Simple AC-coupled solar production monitor /meter to control dump load / relay

fafrd

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I’m not sure my question is ‘advanced’ enough for this Forum but here goes:

I’m looking for a simple way to monitor my AC-coupled solar power production in kW to drive a dump load when it gets close to my 3.5kW export limit.

This is east to do with a current-controlled switch but I’m getting enough variation in grid voltage to I’d really like to find a (hopefully east / straightforward) way to drive a control signal output from a user-defined / controlled measure of power (current x voltage).

There’s a ton of energy meters out there that will display W of generation, but I have not been able to find any with a programmable dry contact output.

There a also a bunch of relatively expensive and complicated ‘smart home’ solutions that will allow you to have a WiFi-enabled solar energy meter communicate with an app that can be configured to control smart switches but that’s just a whole lot of complexity / technology / potential code-writing that I’d rather avoid (primarily because of all of the additional potential points of failure).

So if anyone here has a simple ideas for how I can detect when my AC-coupled power output gets past 3.4kW to drive an output signal I plan to use to drive a simple dump load, I’m all ears…
 

GregTR

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https://a.co/d/fNA4Z2g should do the trick for you. Just slap it on the wire you're trying to measure, it will do up to 30A and drive a second relay with the switch that will control your dump load.
 

fafrd

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https://a.co/d/fNA4Z2g should do the trick for you. Just slap it on the wire you're trying to measure, it will do up to 30A and drive a second relay with the switch that will control your dump load.
Thanks, but that’s exactly the current sending switch I was referring to in the lead post.

The problem with a current switch is that grid voltage can vary between a low of 211Vac to a high of 264Vac (and exported power will vary at any specific current with it).

I’m not too worried about low grid voltage but I need a sensor that knows 10A @ 240VAC is below a 2.45kW average while 10A @ 250VAC is not…
 

fafrd

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My bad, I didn't read your post carefully enough.

How about this one? https://m.aliexpress.com/item/3256801535687870.html?html=static&gatewayAdapt=4itemAdapt
Looks like it might be perfect in terms of a programmable power threshold that activates a relay output, but thus spec has me concerned:

Measure voltage range: AC0-220V

I need to have power measured up to a line voltage of 264VAC, so I’m not sure if this will work…

But in any case, at least I know that the class of device I was looking for exists :).
 

fafrd

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This at least seems like it will allow me to get a relay output when AC voltage increases beyond a programmable threshold: https://www.amazon.com/Monitoring-S...t=&hvlocphy=9032079&hvtargid=pla-786946572609
That one was 3-phase and probably I’ll-suited to my need, but this single-phase relay should do the trick: https://www.amazon.com/gp/aw/d/B085...OZ&sp_csd=d2lkZ2V0TmFtZT1zcF9waG9uZV9kZXRhaWw

‘Overvoltage protection value range: 221V-300V-OFF adjustable (default 280V)

Overvoltage recovery voltage mediation range: 220V-299V (default value 250V)

Overvoltage protection action time: 0.1s - 10s (default 0.1 seconds)’

So for $20, I can program one of these to open for at least 10 seconds whenever grid voltage exceeds 255V and then automatically close after grid voltage has decreased to 251V or less.

This will now allow me to use a simple programmable current switch to activate a dump load whenever AC-coupled solar power current exceeds a programmable threshold.

‘Excess’ solar power generation can be cut out whenever grid voltage exceeds 255VAC or whenever solar current exceeds ‘E’ Amps.

Since the excess power being generated must be at no more than 255VAC, the maximum amount of Excess solar power I can ever get will be no more than 255 x E Watts…

I’ve never seen my grid voltage reach 251VAC let alone 255VAC but since my Microinverters are rated to produce power all the way up to a maximum of 264VAC, this seams like cheap insurance to guarantee that any ‘Excess’ solar power I generate only happens when my grid is within the range I typically see…

If I just used 264V to determine the current threshold to activate dump load instead of 255V, I’d have to set my current switch threshold at E / 264 rather than E / 255 meaning 3.4% lower.

3.4% may not seem like much but means that rather dumping energy on the rare / perfect days than my systems achieves close to maximum possible output (on my particular roof), I’ll likely be dumping any Excess generation for -3-4 hours all summer long.

At the Excess generation rate of 0.6kW I’m aiming for, that amounts to 1.8 to 2.4 kWh per day which over 6-8 months a year can be as much as 330 to 580kWh per year.

Even if I’m only getting that excess generation compensated a t wholesale rates if $0.05, this overvoltsge protection relay will pay for itself in 8 to 15 months and the entire rig with power-resistor-based dump-load, relays, and the programmable current switch will pay for itself in 2-4 years.
 

fafrd

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Awesome! That should work for you.
The other way I’m thinking about going after this is to see if I can talk Emporium into adding more configurable controls for their smart switches in their energy monitor.

They already measure solar power and import / export power, so it’s just a question of them allowing a smart switch to be activated when either export power and / solar power exceed a user-settable fir them to provide a very capable dump-load controller…
 

GregTR

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The other way I’m thinking about going after this is to see if I can talk Emporium into adding more configurable controls for their smart switches in their energy monitor.

They already measure solar power and import / export power, so it’s just a question of them allowing a smart switch to be activated when either export power and / solar power exceed a user-settable fir them to provide a very capable dump-load controller…
Should be an easy add but based on my chats and emails with them they just aren't that agile to make the changes. They're good with support but any new feature you ask for is a dead end.

They don't even have bi-directional metering on the 2.5mm inputs even though they confirmed that it's not a hardware limitation.

Since I can't export any solar at the moment, no PTO yet, I can't use their EV charger to charge my car on excess solar because they can't measure/recognize excess solar on an internal measurement. So I'm using peak shaving and use that to charge my EV with excess solar and pay for the 1kW draw I have on the grid.

