Is discharge programmable?

[John.DS99]

Is there a thing that would allow me to output the stored energy in my solar panel system batteries in a way that I can control?

Something like this set of rules.
1. Wait until the batteries are charged by solar to 100% capacity.
2. Begin discharging (replacing grid power) if there is any significant wattage being received from the solar panels.
3. Continue discharging until the battery is at 1% capacity.
4. Instead of step 2 (OR) If it is 4-9 pm (peak hours) begin discharge until the battery is at 1%.
5. (Reach here after Step 3 or Step 4) Return to grid power and goto 1.

Something like that. I guess this would be some sort of programmable charge controller?

I'm a newbie so don't expect me to explain everything. I think of the setup as something like my powerstation which has both AC and DC input, but the output is very dumb.

If such a thing exists, what would it be called, and if not, why doesn't it exist?

Thanks,

John

 

[400bird]

Here's how my system works:
As the sun comes up, the first thing the PV does is start to cover home loads.
Then once there is excess solar, beyond what is needed to cover home loads, the battery starts charging with excess solar.
If the battery is full before peak rates start at 4 pm the excess is sold to the grid.
At 4 pm, battery charging stops and PV/battery cover loads through peak hours and overnight.

Come the next morning, it doesn't matter what the battery state of charge is, it will charge once there is excess solar.

If the battery runs low in the middle of the night, the grid covers loads.

What your looking for doesn't necessarily have one specific name. Depending on the vendor it could be a hybrid inverter, all in one, or a combination of inverter and solar charge controller.

 

[zanydroid]

As said above, A hybrid or all in one can do this as can discrete components, but there are caveats.

- may not be able to do this natively without an external controller
- may only be able to replace grid in an all or nothing fashion rather than blend grid and inverter output. Inherent limitation of inverter/charger architecture and/or control loop
- utilities can regulate what power source your hardware can charge from (grid vs local solar) and what it can discharge into (grid via local loads). I believe the specific combination you describe is generally allowed (charge from local solar and discharge into local loads).

 

[John.DS99]

I would never make a system that could return power to the grid.

I'm just thinking of the basic components and the ability to control them.

Thanks for your replies.

 

[400bird]

I would never make a system that could return power to the grid.

To each their own ?‍

 

[John.DS99]

Alright, let me try again. Now, I guess I am talking about programmable input. I have a powerstation with AC & DC input. AC is 1800W in and DC is 600 W input.
I want to reduce my grid consumption by using solar panels on the DC in. So I connect AC grid in & DC from the panels at the max of their capacity.
With my setup that might use 150 to 600 watts, the battery would never discharge. It acts as a UPS and the solar panels are never used, except in the case of grid down.
So, how can I put the solar panels to use? I guess I could program an Arduino type microcontroller to switch a relay that shuts off AC in for some # of hours each day so the battery would begin to drain and the solar input might be absorbed. I could adjust the amount of time AC is shut off by season or predicted weather patterns or better by battery voltage & solar panel dc in voltage levels.

I think this would work, but it seems odd that this can't be controlled by some sort of built in settings in the power station. I haven't programmed an Arduino in years. I may have to get the development software set up again.

 

[John.DS99]

To each their own ?‍

Don't feed the grid, replace it.

 

[zanydroid]

Switching AC is generally a better idea than switching DC with a load. Though with this anemic VDC it probably doesn't matter.

Does the PowerStation have an API, WiFi app (may already be reverse engineered by HomeAssistant etc community if so), or control connection (probably no)? Can you open it up to add a battery shunt to provide SoC monitoring (probably not, but a weaker no)? I guess for battery shut-off threshold voltages are sufficient in lieu of a shunt.

Maybe there is a shunt/volt meter combo that can be installed on the PV inputs. DC in voltage can in principle be used to estimate the Pmpp since there is a closed form solution assuming uniform illumination (or an equivalent condition) across the solar panel, and assuming the MPPT spends enough of the time at the MPP. Probably off by 10-20%. Current + voltage monitoring eliminates the need for this kind of predictive math.

 

[John.DS99]

The powerstation does have an app, but it isn't working and not available. The seller told me it should be available in the next week, so maybe I'll learn there are other options. I'm not married to this powerstation, it's just a cheap unit as my entry into backup / grid replacement / solar first try. Thanks for your comments. I'm looking at larger systems after I get something working successfully in one small room.