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  1. #61
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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by the_terrible_triplett View Post
    There about yes ... I had it at over R14 ex VAT at one stage.
    Bi-directional meter was like +-R12k plus installation of +-R2k.

    A rough comparison since we went grid tied:
    Our monthly connection fee is R 172.50, feedback it is R390.90 as per the doc.
    Since we went grid tied, I have NEVER even touched 600 units pm over 12 months, the doc works on 800 units.

    Winter, Total Payment of +-R1172.50 for <600 units pm.
    Summer, Total payment of +-R272.50 - R372.50 for very few units pm.
    Vs that doc's total Payment of R 1551.27 per month for 800 units, having fed back.


    On another forum a sum was done a while ago to calculate where feeding back breaks even, general consensus there was that it is not viable when you do your sums with extreme prejudice, as the overall costs of such a system and the feedback costs, are balanced on a knifes edge.


    What did I do:
    If one does it with data, start small with array size, batts, but buy the core parts with expansion in mind.
    When you have your winter/summer usage data, used that to fine tune your habits and usage, before you go bigger.

    Like I had 2.2kw panels, maxed them out with ease. Could not recharge the batteries most of the time in winter.
    Months later I added more panels, array at 3.5kw ... maxed them out most of the time BUT per day, I could recharge the batteries with ease, even most winter days.
    Now months later again, I'm adding 2 more panels, array will then be at 4.2kw ... will see how that works now for at LEAST one year.

    Legally I'm bound to 3.5kw max, I know I need 3kw during peak hours, which currently is between 11 and 14:30, this time of the year.
    With 4.2 I can start earlier to heat geysers, and for longer, and run more loads earlier and later.
    And I KNOW the batts will be recharge with even more ease.

    See, the part where the savings really started to kick in, was when I bought a 7.2kwh lithium DIY bank.
    I took off 500w from 22h00 till the sun takes over the next morning, most of the winter evenings, batts set to not go lower than a SOC of 40%.
    I can go 20%, but IF Eskom fails before solar takes over, I'm stuffed.

    So to lower my Eskom costs even more, with the 4.2kw array already going to contribute mi n of 500w more daytime, I need more batteries ... will do that one day under WANTS/HOBBY expenses, as I don't NEED it.


    So that is how we roll being grid tied and not feeding anything back.
    Maximizing Eskom savings by:
    1) understanding ones loads,
    2) scheduling the loads,
    3) adding some discipline for the "power users" in the household,
    4) ... and sit on your hands keeping that CC far far away ... unless your data says you need something more.


    This was a good day, and the annual usage, creeping down one day at a time, as the lithium batts have not been in place for a year:
    Red is Eskom, Orange is Solar, Blue is battery usage.
    So you are about 50% Solar, 50% grid powered.

    Don't forget to factor in the cost of consuming the batteries when comparing to feed-in ........
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  2. #62
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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by Richard Mackay View Post
    What loads are your PV panels feeding? Charging batteries??
    1) Recharging batteries from 40% DOD to 100% by latest 5pm.
    2) Powering average household 24/7/365 of 500w during the day
    3) Dishwasher and/or dryer scheduled in-between
    4) Heating 2 x 150l geysers between 11 and 3:30
    5) Running 500w off batts between 10pm till the sun takes over,
    ... go back to point 1, rinse, repeat ...

    Methinks ... a damn good balance from a potential of 3.5kw of panels.


    Quote Originally Posted by Fluffy View Post
    So you are about 50% Solar, 50% grid powered.
    Methinks there are more no's to consider than 50% because one needs to look at the full picture and the background.

    1) 50% over 1 year, from lead acid (20% DOD) batts over to lithium's (60% DOD), lithium's being in place but a few months.
    2) 21% usage from Eskom that day - summer it dips to 9% most days.
    3) 31% Eskom over over 7 days - will see after this summer.
    4) 41% Eskom over 30 days - will see after this summer.

    Keep in mind that Cpt had a lot of weather, i.e. dams are full, in Aug, Sept and some in Oct.
    Ask me again in Apr 2021, the 50% would be lower, as will be the 7 and 30 days.


    Quote Originally Posted by Fluffy View Post
    Don't forget to factor in the cost of consuming the batteries when comparing to feed-in ........
    True.
    Facts are:
    Trojan bank was 5 years old, sold it for more than their lead price, offset that against the lithium's, lithium bank cost me less than a new lead acid bank.

    Cost per kwh ... not a factor. The system must have batteries and I want power at night when Eskom is off. It is a NEED.