You can definitely reach out to them but I wouldn't hold my breath.
 

fafrd

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Should be an easy add but based on my chats and emails with them they just aren't that agile to make the changes. They're good with support but any new feature you ask for is a dead end.

They don't even have bi-directional metering on the 2.5mm inputs even though they confirmed that it's not a hardware limitation.

Since I can't export any solar at the moment, no PTO yet, I can't use their EV charger to charge my car on excess solar because they can't measure/recognize excess solar on an internal measurement. So I'm using peak shaving and use that to charge my EV with excess solar and pay for the 1kW draw I have on the grid.

You can definitely reach out to them but I wouldn't hold my breath.
Wow, you far further into things than I am.

They told me my request was interesting, gave me a ticket number and promised to pass my request on to engineering.

From what you’ve indicated that’ll end up being a dead end.

I don’t have an EV yet but plan to get one next year or 2024 (waiting for the Volkswagen ID.3 to support V2H and bidirectional charging, hopefully followed by others).

I really like the way Emporia has architected their bidirectional charger to support solar absorption and load offsetting but am concerned their system is a black box.

If an outfit like OpenEV introduces bidirectional charging capability, I’d prefer that but I don’t see anyway they could offer anything more than a high voltage DC output feeding a 3rd-party hybrid inverter.

Getting the solar power into the EV without exporting should be easier and easier but getting than stored energy back out to offset loads could remain a hairball for some time.

Where are you based and do you plan to get a PTO?
 

GregTR

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Emporia has solar charging support on their Level 2 AC charger, the one I have and use. As I said it works OK even without grid export but it could work a bit better. Since I have a Sol-Ark 15K I also had to put together a custom CT setup so I could measure my Solar production but once I got it figured out it works really well. Once I start grid charging my batteries I'll be in a bit of trouble because there will be no way to directly measure that (no 2-way measure on the 50A CTs) but I should be able to figure out that data via Excel after exporting the data.

I'm in north Texas in ERCOT/Oncor land. I'm still waiting on my battery and the Tigo communication bridge to enable rapid shutdown and remote monitoring on the Tigo optimizers before I can pass city inspection and I reckon it's a few more weeks after that before I get PTO. So far I'm super pleased with my system and how it's shaping up from an energy perspective, I originally guessed ROI to be about 12 years but with the TOU free nights plan I should be able to recover it much sooner.
 

fafrd

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Emporia has solar charging support on their Level 2 AC charger, the one I have and use. As I said it works OK even without grid export but it could work a bit better. Since I have a Sol-Ark 15K I also had to put together a custom CT setup so I could measure my Solar production but once I got it figured out it works really well. Once I start grid charging my batteries I'll be in a bit of trouble because there will be no way to directly measure that (no 2-way measure on the 50A CTs) but I should be able to figure out that data via Excel after exporting the data.

I'm in north Texas in ERCOT/Oncor land. I'm still waiting on my battery and the Tigo communication bridge to enable rapid shutdown and remote monitoring on the Tigo optimizers before I can pass city inspection and I reckon it's a few more weeks after that before I get PTO. So far I'm super pleased with my system and how it's shaping up from an energy perspective, I originally guessed ROI to be about 12 years but with the TOU free nights plan I should be able to recover it much sooner.
Sounds like a really nice setup.

I’ll tell you how I ‘tricked my GTIL inverters CT sensors into netting out my solar production in case it might help you with whatever CT-based issue you might be facing with your Solark.

Each GTIL has a single CT sensor which it uses to generate power from battery until import is zero (there is one of these on each 120VAC leg, so no backup power capability but true split-phase 240VAC consumption offset within the power limits of the inverters).

I have a 4kW grid-tied system and that means that during daylight hours, the GTILs would produce no power because I’m exporting, not importing.

On clear days, I get enough DC-coupled power coming in that I want theGTILs to begin offsetting loads even though there is no import.

The currents in CT sensors add, so what I did was purchase 2 more of the proper specification and spliced each sensor cable to be connected to 2 CT sensors in parallel.

With that dual CT cable, I could connect in CT sensor to the main wire and the second to the solar input wire (attached the same leg) so that the import current being ‘seen’ by each GTIL corresponds to ‘Mains import current + solar input current’. When there is no import current and the mains current is negative (exporting) the solar input gets added to that so the GTIL ‘sees’ solar generation current - export current = loads currevt.

It works like a charm. The only thing to be careful about is shielding since those CT sensor cables are very well shielded to prevent EMI noise from distorting the measurements and if you make a splice, you want to do your best to shield it equally well.

The Solark is a really nice piece of kit but outside my price range (at least for now).

California is changing the rules on us legacy NEM customers (so much for 20 years!) and the writing is on the wall. It’s only a question of when and not if you will be given essentially no credit for export and charged a monthly tax for any export at all, so I’m trying to prepare in advance for a ‘zero export’ future.

Rather that investing ~$10-20,000 in a house battery, storing as much solar production as you can fit into an EV during the day and using that stored energy to offset loads overnight until the sun is shining again looks like the better choice.

So I’m looking for cheap, effective and easy ways to avoid all export for when the time comes.

With AC-coupled solar, the Emporia will export until export power reaches the minimum of 1.44kW, so in any case it seems like there will be a role to play for a house battery and AC charger.

Emporia is introducing a house battery as well, which is surprisingly reasonably-priced, but the inverter you need to use it costs at least as much as a Solark, if not more.

And in addition Emporua is a ‘black box’ so the only way you can get it to do things it was not designed to do is to fool its sensor inputs.

So it’s a pleasure to meet you virtually and I hope we can keep this dialog going - seems like we share interests in many of the same things…
 
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