Solar geyser backup element usage.





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  1. #1
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    Default Solar geyser backup element usage.

    With winter the backup electric element of our solar geyser naturally gets used more, though I still want to try minimize it as much as possible.

    This had me wondering, do you think it's a waste having the element on while water are being used as in while someone's taking a shower or while the dishes are being done in the kitchen?
    My thinking is as hot water flows out, cold water flows in, so I wonder how effective the element is really during that period where cold water constantly gets added to the tank.

    Rather than having the element on from 7:00 to 9:00 in the morning, I was thinking to maybe switch on from 7:00 to 8:00 and then for another hour from 9:00 to 10:00. 8:00 to 9:00 is basically peak hour in the kitchen when the domestic does the dishes and cleans, otherwise known as using up all the hot water.

    Or will I actually waste electricity if looking at the bigger picture by switching it off for short periods and then on again for a short period?
    Last edited by bigboy529; 2020/05/30 at 03:33 PM.
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    Default Re: Solar geyser backup element usage.

    You will probably save, because, depending on the volume of your geyser(s), you will run out of hot water. You will then just continue cleaning with cold water, or learn to use the warm water more sparingly. Seeing as you will be delegating the inconvenience it makes sense.
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    Default Re: Solar geyser backup element usage.

    My take would be you need a specific amount of power to heat each liter by 1 degree in temp so it makes no difference if the element is off when cold water passes it or it has to heat the cold water after a shower or dishes. The calculation for power used can be worked back from the figure of 7kWh to heat 150L of water by 40 degrees.

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    Default Re: Solar geyser backup element usage.

    Quote Originally Posted by Fluffy View Post
    What system do you have. Between 10.00 and 12.00 your Solar generation is being throttled. You are throwing energy away deluxe.
    This comment from another thread mentions the wastage of PV power when using timers to control the geyser.
    This would be a better way to get more power from your system.

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    Default Re: Solar geyser backup element usage.

    Quote Originally Posted by Richard Mackay View Post
    This comment from another thread mentions the wastage of PV power when using timers to control the geyser.
    This would be a better way to get more power from your system.
    Context.

    You set the timers, like I do, to switch geysers on when I know I have optimal power, like between +-11 - +-3pm.
    Heat two geyser consecutively in that time, 11-1pm and 1pm-3pm. 2 hours enough to take them back to 60+ degrees.
    And if it is cloudy during those times, Eskom assists.

    And they last till the next day ... adjusted our lifestyle a tiny bit.
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    Default Re: Solar geyser backup element usage.

    Quote Originally Posted by the_terrible_triplett View Post
    Context.

    You set the timers, like I do, to switch geysers on when I know I have optimal power, like between +-11 - +-3pm.
    Heat two geyser consecutively in that time, 11-1pm and 1pm-3pm. 2 hours enough to take them back to 60+ degrees.
    And if it is cloudy during those times, Eskom assists.
    I presume this is a grid tie system?
    The issue with adding a big load on a time of day basis is that it doesn't allow you to fine tune the control.
    See this comment from a guy overseas who I respect:

    The real solution to the problem is to add a "power diverting device" into your system. Such device monitors export to the grid and based on it's size it will control a phase-angle SSR (a semiconductor relay). The phase-angle controlling works the very same like a trigger on your cordless drill. With a 3kW load, it's able to smoothly power the load from 0W to 3000W. Long-story-short, even if there's just a 1kW of grid export, the power diverting device will feed this 1kW into a geyser, while pulling 0W from the grid. This approach will continuously heat the water with the maximum utilization of available PV power.

    This is a smarter control system since it diverts power that is available..

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    Default Re: Solar geyser backup element usage.

    Quote Originally Posted by Richard Mackay View Post
    I presume this is a grid tie system?
    The issue with adding a big load on a time of day basis is that it doesn't allow you to fine tune the control.
    See this comment from a guy overseas who I respect:

    The real solution to the problem is to add a "power diverting device" into your system. Such device monitors export to the grid and based on it's size it will control a phase-angle SSR (a semiconductor relay). The phase-angle controlling works the very same like a trigger on your cordless drill. With a 3kW load, it's able to smoothly power the load from 0W to 3000W. Long-story-short, even if there's just a 1kW of grid export, the power diverting device will feed this 1kW into a geyser, while pulling 0W from the grid. This approach will continuously heat the water with the maximum utilization of available PV power.

    This is a smarter control system since it diverts power that is available..
    Yes, I am grid tied.

    Kettles, microwaves, induction stove ... all of them are "big" loads then.
    "Big" loads like 2kw geyser element is not supposed to be an issue on any 3/5kva inverter at all.

    Ps: On solar, you change your 4kw geyser element out with a 2kw element to better "fit" the systems parameters.

    Adding a power diverting devices is definitely a very cool idea ... if you are exporting power to the grid and would rather use that power for your own geyser.

