~6,000	~15,000

Anyway, as I said previously: My money, my choice 🙂

Edited August 5, 20251 yr by HennieL

30 minutes ago, HennieL said:

I am certainly not confused - but I do tend to do my homework before I invest a larger some of money on anything...

Here is an in-depth extracts from peer reviewed scientific studies:

Energies article: Analysis of On-Board Photovoltaics for a Battery Electric Bus and Their Impact on Battery Lifespan - Kevin R. Mallon *, Francis Assadian and Bo Fu, Department of Mechanical and Aerospace Engineering, University of California, Davis

Here are some extracts from various manufacturers:

The Powerech Systems Company: PowerTech Systems is a French company founded in 2013: Internal publication.

Brava Batteries LiFePO4 Battery Discharge and charge Curve

4. Cycle Life Curve at Different DOD

Different DOD Discharge Cycle Life Curve @ 1C 25 0C

And here's an extract from the Battery University: https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries

Table 2 estimates the number of discharge/charge cycles Li-ion can deliver at various DoD levels before the battery capacity drops to 70 percent. DoD constitutes a full charge followed by a discharge to the indicated state-of-charge (SoC) level in the table.

Depth of Discharge	Discharge cycles
	NMC	LiPO4
100% DoD	~300	~600
80% DoD	~400	~900
60% DoD	~600	~1,500and located in Saint Cyr L’Ecole, France.
40% DoD	~1,000	~3,000
20% DoD	~2,000	~9,000
10% DoD	~6,000	~15,000

Anyway, as I said previously: My money, my choice 🙂

I agree with this but it’s not complete. A Lipo battery charger to 85% and discharged to 25 will last longer than one charged to a hundred and discharged to 50 even though the discharge is higher in the first scenario. That’s the main point I was making.

40 minutes ago, Carel.Rossouw said:

This was pulled of from SMH. Some of the first batteries was 2021

That’s kind of bad. 4 years of use and only 30ah left? I was hoping for more out of Lipo lol.

On 2025/08/04 at 9:12 PM, Carel.Rossouw said:

Good evening.

I want to find out what id the best way of saving cost on water heating. On this stage I'm using a cbi smart timer to only switch the geyser on and off, I'm also using a Sunsynk inverter to power my geyser 12:00 to 16:00 when the batteries is full to have warm water for dish washing and handwashing. Our schedule is of a kind that i need to heat the geyser between 19:00 till 22:00 in the evenings and 04:00 till 07:00 in the morning.

We are using 20 units per day.

What is the solutions that is available to do?

If I may add my two cents here:

I installed a Stiebel Eltron 300L heat pump just over a year ago, and I’ve been very happy with it. It sips power—usually between 400W and 500W per hour. We're three adults in the house, and today it ran for about 4.5 hours. Even now, the water is still sitting at 62°C. No washing was done today, and we all shower in the mornings. The insulation is excellent—once it’s heated, it holds the temperature well and doesn’t switch on again until the third person starts showering.

We currently have a top loader that uses a lot of hot water, so on some days, the heat pump can run for up to 12 hours. That said, we plan to replace it with a front loader as soon as it gives in.

Yes, the heat pump cost about four times more than a traditional geyser, but I believe it’s going to be well worth it in the long run. I’m in the Garden Route, where we get a fair amount of cloud, but even so, my solar system is able to cover the base load—something that wasn’t possible with the old geyser. Since making the switch, our electricity usage has dropped by almost 60%. Do your homework and see if it will work for you.

11 hours ago, sproete_za said:

Yes, the heat pump cost about four times more than a traditional geyser, but I believe it’s going to be well worth it in the long run. I’m in the Garden Route, where we get a fair amount of cloud, but even so, my solar system is able to cover the base load—something that wasn’t possible with the old geyser. Since making the switch, our electricity usage has dropped by almost 60%. Do your homework and see if it will work for you.

My heat pump is now heading into it's 14th year. The new ones will perform more in line with the figures that @sproete_za gives. Advances in motors, compressors, gasses all add up to lower consumption than I have, and mine is already a saving over a regular geyser.

12 hours ago, HennieL said:

I am certainly not confused - but I do tend to do my homework before I invest a larger some of money on anything...

Here is an in-depth extracts from peer reviewed scientific studies:

Energies article: Analysis of On-Board Photovoltaics for a Battery Electric Bus and Their Impact on Battery Lifespan - Kevin R. Mallon *, Francis Assadian and Bo Fu, Department of Mechanical and Aerospace Engineering, University of California, Davis

Here are some extracts from various manufacturers:

The Powerech Systems Company: PowerTech Systems is a French company founded in 2013: Internal publication.

Brava Batteries LiFePO4 Battery Discharge and charge Curve

4. Cycle Life Curve at Different DOD

Different DOD Discharge Cycle Life Curve @ 1C 25 0C

And here's an extract from the Battery University: https://batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries

Table 2 estimates the number of discharge/charge cycles Li-ion can deliver at various DoD levels before the battery capacity drops to 70 percent. DoD constitutes a full charge followed by a discharge to the indicated state-of-charge (SoC) level in the table.

Depth of Discharge	Discharge cycles
	NMC	LiPO4
100% DoD	~300	~600
80% DoD	~400	~900
60% DoD	~600	~1,500and located in Saint Cyr L’Ecole, France.
40% DoD	~1,000	~3,000
20% DoD	~2,000	~9,000
10% DoD	~6,000	~15,000

Anyway, as I said previously: My money, my choice 🙂

I'm confused by the data being shared here. To be clear I'm not disputing any of it, I just don't understand.

Is it the case that we get more cycles from a LiPo battery if it gets discharged past 50% remaining SOC on a regular basis?

If so I need to figure out ways to work my battery harder - it seldom gets as far as 50%.

1 hour ago, Bobster. said:

I'm confused by the data being shared here. To be clear I'm not disputing any of it, I just don't understand.

Is it the case that we get more cycles from a LiPo battery if it gets discharged past 50% remaining SOC on a regular basis?

If so I need to figure out ways to work my battery harder - it seldom gets as far as 50%.

https://batteryuniversity.com/article/why-mobile-phone-batteries-do-not-last-as-long-as-an-ev-battery

This should hopefully help explain. DOD is nto the only primary item to be looked at to get the most out of your batteries. You can utilize more of your battery and make it last longer by following some of the guidelines here rather than following the typical 100 to 50 discharge. Its not by a huge milestone though but being able to use 10 to 20% more of your battery and getting more life out of them is still a win

4 hours ago, Denns said:

DOD is nto the only primary item to be looked at to get the most out of your batteries. You can utilize more of your battery and make it last longer by following some of the guidelines here rather than following the typical 100 to 50 discharge. Its not by a huge milestone though but being able to use 10 to 20% more of your battery and getting more life out of them is still a win

Thanks.

With my inverter it is difficult to stop the battery charging to 100% unless the weather is pretty miserable. It maybe easier with Deye/Sunsynk. Can you control the MAXIMUM SOC with those?

Also I note that there's talk of about 500 cycles. My 10/8 is warranted for 6000. And they're comparing cell phone batteries (I think) with EV batteries. I think the sort of battery we use in domestic installations is closer to an EV battery.

Edited August 6, 20251 yr by Bobster.
Correct spelling (and outright wrong whole words)

6 hours ago, Bobster. said:

I'm confused by the data being shared here. To be clear I'm not disputing any of it, I just don't understand.

Is it the case that we get more cycles from a LiPo battery if it gets discharged past 50% remaining SOC on a regular basis?

If so I need to figure out ways to work my battery harder - it seldom gets as far as 50%.

This article refers to non phosphate lithium. Li-Ion.