Deye/Sunsync inverter - battery full, still drawing from grid

[kolek]

What were your objectives, again?

Very simple. Never use grid unless battery is dead. Never charge battery from grid, only from solar.

 

[Hedges]

OK, it is to maximize use of solar.
TOU has nothing to do with meeting that objective.

I would think another objective would be to not have the power go out.
Therefore, you want enough charge in the evening to last until morning.
So when there is less sunshine, use less power to ensure sufficient charge during the day.

That could mean doing without some loads you could have powered during the day, in order to not rely on grid at night.
You could run off PV and battery until battery is dead, then switch to grid. But if grid fails, you are out of power.
So you might want to predict if battery won't last until morning and charge battery from grid, or maybe transfer loads direct to grid and just have PV charge battery.

 

[kolek]

You could run off PV and battery until battery is dead, then switch to grid. But if grid fails, you are out of power.

I understand that's a concern for some people, but here grid practically never fails, so having failover to battery backup is not a goal at the moment. My electric bill, on the other hand, never fails to arrive and the price of electricity here is bonkers, so reducing grid consumption is my only focus at the moment.

 

[Hedges]

No net metering, so PV --> battery --> loads is the only way?
With seasons and weather, PV will sometimes come up short.
Maybe you'll be able to expand PV for bad days.
More battery can also let you last another day, but is many times the price of PV panels. At least over here.

Just saw a US source (GStar sold by liquidator InXeption) for $0.14/W (shipping not included.)
What are your best prices on PV?

With high utility rates and low PV panel prices, you could install 5x or 10x the PV you need on good days.
Well, where the point of no additional savings comes depends on how many lightly overcast days.
Some days I get 10% of peak power, other days 2%.

After a year of logging daily production you can do the financial analysis and make a more reasoned decision.
(I've got piles of panels at home, at my other home, sister's home, neighbors home. Easier to plan and buy than to execute. Planning to install before net metering reservations expire.)

 

[kolek]

No net metering, so PV --> battery --> loads is the only way?

Right, if I did net metering I would have had to comply with regulations and get permits and have an approved electrician do the wiring and I am not aware of any Japanese government-approved inverter here that does "off-grid," plus they keep cutting the price they buy back power for so eventually I expect the price to go to practically zero. Just not worth it in my opinion to sell power back to the power company, but that's what 99% of solar installs here in Japan do.

With seasons and weather, PV will sometimes come up short.
Maybe you'll be able to expand PV for bad days.

Right, unfortunately Deye inverters apparently aren't a good choice for overpaneling but I still don't know enough about that option and the actual limitations of my inverter.

With high utility rates and low PV panel prices, you could install 5x or 10x the PV you need on good days.

I've been thinking a lot about how to be do that. Is there a way other than overpaneling to do that? Previously you mentioned putting parallel strings at different angles, I assume that's my only option, aside from buying more SCC to go with the additional panels? Do you have a recommended charge controller that is cheap and overpaneling friendly?

 

[Hedges]

Two strings oriented 90 degrees or 60 degrees to each other would help extend hours with more flat production.

Separate SCC as you mention. I've got Outback MX60, Midnight Classic 150, SMA/MSTE SIC40.

No experience with others mentioned on the forum.
Victron is popular and has wide range of PV voltage and output current, various prices.
Epever is an economy brand. Some had problems getting stuck in the wrong state, but others I think have been OK.
Renogy also may not be highly regarded, but cheap and readily available.
Some AIO may allow inverter to be switched off, saving power, and use as just SCC. Then you've got a backup inverter available.

 

[kolek]

Actually, I don't see why TOU settings are necessary for this use case, here's why:

On the battery screen, you set the battery shutdown voltage (or percentage) to, say, 10%

Then if the battery goes below 10%, inverter switches to grid and doesn't charge the battery, right?

Then when solar pushes the battery above the "restart" voltage, inverter switches back to running from battery.

That's all I need. Why do I need to mess with TOU?

I'm replying to my own message because I have the answer now and the solution might help someone else.
You DO need to activate TOU to run Deye in SBU mode, which is prioritizing in the following manner:
1. Most desirable is powering load from PV
2. Second most desirable is running load off battery
3. Least desirable is running off utility

The reason you need to activate TOU is if you don't, your inverter will just keep slowly drawing down your battery when there is not enough PV to offset your electrical demands, and eventually you can find yourself running into a low voltage state that could damage your batteries. Obviously your BMS should shut off your batteries before they reaches an excessively low state, but you want your inverter taking care of that process, not your BMS.