My system is set up so that if the grid is up, battery SOC will never go below 40%. So at any time the grid goes down, I will have at least 40%, ok a usable 30% in my batteries. That’s 3 kWh. The pool pump will be getting no power (because it’s not backed up) and I would have to manually manage some big loads, but I can make 3 kWh stretch quite far.
This morning, after my heat pump had run, I had 53% SOC. The battery didn’t go lower than 52% so far today. It’s uncommon for me to see 40%.
This doesn’t give me infinite protection. If the power goes down in the early morning, and it’s overcast, I might make it until 12:00 ish if it’s overcast. If it’s sunny, then my battery starts charging again whilst all the backed up circuits are running (and we may have to exercise a little restraint).
I could set that reserve SOC higher, but so far (since mid 2019) we’ve never run out, and by using the battery as much as possible, I save on my electricity bill and the ROI is improved.
The consumption over night (including the early morning heat pump run) is 4 to 5 kWh. If I save that every day then that adds up to a decent extra saving over a month, and more so over a year.
Most systems have these sort of settings, so one can decide for oneself how they are going to deploy the resources that they have.
Life will become more complicated if TOU tariffs are introduced. Then I want to save my battery for the peak cycle times. But that can be done. These inverters are sold in markets where TOU tariffs apply, and with mine you can actually play the game (without needing solar panels) of charging when the rate is low and selling back when the tariff is high.
I think that CoCT and their eqivalent have realized that most folk will find it a challenge but they have endorsed their list of approved grid-tie inverters. This allows their customers to do (or not do) what they like with minimum collateral damage. The worst that can happen is they pay for electricity from the utility but the grid power is theoretically always available.
And I think all the utilities have to err on the side of assuming that because your inverter has a certain capability then that may be used.
When the City Of Johannesburg came out to inspect my system they weren’t interested in settings. They did check the way the system behaves when grid power is restored (and this is why they want the installer there, because how can the City’s technician be expected to be familiar with every brand of inverter?).
The only interest they had in settings was that I had indicated that I did not want to resell electricity. OK fine… then we leave that one-way meter in place.
Interesting thread. I also use Home Assistant to manage my Inverter & Battery trying to maximize ROI.
During the day, the battery is charged to 100% using PV.
I only have 1x10kWh Battery, so in order to go into the night with a full battery, HA will switch the Inverter to Keep Batteries Charged at dusk. The last bit of PV is used to power loads and then import form the Grid.
Cooking and evening TV typically uses the Grid, unless the Grid is off for whatever reason
Once we wind down to sleep (22:00), the Inverter switches back to the Battery with the Min SOC @ 50%.
We run the A/C off the battery and it reaches 50% at around 2:30AM
3 hours before dawn, HA checks the expected PV production forecast for the day.
If it’s above 10kWh I allow the battery to drain down to 30% to maximize ROI (with 10% spare to get us to sunrise in case of a Grid outage)
If it’s below 10kWh, I keep it at 50% (saving for a rainy day with a potential for a Grid outage)
The coffee machine turns on in the morning, but it first checks if the Grid status.
If the Grid is on, turn on and use the Battery until it reaches Min SoC (30% or 50%).
If the Grid is off, and the battery SoC is above 35%, keep going. We should make it until the sun is up.
If the Grid is off, and the battery SoC is below 35%, sorry, no coffee until the sun is out and we run on PV.
The A/C is not automated, so if the Grid goes down, it could drain the battery leading to a loss of power. To work around this, whenever the Grid is off and the Battery SoC is below 50%, every 5% an announcement is made on all speakers stating what the Battery SoC is and instructing everyone to reduce loads. This usually wakes us up and prompts us to turn off the A/C, lowering the loads enough that we can get through the night.
Up until to day I had Min SoC at 35% when the Battery reaches 50% SoC and the forecast is good, which started importing from the Grid around 5:00 when the battery reached 35%. I now lowered Min SoC to 30% to try and lower the 05:00 - 06:00 red.
This has worked pretty well for me for many months with and without load shedding. I make minor tweaks like the one today every couple of months.
I know it’s quite involved, but you either
pay to import from the grid
pay for additional batteries
pay by putting in some effort
So far 10kWh is sufficient. I can’t yet justify the cost of another battery vs paying to import from the Grid. It will take 5 years of Eskom to break even on the battery installation and I’m not sure I’m going to live here that long. With price increases and increased connection fees, it will obviously have an impact on the break even point, but then I might just cancel Eskom and add a another Battery and gennie for rainy days. We’ll see…
Wow this sounds like something from a futuristic scifi movie! I like!
Just for fun, fiddle with the programming again without telling the family about it. Once you reach say 45 SOC have another announcement come through that says “critical system failure imminent” and have it repeat a few times.
Then once you reach 43%, have something come through that says “auto self destruct sequence initiated”, and have a countdown announcement from 100
It sounds to me like the whole fiasco started when they were bringing a unit back at Majuba. Something went wrong, and 5 others tripped. Apparently a transformer was overloaded. Losing 5 units at 600MW each, means 3 stages of load shedding immediately became necessary. Then another unit at Medupi tripped on under-frequency (not sure if there is cause and effect here), and then about a day later, they had additional issues at Camden.
On top of all this, they had 7000MW out on scheduled maintenance. Let’s give some credit there… they had a huge amount out on maintenance at the time.
Picture wise, I think I can see the spot where things went wrong on Saturday afternoon:
Looks like a peaking plant picks it up for a bit. But then note that pronounced sagging around 17:10, which is around the time the Medupi unit tripped.
Imagine the Venus/Cerbo, based on AI analysis, similar to the AI calculating potential solar production, can give a heads-up that LS may be imminent based on the grid Hz.
Once the AI has been taught what to look for, next level later, when the grid appears unstable, stop using the batts at night … if one wants to activate the feature.
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Cape Town businesses and households have broken through the R50m earnings mark since the start of the City’s Cash for Power programme in 2022/23. Cape Town is the first metro to buy excess solar PV power from small-scale generators, with over 1 800 small scale power sellers now participating.
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