    The problem starts when you don't export. I can add a power diverting device today but unless it communicates with my system to tell it to throttle back / not export after the geyser is heated, my PAYG meter will charge me a lot more and/or start tripping.

    Just be aware of that.
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    Default Re: Solar geyser backup element usage.

    Quote Originally Posted by bigboy529 View Post
    With winter the backup electric element of our solar geyser naturally gets used more, though I still want to try minimize it as much as possible. - Makes me think traditional solar geyser
    ...
    Or will I actually waste electricity if looking at the bigger picture by switching it off for short periods and then on again for a short period? - Makes me think grid tied system
    I am only commenting on the traditional system... grid tied is taken care of...

    The timer for my electric backup element is set for 2 - 3 pm in the afternoon and 2 - 4 am in the morning.

    The afternoon backup is in case of a cloudy day and the early morning backup was in case of heavier than expected usage.

    The settings are in place but it is manually overridden to "OFF" and I have not had a problem this season. I actually have more of a problem in summer with cloudy days, than the cold, but clear winter weather on the highveld.

    ...and yes, we have made some small lifestyle changes to accomodate the system. Making beds and dusting before washing up would probably allow time for the water to get hot again...
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    Default Re: Solar geyser backup element usage.

    OK. So these are grid tie systems. This should be straight forward with a FIT that compares reasonably with the cost of utility power.
    However in this part of the world with grid tie systems we often have to install a 'grid limiter' which will prevent any power feeding back into the grid.
    So do these systems have a grid limiter?

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    Default Re: Solar geyser backup element usage.

    Quote Originally Posted by Richard Mackay View Post
    OK. So these are grid tie systems. This should be straight forward with a FIT that compares reasonably with the cost of utility power.
    However in this part of the world with grid tie systems we often have to install a 'grid limiter' which will prevent any power feeding back into the grid.
    So do these systems have a grid limiter?
    All NRS approved grid tied and hybrid gird tied inverters in SA has the ability to not feed any power back.
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    Default Re: Solar geyser backup element usage.

    I need to get specific info..
    Perhaps bigboy can clarify what system he's got: grid tie or not and if so whether he is feeding back into the grid??

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    Default Re: Solar geyser backup element usage.

    Quote Originally Posted by Richard Mackay View Post
    I need to get specific info..
    Perhaps bigboy can clarify what system he's got: grid tie or not and if so whether he is feeding back into the grid??


    Sorry guys, should have included earlier, it's a thermosiphon passive solar geyser with a electric backup element and Geyserwise control.
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    Default Re: Solar geyser backup element usage.

    Quote Originally Posted by bigboy529 View Post
    Sorry guys, should have included earlier, it's a thermosiphon passive solar geyser with a electric backup element and Geyserwise control.
    Energy is energy and an electrical heater element is fairly efficient in terms of converting electrical energy into heat.

    Whether the cold water is flowing into the geyser or not does not waste energy, you always need X amount of energy ( be it from the sun or electricity) to heat Y amount of water from the temperature that the water comes in to the temperature that you want (set point).


    The timer switching of the geyser element is not going to make difference, in terms of electricity consumption, it will just raise the temperature quicker, but there is no saving.

    The only thing that is going to make a difference is to use less hot water, improve the thermal insulation on the hot water tank or get more solar energy capturing capability.

    The thinking must be that all and any hot water must be heated by sun rays and not by sparky juice
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    Default Re: Solar geyser backup element usage.

    He asked about running the electrical element, not the solar system.
    If the electrical element is off at the time stated, it will not use electricity. The solar energy may still contribute, but between 8:00 and 9:00 the solar radiation is still too little to keep the water warm.
    There is no PV.
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    Default Re: Solar geyser backup element usage.

    Quote Originally Posted by vlakkie View Post
    Energy is energy and an electrical heater element is fairly efficient in terms of converting electrical energy into heat.
    Whether the cold water is flowing into the geyser or not does not waste energy, you always need X amount of energy ( be it from the sun or electricity) to heat Y amount of water from the temperature that the water comes in to the temperature that you want (set point).
    ....
    Yes, in general electrical systems energy losses are mostly heat losses. In a geyser you want heat, so there is nothing to lose. But...

    Quote Originally Posted by vlakkie View Post
    ...
    The timer switching of the geyser element is not going to make difference, in terms of electricity consumption, it will just raise the temperature quicker, but there is no saving.
    The only thing that is going to make a difference is to use less hot water, improve the thermal insulation on the hot water tank or get more solar energy capturing capability.
    The thinking must be that all and any hot water must be heated by sun rays and not by sparky juice
    ...
    The water is warm early in the morning, either from the previous day's solar input or the electrical element. As they use the warm water the geyser cools down. The solar radiation is not sufficient to heat it up again and the electrical element kicks in and uses expensive electricity.
    If the timer disables the electrical element at, say, 8:00, the water in the geyser will keep getting colder until the sun can start heating it up. This way they save electricity. I would suggest just keeping the electrical element off until late in the afternoon, when it will switch run only if there was not enough sun during the day to heat water for family use during the evening.
    It is somewhat inconvenient for their domestic worker, because she either has to get by with less water, or get used to washing dishes with cold water. This might make her work slower or use more soap, or whatever. This the OP then has to balance these costs against the cost of electricity saving.

