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  1. #61
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    Default Re: Avoiding solar power throwaway

    Quote Originally Posted by shaneyake View Post
    I have DC elements on my geyser. Can change output power from 0-400kw in 10w steps, this tracks batter power and holds it around 0W once battery is full.
    Please give details or link to these elements.
    Thanks!
    Dirk Lombard
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  2. #62
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    Default Re: Avoiding solar power throwaway

    Quote Originally Posted by DirkL View Post
    Please give details or link to these elements.
    Thanks!
    I would just get a bigger inverter if I had to do it again.
    I have 2x 2kw DC elements and 1x 2kw AC element.

    They were R700 delivered when I bought them. Then can be split into 1kw sections by changing the links around. Had to make a custom plate to get them all to fit with PLC temp probe and thermostat.
    https://www.banggood.com/48V-1500W-S...r_warehouse=CN

    I have a PLC driving them with some 40A solid-state relays with heatsinks.
    https://za.rs-online.com/web/p/solid...elays/9174838/

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  4. #63
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    Default Re: Avoiding solar power throwaway

    Regarding the geyser elements, for what it's worth, I accidentally stumbled on these: http://www.elexco.co.za/index.php?ro...search=element
    One good thing about music: when it hits you, you feel no pain...

  5. #64
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    Default Re: Avoiding solar power throwaway

    For powering standard 150L geysers / single phase electric motors >2kw with an inverter, I'll recommend the inclusion of a 'soft starter' wired before the load as below link.

    Thyristor soft starters limit the start-up current in adjustable levels / time, allowing a solar mppt to catch up with the load whilst preventing high start-up currents straining the inverter.

    Also much easier than replacing with low power elements.

    https://za.rs-online.com/web/p/motor-starters/3305358/
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  6. #65
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    Default Re: Avoiding solar power throwaway

    This 12V geyser element is also available: https://www.geyserwise.com/products/...tc-ac-element/
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  7. #66
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    Default Re: Avoiding solar power throwaway

    Quote Originally Posted by thabogrobler View Post
    This 12V geyser element is also available: https://www.geyserwise.com/products/...tc-ac-element/
    This isn't a 12V element. These PTC elements are also used in their Dual systems. This is a PV panel water heating system: https://www.geyserwise.com/products/...eating-system/
    These elements are driven by DC current (100V max) direct from the panels (through a MPPT)
    Last edited by Richard Mackay; 2021/05/30 at 07:35 PM.

  8. #67
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    Default Re: Avoiding solar power throwaway

    Quote Originally Posted by rnieckau View Post
    For powering standard 150L geysers / single phase electric motors >2kw with an inverter, I'll recommend the inclusion of a 'soft starter' wired before the load as below link.

    Thyristor soft starters limit the start-up current in adjustable levels / time, allowing a solar mppt to catch up with the load whilst preventing high start-up currents straining the inverter.
    Great idea! I'm aware of the MPPTs needing an initial period to adjust for maximum power so this allows this to happen before the maximum current is drawn.

  9. #68
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    Default Re: Avoiding solar power throwaway

    Quote Originally Posted by rnieckau View Post
    For powering standard 150L geysers / single phase electric motors >2kw with an inverter, I'll recommend the inclusion of a 'soft starter' wired before the load as below link.

    Thyristor soft starters limit the start-up current in adjustable levels / time, allowing a solar mppt to catch up with the load whilst preventing high start-up currents straining the inverter.

    Also much easier than replacing with low power elements.

    https://za.rs-online.com/web/p/motor-starters/3305358/
    Name:  1622315068215.jpg
Views: 84
Size:  28.8 KB

    This isn't needed. You don't have in-rush currents on resistive loads like an element. Only inductive loads like a motor but any decent inverter will allow you to overload it for a few seconds for this exact reason when off-grid, if grid is present this isn't a problem at all as inrush will come from the grid.

    On the MPPT side, I wouldn't worry about it, the capacitors in the inverter and then your battery will act as a buffer.

    I don't really understand this geyserwise product, if you are going to have dedicated panels for your gyser, you might as well go solar thermal which is more effective. The whole point of using PV panels is to use them to first charge your battery and then once you have excess solar dump that energy into your hot water heater.

  10. #69
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    Default Re: Avoiding solar power throwaway

    Quote Originally Posted by shaneyake View Post
    This isn't needed. You don't have in-rush currents on resistive loads like an element. Only inductive loads like a motor but any decent inverter will allow you to overload it for a few seconds for this exact reason when off-grid, if grid is present this isn't a problem at all as inrush will come from the grid.