    Quote Originally Posted by mygoggie View Post
    Grid-tied as then you can deduct your capex on a 50:30:20 basis from tax; meaning your system costs you nothing.
    Only if it is a business expense, no Capex for a home user.
    Last edited by the_terrible_triplett; 2020/10/24 at 03:18 AM.
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  3. #63
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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by the_terrible_triplett View Post
    1) Recharging batteries from 40% DOD to 100% by latest 5pm.
    2) Powering average household 24/7/365 of 500w during the day
    3) Dishwasher and/or dryer scheduled in-between
    4) Heating 2 x 150l geysers between 11 and 3:30
    5) Running 500w off batts between 10pm till the sun takes over,
    ... go back to point 1, rinse, repeat ...
    If you have plenty sun and a light load how do you prevent your grid tie inverter powering back into the grid??

  4. #64
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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by Richard Mackay View Post
    If you have plenty sun and a light load how do you prevent your grid tie inverter powering back into the grid??
    AFAIK Victron do have a 32, 40 and 100A CT clamp that seems to be used for this function. The Solis uses the same method to throttle the inverter to prevent export.

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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by Wetkit View Post
    Just as a suggestion, I too had many fridges and freezers in my house, the old types. They worked fine, but after measuring everything in the house, I found these units to consume around 4kwh per fridge/freezer per day!!! That is same as your oven for 2 hours flat out.
    Even for old type frigdes 4kwh/day is quite high. Below is my power use of a good sized Kelvinator with Defy 210L chest freezer running at 4.5-5.5kwh per 24 hours. Note the increase due to the temp over 30 the last week.

    After I added 2 panels 2 weeks ago my stats for the last 15 days are 6.8kwh per day from PV. 5.2kwh drawn from the grid over the same 15 days.

    Total cost of the grid tied setup for hardware is only R13 000 to date. This works out at a R1911 per kwh of PV produced per day. Cheaper than this is hard to find for a silent easy to install system with no changes to the DB and no settings to do other than to use the right option on the menu to prevent export.
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  6. #66
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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by Richard Mackay View Post
    If you have plenty sun and a light load how do you prevent your grid tie inverter powering back into the grid??
    Question not directed at me, but nevertheless, my Mecer inverter slows down PV watts when no or little load. When I e.g switch on aircon and demand increases, panels react immediately and up the watts to required level. Should system not being able to cope with demand system reverts to grid
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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by Fluffy View Post
    Don't forget to factor in the cost of consuming the batteries when comparing to feed-in ........
    My pal in the US reckons the cost of batteries is $100 pm.

  8. #68
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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by Richard Mackay View Post
    If you have plenty sun and a light load how do you prevent your grid tie inverter powering back into the grid??
    One of the core features of grid tied inverters, is to allow the user the option to not feed back into the grid.
    Political Correctness
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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by the_terrible_triplett View Post
    One of the core features of grid tied inverters, is to allow the user the option to not feed back into the grid.
    Accepted! But the reason why grid tie inverters were designed was to enable the exporting of excess power to the grid.
    Why use a grid tie inverter in the first place?

  10. #70
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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by Richard Mackay View Post
    Accepted! But the reason why grid tie inverters were designed was to enable the exporting of excess power to the grid.
    Why use a grid tie inverter in the first place?
    I doubt many of us with grid tied installed them to export. We knew all along the admin fees and R18000 total cost of new power meters etc makes no sense to feed back to the grid. Further the grid tied uses every bit of PV while you have load to use the power. Fridges, aircon, geyser, charging a cycled battery etc. You will notice the low cost in my earlier post.
    Last edited by ekkekan; 2020/10/26 at 02:21 PM.

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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by Richard Mackay View Post
    Accepted! But the reason why grid tie inverters were designed was to enable the exporting of excess power to the grid.
    Why use a grid tie inverter in the first place?
    because they allow seamless import when needed
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  13. #72
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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by Richard Mackay View Post
    Accepted! But the reason why grid tie inverters were designed was to enable the exporting of excess power to the grid.
    Every country has their limits, laws and how they want, or can, handle thousands of home grid tied inverters.
    Here is a viewpoint/explanation:
    Instead of thinking about feeding the grid i.e. your street i.e. the local transformer in your area, rather see it as feeding back ONLY into YOUR own DB's to power all what is connected to your DB's.
    In other words, all the power is to be consumed on your property, all that is tied to your DB, but not the street.


    Quote Originally Posted by Richard Mackay View Post
    Why use a grid tie inverter in the first place?
    Why? Being grid tied also means you can use a smaller grid tied inverter.
    For example, take a 3kva hybrid grid tied inverter, your house draws 10kw, that 3lva inverter can push 2.4kw back into your DB's, so you only buy 7.6kw from Eskom.
    If you where off-grid, you had to have a +10kw inverter to do that exercise.
    That inverter cost, and batts and panels, to do that off-grid, escalates the costs immensely.
    Last edited by the_terrible_triplett; 2020/10/26 at 10:43 PM.
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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by the_terrible_triplett View Post
    Why? Being grid tied also means you can use a smaller grid tied inverter.
    For example, take a 3kva hybrid grid tied inverter, your house draws 10kw, that 3lva inverter can push 2.4kw back into your DB's, so you only buy 7.6kw from Eskom.
    If you where off-grid, you had to have a +10kw inverter to do that exercise.
    That inverter cost, and batts and panels, to do that off-grid, escalates the costs immensely.
    I agree but isn't there an even simpler solution? Aren't the ubiquitous Axpert inverters able to draw power from the grid and not export?
    The complexity (and cost) of a grid tie inverter is in its ability to synchronise with and feed excess PV power back into the grid.
    Drawing power from the grid is more straight forward. (All the grid needs to do is maintain the voltage of DC bus of the inverter..)

