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Off-grid system co-existing with pre-paid munic connected system


Jan-Hendrik
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Hi guys,

I have been looking at solar PV system mostly a hybrid system, but my munic will force me to another tariff structure that will make it not profitable for me. And a complete off-grid system is too expensive with the battery cost being the culprit.

Now I am thinking of installation a solar PV + Axpert VM III (battery-less) system completely separate from my munic connected DB box. This solar PV system will only run non essential loads like swimming pool and borehole and maybe a small geyser. The idea is that this system will not have any connection with the "grid" thus it does not need to comply to my munic's regulations for grid connected. And I still want to be using my munic's grid as is for my normal loads in the house but I want to stay on "prepaid" tariff.

The one thing I noted was that you need to inform your munic if you want to do a solar installation - grid connect or off-grid. But here I want to do something in-between. Has anyone done something like this, or any suggestions on how to proceed?

Kind regards,

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You don't want to be running off only PV with no batteries or grid to "smooth" out the output. Not even sure if it's possible with the VMIII. Any passing clouds or shadows could interrupt your power and having this happen constantly won't be good for the inverter or the loads.

Off-grid == batteries. What makes more sense to me is leaving the swimming pool, geyser, borehole etc on grid and going off-grid (with battery backup) for your normal household loads. That is if hybrid or grid tied isn't an option. Not sure I understand the reasons why not, as long as you don't feed back why can't you keep your prepaid meter?

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1 hour ago, Jan-Hendrik said:

my munic will force me to another tariff structure

This is only if you plan to feed back excess power you have. If you don't feed back then you stay with your current rate and meter (even prepaid meter)

There are many terms used in the solar and inverter world and each manufacturer has their own set of buzz words which sometimes clash with what others use.
So Off-Grid does not always mean there is no connection to the grid (i.e. totally separate DB)
Also Grid-Tie does not always mean you have to feed back electricity to your electricity provider(although many times it does)

So to feed back you need to get special approval and special inverters. The rate is mostly not favorable (you buy at R1.50 but sell at R0.50 type of thing) and you must be a net consumer and not a net producer (use more than you give). Much of these do make sense from the electricity provider side, but it is not very enticing for a consumer to do this. The grid feedback makes sense if you don't want to put in batteries and you "pay" the electricity provider (you pay R1/kWh for storage in my example). 

The other side is you want to reduce your electricity bill and have some battery backup for when loadshedding happens (the more go to here in SA at the moment as this happens). For this you can have many types of systems that can do this and by using the automatic transfer switch built into these devices they work like a UPS (or smarter). 

If you do want to go completely off grid, then you need to cater for any circumstance that might happen. So you need a large inverter that will handle the very max load you might get, or it will trip. You also need much more battery backup for when it rains for 3 days and the sun does not shine. All this get very expensive. I would not suggest this option (which was what your suggestion looks like)

Go look at the showcases that the members posted. They might give you an idea what options are available. For instance here is mine 

 

Edited by Louisvdw
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1 hour ago, Jan-Hendrik said:

I have been looking at solar PV system mostly a hybrid system, but my munic will force me to another tariff structure that will make it not profitable for me. And a complete off-grid system is too expensive with the battery cost being the culprit.

You don't say where you live. Rules may vary from municipality to municipality, but generally the tariff you refer to is only when you want to sell your excess power back to the grid.

I live in City of Johannesburg. I have had a prepaid meter for years, and last year I had a hybrid solar system installed. The prepaid meter (Itron in my case, but there are at least 2 brands in use by COJ) doesn't live that happily with the hybrid system, but it never actually cuts out. Most of the electricity our home needs is generated by the panels on the roof, but we can draw from the grid if we need to (and in fact we draw a small amount nearly every day).

I don't export my surplus power*. When the batteries are charged and the sun is up the system derates the panels and draws just what it needs.

* OK... actually the system tries to zero the meter. So if I have drawn 0.25 units from the grid, it will send back 0.25 when it has capacity to do so. I think this is what is causing my pre paid meter to beep and buzz and complain, and it does not give me any credit for the amounts fed back. But we're talking about cents most days, and it would cost me a lot more to go on to the SSEG tariff, so it is by far the lesser of the two evils.

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3 hours ago, Jan-Hendrik said:

Hi guys,

I have been looking at solar PV system mostly a hybrid system, but my munic will force me to another tariff structure that will make it not profitable for me. 

As noted by others this might only apply if you choose to feed back to the grid. Also as mentioned feeding back in terms of "selling" to the municipality seldome makes financial sense.

3 hours ago, Jan-Hendrik said:

The one thing I noted was that you need to inform your munic if you want to do a solar installation - grid connect or off-grid. But here I want to do something in-between.

I think you can basically differentiate 3 types of installs/applications

1) the eskom grid part of your home and the solar part of your home are in some way connected (even if technically "separated" by a transfer switch) - and you want to sell back excess power to the municipality. = most complicated process and one that requires approved inverters, fancy electricity meters etc. (that get installed at your cost most of the time).

2) the eskom grid part of your home and the solar part of your home are in some way connected (even if technically "separated" by a transfer switch) - and you do NOT  want to sell back excess power to the municipality. = probably exacly as complicated as option 1 in terms of application/permission process but you should be able to remain on a more sensible tarrif and *potentially* keep your prepaid meter.

3) the solar part of your home has no way to ever come in to contact with any part of the eskom/municipality grid. = simplest process but still need to inform municipailty and usually supply an electrician signed off COC that the install meets all national and local install rules.

2 hours ago, gooseberry said:

as long as you don't feed back why can't you keep your prepaid meter?

Even if the municipality does not force a change, there could be a problem with the meter actually tripping. @Bobster's meter goes a bit strange but other meters will trip during a slight unintended feedback (happens when PV is powering a big load that then suddenly switches off - Inverter is slow to respond and for a short while some power is fed through the meter which most will consider as a tamper type event).

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1 hour ago, introverter said:

Even if the municipality does not force a change, there could be a problem with the meter actually tripping. @Bobster's meter goes a bit strange but other meters will trip during a slight unintended feedback (happens when PV is powering a big load that then suddenly switches off - Inverter is slow to respond and for a short while some power is fed through the meter which most will consider as a tamper type event).

I have an Itron meter. When the system feeds back, the hand held customer interface unit reboots, but the actual connection to the grid is unaffected as far as I can tell. The device in my meter box has flashing LEDs and an LCD panel, and the other day, being bored, I stood outside and watched the flashing lights and the LCD display whilst the CIU was having a thrombie inside. Nothing seemed to change.

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