    On the MPPT side, I wouldn't worry about it, the capacitors in the inverter and then your battery will act as a buffer.

    I don't really understand this geyserwise product, if you are going to have dedicated panels for your gyser, you might as well go solar thermal which is more effective. The whole point of using PV panels is to use them to first charge your battery and then once you have excess solar dump that energy into your hot water heater.
    MPPTs do not adjust for maximum power transfer in a few seconds. They can hunt for a while.. This means your inverter is loaded more than it should be during this period.
    The comparison between a PV solar water heater and a thermal panel isn't the panel size. Sure the PV panels cover more area but this isn't an issue if you have the roof space. The comparison is on cost of the different systems.

    The Geyserwise system is also more efficient than an inverter (it uses DC) and doesn't have the complication of determining if there's enough available power to switch the geyser on.

  11. #70
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    Default Re: Avoiding solar power throwaway

    Not sure how the inverter is loaded more than it should while waiting for the MPPT. What does the inverter do when no sunshine.
    Is the function of the inverter not to use DC to provide its output be it from PV on grid tied of from batteries? Within the power of the inverter.

  12. #71
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    Default Re: Avoiding solar power throwaway

    Quote Originally Posted by ekkekan View Post
    Not sure how the inverter is loaded more than it should while waiting for the MPPT. What does the inverter do when no sunshine.
    Is the function of the inverter not to use DC to provide its output be it from PV on grid tied of from batteries? Within the power of the inverter.
    I think what Richard means, is that when a large load is switched on, the MPPT takes a while to ramp up and provide the PV that is available to the batteries. This can take up to 15 seconds I've seen on my system.

    But yes, until that happens, the inverter will supply the load from either the batteries or from the grid.
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  13. #72
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    Default Re: Avoiding solar power throwaway

    Quote Originally Posted by Die SwartKat View Post
    But yes, until that happens, the inverter will supply the load from either the batteries or from the grid.
    Indeed! The last thing you want is to draw power from your battery. Geyser power from the inverter should only use excess available power from the PV panels.

  14. #73
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    Default Re: Avoiding solar power throwaway

    Quote Originally Posted by Richard Mackay View Post
    Indeed! The last thing you want is to draw power from your battery. Geyser power from the inverter should only use excess available power from the PV panels.
    Why? They will be charged up again once the MPPT ramps up. Lets say 2kw load for 15secs that would be 0.0083kwh or 8.3wh from the battery. That is nothing. You are cycling your pack way more when a cloud blows over.

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  16. #74
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    Default Re: Avoiding solar power throwaway

    Quote Originally Posted by Richard Mackay View Post
    Indeed! The last thing you want is to draw power from your battery.
    BS.
    The batteries are the "buffer" whilst the MPPT's ramp up/scale down daytime with, or without, clouds.

    Powering a kitchen or geyser from a "small" battery bank, THAT is an issue.
    Also to take note of is the kWh cost from a battery vs the cost per kWh from Eskom, to run a kitchen vs batteries ... and the bigger inverter and array and MPPT ...

    The key component I noticed over years is "USE THE DAMN BATTERIES!" or they die of old age.

    The benchmark I found is to first shave off the 24/7/365 loads, <500w, off Eskom ... THOSE are the first "low hanging" fruits to use the batteries on 24/7/365 after a geyser, NOT running off batts, has been taken care of.

    Lithium you go for like 30% SOC.
    Lead acid like 80% SOC.
    Last edited by the_terrible_triplett; 2021/06/01 at 12:43 AM.
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  17. #75
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    Default Re: Avoiding solar power throwaway

    In Melbourne it is very common for houses to have a piped natural gas connection. In my case this is used to power a gas hob, solar/gas assisted water heater, and gas central heating.

    During the cold months (5+ months) the gas central heating is often on all the time. We keep it at a cool 18’C to break the cold, but to keep the gas bill somewhat reasonable.

    I recently installed a 8.5 kW grid-tied solar system, and this week I started to use the air conditioner in the main living area for heating instead of cooling during the sunlight hours. I never thought I’d use the aircon for heating… This appears to be working rather well. It means I can switch the gas heating off during the day, even when it is somewhat cloudy, because I have enough excess juice to power the aircon heat pump without drawing mains electricity. Win…

    With the central heating switched off, my study and a few other rooms are on the cold side, so I’m thinking of buying a few portable heaters to run off the panels as well.

    This should make a significant dent in the gas bill.
    Last edited by boerbok; 2021/06/01 at 01:31 PM.
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  18. #76
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    Default Re: Avoiding solar power throwaway

    Well, today there is no need to prevent solar power throw away.

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