    (My comment is obviously based on power and economics, not how bigboy should manage his domestic worker. I assume he will discuss his strategy to save electricity with her.)
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    Default Re: Solar geyser backup element usage.

    I was under the impression that one's geyser consumes a hellava lot of your electrical power.
    So to check this I installed a kWh meter (Elster A100C) in the supply to the geyser.
    After many months and having set the thermostat at absolute minimum as well as switching the supply manually twice a day (just to get to set point) my Kwh units average out at 4 per day. Even at R2 per unit that is only R8 per day..
    So how does the municipality manage to get the bill up to R1000+ ??

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    Default Re: Solar geyser backup element usage.

    Doen die af gelope paar dae n toets. Ek hardloop offgrid system en dump my extra krag in my geyser in nou. Met die winter tel die solar geyser met geyser wise setup nie genoeg op nie. Ek hardloop n Shelly EM setup met CT clamps op my main input en dan 2de clamp op die geyser se kant. Van daar af n Wifi controller/relay wat n hat het ook. Die die Shelly het n relay output wat in die hat van die wifi controller/relay in gaan so ek kan control oor die hat van die Shelly se kant af. Jy kan die Shelly dan stel dat as dit optel dat die load te groot raak op die main CT clamp se kant dan switch die Shelly die the 2de CT clamp se kant af wat op die geyser se kant is op die solar, tot die load minder weer raak, dan switch die shelly die load weer op die geyser aan.

    Tussen die Solar se kant van die geyser AC en van die Grid se kant van die Geyser wise controller hardloop 2 25A Contactors wat ge interlock is met interlock link. So as die geyser wise manual aan gesit word, dan switch die een contactor aan maar lock die solar/inverter se kant and vasa visa, so niks van grid blend stuff daar nie. Geyser het , 3.2kw element in.

    My MLT inverter kan die goed maar dis n hele storie wat op gestel moet word.

    Teen so 11uur is my lifepo4's vol gelaai, dan dump ek my extra solar krag oor geyser se kant om hom warm te maak. Soos Bv van oggend, was my Geyser 29'c. ek het so 45min se solar krag in gedump daar, en toe weer so 15min sin by. toe staan hy op 58'c. Was so 3.3kw se solar krag wat ek daar in ge dump het.
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  23. #18
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    Default Re: Solar geyser backup element usage.

    Quote Originally Posted by Gerlach View Post
    Doen die af gelope paar dae n toets. Ek hardloop offgrid system en dump my extra krag in my geyser in nou. Met die winter tel die solar geyser met geyser wise setup nie genoeg op nie.
    Wat Geyserwise syteem het jy? PV of Evacuated Tubes?

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    Default Re: Solar geyser backup element usage.

    Quote Originally Posted by Richard Mackay View Post
    After many months and having set the thermostat at absolute minimum as well as switching the supply manually twice a day (just to get to set point) my Kwh units average out at 4 per day.
    As most thermostats can adjust down to 30 degrees C what does one do with water this cold?

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    Default Re: Solar geyser backup element usage.

    Quote Originally Posted by Richard Mackay View Post
    I was under the impression that one's geyser consumes a hellava lot of your electrical power.
    So to check this I installed a kWh meter (Elster A100C) in the supply to the geyser.
    After many months and having set the thermostat at absolute minimum as well as switching the supply manually twice a day (just to get to set point) my Kwh units average out at 4 per day. Even at R2 per unit that is only R8 per day..
    So how does the municipality manage to get the bill up to R1000+ ??
    R8 per day = R243 pm over 12 months. So about 1/4 of your bill because you made an effort.
    Normally geysers are about 1/3 of the bill.

    The rest of the power?
    First place I would start, measure the consumption when everyone is asleep.
    Next level, switch all circuits off at the DB. Then switch then on, one by one, and measure power draw.

    When I did the above, in my case, I found some very interesting power users like:
    1) Kitchen had a 4 tube fluorescent light fitting. Only one fluorescent tube inserted, yet it still drew +-250w.
    Reason: 4 x transformers all on, not just the one with the tube in.
    2) Clock Alarm radios. 3 of them. They drew collectively about 300w.

    Ripped the transformers out, went 11w LED tube and threw the Clock radios into the recycling bin.

    You literally have to do a power audit.
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