This is a question that I have been pondering. I have also switched off grid supply to my system but in my case my hand was forced by my PV inverter that occasionally thinks it’s exporting to the grid and then throttles the PV supply. In order to prevent this I have switched off the grid..
The advantage is if you have enough battery capacity and PV panels you can never have your utility meter bill you for drawing or feeding back power to the grid.
Most days I can actually power the whole property with PV. As far as I know.
The exception is the day my gardener is here. Because he uses the lawn mower, and that device draws a lot of current on start up and it will overload my inverter.
Also I’d need a switch to transfer the non-backed up loads to the backed-up side of the inverter. With my Goodwe if I kill the municipal feed then only the backed up side of the inverter produces any output. In the days of load shedding we used to run an extension lead to the outbuildings so that we could use the washing machine, but the pool pump wouldn’t run.
Now I don’t know what the pool pump draws when it starts. I can always fit a slow start device to that. The drol in die drinkwater is the lawn mower and any other large instanenous loads I don’t know about.
So to me there are two possible risks with dropping the grid
what if you have - as I have - loads that are large for a split second on start up? Or if you have such loads but haven’t yet found out.
what if the sun doesn’t shine for a few days? You need to fall back on something.
The issue here is that it’s all fine and dandy if your grid-tie inverter is operating like it should but often you find it’s gone ape..
If we all had feed-in enabled at a fair rate then one would be more philosophical. But this isn’t the case so you find yourself avoiding the grid as much as possible. It seems every time you have any connection to the grid you lose a couple of fingers..
I’m in Johannesburg, with grid supplied by City Power. I have a pre-paid meter. Right now, because of the pre-paid tariffs, I have to make a minimum payment of R400 each month. That settles the fixes monthly fee on the meter and gives me 55.5 units. That usually gets me through the month with a small amount remaining. So whilst I have ideas about things I could do, it doesn’t actually pay me to do them!
Mine has the export limit set to zero. But it does still export a bit (according to the tools that Goodwe make available). This is an annoyance, but not really a lot more than that. As stated, because of the way COJ has implemented pre-paid tariffs, I am forced to buy a small amount each month. I suspect (but cannot prove) that the consumption as per my meter includes back-fed electricity, but as long as I have to keep on buying that small amount each month the feeding back and the inclusion of the feed back as consumption is not really costing me anything.
Somebody else once explained to me that there’s always a problem when a large load turns off. For a small period of time you have lots of power available but nowhere to put it. Eventually the BMS will start accepting it if SOC < 100, or the inverter will derate the panels, but for that small period of time the only place the inverter can send what is now excess production is back to the grid.
I think I can be assured that solar system owners want to save on their electricity bills. The way you avoid electricity bills is to stop using electricity provided by the utility.
Given all the drama of going off-grid most sensible people keep a grid connection. But there’s a great satisfaction in switching the grid off. (Try it yourself..) This then will reveal the limits of your system.
I’ve always said that managing your solar system is like sailing: You hoist the appropriate sails and trim them to get to where you’re wanting to go to..
Feeding back, the better the software on the equipment, the faster it can react, the better it mitigates feedback.
Going off grid is easy assuming one has spent to actually be able to go off grid.
That is until he weather decides to not play nice for days/weeks on end.
See, feedback will always happen when big loads go off.
Just sit for a few minutes watching the systems real time data when a MW, induction plate runs.
It is like +2000w -2000w +2000w -2000w +2000w -2000w quite fast.
Electric oven, stove, lawnmower, iron does the same, on/off/on/off just much slower than the above appliances.
The right equipment grid tied generating the minimum feedback - software needs to be very fast/accurate - and one has no worries whatsoever be that with weather or te not, variable loads or te not.
To control what a inverter does requires software. Firmware more correctly.
How how fast that software/firmware works, from info from other parts, the faster it can stop the feedback.
In non developer terms …System was producing 2200w:
A 2000w is switched off leaving a 200w load.
What is the battery SOC - if full cannot send the power there.
No problem.
Reduce the draw from the panels to 200w.
No problem.
Now how fast can all that happen in the firmware/software?
The problem.
The power must go somewhere, the batts are full, takes a few seconds to throttle the panel draw, with all the calc that needs to be done with all and sundry - so send it back out on the grid.
The faster the firmware/software works, the better.