  15. #74
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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by Richard Mackay View Post
    Accepted! But the reason why grid tie inverters were designed was to enable the exporting of excess power to the grid.
    Why use a grid tie inverter in the first place?
    Actually not so. Grid tie's are designed to tie into and then synchronise so that they can augment or add extra to the load for own consumption. Exporting back is a nasty side effect that is difficult to tame.

    Unless specifically designed and implemented as an energy generation facility, they always supply own needs first and only export surplus.
    Cheers

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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by Richard Mackay View Post
    I agree but isn't there an even simpler solution? Aren't the ubiquitous Axpert inverters able to draw power from the grid and not export?
    The complexity (and cost) of a grid tie inverter is in its ability to synchronise with and feed excess PV power back into the grid.
    Drawing power from the grid is more straight forward. (All the grid needs to do is maintain the voltage of DC bus of the inverter..)
    Actually, what a grid-tie does is much easier to do. For own AC consumption it simply converts PV derived DC to Grid Synchronized AC.

    To give yo AC for consumption the Axpert has to convert PV derived DC at high voltage, to a well regulated DC battery voltage, and implement a fancy charge algorithm, and then convert the DC voltage to AC mains for consumption. It has a whole bunch of houskeeping and modes to look after. And it cant Convert AC to DC battery, while at the same time Convert DC battery to AC mains. It only has one active circuit which can Either - Charge the battery OR convert Battery to AC Mains. The circuit is Bi-Directional. The poor old AXPERT has to do all this to eventually get AC mains to your load.

    The unfortunate price comparison come when we compare price of Axpert "HYBRIDs" and true Hybrids like GoodWe and others. There is a LOT more to it than just a grid-tie inverter difference.
    Last edited by Fluffy; 2020/10/26 at 08:27 PM.
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  19. #76
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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by Richard Mackay View Post
    The complexity (and cost) of a grid tie inverter )
    I'm not sure what you mean with cost. The cheap 1kw China grid tied inverters cost R2000. The Solis with 5y peace of mind starts at about R4500. Complex is inside the box and for the user plain and simple with PV input and 220V AC output which is the same wires to synch. As easy to connect as a solar controller.

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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by ekkekan View Post
    I'm not sure what you mean with cost. The cheap 1kw China grid tied inverters cost R2000. The Solis with 5y peace of mind starts at about R4500. Complex is inside the box and for the user plain and simple with PV input and 220V AC output which is the same wires to synch. As easy to connect as a solar controller.
    Solis/cheap China grid tied inverter to Axpert comparison is not quite accurate.
    Compare Solis Hybrid with a Axpert ... as both require/have batteries.

    On top of that, you also have to compare NRS approved grid-tied inverters, as that allegedly cost +-R100k per inverter model to get tested.

    We have to stick to the rules of the debate i.e. compare apples with apples as best we can, and NRS approved inverters should be a core comparison factor for any new buyers, caveat emptor.
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  22. #78
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    Default Re: Grid-tied or off-grid. Please consider ...

    Certainly many knowledgeable individuals on this thread.
    Thank you for sharing all the details and enriching others.


    It seems to me that a small grid tied inverter without batteries could certainly help protects against electricity charges, especially in the higher tariff blocks.
    Even more so with most people working from home, so you can control the daytime load better.


    Now I am wondering - I currently have a generator with change over switch - 6500kva
    Will this work in conjunction with a grid tied inverter, in other words, will the inverter sync to the generator frequency and enable you to use both during load shedding.

  23. #79
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    Default Re: Grid-tied or off-grid. Please consider ...

    No expert, but I think you'd need a hybrid inverter.
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    Default Re: Grid-tied or off-grid. Please consider ...

    Quote Originally Posted by the_terrible_triplett View Post
    Solis/cheap China grid tied inverter to Axpert comparison is not quite accurate.

    On top of that, you also have to compare NRS approved grid-tied inverters, as that allegedly cost +-R100k per inverter model to get tested.

    We have to stick to the rules of the debate i.e. compare apples with apples as best we can, and NRS approved inverters should be a core comparison factor for any new buyers, caveat emptor.
    Stick to the rules . I replied on the post from Richard saying grid tied are expensive and complicated.

    You know very well that the Axpert is not approved and I made no reference to it. All Solis models are on the NRS list.

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