Disabling active grid-tied inverters

[Swing]

A tiny bit of planning/prevention for next day can shut off the inverter or its circuit breaker from mains by midnight. If you must disconnect PV panels for whatever, do it at night time. I think...

Well, if following hourly pricing market, you can see the evening before if it will become a net loss or gain for that day.
So yes, you could turn it off and on at night. It would be fine to cut it off at AC or DC, nothing is happening at that time.
I would still prefer a solution which allows you to do it in daylight under power. It can serve more applications.

 

[Hedges]

And, it looks like the dumb inverters are still being sold. Yes, they do support frequency shifting, otherwise they are not allowed.
But that is hardly used, there are more reasons to disable it, before you get to the stage of national frequency shifting.

True, just because inverters are now required to have more control features doesn't mean they will necessarily ever have those connected.

My SMA TriPower was rejected by PG&E even though on the CEC list because they lacked additional features (columns on a downloadable spreadsheet, but not in the table on web page itself.) The newer features required since 2020.

It appears the inverters will require Ethernet connection for the utility to be able to control them, so you're probably correct that uncontrolled exports have increased to where they can be a problem.

I'd rather see loads take advantage of the available power, e.g. A/C cooling homes earlier i the day, rather than curtailing production.

Limited export could help. You could have a 10kW system but run its production up and down to match household loads while limiting export to say 5kW. Unfortunately I haven't seen a simple way to interface CT to my Sunny Boys. The TriPower I think has an input for digital pulses that crudely control it. More sophisticated networking controls could be used. I think SMA promotes something communicating all the way out to their website for export limit, rather than local hardware.

 

[Swing]

Yes. Well, I think the best way forward is to try and control the most sold inverters over here, through software or crude I/O on the inverter. That way you can at least serve quite a market share, the way it is intended.

I agree with powering on several loads. I do that to at home. Water heating, running the AC. Today I kept my home cool using energy that I could otherwise not have exported anyway, so basically for free.

But the irony is, if you run an hourly pricing contract and get negative prices, you actually want to disable your solar inverter, and still turn on the loads because they make you money.
In the end I think it is not such a bad thing. If more and more people do it, it will at least balance it a bit, and improve the business case for solar. Because that is getting less and less.

 

[zanydroid]

Grid going down is not the use case I am talking about.

Ok, sounds like the system type you have in mind is very minimalist. Grid tie without batteries. So there is no charging dump load. Since it is on grid there is no ability to use smart inverter distributed control (FreqWatt etc) since the inverter has to sync to grid.

Are you talking about something to sell as a product or just do with DIY? I think you can probably install a PLC and DC contactor with the contactor as a wear item without too much cost, ongoing maintenance overhead, or safety issue.

Not sure whether you will need to switch one or both poles on the solar string. In the US for a servicing disconnect you would need to switch both but I think in this system the PV is still presumed to be in service.

You would lose access to the inverter's management software when PV is disconnected. Since a lot of them use DC side to power those things.

Note that my microinverters say not to disconnect under load, but that disconnect is MC4 so it is not clear whether it is from arcing the MC4 or extra hard discharge on the input capacitors that they don't want happening. If it is just the MC4 arc then a contactor or SSR disconnect will be fine.

Though it seems common here to discourage folks that someone comes in and ask about switching DC strings between MPPTs for various situations.